Walk through the Amazon rainforest today and you will find it steamy, warm, damp and thick. But if you had been there around 15,000 years ago, during the last ice age, would it have been the same? For more than 30 years, scientists have been arguing about how rainforests might have reacted to the cold, dry climate of the ice ages, but till now, no one has reached a satisfying answer.

Rainforests like the Amazon rainforest are important for mopping up CO₂ from the atmosphere and helping to solve global warming. Currently the trees in the Amazon rainforest take in around 500 million tons of CO₂ each year, equal to the total amount of CO₂ given off in the UK each year. But how will the Amazon rainforest react to the future climate change? If it gets drier, will it survive and continue to draw down CO₂? Scientists hope that they will be able to learn in advance how the rainforest will manage in the future by understanding how rainforests reacted to climate change in the past.

Unfortunately, collecting information is incredibly difficult. To study the past climate, scientists need to look at fossilized pollen(花粉) kept in lake mud. Going back to the last ice age means drilling down into lake sediment(沉积物), which requires specialized equipment and heavy machinery. There are very few roads and paths, or places to land helicopters and aeroplanes. Rivers tend to be the easiest way to enter the rainforest, but this still leaves vast areas between the rivers completely unsampled(未取样). So far, only a handful of cores have been drilled that go back to the last ice age and none of them provide enough information to prove how the Amazon rainforest reacted to climate change.