Estimates of 21st Century global-mean surface temperature increase have generally been based on scenarios that do not include climate policies. Newly developed multigas mitigation scenarios, based on ...a wide range of modeling approaches and socioeconomic assumptions, now allow the assessment of possible impacts of climate policies on projected warming ranges. This article assesses the atmospheric CO₂ concentrations, radiative forcing, and temperature increase for these new scenarios using two reduced-complexity climate models. These scenarios result in temperature increase of 0.5-4.4°C over 1990 levels or 0.3-3.4°C less than the no-policy cases. The range results from differences in the assumed stringency of climate policy and uncertainty in our understanding of the climate system. Notably, an average minimum warming of ≈1.4°C (with a full range of 0.5-2.8°C) remains for even the most stringent stabilization scenarios analyzed here. This value is substantially above previously estimated committed warming based on climate system inertia alone. The results show that, although ambitious mitigation efforts can significantly reduce global warming, adaptation measures will be needed in addition to mitigation to reduce the impact of the residual warming.
Eight earth system models of intermediate complexity (EMICs) are used to project climate change commitments for the recent Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment ...Report (AR4). Simulations are run until the year 3000A.D. and extend substantially farther into the future than conceptually similar simulations with atmosphere–ocean general circulation models (AOGCMs) coupled to carbon cycle models. In this paper the following are investigated: 1) the climate change commitment in response to stabilized greenhouse gases and stabilized total radiative forcing, 2) the climate change commitment in response to earlier CO₂ emissions, and 3) emission trajectories for profiles leading to the stabilization of atmospheric CO₂ and their uncertainties due to carbon cycle processes. Results over the twenty-first century compare reasonably well with results from AOGCMs, and the suite of EMICs proves well suited to complement more complex models. Substantial climate change commitments for sea level rise and global mean surface temperature increase after a stabilization of atmospheric greenhouse gases and radiative forcing in the year 2100 are identified. The additional warming by the year 3000 is 0.6–1.6 K for the low-CO₂ IPCC Special Report on Emissions Scenarios (SRES) B1 scenario and 1.3–2.2 K for the high-CO₂ SRES A2 scenario. Correspondingly, the post-2100 thermal expansion commitment is 0.3–1.1 m for SRES B1 and 0.5–2.2 m for SRES A2. Sea level continues to rise due to thermal expansion for several centuries after CO₂ stabilization. In contrast, surface temperature changes slow down after a century. The meridional overturning circulation is weakened in all EMICs, but recovers to nearly initial values in all but one of the models after centuries for the scenarios considered. Emissions during the twenty-first century continue to impact atmospheric CO₂ and climate even at year 3000. All models find that most of the anthropogenic carbon emissions are eventually taken up by the ocean (49%–62%) in year 3000, and that a substantial fraction (15%–28%) is still airborne even 900 yr after carbon emissions have ceased. Future stabilization of atmospheric CO₂ and climate change requires a substantial reduction of CO₂ emissions below present levels in all EMICs. This reduction needs to be substantially larger if carbon cycle–climate feedbacks are accounted for or if terrestrial CO₂ fertilization is not operating. Large differences among EMICs are identified in both the response to increasing atmospheric CO₂ and the response to climate change. This highlights the need for improved representations of carbon cycle processes in these models apart from the sensitivity to climate change. Sensitivity simulations with one single EMIC indicate that both carbon cycle and climate sensitivity related uncertainties on projected allowable emissions are substantial.
The impact of land use on the global carbon cycle and climate is assessed. The Bern carbon cycle-climate model was used with land use maps from HYDE3.0 for 1700 to 2000 A.D. and from post-SRES ...scenarios for this century. Cropland and pasture expansion each cause about half of the simulated net carbon emissions of 188 Gt C over the industrial period and 1.1 Gt C yr
-1
in the 1990s, implying a residual terrestrial sink of 113 Gt C and of 1.8 Gt C yr
-1
, respectively. Direct CO
2
emissions due to land conversion as simulated in book-keeping models dominate carbon fluxes due to land use in the past. They are, however, mitigated by 25% through the feedback of increased atmospheric CO
2
stimulating uptake. CO
2
stimulated sinks are largely lost when natural lands are converted. Past land use change has eliminated potential future carbon sinks equivalent to emissions of 80-150 Gt C over this century. They represent a commitment of past land use change, which accounts for 70% of the future land use flux in the scenarios considered. Pre-industrial land use emissions are estimated to 45 Gt C at most, implying a maximum change in Holocene atmospheric CO
2
of 3 ppm. This is not compatible with the hypothesis that early anthropogenic CO
2
emissions prevented a new glacial period.
The Bern Simple Climate Model (BernSCM) is a free open-source
re-implementation of a reduced-form carbon cycle–climate model which
has been used widely in previous scientific work and IPCC ...assessments.
BernSCM represents the carbon cycle and climate system with a small
set of equations for the heat and carbon budget, the parametrization
of major nonlinearities, and the substitution of complex component
systems with impulse response functions (IRFs). The IRF approach
allows cost-efficient yet accurate substitution of detailed parent
models of climate system components with near-linear behavior.
Illustrative simulations of scenarios from previous multimodel
studies show that BernSCM is broadly representative of the range of
the climate–carbon cycle response simulated by more complex and
detailed models. Model code (in Fortran) was written from scratch
with transparency and extensibility in mind, and is provided open
source. BernSCM makes scientifically sound carbon cycle–climate
modeling available for many applications. Supporting up to decadal
time steps with high accuracy, it is suitable for studies with high
computational load and for coupling with integrated assessment
models (IAMs), for example. Further applications include climate risk assessment in
a business, public, or educational context and the estimation of
CO2 and climate benefits of emission mitigation options.
•Generating national climate scenarios need to be planned from a broad perspective.•Disseminating user-oriented products increases the uptake of climate projections.•A constant stakeholder dialogue ...is key in the production of climate scenarios.•The CH2018 climate scenarios come as a consolidated climate service in Switzerland.•Communication of climate scenarios should be targeted toward specific user types.
To make sound decisions in the face of climate change, government agencies, policymakers and private stakeholders require suitable climate information on local to regional scales. In Switzerland, the development of climate change scenarios is strongly linked to the climate adaptation strategy of the Confederation. The current climate scenarios for Switzerland CH2018 - released in form of six user-oriented products - were the result of an intensive collaboration between academia and administration under the umbrella of the National Centre for Climate Services (NCCS), accounting for user needs and stakeholder dialogues from the beginning. A rigorous scientific concept ensured consistency throughout the various analysis steps of the EURO-CORDEX projections and a common procedure on how to extract robust results and deal with associated uncertainties. The main results show that Switzerland’s climate will face dry summers, heavy precipitation, more hot days and snow-scarce winters. Approximately half of these changes could be alleviated by mid-century through strong global mitigation efforts. A comprehensive communication concept ensured that the results were rolled out and distilled in specific user-oriented communication measures to increase their uptake and to make them actionable. A narrative approach with four fictitious persons was used to communicate the key messages to the general public. Three years after the release, the climate scenarios have proven to be an indispensable information basis for users in climate adaptation and for downstream applications. Potential for extensions and updates has been identified since then and will shape the concept and planning of the next scenario generation in Switzerland.
This paper presents results from the numerical modelling of the transport of atmospheric noble gases (He, Ne, Ar, Kr, Xe), tritiated water and
3He produced by radioactive decay of
3H, in ...unconsolidated lacustrine sediment. Two case studies are discussed: (1) the evolution of
3H and
3He concentrations in the sediment porewater of Lake Zug (Switzerland) from 1953 up to the present; and (2) the response of dissolved atmospheric noble gas concentrations in the sediment porewater of a subtropical lake to an abrupt climatic change that occurred some 10 kyr before the present. (1) Modelled
3H and
3He porewater concentrations are compared with recent data from Lake Zug. An estimate of the effective diffusion coefficients in the sediment porewater is derived using an original approach which is also applicable also to lakes for which the historical
3H and
3He concentrations in the water column are unknown. (2) The air/water partitioning of atmospheric noble gases is sensitive to water temperature and salinity, and thus provides a mechanism by which these environmental variables are recorded in the concentrations of atmospheric noble gases in lakes. We investigate the feasibility of using noble gas concentrations in the porewater of lacustrine sediments as a proxy for palaeoenvironmental conditions in lakes. Numerical modelling shows that heavy noble gases in sediment porewater, because of their comparatively small diffusion coefficients and the strong temperature sensitivity of their equilibrium concentrations, can preserve concentrations corresponding to past lake temperatures over times on the order of 10 kyr. Noble gas analysis of sediment porewaters therefore promises to yield valuable quantitative information on the past environmental states of lakes.
The impact of land use on the global carbon cycle and climate is assessed. The Bern carbon cycle-climate model was used with land use maps from HYDE3.0 for 1700 to 2000 A.D. and from post-SRES ...scenarios for this century. Cropland and pasture expansion each cause about half of the simulated net carbon emissions of 188 GtC over the industrial period and 1.1 GtC yr super(-1) in the 1990s, implying a residual terrestrial sink of 113 GtC and of 1.8 GtC yr super(-1), respectively. Direct CO sub(2) emissions due to land conversion as simulated in book-keeping models dominate carbon fluxes due to land use in the past. They are, however, mitigated by 25% through the feedback of increased atmospheric CO sub(2) stimulating uptake. CO sub(2) stimulated sinks are largely lost when natural lands are converted. Past land use change has eliminated potential future carbon sinks equivalent to emissions of 80-150 GtC over this century. They represent a commitment of past land use change, which accounts for 70% of the future land use flux in the scenarios considered. Pre-industrial land use emissions are estimated to 45 GtC at most, implying a maximum change in Holocene atmospheric CO sub(2) of 3 ppm. This is not compatible with the hypothesis that early anthropogenic CO sub(2) emissions prevented a new glacial period.
Here we give names to three new species of Paraburkholderia that can remain in symbiosis indefinitely in the spores of a soil dwelling eukaryote, Dictyostelium discoideum. The new species P. ...agricolaris sp. nov., P. hayleyella sp. nov., and P. bonniea sp. nov. are widespread across the eastern USA and were isolated as internal symbionts of wild-collected D. discoideum. We describe these sp. nov. using several approaches. Evidence that they are each a distinct new species comes from their phylogenetic position, average nucleotide identity, genome-genome distance, carbon usage, reduced length, cooler optimal growth temperature, metabolic tests, and their previously described ability to invade D. discoideum amoebae and form a symbiotic relationship. All three of these new species facilitate the prolonged carriage of food bacteria by D. discoideum, though they themselves are not food. Further studies of the interactions of these three new species with D. discoideum should be fruitful for understanding the ecology and evolution of symbioses.
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