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Global Climate Change. What we know, what we are fairly confident about, and where the uncertainties lie. What do we know?. CO2, methane, CFC’s, water vapor trap heat (= “greenhouse gases”). Global average temperature has risen 0.3-0.6 C in the last 100 years.
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Global Climate Change What we know, what we are fairly confident about, and where the uncertainties lie.
What do we know? • CO2, methane, CFC’s, water vapor trap heat (= “greenhouse gases”). • Global average temperature has risen 0.3-0.6 C in the last 100 years. • Global average sea levels rose 10-25 cm over the last 100 years. • The global climate system is very complex.
What do we confidently conclude? • The rise in CO2 is the largely the result of human activity. • More CO2 will probably mean further rise in global average temperatures and sea levels. • Sulfate aerosols have been counteracting the warming trend.
What do we not really know? • Regional changes are very hard to predict at present. Local conditions may change much more than the global average. • Whether regional weather patterns are becoming more extreme or variable.
Major sources of uncertainty • Clouds: warming may mean more clouds, but these could cool or warm the planet. • Oceans: the fate of CO2 over the long term in the ocean is not known. • Interactive effects. Poorly known links in the climate system may lead to surprising changes.