  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.
