Environmental Engineering Reference
In-Depth Information
Synopsis
Emissions of carbon dioxide from the burning of fossil fuels have ush-
ered in a new epoch where human activities will largely determine the
evolution of Earth's climate. Because carbon dioxide in the atmosphere is
long lived, it can effectively lock Earth and future generations into a range
of impacts, some of which could become very severe. Therefore, emissions
reductions choices made today matter in determining impacts experienced
not just over the next few decades, but in the coming centuries and millen-
nia. Policy choices can be informed by recent advances in climate science
that quantify the relationships between increases in carbon dioxide and
global warming, related climate changes, and resulting impacts, such as
changes in streamflow, wildfires, crop productivity, extreme hot summers,
and sea level rise.
Since the beginning of the industrial revolution, concentrations of green-
house gases from human activities have risen substantially. Evidence now
shows that the increases in these gases very likely (>90 percent chance) ac-
count for most of Earth's warming over the past 50 years. Carbon dioxide is
the greenhouse gas produced in the largest quantities, accounting for more
than half of the current impact on Earth's climate. Its atmospheric concentra-
tion has risen about 35 percent since 1750 and is now at about 390 ppmv,
the highest level in at least 800,000 years. Depending on emissions rates,
carbon dioxide concentrations could double or nearly triple from today's
level by the end of the century, greatly amplifying future human impacts
on climate.
Society is beginning to make important choices regarding future green-
house gas emissions. One way to inform these choices is to consider the
projected climate changes and impacts that would occur if greenhouse
gases in the atmosphere were stabilized at a particular concentration level.
The information needed to understand such targets is multifaceted: how
do emissions affect global atmospheric concentrations and in turn global
warming and its impacts?
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