Air Temperatures: More information

The map and bar graph show how air temperatures in the Arctic compare to averages from 1979 to 2015. On the map, areas with higher than average temperatures for the selected month and year are indicated in oranges and reds (positive anomalies), and areas with lower than average temperatures are shown in blues (negative anomalies). The map of anomalies helps show where temperature change is strongest. These are temperatures two meters above the surface, similar to the temperatures given in weather reports and forecasts.

The bar graph indicates the average temperature anomaly for the selected month and year, for the entire Arctic (the area north of 60°N). The graph helps illustrate the Arctic-wide temperature trend for each month of the year.

This sample image shows near-surface air temperature anomalies for October 2012.

Substantial warming is especially noticeable since the year 2000. However, the amount of warming depends on both the region and the time of year, as can be seen when switching between months on the bar chart. Recent warming is strongest in autumn and especially in October, one month after sea ice reaches its annual minimum extent. During summer months, some warming is apparent over Arctic land areas, but there is little warming over ocean. In winter and spring, warming is less evident.

During summer, average air temperatures over the ice-covered Arctic Ocean tend to stay just above the freezing point. This is because the temperature of melting sea ice is itself at the freezing point, so there can be little warming of the air above. In areas where ice has melted away, the dark ocean absorbs a great deal of solar energy. Because the heat is going into the ocean, the overlying air also stays fairy cool, although certainly warmer than above areas of melting ice. As solar radiation wanes in autumn, the heat the ocean gained in summer is released back to the atmosphere. As darkness descends on the Arctic and winter gets underway, ocean water cools to -1.8 degrees Celsius, the freezing temperature of sea water. 

An interesting aspect of Arctic change seen in the temperature maps is the phenomenon of “Arctic amplification.” This refers to the outsized warming of the Arctic relative to the rest of the globe. While a number of mechanisms contribute to Arctic amplification, the loss of Arctic sea ice cover plays a dominant role. Basically, because there is so much more dark, open water than was the case even a decade ago, the ocean gains much more heat in summer than it used to. This in turn means that more heat is released back to the atmosphere in autumn as sunlight wanes. An important piece of evidence here is that warming is strongest during autumn and in areas that have shown the largest declines in summer ice extent. Another is that the warming is strongest at and near the surface. It appears that a further  contributor to Arctic amplification is an increase in the horizontal transport of energy from lower latitudes.

The data shown here are from the NASA MERRA reanalysis project. Reanalyses are a form of retrospective numerical weather prediction. Observations of atmospheric pressure, air temperature, humidity and wind speed—collected by satellites, commercial aircraft, balloon-borne instruments (radiosondes) and ground stations—are blended with short term forecasts from weather forecast models to provide the best estimate of atmospheric and surface conditions. The blending of model forecasts and observations allows surface temperatures to be estimated where observations may be sparse. While surface observations are sparse in many parts of the Arctic, the region gets extensive coverage from polar-orbiting satellites. Although no reanalysis product is perfect, air temperature is one of the more reliable products. Estimates of surface air temperature from reanalyses compare well with air temperatures measured at ground stations, such as GISS-TEMP. While there are differences between the different reanalyses, all show a warming trend over the 1979 to present period. Most of the differences between reanalyses tend to be over the ocean where surface observations are more sparse. 

REFERENCES

Serreze, M. C., and R. G. Barry. 2011. Processes and impacts of Arctic amplification: A research synthesis. Global and Planetary Change 77: 85-96, doi:10.1016/j.gloplacha.2011.03.004.

C. E. Chung, C. E., H. Cha, T. Vihma, P. Räisänen, and D. Decremer. 2013. On the possibilities to use atmospheric reanalyses to evaluate the warming structure in the Arctic. Atmos. Chem. Phys., 13, 11209–11219. doi:10.5194/acp-13-11209-2013.

Back to map >>