Page 379 - Earth's Climate Past and Future

CHAPTER 19 • Future Climatic Change 355

4.25°C In the tropics and subtropics, where 80% of humans
7.5°F live, the temperature increase will be smaller, but it will
have a significant effect on moisture balances. The greater
warmth will increase the global mean rate of evaporation
and in dry regions put greater stress on other sources of
3.25°C
6°F water. In regions where evaporation increases but precip-
itation does not, agriculture will depend more on irriga-
tion. Areas that depend on runoff from snowmelt and
2.5°C glacial meltwater for irrigation late in the growing season
4.5°F will suffer as both sources of water decrease. Regions that
have for decades been pumping deep subsurface water for
irrigation may run out of usable groundwater. In areas
where rainfall increases, more precipitation will fall as
2 CO 2 temperature increases frontal systems during cooler seasons.
localized summer cloudbursts than as the longer-lasting
precipitation typically associated with the passage of

The future sea level rise caused by melting of land
ice and expansion of ocean water will have an adverse
effect on coastal populations. The same factors that
caused the 17-cm rise in sea level during the last 100
years will continue to operate: thermal expansion of

melting of the Greenland and perhaps the West Antarc-
tic ice sheets.
Global High latitudes High-latitude ocean water, melting of mountain glaciers, and partial
winters Although the IPCC mid-range projection of a 30-cm
sea level rise during this century sounds trivial, it will
FIGURE 19-13 Larger temperature increases at high
translate into a 300-m (~1000-ft) advance of the ocean
latitudes Temperature changes caused by a doubling of
atmospheric CO concentrations will be larger than the across flat coastal regions where many people live. In
2 heavily populated Bangladesh, a sea level rise of 30 cm
global average at high mid-latitudes, especially in winter.
would displace millions of people currently living within
1 m in elevation above the present sea level.
from region to region, and the range of effects on
humans and other life will also vary. A few examples
from the vast range of future changes are noted here.
Some of the most striking changes will occur in regions 80
where snow and ice retreat northward. For today’s ski
resorts at relatively low latitudes, a loss of two months
of subfreezing winter cold may so truncate the snow- 70
making season that business will be impossible. On the
other hand, in far-northern regions of Hudson Bay and
the Arctic coast of Siberia, the sea ice retreat will open 60
up new year-round shipping lanes. The length of the Temperature (°F)
shipping season in existing lanes is already lengthen-
ing, and nations are actively considering new (shorter) 50
Arctic routes. In addition, less energy will be required Current 2 × CO 2
for winter heating at middle and higher latitudes, but
more energy will be needed for summer cooling at 40
lower and middle latitudes.
Warmer winters at high latitudes should extend ?
the northern limit for growing many crops, especially 30 J A S O N D J F M A M J
wheat across broad regions of Canada and Russia. Also, Month
higher CO levels in the atmosphere should allow some
2
plants to obtain the CO necessary for photosynthesis FIGURE 19-14 Changes in length of seasons The warming
2
more quickly without exposure to the drying effects of caused by 2 × CO levels will shorten winters and lengthen
2
evaporation. summers by about one month at middle latitudes.