Geoscience Reference
In-Depth Information
• The range of estimates of sea-level rise over the twenty-fi rst cen-
tury is between 18 and 60 centimeters (7-23 inches) depending
upon the scenario but excluding the effects of the large ice sheets.
• Temperatures are expected to rise more rapidly over land and
much more rapidly in the Arctic than the global average rise.
• The Arctic Ocean is expected to be largely ice free during the sum-
mer by the end of the twenty-fi rst century, and it might occur
much sooner.
• The intensity of hurricanes is expected to increase.
• Increasing atmospheric CO
2
concentrations will lead directly to
acidifi cation of the oceans.
• Many regions will see more hot days and fewer cold days, but the
evidence on other extreme events is still unclear.
• Major uncertainties in many projections include the role and im-
pact of small particles known as aerosols. They are expected to
cool the climate, but the extent and regional dimensions of this
cooling are diffi cult to determine.
13
The different models provide different answers about the projected
increases and regional impacts over the next century. However, even
with the disagreement among models, we should not lose sight of the
central fi nding, which is that all modeling groups project large climatic
changes over the twenty-fi rst century. These fi ndings are at the cutting
edge of modern climate science, and the basic message should not get
lost in the differences.
Climate models can teach us much more, particularly regarding
impacts, but that discussion will have to wait until later chapters.
THE CLIMATIC ROULETTE WHEEL
Figures 7 and 9 are warnings about the limitations of our knowledge
of the climate system. In the most carefully studied part of all climate-
change science—the response of the climate to a doubling of atmo-
spheric CO
2
concentrations—major uncertainties remain about the way
the system works.
