11 March 2013
Dateline NASA Science News ~ "Vegetation growth at Earth's northern latitudes increasingly resembles lusher latitudes to the south, according to a NASA-funded study based on a 30-year record of ground-based and satellite data sets.
"In a paper published Sunday, March 10, in the journal Nature Climate Change, an international team of university and NASA scientists examined the relationship between changes in surface temperature and vegetation growth from 45 degrees north latitude to the Arctic Ocean. Results show temperature and vegetation growth at northern latitudes now resemble those found 4 degrees to 6 degrees of latitude farther south as recently as 1982 (see image above, click to enlarge).
"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 .... 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 Arctic's greenness is visible on the ground as an increasing abundance of tall shrubs and trees in locations all over the circumpolar Arctic. Greening in the adjacent boreal areas is more pronounced in Eurasia than in North America.
"An amplified greenhouse effect is driving the changes. Increased concentrations of heat-trapping gasses, such as water vapor, carbon dioxide and methane, cause Earth's surface, ocean and lower atmosphere to warm. Warming reduces the extent of polar sea ice and snow cover, and in turn, the darker ocean and land surfaces absorb more energy, thus heating the air above them. This sets in motion a cycle of positive reinforcement between warming and loss of sea ice and snow cover, [setting up] the amplified greenhouse effect. The greenhouse effect could be further amplified in the future as soils in the north thaw, releasing potentially significant amounts of carbon dioxide and methane.
" .... 17 climate models show that increased temperatures in Arctic and boreal regions could be the equivalent of a 20-degree latitude shift by the end of this century, relative to a period of comparison from 1951-1980."
What applies to the region from 45 degrees latitude to the poles, equally applies from the equator to 45 degrees latitude. As the entire planet warms, the broad climate zones which circle the earth ~ tropical, sub-tropical, desert, temperate, subpolar, polar ~ are steadily creeping toward Earth's poles.. In the past, cycles of climate change occurred much more gradually, spanning centuries and millenia. The communities of plants and animals endemic to a particular zone were able to shift north or south as needed to survive. But the present cycle is homogenetic ~ caused by human activity ~ and is shifting much more rapidly. Surely human agriculture can (and will) relocate as needed, but it remains to be seen whether natural biomes can keep pace.
So if you live on the mid-Atlantic coast and always wanted a vacation home in the Bahamas, just hang around a few decades right where you are. The tropics are working their way to you.