Geoscience Reference
In-Depth Information
6
4
2
-0
-2
-4
-6
400,000
300,000
200,000
100,000
0
Date (years before present)
Figure 28.
Estimated global temperature variations for the last 400,000 years along
with model projections for the next two centuries. This fi gure shows a reconstruction of
global temperatures using Antarctic ice core data for the last half-million years. The
present temperature is normalized at 0°C. The line with dots shooting up at the far
right shows a projection of future temperature increases from the DICE model in a
no-controls baseline scenario. If global warming continues unchecked, future
temperatures will soon surpass the historical maximum of the last half-million years.
a baseline for comparison. Where the line dips below zero, it refl ects
cooling trends and ice ages (low global temperatures), and where it rises
above zero, it indicates warm or interglacial periods (high global tem-
peratures).
According to this reconstruction, global temperatures may have
been as much as 2°C higher than today, but these warm periods lasted
for relatively short intervals. As best we can tell, global temperatures
have not exceeded today's temperatures by more than 2°C for the last
half- million years.
