By simulating the future atmosphere, scientists hope to understand whether trees will continue to act as the lungs of the planet.

"The oak is the queen of her domain," says Rob MacKenzie as he gestures towards a giant towering above us. This oak tree has stood in this very spot since long before he or I walked the Earth.

It is early winter when MacKenzie, an atmospheric scientist and director of Birmingham University Institute of Forest Research, leads me further into this small patch of woodland here in Staffordshire, England.

He treads steadily along the track, snow crunching underfoot. The low winter Sun casts long shadows, and a few birds, braving the cold, sing to each other across the forest. Autumn's final leaves tumble to the ground – where they land not on the floor, but in nets. Because this is no ordinary forest.

Where roots tangle across the earth, pipes and wires intertwine. This forest has plumbing. Silhouetted oak, birch and sycamore trees stand shoulder to shoulder with towering metal frames supporting drainpipes, which reach up to the very tops of the trees.

MacKenzie and his colleagues have sent this quiet forest just outside Birmingham into the future – in a manner of speaking. They have pumped carbon dioxide (CO2) around the mature oak trees here in order to simulate the atmosphere that is expected to swathe planet Earth by the year 2050.

This small wooded area, close to an urban metropolis, is not the only one getting a blast of the future with artificially elevated levels of CO2. Researchers across the globe, from Australia to the Amazon rainforest, are experimenting on forests in a bid to better understand the role trees play in keeping the Earth cool. Their findings could transform our understanding of how the forests of the future will respond to climate change.

MacKenzie and his colleagues have been running their experiment for seven years to date, and the results have surprised them. Contrary to some previous analyses, their study suggests that trees can actually absorb more carbon as they age. It's a finding that highlights the immense importance of mature, temperate forests in terms of climate regulation.

What's more, for the first time, MacKenzie and his fellow forest-watchers have also shown that microscopic organisms living on these trees capture methane, another greenhouse gas harmful to the atmosphere. "[We] found the trees are providing another unexpected service for us," says MacKenzie. "The canopy hosts microbes, and these microbes eat the methane. There are lots of reasons to nurture forests.

Earth's natural greenhouse effect – whereby gases such as CO2 and methane absorb the Sun's heat as it radiates back from the Earth's surface, trapping it in the atmosphere – is vital for life as we know it. It helps to keep the average global surface temperature comfortably above freezing.

Carbon sinks, meanwhile – such as forests, oceans and soils – absorb CO2 from the atmosphere, preventing the Earth from overheating due to this greenhouse effect. Our climate has existed this way for millennia, in a delicate state of balance.

However, with rising greenhouse gas emissions from human activities, the amount of those gases absorbed by nature has increased, too. It has made plants grow faster, a process known as CO2 fertilisation. Natural carbon sinks currently absorb roughly half of all human-produced carbon emissions, according to estimates. But experts warn we may be on the verge of tipping the balance – with both

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