This modelling study demonstrates at what level of global mean temperature rise. 1Tg/ regions will be to significant decreases of freshwater availability and changes to terrestrial ecosystems. Projections based on a new, consistent set of 152 climate scenarios (eight 1Tg trajectories reaching 1. 5–5 C above -industrial levels by 2100, each scaled with spatial patterns from 19 general circulation models). The results that already at a 1Tg of 2 C and mainly in the subtropics, higher water scarcity would occur in >50% of the 19 climate scenarios. Substantial biogeochemical and vegetation structural changes would also occur 2 C, but mainly in subpolar and semiarid ecosystems. Other regions would be affected at higher 1Tg levels, lower intensity or with lower confidence. In total, mean global warming levels of 2 C, 3. 5 C and 5 C are to expose an additional 8%, 11% and 13% of the world population to new or aggravated water, respectively, with >50% confidence (while 1. 3 billion people already live in water-scarce regions). , substantial habitat transformations would occur in biogeographic regions that contain 1% (in affected at 2 C), 10% (3. 5 C) and 74% (5 C) of present endemism-weighted vascular plant species,. The results suggest nonlinear growth of impacts along with 1Tg and highlight regional disparities impact magnitudes and critical 1Tg levels.
Gerten et al. (Sun,) studied this question.