Arctic Summer Climate Trends
Warmer but not yet wetter
June through August is traditionally the “summer” season in the northern hemisphere, and for the Arctic as a whole this is indeed the warmest three months of the year (based on the 1991-2020 reference period). However, this varies regionally. June through August is the warmest season over nearly all Arctic land areas1 as well as the Arctic ocean poleward of 80°N, but otherwise for most of the Arctic seas except from the Laptev Sea eastward to the northern Chukchi and Beaufort Seas, July through September has a slightly higher average temperature, due much more open water in September than June.
Temperature
Temperatures in the summer around the Arctic are warming, just like other times of year. But the warming pattern is quite different from other seasons, with limited warming over the Arctic Ocean and more warming over the land. And yes, this makes complete physical sense.
Figure 1 shows the 50-year change in average summer (June through August) temperature in and around the Arctic based on ERA5 reanalysis. Nearly the entire Arctic Ocean basin shows very little change, and the largest increases are in portions of north-central Siberia and the Canadian Arctic. This pattern is completely different than the winter temperatures changes (see Fig. 1 in my post on winter trends, here).
The reason that there’s much less warming during the summer season over the Arctic Ocean is simple: most of the energy from the sun, nearby land areas and warmer air from much farther south is going into melting sea ice and the snow on top of that ice (the same effect is evident on the southeast portion of the Greenland Ice Sheet). This “adding energy to stand still” is the result of the extra energy (latent heat) required to change the phase of water from solid (snow, ice) to liquid. Most of the year in the Arctic this is not an issue: water is in solid phase and so more of the energy goes to warming the air. Some Arctic lands maintain snow cover year-round (high mountains and the Greenland Ice Sheet) and some lower elevation areas north of roughly 70°N routinely maintain a snow cover into June, but otherwise most of the summer is snow and ice free, so energy goes into warming the air and ground.
These effects can be seen in the time series of summer average temperatures in Fig. 2. Here I’ve plotted the June through August average temperature each year since 1950 for the entire Arctic (land and seas north of 60°N) and just the land area north of 60°N. Unsurprisingly, the average temperature over the land is higher than the full Arctic, but the rate of warming since the mid 1980s is also higher over land. Warming over land since 1986 has averaged 0.47°C per decade. Over the oceans north of 60°N, the air temperature warming has averaged just 0.22°C per decade, less than half of the land value.
Precipitation
Unlike temperatures, precipitation changes over the past 50 years show no correlation with land vs. ocean in the Arctic, which is evident in Fig. 3. While there are regionally significant increases in summer precipitation, e.g. parts of Alaska and northwest Canada, overall there hasn’t been much change. For the Arctic as a whole, the 50-year change in total precipitation is just +3 percent, which is not statistically significant, i.e. we don’t have strong evidence that the overall increase is not just random variation.
Technical details:
As usual in this newsletter, Arctic means “poleward of 60°N” unless otherwise specified.
ERA5 monthly temperatures and precipitation data available here.
Code by B. Brettschneider/NWS Alaska Region allowing rapid ERA5 regional analysis is invaluable for my work.
Small portions of Arctic lands, principally in eastern Canada, Iceland and the Russian coastal area bordering the Kara Sea, the June through August average temperature is not appreciably warmer than the July through September average.
Good explanations and very helpful.