Geoscience Reference
In-Depth Information
Vulnerability of tipping elements to a 4°C global warming
Tipping element
Level of
global
warming
Transition
timescale
Key impacts
Arctic sea ice
0.5-2°C
~10 yr (rapid)
Amplified warming,
ecosystem change
Greenland ice sheet
1-2°C
>300 yr (slow)
Sea level,
1
2-7 m
West Antarctic ice
sheet
3-5°C
>300 yr (slow)
Sea level,
1
5 m
Atlantic thermohaline
circulation
3-5°C
~100 yr (gradual)
Regional cooling, ITCZ
shift, regional sea level
El Nino-Southern
Oscillation (ENSO)
3-6°C
~100 yr (gradual)
Drought in SE Asia and
elsewhere
Indian summer
monsoon
N/A
~1 yr (rapid)
Drought, decreased
carrying capacity
3-5°C ~10 yr (rapid) Wetting or drying of the
Sahel
Amazon rainforest 3-4°C ~50 yr (gradual) Biodiversity loss,
decreased rainfall, biome
switch to grassland or
savanna
Boreal forest 3-5°C ~50 yr (gradual) Dieback and biome
switch to grassland or
woodland
Yedoma permafrost 4-6°C ~100 yr (gradual) CH
4
and CO
2
release
Source: Estimates are based on Lenton et al., 2008 and have been updated by T. Lenton
in Richardson et al., 2011
Sahara/Sahel and West
African monsoon
major, or one of the most important, forcing factors that could drive a shift in the
system. The exception is the Indian summer monsoon, where the forcing factor
is aerosol loading over the subcontinent, which affects the land-sea temperature
differential and thus the behaviour of the monsoon.
The transition times for a system to shift from one state to another once a
threshold is crossed vary greatly between systems. For example, it is possible that
the thresholds for loss of most of the Greenland and West Antarctic ice sheets
could be crossed later this century, but the time needed for that volume of ice to
be lost would be centuries or millennia. By contrast, it is likely that the tipping
point for the Arctic sea ice has already been crossed and that within a few
decades the Arctic Sea will be ice free during the northern hemisphere summer
months.
All of the tipping elements shown in
Table 7.1
have estimated thresholds that
could be crossed in a Four Degree World. For several of them - Arctic sea ice, the
Greenland ice sheet, and conversion of the Amazon rainforest to a savannah or
