This is Chapter 2 of the Arctic Climate Impact Assessment
Lead Author: Gordon McBean. Contributing Authors: Genrikh Alekseev, Deliang Chen, Eirik Førland, John Fyfe, Pavel Y. Groisman, Roger King, Humfrey Melling, Russell Vose, Paul H.Whitfield
The arctic climate is characterized by a low amount or absence of sunlight in winter and long periods of daylight during summer, with significant spatial and temporal variation.The cryosphere is a prominent feature of the Arctic.The sensitivities of snow and ice regimes to small temperature increases and of cold oceans to small changes in salinity are processes that could contribute to unusually large and rapid climate change in the Arctic.
The arctic climate is a complex system with multiple interactions with the global climate system.The phase of the Arctic Oscillation (AO) was at its most negative in the 1960s, exhibited a general trend toward a more positive phase from about 1970 to the early 1990s, and has remained mostly positive since. Sea ice is an important means by which the Arctic exerts leverage on global climate, and sea-ice extent has been decreasing in recent years. In terrestrial areas, temperature increases over the past 80 years have increased the frequency of mild winter days, causing changes in aquatic ecosystems; the timing of river-ice breakups; and the frequency and severity of extreme ice jams, floods, and low flows.
The observational database for the Arctic is quite limited, with few long-term stations and a paucity of observations in general, making it difficult to distinguish with confidence between the signals of climate variability and change. Based on the analysis of the climate of the 20th century, it is very probable that the Arctic has warmed over the past century, although the warming has not been uniform. Land stations north of 60º N indicate that the average surface temperature increased by approximately 0.09 ºC/decade during the past century, which is greater than the 0.06 ºC/decade increase averaged over the Northern Hemisphere. It is not possible to be certain of the variation in mean land-station temperature over the first half of the 20th century because of a scarcity of observations across the Arctic before about 1950. However, it is probable that the past decade was warmer than any other in the period of the instrumental record.
Evidence of polar amplification depends on the timescale of examination. Over the past 100 years, it is possible that there has been polar amplification, however, over the past 50 years it is probable that polar amplification has occurred.
It is very probable that atmospheric pressure over the Arctic Basin has been dropping, and it is probable that there has been an increase in total precipitation over the past century at the rate of about 1% per decade.Trends in precipitation are hard to assess because it is difficult to measure with precision in the cold arctic environment.
It is very probable that snow-cover extent around the periphery of the Arctic has decreased. It is also very probable that there have been decreases in average arctic sea ice extent over at least the past 40 years and a decrease in multi-year sea-ice extent in the central Arctic.
Reconstruction of arctic climate over the past thousands to millions of years demonstrates that arctic climate can vary substantially.There appears to be no natural impediment to anthropogenic climate change being very significant and greater in the Arctic than the change at the global scale. Especially during past cold periods, there have been times when temperature transitions have been quite rapid – from a few to several degrees change over a century.
Chapter 2: Arctic Climate - Past and Present
2.1 Introduction to Arctic climate: Past and Present
2.2 Arctic atmosphere
2.3 Marine Arctic
2.4 Terrestrial Water Balance in the Arctic
2.5 Influence of the Arctic on global climate
2.6 Arctic climate variability in the twentieth century
2.7 Arctic climate variability prior to 100 years BP
2.8 Summary and key findings of ACIA on Arctic Climate - Past and Present
Acknowledgements (by Lead Author: Gordon McBean)
I would like to offer a special acknowledgement for David Wuertz, NOAA National Climate Data Center. I would also like to thank Mark Serreze, Inger Hanssen-Bauer, and Thorstein Thorsteinsson who helped by participating in meetings and providing comments on the text. Supporting me in my work have been Jaime Dawson and Anna Ziolecki.