With temperatures topping 100 degrees Fahrenheit this month in
Chicago, thoughts turn to global warming. Whether any particular
extreme weather event could be a symptom of climate change is
difficult to say. Even higher-than-normal regional temperature
patterns may not be direct evidence of the planet's warming
overall. Climate models cannot forecast changes in temperature
or rainfall at local levels. All they can tell us is that on
average Earth's temperature is gradually rising and that the
rise in temperature will have cascading effects on global
weather, rainfall patterns, growing seasons, species' survival,
and the habitats we depend upon for our own survival. But
climate models can't tell us exactly where and how the effects
-- or the symptoms -- will be felt. Climate science can be
frustrating. Still, from years of careful study of Earth and
ocean temperatures, atmospheric chemistry, and ice cores, among
other data, we know a great deal about global warming.
Scientists are observing rapid changes in ne