The
greenhouse effect
The atmosphere has a natural supply of "greenhouse gases."
They capture heat and keep the surface of the Earth warm enough for us to live
on. Without the greenhouse effect, the planet would be an uninhabitable, frozen
wasteland.
Before the Industrial Revolution, the amount of carbon dioxide (CO2)
and other greenhouse gases released into the atmosphere was in a rough balance
with what could be stored on Earth. Natural emissions of heat-trapping gases matched
what could be absorbed in natural sinks. For example, plants take in CO2 when
they grow in spring and summer, and release it back to the atmosphere when they
decay and die in fall and winter.
Too much greenhouse effect
Industry
took off in the mid-1700s, and people started emitting large amounts of greenhouse
gases. Fossil fuels were burned more and more to run our cars, trucks, factories,
planes and power plants, adding to the natural supply of greenhouse gases. The
gases-which can stay in the atmosphere for at least fifty years and up to centuries-are
building up beyond the Earth's capacity to remove them and, in effect, creating
an extra-thick heat blanket around the Earth.
The result is that the globe
has heated up by about one degree Fahrenheit over the past century-and it has
heated up more intensely over the past two decades.
If one degree doesn't sound
like a lot, consider this: the difference in global average temperatures between
modern times and the last ice age-when much of Canada and the northern U.S. were
covered with thick ice sheets-was only about 9 degrees Fahrenheit. So in fact
one degree is very significant-especially since the unnatural warming will continue
as long as we keep putting extra greenhouse gases in the atmosphere.
How
much is too much?
Already, people have increased the amount of CO2, the chief
global warming pollutant, in the atmosphere to 31 percent above pre-industrial
levels. There is more CO2 in the atmosphere now than at any time in the last 650,000
years. Studies of the Earth's climate history show that even small changes in
CO2 levels generally have come with significant shifts in the global average temperature.
Scientists
expect that, in the absence of effective policies to reduce greenhouse gas pollution,
the global average temperature will increase another 2.0 degrees Fahrenheit to
11.5 degrees Fahrenheit by 2100.
Even if the temperature change is at the small
end of the predictions, the alterations to the climate are expected to be serious:
more intense storms, more pronounced droughts, coastal areas more severely eroded
by rising seas. At the high end of the predictions, the world could face abrupt,
catastrophic and irreversible consequences..
The science is clear
Scientists
are no longer debating the basic facts of climate change. In February 2007, the
thousands of scientific experts collectively known as the Intergovernmental Panel
on Climate Change (IPCC) concluded that there is greater than 90 percent likelihood
that people are causing global warming. (IPCC, 2007)
These latest findings
amplify what other highly respected science organizations say:
" In a
joint statement with 10 other National Academies of Science, the U.S. National
Academy of Sciences said:
"The scientific understanding of climate change
is now sufficiently clear to justify nations taking prompt action. It is vital
that all nations identify cost-effective steps that they can take now, to contribute
to substantial and long-term reduction in net global greenhouse gas emissions."-Joint
Statement of Science Academies: Global Response to Climate Change, 2005
"
The American Geophysical Union, a respected organization comprising over 41,000
Earth and space scientists, wrote in its position on climate change that "natural
influences cannot explain the rapid increase in global near-surface temperatures
observed during the second half of the 20th century."