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- ItemPredictability of twentieth century sea-level rise from past data(Bristol : IOP Publishing, 2013) Bittermann, Klaus; Rahmstorf, Stefan; Perrette, Mahé; Vermeer, MartinThe prediction of global sea-level rise is one of the major challenges of climate science. While process-based models are still being improved to capture the complexity of the processes involved, semi-empirical models, exploiting the observed connection between global-mean sea level and global temperature and calibrated with data, have been developed as a complementary approach. Here we investigate whether twentieth century sea-level rise could have been predicted with such models given a knowledge of twentieth century global temperature increase. We find that either proxy or early tide gauge data do not hold enough information to constrain the model parameters well. However, in combination, the use of proxy and tide gauge sea-level data up to 1900 AD allows a good prediction of twentieth century sea-level rise, despite this rise being well outside the rates experienced in previous centuries during the calibration period of the model. The 90% confidence range for the linear twentieth century rise predicted by the semi-empirical model is 13–30 cm, whereas the observed interval (using two tide gauge data sets) is 14–26 cm.
- ItemExtreme fire events are related to previous-year surface moisture conditions in permafrost-underlain larch forests of Siberia(Bristol : IOP Publishing, 2012) Forkel, Matthias; Thonicke, Kirsten; Beer, Christian; Cramer, Wolfgang; Bartalev, Sergey; Schmullius, ChristianeWildfires are a natural and important element in the functioning of boreal forests. However, in some years, fires with extreme spread and severity occur. Such severe fires can degrade the forest, affect human values, emit huge amounts of carbon and aerosols and alter the land surface albedo. Usually, wind, slope and dry air conditions have been recognized as factors determining fire spread. Here we identify surface moisture as an additional important driving factor for the evolution of extreme fire events in the Baikal region. An area of 127 000 km2 burned in this region in 2003, a large part of it in regions underlain by permafrost. Analyses of satellite data for 2002–2009 indicate that previous-summer surface moisture is a better predictor for burned area than precipitation anomalies or fire weather indices for larch forests with continuous permafrost. Our analysis advances the understanding of complex interactions between the atmosphere, vegetation and soil, and how coupled mechanisms can lead to extreme events. These findings emphasize the importance of a mechanistic coupling of soil thermodynamics, hydrology, vegetation functioning, and fire activity in Earth system models for projecting climate change impacts over the next century.
- ItemStrong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere(Washington, DC : NAS, 2018) Ditas, Jeannine; Ma, Nan; Zhang, Yuxuan; Assmann, Denise; Neumaier, Marco; Riede, Hella; Karu, Einar; Williams, Jonathan; Scharffe, Dieter; Wang, Qiaoqiao; Saturno, Jorge; Schwarz, Joshua P.; Katich, Joseph M.; McMeeking, Gavin R.; Zahn, Andreas; Hermann, Markus; Brenninkmeijer, Carl A. M.; Andreae, Meinrat O.; Pöschl, Ulrich; Su, Hang; Cheng, YafangWildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (∼140 ng·m−3, standard temperature and pressure) were over 20 times higher than the background concentration (∼6 ng·m−3) with more than 100-fold enhanced peak values (up to ∼720 ng·m−3). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was ∼120 nm with a mean coating thickness of ∼150 nm in the BB plume and ∼90 nm with a coating of ∼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of ∼1 nm·h−1 due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.
- ItemThe Vulnerability, Impacts, Adaptation and Climate Services Advisory Board (VIACS AB v1.0) contribution to CMIP6(München : European Geopyhsical Union, 2016) Ruane, Alex C.; Teichmann, Claas; Arnell, Nigel W.; Carter, Timothy R.; Ebi, Kristie L.; Frieler, Katja; Goodess, Clare M.; Hewitson, Bruce; Horton, Radley; Kovats, R. Sari; Lotze, Heike K.; Mearns, Linda O.; Navarra, Antonio; Ojima, Dennis S.; Riahi, Keywan; Rosenzweig, Cynthia; Themessl, Matthias; Vincent, KatharineThis paper describes the motivation for the creation of the Vulnerability, Impacts, Adaptation and Climate Services (VIACS) Advisory Board for the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6), its initial activities, and its plans to serve as a bridge between climate change applications experts and climate modelers. The climate change application community comprises researchers and other specialists who use climate information (alongside socioeconomic and other environmental information) to analyze vulnerability, impacts, and adaptation of natural systems and society in relation to past, ongoing, and projected future climate change. Much of this activity is directed toward the co-development of information needed by decision-makers for managing projected risks. CMIP6 provides a unique opportunity to facilitate a two-way dialog between climate modelers and VIACS experts who are looking to apply CMIP6 results for a wide array of research and climate services objectives. The VIACS Advisory Board convenes leaders of major impact sectors, international programs, and climate services to solicit community feedback that increases the applications relevance of the CMIP6-Endorsed Model Intercomparison Projects (MIPs). As an illustration of its potential, the VIACS community provided CMIP6 leadership with a list of prioritized climate model variables and MIP experiments of the greatest interest to the climate model applications community, indicating the applicability and societal relevance of climate model simulation outputs. The VIACS Advisory Board also recommended an impacts version of Obs4MIPs and indicated user needs for the gridding and processing of model output.
- ItemProjections for headwater catchments of the Tarim River reveal glacier retreat and decreasing surface water availability but uncertainties are large(Bristol : IOP Publishing, 2016) Duethmann, Doris; Menz, Christoph; Jiang, Tong; Vorogushyn, SergiyIn the Tarim River Basin, water resources from the mountain areas play a key role due to the extremely arid climate of the lowlands. This study presents an analysis of future climate change impacts on glaciers and surface water availability for headwater catchments of the Aksu River, the most important tributary to the Tarim River. We applied a glacio-hydrological model that underwent a comprehensive multivariable and multiobjective model calibration and evaluation, based on daily and interannual discharge variations and glacier mass changes. Transient glacier geometry changes are simulated using the Δh-approach. For the ensemble-based projections, we considered three different emission scenarios, nine global climate models (GCMs) and two regional climate models, and different hydrological model parameters derived from the multiobjective calibration. The results show a decline in glacier area of −90% to −32% until 2099 (reference ~2008) (based on the 5–95 percentile range of the ensemble). Glacier melt is anticipated to further increase or stay at a high level during the first decades of the 21st century, but then declines because of decreased glacier extents. Overall discharge in the Aksu headwaters is expected to be increased in the period 2010–2039 (reference 1971–2000), but decreased in 2070–2099. Seasonally, projections show an increase in discharge in spring and early summer throughout the 21st century. Discharge changes in mid to late summer are more variable, with increases or decreases depending on the considered period and GCM. Uncertainties are largely caused by differences between the different GCMs, with further important contributions from different emission scenarios in the second half of the 21st century. Contributions from the hydrological model parameters to the ensemble uncertainty were generally found to be small.
- ItemDeforestation in Amazonia impacts riverine carbon dynamics(München : European Geopyhsical Union, 2016) Langerwisch, Fanny; Walz, Ariane; Rammig, Anja; Tietjen, Britta; Thonicke, Kirsten; Cramer, WolfgangFluxes of organic and inorganic carbon within the Amazon basin are considerably controlled by annual flooding, which triggers the export of terrigenous organic material to the river and ultimately to the Atlantic Ocean. The amount of carbon imported to the river and the further conversion, transport and export of it depend on temperature, atmospheric CO2, terrestrial productivity and carbon storage, as well as discharge. Both terrestrial productivity and discharge are influenced by climate and land use change. The coupled LPJmL and RivCM model system (Langerwisch et al., 2016) has been applied to assess the combined impacts of climate and land use change on the Amazon riverine carbon dynamics. Vegetation dynamics (in LPJmL) as well as export and conversion of terrigenous carbon to and within the river (RivCM) are included. The model system has been applied for the years 1901 to 2099 under two deforestation scenarios and with climate forcing of three SRES emission scenarios, each for five climate models. We find that high deforestation (business-as-usual scenario) will strongly decrease (locally by up to 90%) riverine particulate and dissolved organic carbon amount until the end of the current century. At the same time, increase in discharge leaves net carbon transport during the first decades of the century roughly unchanged only if a sufficient area is still forested. After 2050 the amount of transported carbon will decrease drastically. In contrast to that, increased temperature and atmospheric CO2 concentration determine the amount of riverine inorganic carbon stored in the Amazon basin. Higher atmospheric CO2 concentrations increase riverine inorganic carbon amount by up to 20% (SRES A2). The changes in riverine carbon fluxes have direct effects on carbon export, either to the atmosphere via outgassing or to the Atlantic Ocean via discharge. The outgassed carbon will increase slightly in the Amazon basin, but can be regionally reduced by up to 60% due to deforestation. The discharge of organic carbon to the ocean will be reduced by about 40% under the most severe deforestation and climate change scenario. These changes would have local and regional consequences on the carbon balance and habitat characteristics in the Amazon basin itself as well as in the adjacent Atlantic Ocean.
- ItemImpacts of 1.5 versus 2.0 °c on cereal yields in the West African Sudan Savanna(Bristol : IOP Publishing, 2018) Faye, Babacar; Webber, Heidi; Naab, Jesse B.; MacCarthy, Dilys S.; Adam, Myriam; Ewert, Frank; Lamers, John P.A.; Schleussner, Carl-Friedrich; Ruane, Alex; Gessner, Ursula; Hoogenboom, Gerrit; Boote, Ken; Shelia, Vakhtang; Saeed, Fahad; Wisser, Dominik; Hadir, Sofia; Laux, Patrick; Gaiser, ThomasTo reduce the risks of climate change, governments agreed in the Paris Agreement to limit global temperature rise to less than 2.0 °C above pre-industrial levels, with the ambition to keep warming to 1.5 °C. Charting appropriate mitigation responses requires information on the costs of mitigating versus associated damages for the two levels of warming. In this assessment, a critical consideration is the impact on crop yields and yield variability in regions currently challenged by food insecurity. The current study assessed impacts of 1.5 °C versus 2.0 °C on yields of maize, pearl millet and sorghum in the West African Sudan Savanna using two crop models that were calibrated with common varieties from experiments in the region with management reflecting a range of typical sowing windows. As sustainable intensification is promoted in the region for improving food security, simulations were conducted for both current fertilizer use and for an intensification case (fertility not limiting). With current fertilizer use, results indicated 2% units higher losses for maize and sorghum with 2.0 °C compared to 1.5 °C warming, with no change in millet yields for either scenario. In the intensification case, yield losses due to climate change were larger than with current fertilizer levels. However, despite the larger losses, yields were always two to three times higher with intensification, irrespective of the warming scenario. Though yield variability increased with intensification, there was no interaction with warming scenario. Risk and market analysis are needed to extend these results to understand implications for food security.
- ItemCombustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet(Washington, DC [u.a.] : Assoc., 2015) Winkelmann, Ricarda; Levermann, Anders; Ridgwell, Andy; Caldeira, KenThe Antarctic Ice Sheet stores water equivalent to 58 m in global sea-level rise. We show in simulations using the Parallel Ice Sheet Model that burning the currently attainable fossil fuel resources is sufficient to eliminate the ice sheet. With cumulative fossil fuel emissions of 10,000 gigatonnes of carbon (GtC), Antarctica is projected to become almost ice-free with an average contribution to sea-level rise exceeding 3 m per century during the first millennium. Consistent with recent observations and simulations, the West Antarctic Ice Sheet becomes unstable with 600 to 800 GtC of additional carbon emissions. Beyond this additional carbon release, the destabilization of ice basins in both West and East Antarctica results in a threshold increase in global sea level. Unabated carbon emissions thus threaten the Antarctic Ice Sheet in its entirety with associated sea-level rise that far exceeds that of all other possible sources.
- ItemUS power plant sites at risk of future sea-level rise(Bristol : IOP Publishing, 2015) Bierkandt, R.; Auffhammer, M.; Levermann, A.Unmitigated greenhouse gas emissions may increase global mean sea-level by about 1 meter during this century. Such elevation of the mean sea-level enhances the risk of flooding of coastal areas. We compute the power capacity that is currently out-of-reach of a 100-year coastal flooding but will be exposed to such a flood by the end of the century for different US states, if no adaptation measures are taken. The additional exposed capacity varies strongly among states. For Delaware it is 80% of the mean generated power load. For New York this number is 63% and for Florida 43%. The capacity that needs additional protection compared to today increases by more than 250% for Texas, 90% for Florida and 70% for New York. Current development in power plant building points towards a reduced future exposure to sea-level rise: proposed and planned power plants are less exposed than those which are currently operating. However, power plants that have been retired or canceled were less exposed than those operating at present. If sea-level rise is properly accounted for in future planning, an adaptation to sea-level rise may be costly but possible.
- ItemHistoric and future increase in the global land area affected by monthly heat extremes(Bristol : IOP Publishing, 2013) Coumou, Dim; Robinson, AlexanderClimatic warming of about 0.5 ° C in the global mean since the 1970s has strongly increased the occurrence-probability of heat extremes on monthly to seasonal time scales. For the 21st century, climate models predict more substantial warming. Here we show that the multi-model mean of the CMIP5 (Coupled Model Intercomparison Project) climate models accurately reproduces the evolution over time and spatial patterns of the historically observed increase in monthly heat extremes. For the near-term (i.e., by 2040), the models predict a robust, several-fold increase in the frequency of such heat extremes, irrespective of the emission scenario. However, mitigation can strongly reduce the number of heat extremes by the second half of the 21st century. Unmitigated climate change causes most (>50%) continental regions to move to a new climatic regime with the coldest summer months by the end of the century substantially hotter than the hottest experienced today. We show that the land fraction experiencing extreme heat as a function of global mean temperature follows a simple cumulative distribution function, which depends only on natural variability and the level of spatial heterogeneity in the warming.