Asynchronous exposure to global warming: freshwater resources and terrestrial ecosystems

Abstract

This modelling study demonstrates at what level of global mean temperature rise .1Tg/ regions will be
\nexposed to significant decreases of freshwater availability and changes to terrestrial ecosystems. Projections
\nare based on a new, consistent set of 152 climate scenarios (eight 1Tg trajectories reaching 1.5–5 C above
\npre-industrial levels by 2100, each scaled with spatial patterns from 19 general circulation models). The results
\nsuggest that already at a 1Tg of 2 C and mainly in the subtropics, higher water scarcity would occur in >50%
\nout of the 19 climate scenarios. Substantial biogeochemical and vegetation structural changes would also occur
\nat 2 C, but mainly in subpolar and semiarid ecosystems. Other regions would be affected at higher 1Tg levels,
\nwith lower intensity or with lower confidence. In total, mean global warming levels of 2 C, 3.5 C and 5 C are
\nsimulated to expose an additional 8%, 11% and 13% of the world population to new or aggravated water
\nscarcity, respectively, with >50% confidence (while 1.3 billion people already live in water-scarce regions).
\nConcurrently, substantial habitat transformations would occur in biogeographic regions that contain 1% (in
\nzones affected at 2 C), 10% (3.5 C) and 74% (5 C) of present endemism-weighted vascular plant species,
\nrespectively. The results suggest nonlinear growth of impacts along with 1Tg and highlight regional disparities
\nin impact magnitudes and critical 1Tg levels.