Risk to Amazon rainforest from land use and climate change

A new LMU study estimates that land use changes in conjunction with climate change could lead to the loss of up to 38 percent of the Amazon rainforest by the end of the 21st century.

The Amazon is the largest rainforest in the world. Its 5.5 million square kilometers are a hotspot of species diversity, a home for indigenous communities, and a lever for climate action. In biomass and soil, the rainforest stores a tenth of the entire carbon of terrestrial ecosystems. Through its enormous evaporative power, the Amazon forest draws moisture from the ocean into the interior of the country, where precipitation is constantly evaporating and raining down again. In this way, the forest keeps itself alive.

However, this also puts the Amazon rainforest at risk when arable land and livestock farming expand at the expense of forested areas, and when global warming causes droughts and heatwaves in the Amazon basin. Although both these factors – land use change and climate change – have already caused progressive damage, we have lacked clear knowledge of how they interacted and, above all, how the forested areas would develop in the future. Most concerning here are abrupt transitions from dense forest coverage to a savannah-like open landscape. If this happens on a large scale, it could create a tipping point at which the ecosystem would be irrevocably lost.

A team led by LMU geographer Selma Bultan has conducted the first analysis to systematically consider the effects of land use change and climate change in conjunction. Its results have just been published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS). Using Earth system models with dynamic vegetation, the researchers analyzed deforestation in the Amazon basin from 1950 to 2014 and forecast future decline under two different climate scenarios. “Our analysis shows that up to 38 percent of the forest area which existed in 1950 could be lost by the end of the century, with 25 percent attributable to land use changes and 13 percent to rising temperatures,” explains Selma Bultan. “This would take us past the threshold of 20 to 25 percent, which earlier studies warned was the tipping point for the Amazon rainforest.”

Moreover, the team’s analyses show that the risk of an abrupt loss of forest area, as opposed to gradual decline, significantly increases when warming surpasses 2.3°C. “Based on current policies and definite commitments to climate action, we’re heading toward global warming of at least 2.5°C,” explains co-author Julia Pongratz, Professor of Physical Geography and Land Use Systems at LMU. “Positive developments such as the enhanced rainforest protections agreed at the climate conference in Belém need to be expanded, while we step up the pace of our fight against global warming. The value of the Amazon rainforest is much too great to put its existence on the line.”