A remarkable transformation in the vegetation of the Arctic has occurred over the past 30 years, according to a study of satellite data published on March 10, 2013, in Nature Climate Change. The authors found that Arctic vegetation growth and temperatures in 2011 resembled what occurred 250 - 430 miles farther to the south back in 1982. That's the approximate distance in latitude between San Francisco and San Diego, or Washington D.C. and Atlanta. More greening occurred in Eurasia than North America, and the Arctic's new greenness is visible on the ground as an increasing abundance of tall shrubs and trees. Large patches of vigorously productive vegetation now span a third of the northern landscape, an area about equal to the contiguous United States. "Higher northern latitudes are getting warmer, Arctic sea ice and the duration of snow cover are diminishing, the growing season is getting longer and plants are growing more," said co-author Dr. Ranga Myneni of Boston University's Department of Earth and Environment, in a NASA press release. "In the north's Arctic and boreal areas, the characteristics of the seasons are changing, leading to great disruptions for plants and related ecosystems." The changes in the Arctic's vegetation are being driven by human-caused global warming, which is occurring in the Arctic at more than double the rate of the rest of the planet. This so-called "Arctic amplification" is due, in part, to the increased melting of ice and snow near the pole. When ice and snow melt, they uncover darker surfaces underneath, which absorb more sunlight and increase Arctic temperatures in a vicious cycle which melts even more ice and snow. Using 17 climate models, the researchers predicted that a continuation of warming in the Arctic in coming decades could lead to over a 1300 mile latitudinal shift in Arctic vegetation zones by the year 2100, compared to the period 1951 - 1980. That's a distance greater than the north-south extent of the contiguous United States. However, more frequent forest fires, increased pest outbreaks, and summertime droughts due to a warming climate might slow down Arctic plant growth.


Figure 1. Of the 10 million square miles (26 million square kilometers) of northern vegetated lands, 34 to 41 percent showed increases in plant growth (green and blue), 3 to 5 percent showed decreases in plant growth (orange and red), and 51 to 62 percent showed no changes (yellow) over the past 30 years. Satellite data in this visualization are from AVHRR and MODIS. Credit: NASA's Goddard Space Flight Center Scientific Visualization Studio.


Figure 2. Trees take hold as permafrost thaws near the Altai Mountains in Russia. Credit: Terry Callaghan, EU-Interact/Sergey Kirpotin, Tomsk State University.

Commentary
One often hears complaints that global warming may be greatly overestimated, due to many temperature sensors being located in increasingly urbanized areas where local "urban heat island" effects are not being properly considered. If this were true (and it isn't), then we would not expect to see "nature's thermometers"--plants and animals--change their behavior and ranges much. But plants and animals are responding in major ways to the warming climate, and the greening of the Arctic is merely one more example of "nature's thermometers" telling us that the planet is warming significantly. Some other examples:

Fall is falling back: During 1982 to 1999, the end of the growing season was delayed by 4.3 days in the Northern Hemisphere. During 2000 to 2008, the end of the growing season was further delayed by an additional 2.3 days. In the U.S., fall now occurs ten days later than it did 30 years ago.

Spring is springing forward: Spring events, like bird and butterfly migrations, flower blooming times, and frog mating, have been advancing by about three days per decade over the past 30 years.

Animals are changing migration patterns: New species have colonized previously ‘cool’ regions, including sea anemones in Monterey Bay, and lichens and butterflies in Europe. Over the past 50 years, maximum range shifts vary from 200 km (butterflies) to 1,000 km (marine copepods).

Related blog post: New USDA Plant Hardiness Zone Map for gardeners shows a warming climate

Jeff Masters