This is Chapter 4 of the Arctic Climate Impact Assessment.
Lead Authors: Vladimir M. Kattsov, Erland Källén; Contributing Authors: Howard Cattle, Jens Christensen, Helge Drange, Inger Hanssen-Bauer,Tómas Jóhannesen, Igor Karol, Jouni Räisänen, Gunilla Svensson, Stanislav Vavulin; Consulting Authors: Deliang Chen, Igor Polyakov, Annette Rinke
Increased atmospheric concentrations of greenhouse gases (GHGs) are very likely to have a larger effect on climate in the Arctic than anywhere else on the globe. Physically based, global coupled atmosphere-land-ocean climate models are used to project possible future climate change. Given a change in GHG concentrations, the resulting changes in temperature, precipitation, seasonality, etc. can be projected. Future emissions of GHGs and aerosols can be estimated by making assumptions about future demographic, socioeconomic, and technological changes.The Intergovernmental Panel on Climate Change (IPCC) prepared a set of emissions scenarios for use in projecting future climate change. This assessment uses the A2 and B2 emissions scenarios, which are in the middle of the range of scenarios provided by the IPCC. Projections from the IPCC climate models indicate a global mean temperature increase of 1.4 ºC by the mid-21st century compared to the present climate for both the A2 and B2 scenarios. Toward the end of the century, the global mean temperature increase is projected to be 3.5 ºC and 2.5 ºC for the two scenarios, respectively.
Over the Arctic, the Arctic Climate Impact Assessment (ACIA)-designated models project a larger mean temperature increase: for the region north of 60º N, both emissions scenarios result in a 2.5 ºC increase by the mid-21st century. By the end of the 21st century, arctic temperature increases are projected to be 7 ºC and 5 ºC for the A2 and B2 scenarios, respectively, compared to the present climate. By then, in the B2 scenario, the models project temperature increases of around 3 ºC for Scandinavia and East Greenland, about 2 ºC for Iceland, and up to 5 ºC for the Canadian Archipelago and Russian Arctic.The five-model mean warming over the central Arctic Ocean is greatest in autumn and winter (up to 9 ºC by the late 21st century in the B2 scenario), as the air temperature reacts strongly to reduced ice cover and thickness.Average autumn and winter temperatures are projected to rise by 3 to 5 ºC over most arctic land areas by the end of the 21st century. By contrast, summer temperature increases over the Arctic Ocean are projected to remain below 1 ºC throughout the 21st century.The contrast between greater projected warming in autumn and winter and lesser warming in summer also extends to the surrounding land areas but is less pronounced there. In summer, the projected warming over northern Eurasia and northern North America is greater than that over the Arctic Ocean, while in winter the reverse is projected. All of the models suggest substantially smaller temperature increases over the northern North Atlantic sector than in the other parts of the Arctic.
By the late 21st century, projected precipitation increases in the Arctic range from about 5 to 10% in the Atlantic sector to as much as 35% in certain high Arctic locations (for the B2 scenario). As for temperature, the projected increase in precipitation is generally greatest in autumn and winter and smallest in summer.
A slight decrease in pressure in the polar region is projected for throughout the year.While impact studies would benefit from projections of wind characteristics and storm tracks in the Arctic, available analyses in the literature are insufficient to justify firm conclusions about possible changes in the 21st century. The models also project a substantial decrease in snow and sea-ice cover over most of the Arctic by the end of the 21st century.
The projected increase in arctic temperatures is accompanied by large between-model differences and considerable interdecadal variability. Dividing the average projected temperature change by the magnitude of projected variability suggests that, despite the large warming projected for the Arctic, the signal-to-noise ratio is actually lower in the Arctic than in many other areas.
The Arctic is a region characterized by complex and insufficiently understood climate processes and feedbacks, contributing to the challenge that the Arctic poses from the view of climate modeling. Several weaknesses of the models related to descriptions of high-latitude
surface processes have been identified, and these are among the most serious shortcomings of present-day arctic climate modeling.
Local and regional climate features, such as enhanced precipitation close to steep mountains, are not well represented in global climate models due to the limited horizontal resolution of the models.To describe local climate, physical modeling or statistically based empirical
links between the large-scale flow and local climate can be used. Despite rapid developments in arctic regional climate modeling, the current status of developments in this field did not allow regional models to be used as principal tools for the ACIA.Therefore, the
ACIA used projections from coupled global models, either directly or in combination with statistical downscaling techniques.
A model simulation provides one possible climate scenario. This is not a prediction of future climate change, but a projection based on a prescribed change in the concentration of atmospheric GHGs.A climate shift can be caused by natural variability as well as by changes in
GHG concentrations. Natural variability in the Arctic is large and could mask or amplify a change resulting from increased atmospheric GHG concentrations.To assess the relative importance of natural variability versus a prescribed climate forcing, an ensemble of differently
formulated climate models should be used. For this assessment, five different models are used to give an indication of simulation uncertainty versus forced changes, although greater numbers of simulations would provide a better estimate of climate change probability
distributions, and perhaps allow the estimation of changes in the frequency of winter storms, and temperature and precipitation extremes, etc.
While the level of uncertainty in climate simulations can probably be reduced with improved model formulations, it will never be certain that all physical processes relevant to climate change have been included in a model simulation.There can still be surprises in the understanding of climate change.The projections presented here are based on the best knowledge available today about climate change; as climate-change science progresses there will always be new results that may change the understanding of how the arctic climate system works.
Chapter 4: Future Climate Change: Modeling and Scenarios for the Arctic
4.2. Global coupled atmosphere-ocean general circulation models
4.3. Simulation of observed arctic climate with the ACIA designated models
4.4. Arctic climate change scenarios for the 21st century projected by the ACIA-designated models
4.5. Regional modeling of the Arctic
4.6. Statistical downscaling approach and downscaling of AOGCM climate change projections
4.7. Outlook for improving climate change projections for the Arctic
- IPCC, 2001. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell and C.A. Johnson (eds.). Intergovernmental Panel on Climate Change. Cambridge University Press, 881pp.