US: In the last thirty years, vegetation has changed significantly the world over. Until recently, the extent to which the climate or humankind was responsible remained unclear. However, geographers from the University of Zurich and colleagues from the Netherlands now reveal that over half of these changes are climatological, humans or as yet unknown human-climate interactions cause over a third and around ten percent cannot be explained fully by either the climate or human activity.
Geographers used satellite data on the vegetation increase or decline from the last thirty years, climate measurements and models, and data on the kind of land cover to reveal this. The scientists demonstrate that around 54 percent of the changes in global vegetation activity can be attributed to climate variability.
“The majority of the changes – more than 30 percent overall – were caused by human activity,” explains de Jong, a postdoctoral student at the University of Zurich”s Remote Sensing Laboratories (RSL). Vegetation activity primarily declined south of the Sahel region, such as in Tanzania, Zimbabwe and in the Congo. “We assume that this was caused by clear cutting, the transformation of rainforest into plantations or changes in agriculture in general,” explains de Jong. Around ten percent cannot be explained fully by climatology or human activity. “We suspect that this is due to unexplained effects of the interactions between humans and the climate,” says Head of the RSL Michael Schaepman.