Climate Certainies by David Adam
5/2/2010 Guardian CLIMATE CERTAINTIESCLIMATE CERTAINTIES
1 Carbon dioxide levels in the atmosphere are rising. Measured in parts per million (ppm), the figure stood at 28oppm before the industrial revolution and is now 387ppm, the highest for at least 650,000 years. It rises at about 2ppm each year. The rise is down to human activity, mostly the burning of fossil fuels such as coal, oil and gas.
2 Carbon dioxide, and other greenhouse gases such as methane, trap heat in the atmosphere. Known as the greenhouse effect, this principle was identified in 1824.
3 The Earth is warming. The last decade was the warmest on record and 2009 the second warmest year, according to Nasa. The eight warmest years on record have occurred since 2001. Temperatures have risen by 0.2C per decade, over the past 30 years. Average global
temperatures have increased by o.8C since 1880.
4 The warming is unusual and not down to natural variation. Study after study has shown that warming over the last 50 years is unprecedented in the last few centuries, and probably longer. While the Earth’s climate has always warmed and cooled, the only plausi- ble explanation for recent warming is human emissions ofgreerthouse gases.
Some questions remain. While there is general agreement that human activity is warming the planet, exactly how this will continue is unclear. Last week scientists found that water vapour has a larger role than expected in buffering temperature rise. The scientific basis for political action is settled, the wider science of climate change is not.
David Adam’
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