Arctic Climate and Climate Change with a Focus on Greenland

TY - CHAP

T1 - Arctic Climate and Climate Change with a Focus on Greenland

AU - Stendel, Martin

AU - Christensen, Jens Hesselbjerg

AU - Petersen, Dorthe

PY - 2008/4/4

Y1 - 2008/4/4

N2 - Paleoclimatic evidence suggests that the Arctic presently is warmer than during the last 125,000 years, and it is very likely11The term "likelihood" is used here as in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). According to the definition in this report, "very likely" corresponds to a likelihood of more than 90%. that the increase in concentration of greenhouse gases in the atmosphere has an effect, which is larger in the Arctic than elsewhere on the globe (Christensen et al., 2007a). In recent years, concerns about the stability of the Greenland Ice Sheet, the fate of arctic sea ice and a possible weakening of the thermohaline circulation (THC) under future warming conditions have led to increased research activities, including an assessment of arctic climate and climate change (ACIA, 2005), the fourth assessment report (AR4) of the International Panel on Climate Change (IPCC, 2007) and a large number of research project related to the International Polar Year (IPY). Assessments of climate variability and change with a focus on the Arctic in general and Greenland in particular have to consider uncertainties related to the paucity of reliable observations and, for projections of future climate, the large natural variability that makes it difficult to detect an anthropogenic climate signal. Further uncertainties are due to the underlying emission scenarios as well as model uncertainties and deficiencies including insufficient horizontal resolution. Most of these uncertainties can be addressed by considering large ensembles of model simulations instead of a single realization with only one model. In this chapter, we summarize the findings of two such approaches that have focused on the Arctic, ACIA (2005), based on 5 global circulation models (GCMs) and Christensen et al. (2007a), based on 21 AR4 GCMs of the most recent generation. In opposition to the ACIA models, the AR4 models no longer need a flux correction to keep their climate stable. We can thus also demonstrate the advance from ACIA to AR4. As the typical resolution of the AR4 models of 150-200 km is hardly adequate to realistically simulate many arctic processes, we also present results from a new transient simulation using a regional climate model (RCM) for Greenland and surrounding seas with a horizontal resolution of 25 km. Thus, differences related to model resolution can be addressed. The ensemble of global models indicate an increase of 3 °C in global mean temperature by the end of the twenty-first century, whereas for the Arctic, temperature increases of up to 6 °C in the annual mean and up to 10 °C in winter are projected for the same period. The regional model gives locally much larger temperature increases of up to 18 °C in winter, which is related to the retreat of sea ice, in particular along Greenland's east coast. Precipitation is projected to increase everywhere in the Arctic with respect to present-day conditions, ranging from 5%-10% in the south to 35% in the High Arctic for the global models and more than 60% for the regional model. A considerably larger percentage of this precipitation than under present-day conditions is expected to fall as rain, along with an increase in snow depth in the northern half and a decrease in the southern half of Greenland. A substantial decrease in sea ice is also projected. With a northward retreat of the ice edge, continentality is projected to decrease in Northeast Greenland in general and in the Zackenberg area in particular. This goes along with an increase in both temperature and precipitation, especially in winter. Consequently, climate conditions will develop in the direction of conditions in the Low Arctic with higher snow-cover, lengthening of the thawing season and increased variability including possible thaw periods during winter.

AB - Paleoclimatic evidence suggests that the Arctic presently is warmer than during the last 125,000 years, and it is very likely11The term "likelihood" is used here as in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). According to the definition in this report, "very likely" corresponds to a likelihood of more than 90%. that the increase in concentration of greenhouse gases in the atmosphere has an effect, which is larger in the Arctic than elsewhere on the globe (Christensen et al., 2007a). In recent years, concerns about the stability of the Greenland Ice Sheet, the fate of arctic sea ice and a possible weakening of the thermohaline circulation (THC) under future warming conditions have led to increased research activities, including an assessment of arctic climate and climate change (ACIA, 2005), the fourth assessment report (AR4) of the International Panel on Climate Change (IPCC, 2007) and a large number of research project related to the International Polar Year (IPY). Assessments of climate variability and change with a focus on the Arctic in general and Greenland in particular have to consider uncertainties related to the paucity of reliable observations and, for projections of future climate, the large natural variability that makes it difficult to detect an anthropogenic climate signal. Further uncertainties are due to the underlying emission scenarios as well as model uncertainties and deficiencies including insufficient horizontal resolution. Most of these uncertainties can be addressed by considering large ensembles of model simulations instead of a single realization with only one model. In this chapter, we summarize the findings of two such approaches that have focused on the Arctic, ACIA (2005), based on 5 global circulation models (GCMs) and Christensen et al. (2007a), based on 21 AR4 GCMs of the most recent generation. In opposition to the ACIA models, the AR4 models no longer need a flux correction to keep their climate stable. We can thus also demonstrate the advance from ACIA to AR4. As the typical resolution of the AR4 models of 150-200 km is hardly adequate to realistically simulate many arctic processes, we also present results from a new transient simulation using a regional climate model (RCM) for Greenland and surrounding seas with a horizontal resolution of 25 km. Thus, differences related to model resolution can be addressed. The ensemble of global models indicate an increase of 3 °C in global mean temperature by the end of the twenty-first century, whereas for the Arctic, temperature increases of up to 6 °C in the annual mean and up to 10 °C in winter are projected for the same period. The regional model gives locally much larger temperature increases of up to 18 °C in winter, which is related to the retreat of sea ice, in particular along Greenland's east coast. Precipitation is projected to increase everywhere in the Arctic with respect to present-day conditions, ranging from 5%-10% in the south to 35% in the High Arctic for the global models and more than 60% for the regional model. A considerably larger percentage of this precipitation than under present-day conditions is expected to fall as rain, along with an increase in snow depth in the northern half and a decrease in the southern half of Greenland. A substantial decrease in sea ice is also projected. With a northward retreat of the ice edge, continentality is projected to decrease in Northeast Greenland in general and in the Zackenberg area in particular. This goes along with an increase in both temperature and precipitation, especially in winter. Consequently, climate conditions will develop in the direction of conditions in the Low Arctic with higher snow-cover, lengthening of the thawing season and increased variability including possible thaw periods during winter.

UR - http://www.scopus.com/inward/record.url?scp=41449109421&partnerID=8YFLogxK

U2 - 10.1016/S0065-2504(07)00002-5

DO - 10.1016/S0065-2504(07)00002-5

M3 - Book chapter

AN - SCOPUS:41449109421

SN - 9780123736659

VL - 40

T3 - Advances in Ecological Research

SP - 13

EP - 43

BT - High-Arctic Ecosystem Dynamics in a Changing Climate

ER -