Evidence of Amazon rainforest dieback in CMIP6 models

TL;DR

This study analyzes CMIP6 climate models to identify potential Amazon rainforest dieback events, revealing localized abrupt reductions in vegetation carbon linked to increased dry season severity and climate change.

Contribution

It provides the first comprehensive assessment of Amazon dieback likelihood in CMIP6 models, highlighting regional vulnerabilities and fire-related processes.

Findings

Five out of seven models show localized dieback events.

Approximately 7% of NSA region may experience abrupt vegetation carbon loss per degree of warming.

Dieback events are preceded by increased seasonal temperature variability.

Abstract

Amazon forest dieback is seen as a potential tipping point under climate change. These concerns are partly based-on an early coupled climate-carbon cycle simulation, that produced unusually strong drying and warming in Amazonia. In contrast, the 5th generation Earth System Models (CMIP5) produced few examples of Amazon dieback under climate change. Here we examine results from seven 6th generation models (CMIP6) which include vegetation dynamics, and in some cases interactive forest fires. Although these models typically project increases in area-mean forest carbon across Amazonia under CO2-induced climate change, five of the seven models also produce abrupt reductions in vegetation carbon which indicate localised dieback events. The Northern South America region (NSA), which contains most of the rainforest, is especially vulnerable in the models. These dieback events, some of which are mediated by fire, are preceded by an increase in the amplitude of the seasonal cycle in near surface temperature, which is consistent with more extreme dry seasons. Based-on the ensemble mean of the detected dieback events we estimate that 7 +/-5% of the NSA region will experience abrupt downward shifts in vegetation carbon per degree of global warming above 1.5 degrees.