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Earth System Dynamics

Global and regional effects of land-use change on climate in 21st century simulations with interactive carbon cycleEarth System Dynamics, 5, 309-319, 2014Author(s): L. R. Boysen, V. Brovkin, V. K. Arora, P. Cadule, N. de Noblet-Ducoudré, E. Kato, J. Pongratz, and V. GaylerBiogeophysical (BGP) and biogeochemical (BGC) effects of land-use
and land cover change (LULCC) are separated at the global and
regional scales in new interactive CO2 simulations for the
21st century. Results from four earth system models (ESMs) are
analyzed for the future RCP8.5 scenario from simulations with and
without land-use and land cover change (LULCC), contributing to the
Land-Use and Climate, IDentification of robust impacts (LUCID)
project. Over the period 2006–2100, LULCC causes the atmospheric
CO2 concentration to increase by 12, 22, and 66 ppm
in CanESM2, MIROC-ESM, and MPI-ESM-LR, respectively. Statistically
significant changes in global near-surface temperature are found in
three models with a BGC-induced global mean annual warming between
0.07 and 0.23 K. BGP-induced responses are simulated by
three models in areas of intense LULCC of varying sign and magnitude
(between −0.47 and 0.10 K). Modifications of the land carbon pool by
LULCC are disentangled in accordance with processes that can lead to
increases and decreases in this carbon pool. Global land carbon losses due
to LULCC are simulated by all models: 218, 57, 35 and 34 Gt C by
MPI-ESM-LR, MIROC-ESM, IPSL-CM5A-LR and CanESM2, respectively. On
the contrary, the CO2-fertilization effect caused by
elevated atmospheric CO2 concentrations due to LULCC leads
to a land carbon gain of 39 Gt C in MPI-ESM-LR and is almost
negligible in the other models. A substantial part of the spread in
models' responses to LULCC is attributed to the differences in
implementation of LULCC (e.g., whether pastures or crops are
simulated explicitly) and the simulation of specific
processes. Simple idealized experiments with clear protocols for
implementing LULCC in ESMs are needed to increase the understanding
of model responses and the statistical significance of results,
especially when analyzing the regional-scale impacts of LULCC. 2014/10/01 - 23:45

Long-range memory in internal and forced dynamics of millennium-long climate model simulationsEarth System Dynamics, 5, 295-308, 2014Author(s): L. Østvand, T. Nilsen, K. Rypdal, D. Divine, and M. RypdalNorthern Hemisphere (NH) temperature records from a palaeoclimate reconstruction and a number of
millennium-long climate model experiments are investigated for long-range memory (LRM). The
models are two Earth system models and two atmosphere–ocean general circulation models. The
periodogram, detrended fluctuation analysis and wavelet variance analysis are applied to examine
scaling properties and to estimate a scaling exponent of the temperature records. A simple
linear model for the climate response to external forcing is also applied to the reconstruction
and the forced climate model runs, and then compared to unforced control runs to extract the LRM
generated by internal dynamics of the climate system. The climate models show strong persistent
scaling with power spectral densities of the form S(f) ~ f −β with 0.8 < β < 1 on
timescales from years to several centuries. This is somewhat stronger persistence than found
in the reconstruction (β ≈ 0.7). We find no indication that LRM found in these model
runs is induced by external forcing, which suggests that LRM on sub-decadal to century time
scales in NH mean temperatures is a property of the internal dynamics of the climate system.
Reconstructed and instrumental sea surface temperature records for a local site, Reykjanes Ridge,
are also studied, showing that strong persistence is found also for local ocean temperature. 2014/08/29 - 02:28

Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet modelsEarth System Dynamics, 5, 271-293, 2014Author(s): A. Levermann, R. Winkelmann, S. Nowicki, J. L. Fastook, K. Frieler, R. Greve, H. H. Hellmer, M. A. Martin, M. Meinshausen, M. Mengel, A. J. Payne, D. Pollard, T. Sato, R. Timmermann, W. L. Wang, and R. A. BindschadlerThe largest uncertainty in projections of future sea-level change results
from the potentially changing dynamical ice discharge from Antarctica. Basal
ice-shelf melting induced by a warming ocean has been identified as a major
cause for additional ice flow across the grounding line. Here we attempt to
estimate the uncertainty range of future ice discharge from Antarctica by
combining uncertainty in the climatic forcing, the oceanic response and the
ice-sheet model response. The uncertainty in the global mean temperature
increase is obtained from historically constrained emulations with the
MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the
subsurface with the atmospheric warming from 19 comprehensive climate models
of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models
from the EU-project Ice2Sea. The dynamic ice-sheet response is derived
from linear response functions for basal ice-shelf melting for four different
Antarctic drainage regions using experiments from the Sea-level Response to
Ice Sheet Evolution (SeaRISE) intercomparison project with five different
Antarctic ice-sheet models.
The resulting uncertainty range for the historic Antarctic contribution to
global sea-level rise from 1992 to 2011 agrees with the observed
contribution for this period if we use the three ice-sheet models with an
explicit representation of ice-shelf dynamics and account for the
time-delayed warming of the oceanic subsurface compared to the surface air
temperature. The median of the additional ice loss for the 21st century
is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m)
of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and
0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the
strongest RCP-8.5. Assuming no time delay between the atmospheric warming
and the oceanic subsurface, these values increase to 0.09 m (66% range:
0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range:
0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5.
All probability distributions are highly skewed towards high values. The
applied ice-sheet models are coarse resolution with limitations in the
representation of grounding-line motion. Within the constraints of the
applied methods, the uncertainty induced from different ice-sheet models is
smaller than that induced by the external forcing to the ice sheets. 2014/08/15 - 09:08

Bimodality of woody cover and biomass across the precipitation gradient in West AfricaEarth System Dynamics, 5, 257-270, 2014Author(s): Z. Yin, S. C. Dekker, B. J. J. M. van den Hurk, and H. A. DijkstraMultiple states of woody cover under similar climate conditions are found in
both conceptual models and observations. Due to the limitation of the
observed woody cover data set, it is unclear whether the observed bimodality
is caused by the presence of multiple stable states or is due to dynamic
growth processes of vegetation. In this study, we combine a woody cover data
set with an aboveground biomass data set to investigate the simultaneous
occurrences of savanna and forest states under the same precipitation
forcing. To interpret the results we use a recently developed vegetation
dynamics model (the Balanced Optimality Structure Vegetation Model), in which
the effect of fires is included. Our results show that bimodality also exists
in aboveground biomass and retrieved vegetation structure. In addition, the
observed savanna distribution can be understood as derived from a stable
state and a slightly drifting (transient) state, the latter having the
potential to shift to the forest state. Finally, the results indicate that
vegetation structure (horizontal vs. vertical leaf extent) is a crucial
component for the existence of bimodality. 2014/07/11 - 06:14

Comparing tide gauge observations to regional patterns of sea-level change (1961–2003)Earth System Dynamics, 5, 243-255, 2014Author(s): A. B. A. Slangen, R. S. W. van de Wal, Y. Wada, and L. L. A. VermeersenAlthough the global mean sea-level budget for the 20th century can now be
closed, the understanding of sea-level change on a regional scale is still
limited. In this study we compare observations from tide gauges to regional
patterns from various contributions to sea-level change to see how much of
the regional measurements can be explained. Processes that are included are
land ice mass changes and terrestrial storage changes with associated
gravitational, rotational and deformational effects, steric/dynamic changes,
atmospheric pressure loading and glacial isostatic adjustment (GIA). The
study focuses on the mean linear trend of regional sea-level rise between
1961 and 2003. It is found that on a regional level the explained variance of
the observed trend is 0.87 with a regression coefficient of 1.07. The
observations and models overlap within the 1σ uncertainty range in all
regions. The main processes explaining the variability in the observations
appear to be the steric/dynamic component and the GIA. Local observations
prove to be more difficult to explain because they show larger spatial
variations, and therefore require more information on small-scale processes. 2014/06/28 - 15:36

Inter-hemispheric asymmetry in the sea-ice response to volcanic forcing simulated by MPI-ESM (COSMOS-Mill)Earth System Dynamics, 5, 223-242, 2014Author(s): D. Zanchettin, O. Bothe, C. Timmreck, J. Bader, A. Beitsch, H.-F. Graf, D. Notz, and J. H. JungclausThe decadal evolution of Arctic and Antarctic sea ice following strong
volcanic eruptions is investigated in four climate simulation ensembles
performed with the COSMOS-Mill version of the Max Planck Institute Earth System Model. The ensembles differ in the magnitude of the imposed volcanic
perturbations, with sizes representative of historical tropical eruptions
(1991 Pinatubo and 1815 Tambora) and of tropical and extra-tropical
"supervolcano" eruptions. A post-eruption Arctic sea-ice expansion is
robustly detected in all ensembles, while Antarctic sea ice responds only to
supervolcano eruptions, undergoing an initial short-lived expansion and
a subsequent prolonged contraction phase. Strong volcanic forcing therefore
emerges as a potential source of inter-hemispheric interannual-to-decadal
climate variability, although the inter-hemispheric signature is weak in the
case of eruptions comparable to historical eruptions. The post-eruption inter-hemispheric
decadal asymmetry in sea ice is interpreted as a consequence mainly of the different exposure of Arctic and Antarctic regional climates to induced
meridional heat transport changes and of dominating local feedbacks that set
in within the Antarctic region. Supervolcano experiments help to clarify
differences in simulated hemispheric internal dynamics related to imposed
negative net radiative imbalances, including the relative importance of the
thermal and dynamical components of the sea-ice response. Supervolcano experiments could therefore serve the assessment of climate models' behavior
under strong external forcing conditions and, consequently, favor
advancements in our understanding of simulated sea-ice dynamics. 2014/06/25 - 23:45

The sensitivity of carbon turnover in the Community Land Model to modified assumptions about soil processesEarth System Dynamics, 5, 211-221, 2014Author(s): B. Foereid, D. S. Ward, N. Mahowald, E. Paterson, and J. LehmannSoil organic matter (SOM) is the largest store of organic carbon (C) in the
biosphere, but the turnover of SOM is still incompletely understood and not
well described in global C cycle models. Here we use the Community Land
Model (CLM) and compare the output for soil organic C stocks (SOC) to
estimates from a global data set. We also modify the assumptions about SOC
turnover in two ways: (1) we assume distinct temperature sensitivities of SOC
pools with different turnover time and (2) we assume a priming effect, such
that the decomposition rate of native SOC increases in response to a supply
of fresh organic matter. The standard model predicted the global
distribution of SOC reasonably well in most areas, but it failed to predict
the very high stocks of SOC at high latitudes. It also predicted too much
SOC in areas with high plant productivity, such as tropical rainforests and
some midlatitude areas. Total SOC at equilibrium was reduced by a small amount
(<1% globally) when we assume that the temperature sensitivity of SOC
decomposition is dependent on the turnover rate of the component pools.
Including a priming effect reduced total global SOC more (6.6%
globally) and led to decreased SOC in areas with high plant input (tropical
and temperate forests), which were also the areas where the unmodified model
overpredicted SOC (by about 40%). The model was then run with climate
change prediction until 2100 for the standard and modified versions. Future
simulations showed that differences between the standard and modified
versions were maintained in a future with climate change (4–6 and 23–47 Pg
difference in soil carbon between standard simulation and the modified
simulation with temperature sensitivity and priming respectively). Although the
relative changes are small, they are likely to be larger in a fully coupled
simulation, and thus warrant future work. 2014/06/03 - 21:13

Quantifying uncertainties in soil carbon responses to changes in global mean temperature and precipitationEarth System Dynamics, 5, 197-209, 2014Author(s): K. Nishina, A. Ito, D. J. Beerling, P. Cadule, P. Ciais, D. B. Clark, P. Falloon, A. D. Friend, R. Kahana, E. Kato, R. Keribin, W. Lucht, M. Lomas, T. T. Rademacher, R. Pavlick, S. Schaphoff, N. Vuichard, L. Warszawaski, and T. YokohataSoil organic carbon (SOC) is the largest carbon pool in terrestrial
ecosystems and may play a key role in biospheric feedbacks with elevated
atmospheric carbon dioxide (CO2) in a warmer future world. We examined the
simulation results of seven terrestrial biome models when forced with climate
projections from four representative-concentration-pathways (RCPs)-based
atmospheric concentration scenarios. The goal was to specify calculated
uncertainty in global SOC stock projections from global and regional
perspectives and give insight to the improvement of SOC-relevant processes in
biome models. SOC stocks among the biome models varied from 1090 to
2650 Pg C even in historical periods (ca. 2000). In a higher forcing
scenario (i.e., RCP8.5), inconsistent estimates of impact on the total SOC
(2099–2000) were obtained from different biome model simulations, ranging
from a net sink of 347 Pg C to a net source of 122 Pg C. In all models,
the increasing atmospheric CO2 concentration in the RCP8.5 scenario
considerably contributed to carbon accumulation in SOC. However, magnitudes
varied from 93 to 264 Pg C by the end of the 21st century across biome
models. Using the time-series data of total global SOC simulated by each
biome model, we analyzed the sensitivity of the global SOC stock to global
mean temperature and global precipitation anomalies (ΔT and
ΔP respectively) in each biome model using a state-space model. This analysis
suggests that ΔT explained global SOC stock changes in most models
with a resolution of 1–2 °C, and the magnitude of global SOC
decomposition from a 2 °C rise ranged from almost 0
to 3.53 Pg C yr−1 among the biome models. However,
ΔP had a negligible impact on change in the global SOC changes.
Spatial heterogeneity was evident and inconsistent among the biome models,
especially in boreal to arctic regions. Our study reveals considerable
climate uncertainty in SOC decomposition responses to climate and CO2 change
among biome models. Further research is required to improve our ability to
estimate biospheric feedbacks through both SOC-relevant and
vegetation-relevant processes. 2014/04/02 - 18:15

Terminology as a key uncertainty in net land use and land cover change carbon flux estimatesEarth System Dynamics, 5, 177-195, 2014Author(s): J. Pongratz, C. H. Reick, R. A. Houghton, and J. I. HouseReasons for the large uncertainty in land use and land cover change (LULCC)
emissions go beyond recognized issues related to the available data on land
cover change and the fact that model simulations rely on a simplified and
incomplete description of the complexity of biological and LULCC processes.
The large range across published LULCC emission estimates is also
fundamentally driven by the fact that the net LULCC flux is defined and
calculated in different ways across models. We introduce a conceptual
framework that allows us to compare the different types of models and
simulation setups used to derive land use fluxes. We find that published
studies are based on at least nine different definitions of the net LULCC flux.
Many multi-model syntheses lack a clear agreement on definition. Our
analysis reveals three key processes that are accounted for in different
ways: the land use feedback, the loss of additional sink capacity, and
legacy (regrowth and decomposition) fluxes. We show that these
terminological differences, alone, explain differences between published net
LULCC flux estimates that are of the same order as the published estimates
themselves. This has consequences for quantifications of the residual
terrestrial sink: the spread in estimates caused by terminological
differences is conveyed to those of the residual sink. Furthermore, the
application of inconsistent definitions of net LULCC flux and residual sink
has led to double-counting of fluxes in the past. While the decision to use
a specific definition of the net LULCC flux will depend on the scientific
application and potential political considerations, our analysis shows that
the uncertainty of the net LULCC flux can be substantially reduced when the
existing terminological confusion is resolved. 2014/03/27 - 12:33

A lower and more constrained estimate of climate sensitivity using updated observations and detailed radiative forcing time seriesEarth System Dynamics, 5, 139-175, 2014Author(s): R. B. Skeie, T. Berntsen, M. Aldrin, M. Holden, and G. MyhreEquilibrium climate sensitivity (ECS) is constrained
based on observed near-surface temperature change, changes in ocean heat
content (OHC) and detailed radiative forcing (RF) time series from
pre-industrial times to 2010 for all main anthropogenic and natural forcing
mechanism. The RF time series are linked to the observations of OHC and
temperature change through an energy balance model (EBM) and a stochastic
model, using a Bayesian approach to estimate the ECS and other unknown
parameters from the data. For the net anthropogenic RF the posterior mean in
2010 is 2.0 Wm−2, with a 90% credible interval (C.I.) of 1.3 to
2.8 Wm−2, excluding present-day total aerosol effects
(direct + indirect) stronger than −1.7 Wm−2. The posterior mean
of the ECS is 1.8 °C, with 90% C.I. ranging from 0.9 to
3.2 °C, which is tighter than most previously published estimates. We
find that using three OHC data sets simultaneously and data for global mean
temperature and OHC up to 2010 substantially narrows the range in ECS
compared to using less updated data and only one OHC data set. Using only one
OHC set and data up to 2000 can produce comparable results as previously
published estimates using observations in the 20th century, including the
heavy tail in the probability function. The analyses show a significant
contribution of internal variability on a multi-decadal scale to the global
mean temperature change. If we do not explicitly account for long-term
internal variability, the 90% C.I. is 40% narrower than in the main
analysis and the mean ECS becomes slightly lower, which demonstrates that the
uncertainty in ECS may be severely underestimated if the method is too
simple. In addition to the uncertainties represented through the estimated
probability density functions, there may be uncertainties due to limitations
in the treatment of the temporal development in RF and structural
uncertainties in the EBM. 2014/03/26 - 15:48

Towards decision-based global land use models for improved understanding of the Earth systemEarth System Dynamics, 5, 117-137, 2014Author(s): M. D. A. Rounsevell, A. Arneth, P. Alexander, D. G. Brown, N. de Noblet-Ducoudré, E. Ellis, J. Finnigan, K. Galvin, N. Grigg, I. Harman, J. Lennox, N. Magliocca, D. Parker, B. C. O'Neill, P. H. Verburg, and O. YoungA primary goal of Earth system modelling is to improve understanding of the
interactions and feedbacks between human decision making and biophysical
processes. The nexus of land use and land cover change (LULCC) and the
climate system is an important example. LULCC contributes to global and
regional climate change, while climate affects the functioning of
terrestrial ecosystems and LULCC. However, at present, LULCC is poorly
represented in global circulation models (GCMs). LULCC models that are
explicit about human behaviour and decision-making processes have been
developed at local to regional scales, but the principles of these
approaches have not yet been applied to the global scale level in ways that
deal adequately with both direct and indirect feedbacks from the climate
system. In this article, we explore current knowledge about LULCC modelling
and the interactions between LULCC, GCMs and dynamic global vegetation
models (DGVMs). In doing so, we propose new ways forward for improving LULCC
representations in Earth system models. We conclude that LULCC models need
to better conceptualise the alternatives for upscaling from the local to
global scale. This involves better representation of human agency, including
processes such as learning, adaptation and agent evolution, formalising the
role and emergence of governance structures, institutional arrangements and
policy as endogenous processes and better theorising about the role of
teleconnections and connectivity across global networks. Our analysis
underlines the importance of observational data in global-scale assessments
and the need for coordination in synthesising and assimilating available data. 2014/02/27 - 11:56

The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variabilityEarth System Dynamics, 5, 103-115, 2014Author(s): C. F. Schleussner, J. Runge, J. Lehmann, and A. LevermannEarth's climate exhibits internal modes of variability on various
timescales. Here we investigate multi-decadal variability of the
Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extent
and global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions.
We report an inter-annual GMT variability of about ±0.1° C
originating solely from natural variability in the model ensemble.
By decomposing the GMT variance into contributions of the
AMOC and Northern Hemisphere sea-ice extent using
a graph-theoretical statistical approach, we find the AMOC to
contribute 8% to GMT variability in the ensemble mean. Our
results highlight the importance of AMOC sea-ice feedbacks that
explain 5% of the GMT variance, while the contribution solely
related to the AMOC is found to be about 3%. As a consequence
of multi-decadal AMOC variability, we report substantial variations
in North Atlantic deep-ocean heat content with trends of up to
0.7 × 1022 J decade−1 that are of the order of
observed changes over the last decade and consistent with the
reduced GMT warming trend over this period. Although these
temperature anomalies are largely density-compensated by salinity
changes, we find a robust negative correlation between the AMOC and
North Atlantic deep-ocean density with density lagging the AMOC by 5
to 11 yr in most models. While this would in principle allow
for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean
system, our results are inconclusive about the role of
this feedback in the model ensemble. 2014/02/21 - 11:22

Background albedo dynamics improve simulated precipitation variability in the Sahel regionEarth System Dynamics, 5, 89-101, 2014Author(s): F. S. E. Vamborg, V. Brovkin, and M. ClaussenUsing the general circulation model ECHAM5–JSBACH forced by observed
sea surface temperatures (SSTs) for the 20th century, we
investigate the role of vegetation and land surface albedo dynamics
in shaping rainfall variability in the Sahel. We use two different
land surface albedo schemes, one in which the albedo of the canopy
is varying and one in which the albedo changes of the
surface below the canopy are also taken into account. The SST forcing
provides the background for simulating the observed decadal signal
in Sahelian rainfall, though the response to SST forcing only is not
strong enough to fully capture the observed signal. The introduction
of dynamic vegetation leads to an increase in interannual
variability of the rainfall, and gives rise to an increased number
of high-amplitude rainfall anomaly events. The dynamic background
albedo leads to an increased persistence of the rainfall anomalies. The increase in persistence means
that the difference between the dry and the wet decades is increased
compared to the other simulations, and thus more closely matching
the observed absolute change between these two periods. These
results highlight the need for a consistent representation of land
surface albedo dynamics for capturing the full extent of rainfall
anomalies in the Sahel. 2014/02/07 - 13:29

Seasonality of the hydrological cycle in major South and Southeast Asian river basins as simulated by PCMDI/CMIP3 experimentsEarth System Dynamics, 5, 67-87, 2014Author(s): S. Hasson, V. Lucarini, S. Pascale, and J. BöhnerIn this study, we investigate how PCMDI/CMIP3 general circulation models
(GCMs) represent the seasonal properties of the hydrological cycle in four
major South and Southeast Asian river basins (Indus, Ganges, Brahmaputra and
Mekong). First, we examine the skill of the GCMs by analysing their
performance in simulating the 20th century climate (1961–2000 period) using
historical forcing (20c3m experiment), and then we analyse the projected
changes for the corresponding 21st and 22nd century climates under the
SRESA1B scenario. The CMIP3 GCMs show a varying degree of skill in
simulating the basic characteristics of the monsoonal precipitation regimes
of the Ganges, Brahmaputra and Mekong basins, while the representation of
the hydrological cycle over the Indus Basin is poor in most cases, with a few
GCMs not capturing the monsoonal signal at all. While the model outputs
feature a remarkable spread for the monsoonal precipitation, a satisfactory
representation of the western mid-latitude precipitation regime is instead
observed. Similarly, most of the models exhibit a satisfactory agreement for
the basin-integrated runoff in winter and spring, while their spread is
large for the runoff during the monsoon season. For the future climate
scenarios, most models foresee a decrease in the winter P − E over all four
basins, while agreement is found on the decrease of the spring P − E over the Indus and Ganges basins only. Such decreases in P − E are mainly due to the
decrease in precipitation associated with the western mid-latitude
disturbances. Consequently, for the Indus and Ganges basins, the runoff
drops during the spring season while it rises during the winter season. Such
changes indicate a shift from rather glacial and nival to more pluvial
runoff regimes, particularly for the Indus Basin. Furthermore, the rise in
the projected runoff, along with the increase in precipitation during summer
and autumn, indicates an intensification of the summer monsoon regime for all
study basins. 2014/02/05 - 07:11

Modelling multiple threats to water security in the Peruvian Amazon using the WaterWorld policy support systemEarth System Dynamics, 5, 55-65, 2014Author(s): A. J. J. van Soesbergen and M. MulliganThis paper describes the application of WaterWorld (
to the Peruvian Amazon, an area that is increasingly under
pressure from deforestation and water pollution as a result of population
growth, rural-to-urban migration and oil and gas extraction, potentially
impacting both water quantity and water quality. By applying single and
combined plausible scenarios of climate change, deforestation around
existing and planned roads, population growth and rural–urban migration,
mining and oil and gas exploitation, we explore the potential combined impacts of
these multiple changes on water resources in the Peruvian Amazon. 2014/01/31 - 16:11

Applying the concept of "energy return on investment" to desert greening of the Sahara/Sahel using a global climate modelEarth System Dynamics, 5, 43-53, 2014Author(s): S. P. K. Bowring, L. M. Miller, L. Ganzeveld, and A. KleidonAltering the large-scale dynamics of the Earth system through continual and
deliberate human intervention now seems possible. In doing so, one should
question the energetic sustainability of such interventions. Here, from the
basis that a region might be unnaturally vegetated by employing
technological means, we apply the metric of "energy return on investment"
(EROI) to benchmark the energetic sustainability of such a scenario. We do
this by applying EROI to a series of global climate model simulations where
the entire Sahara/Sahel region is irrigated with increased rates of
desalinated water to produce biomass. The energy content of this biomass is
greater than the energy input rate for a minimum irrigation rate of about
200 mm yr−1 in the winter and 500 mm yr−1 in the summer,
thereby yielding an EROI ratio >1 : 1, expressing energetic
sustainability. Quantified annually, the EROI was >1 : 1 for irrigation
rates more than 500 mm yr−1, progressively increasing to a maximum of
1.8 : 1 with 900 mm yr−1, and then decreasing with further increases
in the irrigation rate. Including the precipitation feedback arising from
changes in moisture recycling within the study region approximately doubles
these EROI ratios. This overall result varies spatially and temporally, so
while the entire Sahara/Sahel region is irrigated equally, the western
coastal region from June to August had the highest EROI. Other factors would
complicate such a large-scale modification of the Earth system, but this
sensitivity study concludes that with a required energy input, desert
greening may be energetically sustainable. More specifically, we have shown
how this type of EROI analysis could be applied as a metric to assess a
diverse range of human alterations to, and interventions within, the Earth
system. 2014/01/30 - 16:43

Comment on "Carbon farming in hot, dry coastal areas: an option for climate change mitigation" by Becker et al. (2013)Earth System Dynamics, 5, 41-42, 2014Author(s): M. HeimannBecker et al. (2013) argue that an afforestation of
0.73 × 109 ha with Jatropha curcas plants would generate an additional terrestrial
carbon sink of 4.3 PgC yr−1, enough to stabilise the atmospheric
mixing ratio of carbon dioxide (CO2) at current levels. However, this is
not consistent with the dynamics of the global carbon cycle. Using a
well-established global carbon cycle model, the effect of adding such a
hypothetical sink leads to a reduction of atmospheric CO2 levels in the
year 2030 by 25 ppm compared to a reference scenario. However, the
stabilisation of the atmospheric CO2 concentration requires a much
larger additional sink or corresponding reduction of anthropogenic emissions. 2014/01/29 - 11:15

Global modeling of withdrawal, allocation and consumptive use of surface water and groundwater resourcesEarth System Dynamics, 5, 15-40, 2014Author(s): Y. Wada, D. Wisser, and M. F. P. BierkensTo sustain growing food demand and increasing standard of living, global
water withdrawal and consumptive water use have been increasing rapidly. To
analyze the human perturbation on water resources consistently over large
scales, a number of macro-scale hydrological models (MHMs) have been
developed in recent decades. However, few models consider the interaction
between terrestrial water fluxes, and human activities and associated water
use, and even fewer models distinguish water use from surface water and
groundwater resources. Here, we couple a global water demand model with a
global hydrological model and dynamically simulate daily water withdrawal
and consumptive water use over the period 1979–2010, using two re-analysis
products: ERA-Interim and MERRA. We explicitly take into account the mutual
feedback between supply and demand, and implement a newly developed water
allocation scheme to distinguish surface water and groundwater use.
Moreover, we include a new irrigation scheme, which works dynamically with a
daily surface and soil water balance, and incorporate the newly available
extensive Global Reservoir and Dams data set (GRanD). Simulated surface water and
groundwater withdrawals generally show good agreement with reported national
and subnational statistics. The results show a consistent increase in both
surface water and groundwater use worldwide, with a more rapid increase in
groundwater use since the 1990s. Human impacts on terrestrial water storage
(TWS) signals are evident, altering the seasonal and interannual
variability. This alteration is particularly large over heavily regulated
basins such as the Colorado and the Columbia, and over the major irrigated
basins such as the Mississippi, the Indus, and the Ganges. Including human
water use and associated reservoir operations generally improves the
correlation of simulated TWS anomalies with those of the GRACE observations. 2014/01/14 - 23:45

An interaction network perspective on the relation between patterns of sea surface temperature variability and global mean surface temperatureEarth System Dynamics, 5, 1-14, 2014Author(s): A. Tantet and H. A. DijkstraOn interannual- to multidecadal timescales variability in sea surface temperature
appears to be organized in large-scale spatiotemporal patterns. In this paper, we
investigate these patterns by studying the community structure of interaction
networks constructed from sea surface temperature observations. Much of the
community structure can be interpreted using
known dominant patterns of variability, such as the El Niño/Southern Oscillation
and the Atlantic Multidecadal Oscillation. The community
detection method allows us to bypass some shortcomings of Empirical Orthogonal
Function analysis or composite analysis and can provide additional
information with respect to these classical analysis tools.
In addition, the study of the relationship
between the communities and indices of global surface temperature shows that,
while El Niño–Southern Oscillation is most dominant on interannual timescales,
the Indian West Pacific and
North Atlantic may also play a key role on decadal timescales. Finally, we show
that the comparison of the community structure from simulations and observations
can help detect model biases. 2014/01/04 - 12:56

A simple explanation for the sensitivity of the hydrologic cycle to surface temperature and solar radiation and its implications for global climate changeEarth System Dynamics, 4, 455-465, 2013Author(s): A. Kleidon and M. RennerThe global hydrologic cycle is likely to increase in strength with global
warming, although some studies indicate that warming due to solar absorption
may result in a different sensitivity than warming due to an elevated
greenhouse effect. Here we show that these sensitivities of the hydrologic
cycle can be derived analytically from an extremely simple surface energy
balance model that is constrained by the assumption that vertical convective
exchange within the atmosphere operates at the thermodynamic limit of maximum
power. Using current climatic mean conditions, this model predicts a
sensitivity of the hydrologic cycle of 2.2% K−1 to
greenhouse-induced surface warming which is the sensitivity reported from
climate models. The sensitivity to solar-induced warming includes an
additional term, which increases the total sensitivity to 3.2% K−1.
These sensitivities are explained by shifts in the turbulent fluxes in the
case of greenhouse-induced warming, which is proportional to the change in
slope of the saturation vapor pressure, and in terms of an additional
increase in turbulent fluxes in the case of solar radiation-induced warming.
We illustrate an implication of this explanation for geoengineering, which
aims to undo surface temperature differences by solar radiation management.
Our results show that when such an intervention compensates surface warming,
it cannot simultaneously compensate the changes in hydrologic cycling because
of the differences in sensitivities for solar vs. greenhouse-induced surface
warming. We conclude that the sensitivity of the hydrologic cycle to surface
temperature can be understood and predicted with very simple physical
considerations but this needs to reflect on the different roles that solar and
terrestrial radiation play in forcing the hydrologic cycle. 2013/12/06 - 09:18

Do GCMs predict the climate ... or macroweather?Earth System Dynamics, 4, 439-454, 2013Author(s): S. Lovejoy, D. Schertzer, and D. VaronWe are used to the weather–climate dichotomy, yet the great majority of
the spectral variance of atmospheric fields is in the continuous
"background" and this defines instead a trichotomy with a "macroweather"
regime in the intermediate range from ≈10 days to 10–30 yr
(≈100 yr in the preindustrial period). In the weather,
macroweather and climate regimes, exponents characterize the type of
variability over the entire regime and it is natural to identify them with
qualitatively different synergies of nonlinear dynamical mechanisms that
repeat scale after scale. Since climate models are essentially
meteorological models (although with extra couplings) it is thus important
to determine whether they currently model all three regimes. Using last
millennium simulations from four GCMs (global circulation models), we show that control runs only
reproduce macroweather. When various (reconstructed) climate forcings are
included, in the recent (industrial) period they show global fluctuations
strongly increasing at scales > ≈10–30 yr, which is quite
close to the observations. However, in the preindustrial period we find
that the multicentennial variabilities are too weak and by analysing the
scale dependence of solar and volcanic forcings, we argue that these forcings are
unlikely to be sufficiently strong to account for the multicentennial and
longer-scale temperature variability. A likely explanation is that the
models lack important slow "climate" processes such as land ice or various
biogeochemical processes. 2013/11/29 - 07:23

The dynamics of the Snowball Earth Hadley circulation for off-equatorial and seasonally varying insolationEarth System Dynamics, 4, 425-438, 2013Author(s): A. VoigtI study the Hadley circulation of a completely ice-covered Snowball Earth
through simulations with a comprehensive atmosphere general circulation
model. Because the Snowball Earth atmosphere is an example of a dry
atmosphere, these simulations allow me to test to what extent dry theories
and idealized models capture the dynamics of realistic dry Hadley circulations.
Perpetual off-equatorial as well as seasonally varying insolation is used,
extending a previous study for perpetual on-equatorial (equinox) insolation.
Vertical diffusion of momentum, representing the momentum transport of dry
convection, is fundamental to the momentum budgets of both the winter and
summer cells. In the zonal budget, it is the primary process balancing the
Coriolis force. In the meridional budget, it mixes meridional momentum
between the upper and the lower branch and thereby decelerates the
circulation. Because of the latter, the circulation intensifies by a factor
of three when vertical diffusion of momentum is suppressed. For
seasonally varying insolation, the circulation undergoes rapid transitions
from the weak summer into the strong winter regime. Consistent with previous
studies in idealized models, these transitions result from a mean-flow
feedback, because of which they are insensitive to the treatment of vertical
diffusion of momentum. Overall, the results corroborate previous findings for
perpetual on-equatorial insolation. They demonstrate that descriptions of
realistic dry Hadley circulations, in particular their strength, need
to incorporate the vertical momentum transport by dry convection, a process
that is neglected in most dry theories and idealized models. An improved
estimate of the strength of the Snowball Earth Hadley circulation will also
help to better constrain the climate of a possible Neoproterozoic Snowball
Earth and its deglaciation threshold. 2013/11/29 - 07:23

Can bioenergy cropping compensate high carbon emissions from large-scale deforestation of high latitudes?Earth System Dynamics, 4, 409-424, 2013Author(s): P. Dass, C. Müller, V. Brovkin, and W. CramerNumerous studies have concluded that deforestation of the high latitudes
result in a global cooling. This is mainly because of the increased albedo
of deforested land which dominates over other biogeophysical and
biogeochemical mechanisms in the energy balance. This dominance, however, may
be due to an underestimation of the biogeochemical response, as carbon
emissions are typically at or below the lower end of estimates. Here, we use
the dynamic global vegetation model LPJmL for a better estimate of the
carbon cycle under such large-scale deforestation. These studies are purely
theoretical in order to understand the role of vegetation in the energy balance and the
earth system. They must not be mistaken as possible mitigation options,
because of the devastating effects on pristine ecosystems. For realistic
assumptions of land suitability, the total emissions computed in this study
are higher than that of previous studies assessing the effects of boreal
deforestation. The warming due to biogeochemical effects ranges from 0.12 to
0.32 °C, depending on the climate sensitivity. Using LPJmL to
assess the mitigation potential of bioenergy plantations in the suitable
areas of the deforested region, we find that the global biophysical
bioenergy potential is 68.1 ± 5.6 EJ yr−1 of primary energy at
the end of the 21st century in the most plausible scenario. The
avoided combustion of fossil fuels over the time frame of this experiment
would lead to further cooling. However, since the carbon debt caused
by the cumulative emissions is not repaid by the end of the 21st
century, the global temperatures would increase by 0.04 to 0.11 °C.
The carbon dynamics in the high latitudes especially with respect to
permafrost dynamics and long-term carbon losses, require additional
attention in the role for the Earth's carbon and energy budget. 2013/11/19 - 23:08

Implications of accounting for land use in simulations of ecosystem carbon cycling in AfricaEarth System Dynamics, 4, 385-407, 2013Author(s): M. Lindeskog, A. Arneth, A. Bondeau, K. Waha, J. Seaquist, S. Olin, and B. SmithDynamic global vegetation models (DGVMs) are important tools for modelling
impacts of global change on ecosystem services. However, most models do not
take full account of human land management and land use and land cover
changes (LULCCs). We integrated croplands and pasture and their management
and natural vegetation recovery and succession following cropland
abandonment into the LPJ-GUESS DGVM. The revised model was applied to Africa
as a case study to investigate the implications of accounting for land use
on net ecosystem carbon balance (NECB) and the skill of the model in
describing agricultural production and reproducing trends and patterns in
vegetation structure and function. The seasonality of modelled monthly
fraction of absorbed photosynthetically active radiation (FPAR) was shown to
agree well with satellite-inferred normalised difference vegetation index
(NDVI). In regions with a large proportion of cropland, the managed land
addition improved the FPAR vs. NDVI fit significantly. Modelled 1991–1995
average yields for the seven most important African crops, representing
potential optimal yields limited only by climate forcings, were generally
higher than reported FAO yields by a factor of 2–6, similar to previous
yield gap estimates. Modelled inter-annual yield variations during 1971–2005
generally agreed well with FAO statistics, especially in regions with
pronounced climate seasonality. Modelled land–atmosphere carbon fluxes for
Africa associated with land use change (0.07 PgC yr−1 release to the
atmosphere for the 1980s) agreed well with previous estimates. Cropland
management options (residue removal, grass as cover crop) were shown to be
important to the land–atmosphere carbon flux for the 20th century. 2013/11/02 - 13:10

Comment on "Polynomial cointegration tests of anthropogenic impact on global warming" by Beenstock et al. (2012) – some hazards in econometric modelling of climate changeEarth System Dynamics, 4, 375-384, 2013Author(s): F. Pretis and D. F. HendryWe outline six important hazards that can be encountered in econometric
modelling of time-series data, and apply that analysis to demonstrate errors
in the empirical modelling of climate data in Beenstock et al. (2012). We show that
the claim made in Beenstock et al. (2012) as to the different degrees of
integrability of CO2 and temperature is incorrect. In particular, the
level of integration is not constant and not intrinsic to the process.
Further, we illustrate that the measure of anthropogenic forcing in
Beenstock et al. (2012), a constructed "anthropogenic anomaly", is not appropriate
regardless of the time-series properties of the data. 2013/10/23 - 12:10

Comparing projections of future changes in runoff from hydrological and biome models in ISI-MIPEarth System Dynamics, 4, 359-374, 2013Author(s): J. C. S. Davie, P. D. Falloon, R. Kahana, R. Dankers, R. Betts, F. T. Portmann, D. Wisser, D. B. Clark, A. Ito, Y. Masaki, K. Nishina, B. Fekete, Z. Tessler, Y. Wada, X. Liu, Q. Tang, S. Hagemann, T. Stacke, R. Pavlick, S. Schaphoff, S. N. Gosling, W. Franssen, and N. ArnellFuture changes in runoff can have important implications for water
resources and flooding. In this study, runoff projections from ISI-MIP
(Inter-sectoral Impact Model Intercomparison Project) simulations
forced with HadGEM2-ES bias-corrected climate data under the Representative
Concentration Pathway 8.5 have been analysed for differences between
impact models. Projections of change from a baseline period (1981–2010)
to the future (2070–2099) from 12 impacts models which contributed
to the hydrological and biomes sectors of ISI-MIP were studied. The
biome models differed from the hydrological models by the inclusion
of CO2 impacts and most also included a dynamic vegetation
distribution. The biome and hydrological models agreed on the sign
of runoff change for most regions of the world. However, in West
Africa, the hydrological models projected drying, and the biome models
a moistening. The biome models tended to produce larger increases
and smaller decreases in regionally averaged runoff than the hydrological
models, although there is large inter-model spread. The timing of
runoff change was similar, but there were differences in magnitude,
particularly at peak runoff. The impact of vegetation distribution
change was much smaller than the projected change over time, while
elevated CO2 had an effect as large as the magnitude
of change over time projected by some models in some regions. The
effect of CO2 on runoff was not consistent across the
models, with two models showing increases and two decreases. There
was also more spread in projections from the runs with elevated CO2
than with constant CO2. The biome models which gave increased
runoff from elevated CO2 were also those which differed
most from the hydrological models. Spatially, regions with most difference
between model types tended to be projected to have most effect from
elevated CO2, and seasonal differences were also similar,
so elevated CO2 can partly explain the differences between
hydrological and biome model runoff change projections. Therefore,
this shows that a range of impact models should be considered to give
the full range of uncertainty in impacts studies. 2013/10/11 - 10:10

Critical impacts of global warming on land ecosystemsEarth System Dynamics, 4, 347-357, 2013Author(s): S. Ostberg, W. Lucht, S. Schaphoff, and D. GertenGlobally increasing temperatures are likely to have impacts on terrestrial,
aquatic and marine ecosystems that are difficult to manage. Quantifying
impacts worldwide and systematically as a function of global warming is
fundamental to substantiating the discussion on climate mitigation targets
and adaptation planning. Here we present a macro-scale analysis of climate
change impacts on terrestrial ecosystems based on newly developed sets of
climate scenarios featuring a step-wise sampling of global mean temperature
increase between 1.5 and 5 K by 2100. These are processed by a
biogeochemical model (LPJmL) to derive an aggregated metric of simultaneous
biogeochemical and structural shifts in land surface properties which we
interpret as a proxy for the risk of shifts and possibly disruptions in

Our results show a substantial risk of climate change to transform
terrestrial ecosystems profoundly. Nearly no area of the world is free from
such risk, unless strong mitigation limits global warming to around 2 degrees
above preindustrial level. Even then, our simulations for most climate models
agree that up to one-fifth of the land surface may experience at least
moderate ecosystem change, primarily at high latitudes and high altitudes. If
countries fulfil their current emissions reduction pledges, resulting in
roughly 3.5 K of warming, this area expands to cover half the land surface,
including the majority of tropical forests and savannas and the boreal zone.
Due to differences in regional patterns of climate change, the area
potentially at risk of major ecosystem change considering all climate models
is up to 2.5 times as large as for a single model. 2013/10/09 - 08:55

The impact of nitrogen and phosphorous limitation on the estimated terrestrial carbon balance and warming of land use change over the last 156 yrEarth System Dynamics, 4, 333-345, 2013Author(s): Q. Zhang, A. J. Pitman, Y. P. Wang, Y. J. Dai, and P. J. LawrenceWe examine the impact of land use and land cover change (LULCC) over the
period from 1850 to 2005 using an Earth system model that incorporates
nitrogen and phosphorous limitation on the terrestrial carbon cycle. We
compare the estimated CO2 emissions and warming from land use change in
a carbon-only version of the model with those from simulations, including
nitrogen and phosphorous limitation. If we omit nutrients, our results
suggest LULCC cools on the global average by about 0.1 °C. Including
nutrients reduces this cooling to ~ 0.05 °C. Our results
also suggest LULCC has a major impact on total land carbon over the period
1850–2005. In carbon-only simulations, the inclusion of LULCC decreases the
total additional land carbon stored in 2005 from around 210 Pg C to 85 Pg C.
Including nitrogen and phosphorous limitation also decreases the scale of
the terrestrial carbon sink to 80 Pg C. Shown as corresponding fluxes,
adding LULCC on top of the nutrient-limited simulations changes the sign of
the terrestrial carbon flux from a sink to a source (12 Pg C). The CO2
emission from LULCC from 1850 to 2005 is estimated to be 130 Pg C for carbon
only simulation, or 97 Pg C if nutrient limitation is accounted for in our
model. The difference between these two estimates of CO2 emissions from
LULCC largely results from the weaker response of photosynthesis to
increased CO2 and smaller carbon pool sizes, and therefore lower carbon
loss from plant and wood product carbon pools under nutrient limitation. We
suggest that nutrient limitation should be accounted for in simulating the
effects of LULCC on the past climate and on the past and future carbon
budget. 2013/09/16 - 17:54

Quantifying drivers of chemical disequilibrium: theory and application to methane in the Earth's atmosphereEarth System Dynamics, 4, 317-331, 2013Author(s): E. Simoncini, N. Virgo, and A. KleidonIt has long been observed that Earth's atmosphere is uniquely far from its
thermochemical equilibrium state in terms of its chemical composition.
Studying this state of disequilibrium is important both for understanding the
role that life plays in the Earth system, and for its potential role in the
detection of life on exoplanets. Here we present a methodology for assessing
the strength of the biogeochemical cycling processes that drive
disequilibrium in planetary atmospheres. We apply it to the simultaneous
presence of CH4 and O2 in Earth's atmosphere, which has long been
suggested as a sign of life that could be detected remotely. Using a
simplified model, we identify that the most important property to quantify is
not the distance from equilibrium, but the power required to drive it. A weak
driving force can maintain a high degree of disequilibrium if the residence
times of the compounds involved are long; but if the disequilibrium is high
and the kinetics fast, we can conclude that the disequilibrium must be driven
by a substantial source of energy. Applying this to Earth's atmosphere, we
show that the biotically generated portion of the power required to maintain
the methane–oxygen disequilibrium is around 0.67 TW, although the
uncertainty in this figure is about 10% due to uncertainty in the global
CH4 production. Compared to the chemical energy generated by the biota
by photosynthesis, 0.67 TW represents only a very small fraction and,
perhaps surprisingly, is of a comparable magnitude to abiotically driven
geochemical processes at the Earth's surface. We discuss the implications of
this new approach, both in terms of enhancing our understanding of the Earth
system, and in terms of its impact on the possible detection of distant
photosynthetic biospheres. 2013/09/12 - 10:59

Climate response to imposed solar radiation reductions in high latitudesEarth System Dynamics, 4, 301-315, 2013Author(s): M. C. MacCracken, H.-J. Shin, K. Caldeira, and G. A. Ban-WeissWith human-induced climate change leading to amplified warming in high
latitudes, mitigation alone is unlikely to be rapid enough to prevent
significant, even irreversible, impacts. Model simulations in which solar
insolation was arbitrarily reduced poleward of 51, 61, or 71°
latitude in one or both hemispheres not only cooled those regions, but also
drew energy from lower latitudes, exerting a cooling influence over much of
the particular hemisphere in which the reduction was imposed. The
simulations, conducted using the National Center for Atmospheric Research's
CAM3.1 atmospheric model coupled to a slab ocean, indicated that
high-latitude reductions in absorbed solar radiation have a significantly
larger cooling influence than solar reductions of equivalent magnitude
spread evenly over the Earth. This amplified influence occurred primarily
because concentrated high-latitude reductions in solar radiation led to
increased sea ice fraction and surface albedo, thereby amplifying the energy
deficit at the top of the atmosphere as compared to the response for an
equivalent reduction in solar radiation spread evenly over the globe.
Reductions in incoming solar radiation in one polar region (either north or
south) resulted in increased poleward energy transport during that
hemisphere's cold season and shifted the Inter-Tropical Convergence Zone
(ITCZ) away from that pole, whereas comparable solar reductions in both
polar regions resulted in increased poleward energy transport, but tended to
leave the ITCZ approximately in place. Together, these results suggest that,
until emissions reductions are sufficient to limit the warming influence of
increasing greenhouse gas concentrations, polar reductions in solar
radiation, if they could be efficiently and effectively implemented, warrant
further research as an approach to moderating the early stages of both
high-latitude and global warming. 2013/09/02 - 21:08

Consistent increase in Indian monsoon rainfall and its variability across CMIP-5 modelsEarth System Dynamics, 4, 287-300, 2013Author(s): A. Menon, A. Levermann, J. Schewe, J. Lehmann, and K. FrielerThe possibility of an impact of global warming on the Indian monsoon is of
critical importance for the large population of this region. Future
projections within the Coupled Model Intercomparison Project Phase 3 (CMIP-3)
showed a wide range of trends with varying magnitude and sign across models.
Here the Indian summer monsoon rainfall is evaluated in 20 CMIP-5 models for
the period 1850 to 2100. In the new generation of climate models, a consistent
increase in seasonal mean rainfall during the summer monsoon periods arises.
All models simulate stronger seasonal mean rainfall in the future compared to
the historic period under the strongest warming scenario RCP-8.5. Increase in
seasonal mean rainfall is the largest for the RCP-8.5 scenario compared to
other RCPs. Most of the models show a northward shift in monsoon circulation
by the end of the 21st century compared to the historic period under
the RCP-8.5 scenario. The interannual variability of the Indian monsoon
rainfall also shows a consistent positive trend under unabated global
warming. Since both the long-term increase in monsoon rainfall as well as the
increase in interannual variability in the future is robust across a wide
range of models, some confidence can be attributed to these projected trends. 2013/08/28 - 16:17

Variation in emission metrics due to variation in CO2 and temperature impulse response functionsEarth System Dynamics, 4, 267-286, 2013Author(s): D. J. L. Olivié and G. P. PetersEmission metrics are used to compare the climate effect of the emission of
different species, such as carbon dioxide (CO2) and methane (CH4).
The most common metrics use linear impulse response functions (IRFs)
derived from a single more complex model. There is currently little
understanding on how IRFs vary across models, and how the model variation
propagates into the metric values.

In this study, we first derive CO2 and temperature IRFs for a large
number of complex models participating in different intercomparison
exercises, synthesizing the results in distributions representing the variety
in behaviour. The derived IRF distributions differ considerably, which is
partially related to differences among the underlying models, and partially
to the specificity of the scenarios used (experimental setup).

In a second part of the study, we investigate how differences among the IRFs
impact the estimates of global warming potential (GWP), global temperature
change potential (GTP) and integrated global temperature change potential
(iGTP) for time horizons between 20 and 500 yr.

Within each derived CO2 IRF distribution, underlying model
differences give similar spreads on the metrics in the range of −20 to
+40% (5–95% spread), and these spreads are similar among the three

GTP and iGTP metrics are also impacted by variation in the temperature IRF.
For GTP, this impact depends strongly on the lifetime of the species and the
time horizon. The GTP of black carbon shows spreads of up to −60 to +80% for
time horizons to 100 yr, and even larger spreads for longer time horizons.
For CH4 the impact from variation in the temperature IRF is still
large, but it becomes smaller for longer-lived species. The impact from
variation in the temperature IRF on iGTP is small and falls within a range of
±10% for all species and time horizons considered here.

We have used the available data to estimate the IRFs, but we suggest the use
of tailored intercomparison projects specific for IRFs in emission metrics.
Intercomparison projects are an effective means to derive an IRF and its
model spread for use in metrics, but more detailed analysis is required to
explore a wider range of uncertainties. Further work can reveal which
parameters in each IRF lead to the largest uncertainties, and this
information may be used to reduce the uncertainty in metric values. 2013/08/09 - 20:16

The sensitivity of the modeled energy budget and hydrological cycle to CO2 and solar forcingEarth System Dynamics, 4, 253-266, 2013Author(s): N. Schaller, J. Cermak, M. Wild, and R. KnuttiThe transient responses of the energy budget and the hydrological cycle to
CO2 and solar forcings of the same magnitude in a global climate model
are quantified in this study. Idealized simulations are designed to test the
assumption that the responses to forcings are linearly additive, i.e. whether
the response to individual forcings can be added to estimate the responses to
the combined forcing, and to understand the physical processes occurring as a
response to a surface warming caused by CO2 or solar forcing increases
of the same magnitude. For the global climate model considered, the responses
of most variables of the energy budget and hydrological cycle, including
surface temperature, do not add linearly. A separation of the response into a
forcing and a feedback term shows that for precipitation, this non-linearity
arises from the feedback term, i.e. from the non-linearity of the temperature
response and the changes in the water cycle resulting from it. Further,
changes in the energy budget show that less energy is available at the
surface for global annual mean latent heat flux, and hence global annual mean
precipitation, in simulations of transient CO2 concentration increase
compared to simulations with an equivalent transient increase in the solar
constant. On the other hand, lower tropospheric water vapor increase is
similar between simulations with CO2 and solar forcing increase of the
same magnitude. The response in precipitation is therefore more muted
compared to the response in water vapor in CO2 forcing simulations,
leading to a larger increase in residence time of water vapor in the
atmosphere compared to solar forcing simulations. Finally, energy budget
calculations show that poleward atmospheric energy transport increases more
in solar forcing compared to equivalent CO2 forcing simulations, which
is in line with the identified strong increase in large-scale precipitation
in solar forcing scenarios. 2013/08/02 - 21:25

Carbon farming in hot, dry coastal areas: an option for climate change mitigationEarth System Dynamics, 4, 237-251, 2013Author(s): K. Becker, V. Wulfmeyer, T. Berger, J. Gebel, and W. MünchWe present a comprehensive, interdisciplinary project which demonstrates that
large-scale plantations of Jatropha curcas – if established in hot,
dry coastal areas around the world – could capture 17–25 t of carbon
dioxide per hectare per year from the atmosphere (over a 20 yr period). Based
on recent farming results it is confirmed that the Jatropha curcas
plant is well adapted to harsh environments and is capable of growing alone
or in combination with other tree and shrub species with minimal irrigation
in hot deserts where rain occurs only sporadically. Our investigations
indicate that there is sufficient unused and marginal land for the widespread
cultivation of Jatropha curcas to have a significant impact on
atmospheric CO2 levels at least for several decades.

In a system in which desalinated seawater is used for irrigation and for
delivery of mineral nutrients, the sequestration costs were estimated to
range from 42–63 EUR per tonne CO2. This result makes carbon
farming a technology that is competitive with carbon capture and storage
(CCS). In addition, high-resolution simulations using an advanced
land-surface–atmosphere model indicate that a 10 000 km2 plantation
could produce a reduction in mean surface temperature and an onset or
increase in rain and dew fall at a regional level. In such areas, plant
growth and CO2 storage could continue until permanent woodland or forest
had been established. In other areas, salinization of the soil may limit
plant growth to 2–3 decades whereupon irrigation could be ceased and the
captured carbon stored as woody biomass. 2013/07/31 - 19:11

A trend-preserving bias correction – the ISI-MIP approachEarth System Dynamics, 4, 219-236, 2013Author(s): S. Hempel, K. Frieler, L. Warszawski, J. Schewe, and F. PiontekStatistical bias correction is commonly applied within climate impact
modelling to correct climate model data for systematic deviations of the
simulated historical data from observations. Methods are based on transfer
functions generated to map the distribution of the simulated historical data
to that of the observations. Those are subsequently applied to correct the
future projections. Here, we present the bias correction method that was developed
within ISI-MIP, the first Inter-Sectoral Impact Model Intercomparison Project.
ISI-MIP is designed to synthesise impact projections in the agriculture,
water, biome, health, and infrastructure sectors at different levels of
global warming.

Bias-corrected climate data that are used as input for the impact simulations
could be only provided over land areas. To ensure consistency with the global
(land + ocean) temperature information the bias correction method has to preserve
the warming signal. Here we present the applied method that preserves the absolute
changes in monthly temperature, and relative changes in monthly values of precipitation
and the other variables needed for ISI-MIP. The proposed methodology represents a
modification of the transfer function approach applied in the Water Model Intercomparison
Project (Water-MIP). Correction of the monthly mean is followed by correction of the daily
variability about the monthly mean.

Besides the general idea and technical details of the ISI-MIP method, we show and discuss the
potential and limitations of the applied bias correction. In particular, while
the trend and the long-term mean are well represented, limitations with regards
to the adjustment of the variability persist which may affect, e.g. small scale
features or extremes. 2013/07/31 - 19:11

Hydrological cycle over South and Southeast Asian river basins as simulated by PCMDI/CMIP3 experimentsEarth System Dynamics, 4, 199-217, 2013Author(s): S. Hasson, V. Lucarini, and S. PascaleWe investigate how the climate models contributing to
the PCMDI/CMIP3 dataset describe the hydrological cycle over four major South
and Southeast Asian river basins (Indus, Ganges, Brahmaputra and Mekong) for
the 20th, 21st (13 models) and 22nd (10 models) centuries. For the 20th century,
some models do not seem to conserve water at the river basin scale up to a
good degree of approximation. The simulated precipitation minus evaporation
(P − E), total runoff (R) and precipitation (P) quantities are
neither consistent with the observations nor among the models themselves.
Most of the models underestimate P − E for all four river basins,
which is mainly associated with the underestimation of precipitation. This is
in agreement with the recent results on the biases of the representation of
monsoonal dynamics by GCMs. Overall, a modest inter-model agreement is found
only for the evaporation and inter-annual variability of P − E. For
the 21st and 22nd centuries, models agree on the negative (positive) changes
of P − E for the Indus basin (Ganges, Brahmaputra and Mekong basins).
Most of the models foresee an increase in the inter-annual variability of
P − E for the Ganges and Mekong basins, thus suggesting an increase
in large low-frequency dry/wet events. Instead, no considerable future change
in the inter-annual variability of P − E is found for the Indus and
Brahmaputra basins. 2013/07/31 - 19:11

A stochastic model for the polygonal tundra based on Poisson–Voronoi diagramsEarth System Dynamics, 4, 187-198, 2013Author(s): F. Cresto Aleina, V. Brovkin, S. Muster, J. Boike, L. Kutzbach, T. Sachs, and S. ZuyevSubgrid processes occur in various ecosystems and landscapes but, because of
their small scale, they are not represented or poorly parameterized in
climate models. These local heterogeneities are often important or even
fundamental for energy and carbon balances. This is especially true for
northern peatlands and in particular for the polygonal tundra, where methane
emissions are strongly influenced by spatial soil heterogeneities. We present
a stochastic model for the surface topography of polygonal tundra using
Poisson–Voronoi diagrams and we compare the results with available recent
field studies. We analyze seasonal dynamics of water table variations and the
landscape response under different scenarios of precipitation income. We
upscale methane fluxes by using a simple idealized model for methane
emission. Hydraulic interconnectivities and large-scale drainage may also be
investigated through percolation properties and thresholds in the Voronoi
graph. The model captures the main statistical characteristics of the
landscape topography, such as polygon area and surface properties as well as
the water balance. This approach enables us to statistically relate
large-scale properties of the system to the main small-scale processes within
the single polygons. 2013/07/11 - 09:10

A theoretical framework for the net land-to-atmosphere CO2 flux and its implications in the definition of "emissions from land-use change"Earth System Dynamics, 4, 171-186, 2013Author(s): T. Gasser and P. CiaisWe develop a theoretical framework and analysis of the net land-to-atmosphere
CO2 flux in order to discuss possible definitions of "emissions from
land-use change". The terrestrial biosphere is affected by two
perturbations: the perturbation of the global carbon-climate-nitrogen system
(CCN) with elevated atmospheric CO2, climate change and nitrogen
deposition; and the land-use change perturbation (LUC). Here, we
progressively establish mathematical definitions of four generic components
of the net land-to-atmosphere CO2 flux. The two first components are the
fluxes that would be observed if only one perturbation occurred. The two
other components are due to the coupling of the CCN and LUC perturbations,
which shows the non-linear response of the terrestrial carbon cycle. Thanks
to these four components, we introduce three possible definitions of
"emissions from land-use change" that are indeed used in the scientific
literature, often without clear distinctions, and we draw conclusions as for
their absolute and relative behaviors. Thanks to the OSCAR v2 model, we
provide quantitative estimates of the differences between the three
definitions, and we find that comparing results from studies that do not use
the same definition can lead to a bias of up to 20% between estimates of
those emissions. After discussion of the limitations of the framework, we
conclude on the three major points of this study that should help the
community to reconcile modeling and observation of emissions from land-use
change. The appendix mainly provides more detailed mathematical expressions
of the four components of the net land-to-atmosphere CO2 flux. 2013/06/07 - 17:25

Simple emission metrics for climate impactsEarth System Dynamics, 4, 145-170, 2013Author(s): B. Aamaas, G. P. Peters, and J. S. FuglestvedtIn the context of climate change, emissions of different species (e.g.,
carbon dioxide and methane) are not directly comparable since they have
different radiative efficiencies and lifetimes. Since comparisons via
detailed climate models are computationally expensive and complex, emission
metrics were developed to allow a simple and straightforward comparison of
the estimated climate impacts of emissions of different species. Emission
metrics are not unique and variety of different emission metrics has been
proposed, with key choices being the climate impacts and time horizon to use
for comparisons. In this paper, we present analytical expressions and
describe how to calculate common emission metrics for different species. We
include the climate metrics radiative forcing, integrated radiative forcing,
temperature change and integrated temperature change in both absolute form
and normalised to a reference gas. We consider pulse emissions, sustained
emissions and emission scenarios. The species are separated into three
types: CO2 which has a complex decay over time, species with a simple
exponential decay, and ozone precursors (NOx, CO, VOC) which indirectly
effect climate via various chemical interactions. We also discuss deriving
Impulse Response Functions, radiative efficiency, regional dependencies,
consistency within and between metrics and uncertainties. We perform
various applications to highlight key applications of emission metrics,
which show that emissions of CO2 are important regardless of what
metric and time horizon is used, but that the importance of short lived
climate forcers varies greatly depending on the metric choices made.
Further, the ranking of countries by emissions changes very little with
different metrics despite large differences in metric values, except for the
shortest time horizons (GWP20). 2013/06/07 - 17:25

Climate change impact on available water resources obtained using multiple global climate and hydrology modelsEarth System Dynamics, 4, 129-144, 2013Author(s): S. Hagemann, C. Chen, D. B. Clark, S. Folwell, S. N. Gosling, I. Haddeland, N. Hanasaki, J. Heinke, F. Ludwig, F. Voss, and A. J. WiltshireClimate change is expected to alter the hydrological cycle resulting in
large-scale impacts on water availability. However, future climate change
impact assessments are highly uncertain. For the first time, multiple global
climate (three) and hydrological models (eight) were used to systematically
assess the hydrological response to climate change and project the future
state of global water resources. This multi-model ensemble allows us to
investigate how the hydrology models contribute to the uncertainty in
projected hydrological changes compared to the climate models. Due to their
systematic biases, GCM outputs cannot be used directly in hydrological impact
studies, so a statistical bias correction has been applied. The results show
a large spread in projected changes in water resources within the
climate–hydrology modelling chain for some regions. They clearly
demonstrate that climate models are not the only source of uncertainty for
hydrological change, and that the spread resulting from the choice of the
hydrology model is larger than the spread originating from the climate
models over many areas. But there are also areas showing a robust change
signal, such as at high latitudes and in some midlatitude regions, where
the models agree on the sign of projected hydrological changes, indicative
of higher confidence in this ensemble mean signal. In many catchments an
increase of available water resources is expected but there are some severe
decreases in Central and Southern Europe, the Middle East, the Mississippi
River basin, southern Africa, southern China and south-eastern Australia. 2013/05/07 - 21:44