The threat to tropical rainforests from climate change may have been exaggerated by environmentalists, according to a new study.
Researchers have shown that the world's tropical forests thrived in the far distant past when temperatures were 3 to 5C warmer than today.
They believe that a wetter, warmer future may actually boost plants and animals living the tropics.
The findings, published in the respected journal Science, come from a study of pollen trapped in rocks during a natural period of global warming 56.3million years ago.
The extreme warm spell - called the Paleocene-Eocene Thermal Maximum - saw global temperatures soar by 6C (11F) within a few thousand years.
The cause of the PETM is unknown. However, some scientists believe it was triggered by the release of vast amounts of carbon dioxide from volcanic activity over a few thousand years.
The injection of carbon dioxide into the atmosphere set off a spiral of events that warmed the climate and led to even more greenhouse gas entering the atmosphere, they say.
Researchers at the Smithsonian Tropical Research Institute in Panama examined pollen trapped in rocks in Colombia and Venezuela before, during and after the PETM.
They found that the amount of plant-life in the forests increased rapidly during the warming event with new plant species evolving much more quickly than the older species became extinct.
Pollen from the chocolate family and passionflower plant family were found for the first time.
The researchers believe the hotter, wetter conditions - and additional carbon dioxide in the atmosphere - boosted plant-life and increased biodiversity.
The findings could shed light on man-made global warming caused by the release of carbon dioxide from burning coal and destroying forests.
Conservative computer models of climate change suggest the world will warm by at least 2C over the next century.
'It is remarkable that there is so much concern about the effects of greenhouse conditions on tropical forests,' said Dr Klaus Winter of the institute.
'However, these horror scenarios probably have some validity if increased temperatures lead to more frequent or more severe drought as some of the current predictions for similar scenarios suggest.'
British forest expert Dr Simon Lewis of Leeds University said warmer, wetter weather could boost rain-forests. However, if climate change led to more droughts, it could be disastrous for regions like the Amazon.
In the last five years, the Amazon has experienced two 'one in a century' droughts, he said.
'The 2005 Amazon drought was widely characterised as an unusual 1-in-100 year event, which caused tree deaths leading to rotting trees releasing over four billion tonnes of carbon dioxide,' he said.
'And now in 2010, another drought has stuck, which initial analyses show is more extensive than 2005, even though it is only five years later.
'These droughts are consistent with model projections showing a die-back of the Amazon, further accelerating climate change in a dangerous loop.
'The new paper is useful, but doesn’t address present-day concerns of drought-impacts that affect the forest itself and the millions of people who live there.'
The speed of modern day man-made climate change was much faster than the global warming of 60million years ago, he added.