This is Section 6.2.1 of the Arctic Climate Impact Assessment.
Lead Author: Arne Instanes; Contributing Authors:  Oleg Anisimov, Lawson Brigham, Douglas Goering, Lev N. Khrustalev, Branko Ladanyi, Jan Otto Larsen; Consulting Authors: Orson Smith, Amy Stevermer, Betsy Weatherhead, Gunter Weller  

Changes in arctic climate over the past century can be determined by using data from standard climate stations on land and measurements taken on drifting ice floes in the Arctic Ocean. These data show a consistent trend of increasing air temperatures in the Northern Hemisphere during the 20th century, although the observed changes are not spatially uniform^[2]. While in some regions of the Arctic the warming trend was as great as 5 ºC per century, areas of decreasing temperatures were observed in eastern Canada, the North Atlantic, and Greenland.^[3]

Figure 16.2 shows the change in observed surface air temperature between 1954 and 2003 (see also section 2.6.2). Patterns of annual air temperature change indicate that the recent warming has been greatest in Alaska, northwestern Canada, and Siberia (Fig. 16.2a). Temperature increases in winter were much greater than increases in the annual mean temperature: up to 3 to 4 ºC over Alaska, northwestern Canada, and Siberia (Fig. 16.2b). In southern Greenland and Iceland, annual mean temperatures decreased by approximately 1 ºC, while winter temperatures decreased by 1 to 2 ºC. A winter temperature decrease of 1 to 2 ºC was also observed in Chukotka.

On the North Slope of Alaska and in northern Siberia, air temperatures increased by 2 to 4 ºC, while the global mean air temperature increase over the 20th century was only about 0.6 ºC. This pattern is consistent with the hypothesis that the contemporary warming is largely caused by anthropogenic greenhouse gas emissions. Section 2.6.2 discusses observed arctic temperature changes in detail, while section 4.4.2 provides projections of future arctic temperature change.

Fig. 16.2. Change in observed surface air temperature between 1954 and 2003: (a) annual mean; (b) winter^[1].

Chapter 16: Infrastructure: Buildings, Support Systems, and Industrial Facilities
16.1 Introduction
16.2. Physical environment and processes related to infrastructure
    16.2.1. Observed changes in air temperature
    16.2.2. Permafrost
    16.2.3. Natural hazards
    16.2.4. Coastal environment
    16.2.5. Arctic Ocean
16.3. Infrastructure in the Arctic
16.4. Engineering design for a changing climate
16.5. Gaps in knowledge and research needs

References 

1. ^ Chapman,W.L. and J.E.Walsh, 2003. Observed climate change in the Arctic, updated from Chapman and Walsh, 1993. Recent variations of sea ice and air temperatures in high latitudes. Bulletin of the American Meteorological Society, 74(1):33–47. http://arctic.atmos.uiuc.edu/CLIMATESUMMARY/2003/ using data from the Climatic Research Unit, University of East Anglia, www.cru.uea.ac.uk/temperature
2. ^Anisimov, O.A. 2001. Predicting patterns of near-surface air temperature using empirical data. Climatic Change, 50:297–315.
3. ^ Anisimov, O.A. and B. Fitzharris, 2001. Polar Regions (Arctic and Antarctic). In: J. McCarthy, O. Canziani, N.A. Leary, D.J. Dokken and K.S. White (eds.). Climate Change 2001: Impacts, Adaptation, and Vulnerability, pp. 801–841. Contribution of Working Group II
   to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.;
   -- Borzenkova, I.I., 1999a. Environmental indicators of recent global warming. In:Yu.A. Pykh (ed.). Environmental Indices, pp. 455–465. EOLSS Publishing;
   -- Borzenkova, I.I., 1999b. About natural indicators of the present global warming. Meteorology and Hydrology, 6:98–116.;
   -- Jones, P.D., M. New, D.E. Parker, S. Martin and I.G. Rigor, 1999. Surface air temperature and its changes over the past 150 years. Reviews of Geophysics, 37:173–199.;
   -- Serreze, M.C., J.E.Walsh, F.S. Chapin III,T.E. Osterkamp, V. Dyurgerov and D.M. Smith, 2000. Recent increase in the length of the melt season of perennial Arctic sea ice. Geophysical Research Letters, 25:655–658.