Hot Arctic drives North American freeze

Warmer-than-average years in the Arctic cause colder winters and springs in North America, according to a study published online in Nature Geoscience. The study finds that these cooler winters and springs result in decreased vegetation growth in North American ecosystems, and hence reduced capacity for those ecosystems to uptake CO2.

Although it has long been known that interannual variability in ocean temperatures can affect climate and productivity (as during El Nino), Arctic temperatures have not been previously linked to North American plant productivity.

Jong-Seong Kug and colleagues analyse an index of sea-surface temperatures from the Bering Sea and find that in years with higher Arctic temperatures, changes in atmospheric circulation over Alaska create corresponding changes in circulation to the west, resulting in substantial cooling over most of North America and drying in the southern part of the continent. In years with these lower temperatures and precipitation, they find that the capacity of North American ecosystems to take up CO2 declined by about 14%, including reductions in crop yields of 1 to 4% on average.

The authors’ examination of the effect of warmer-than-average years focused on the effects of climate variability, rather than climate change. However, they suggest that a strengthening of interannual variability in the Arctic over the past thirty years - related to the rapid decline in Arctic sea-ice - could have resulted in a decline in terrestrial productivity in North America.

In an accompanying News & Views, Ana Bastos writes: “Whether the relationship found implies a decreasing carbon sink capacity of North American ecosystems in the coming decades is unclear.”