The scientists used satellite data to determine changes in plant growth over the years they have studied. The satellites in use from NASA, which contained NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instruments, also held NOAA's Advanced Very High Resolution Radiometers (AVHRR); these devices provided the high-resolution information used to determine their study results.
The study, published in the March issue of Nature Climate Change, examined the relationship between temperature change and plant growth spanning from 45 degrees north latitude to the Arctic Ocean. According to the study, increased temperatures have warmed the atmosphere, which in turn melts ice found in northern latitudes. As the ice melts, the ground becomes exposed, further warming the atmosphere and causing plant growth. The scientists define two main study areas where this is occurring: the boreal vegetated region (45-65 degrees N latitude) and the Arctic (areas north of 65 degrees N latitude). According to the study, in those areas between the latitudes of 50 degrees N and 75 degrees N, there has been a measured increase in temperature of 1 to 2 degrees Celsius between the early 1980s and the late 2000s, when there was also a smaller difference between summer and winter temperatures recorded. During this time, the amount of vegetation in this region increased so that it is similar to vegetative covering on lands 4 to 6 degrees farther south. The area of landscape that is now productive in these northern regions is equal to the size of the contiguous United States.
As a result of this vegetative change brought on by warming, the study predicts other outcomes, including thawing of ice in mid-winter, droughts, increased fire and pest outbreaks, and shrinking ponds. Some of these effects may actually slow the growth of vegetation, which could stop this cycle from continuing. In addition, the warming temperatures do not always cause plant growth in that water and sunlight are also necessary for the growth of vegetation. Those areas studied that were warmer and wetter measured more plant growth than those that were warmer and drier.
Photo credit: Terry Callaghan, EU-Interact/Sergey Kirpotin, Tomsk State University. The picture depicts melting permafrost and increased vegetative growth near the Altai Mountains in Russia.