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10.1. What's known for certain?
- Human activities are increasing the levels of
greenhouse gases, like carbon dioxide (CO2),
in the atmosphere.
- Greenhouse gases trap heat in the earth's atmosphere
and tend to warm the planet.
Therefore, human activities are strengthening the earth's natural
greenhouse
effect.
- A warming of about 0.6 °C (1°F) has
been recorded since the late 19th century.
It has occurred in both the northern and southern hemispheres,
and over the oceans. More..
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10.2. What's likely but not certain?
- To what extent the human-induced greenhouse gases
are responsible for the global warming is uncertain, but "there
is new and stronger evidence that most of the warming observed
over the last 50 years is attributable to human activities."
- Temperatures will continue to rise as a result
of rising levels of greenhouse gases;
but by how much and how fast remain uncertain. More...
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10.3. What are the big unknowns?
Scientists do not know yet:
- What will be the exact impacts of climate
change over the 21st century, especially for small areas.
- Surprises produced by the complex climate
system that could pose the greatest risk.
- Whether or not hurricanes and other storms (which
could become more intense) will become more frequent.
- Whether events like El Niño will become
more frequent and fierce. More..
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10.4. Living with uncertainty
There is certainty that human activities are rapidly
adding greenhouse gases to the atmosphere, which tend to warm the
planet. Fundamental scientific uncertainties remain concerning the
amplitude and rate of the future warming and about its potential
adverse and beneficial effects.
Global warming poses real risks. The exact nature
of these risks remains uncertain. We have to use our best judgment
– guided by the current state of science – to determine
what the most appropriate response should be. More...
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