A new study revealing that trees release a climate-influencing chemical is just the latest evidence showing how crucial forests are to the globe’s climatic balance – and how potentially disastrous is their decline.

Scientists from Institute for Climate and Atmospheric Science at Leeds University and the Institute for Atmospheric and Environmental Sciences at Frankfurt University have now offered yet another reason to preserve forests.

In a study published in the journal Philosophical Transactions of the Royal Society A, a team led by Dominick Spracklen found that emissions of chemicals called terpenes from all trees helps clouds to form over forests. Lighter coloured cloud reflects more sunlight, helping cool the atmosphere.

Spracklen told the UK’s Guardian newspaper that terpenes from pine trees found in the boreal forests of the Northern Hemisphere could double cloud concentrations 1000 metres above, reflecting an extra 5 per cent of solar rays back into space. "It might not sound a lot, but that is quite a strong cooling effect,” he is quoted as saying.

The study is at odds with the conclusions of a 2006 study that found these cool climate forests may add to global warming rather than help cool the planet as forests do in general.

“Previous studies have concluded that boreal forests warm the climate because the cooling from storage of carbon in vegetation and soils is cancelled out by the warming due to the absorption of the Sun's heat by the dark forest canopy,” the study’s authors say.

But that research did not take account of the effect of terpene emissions in increasing cloud formation and this “may be sufficiently large to result in boreal forests having an overall cooling impact on climate”, they conclude.

The Spracklen team’s findings also appear to fit with previous thinking that forests have an influential role on the climatic conditions around them, including rainfall.

Separate research earlier this year concluded that the demise of the Mayan civilisation around 800 AD in Central America may have been in part due to localised climate change – permanent drought brought on by the clearing of forests and draining of wetlands.

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Forestry Carbon Standards 2008