Fresh evidence that carbon pollution is greening our planet will be billed as good news by climate deniers. It isn't, says Olive Heffernan.
Olive Heffernan

New Scientist
29 Apr 2016 - 11:10 AM  UPDATED 29 Apr 2016 - 11:10 AM

Half our planet’s vegetated surface has become significantly greener in the past three decades. Plants in many regions – from stocky shrubs of the Arctic to towering trees of the rainforest canopy – are growing more and bigger leaves, according to the latest evidence. Leaf for leaf, it’s as though 4.4 billion giant Sequoia trees have been added to the Earth.

This sounds like good news, but there is a sting in the tale. In the short term, this may buy us a little time, but the Artic is also greening rapidly, and that could be catastrophic.

The great greening is mostly the result of unabated greenhouse gas pollution. And while it is no surprise that plants thrive when there’s more carbon around, the fertilising effect of extra CO2 in the air – blamed for 70 per cent of the greening in the new research – has never been shown on this scale before.

This is worrying, for the simple fact that climate deniers like Rupert Murdoch have previously invoked CO2 fertilisation as a force for good that counters the need to curb emissions, from industry or elsewhere. Their woefully misguided vision of a more verdant, healthier Earth under climate change may now see a renaissance.

However, they should ponder what this actually means for the planet.

Trouble in store

OK, trees grow, they suck CO2 from the air and lock it up in leaves, shoots and roots until they’re chopped or burned or die. Each year, a quarter of the 10 billion tonnes of CO2 poured into the atmosphere ends up stored short-term in plants. That could buy us some time to deal with the other effects of climate change – ocean acidification, sea-level rise, warming and so on. What’s more, it could boost plant growth enough to save diverse ecosystems such as the Amazon from dieback as the world warms.

But it’s not that simple. Before long, plants adjust and the effects of all that extra CO2 will start to plateau. In the meantime, other outcomes of climate change have worsened. For example, as the Arctic – and other snowy regions – green, warming accelerates. That’s because white surfaces reflect light, while grassy or shrubby land does the opposite.

The Arctic is now warming four times faster than the rest of the planet and greening is helping this along nicely. One possible outcome is that the Arctic’s permanently frozen ground will thaw and release copious amounts of stored methane, a potent greenhouse gas. That could be a disaster.

There are other downsides, such as denser forests catching fire more often and becoming more attractive homes for pests, such as bark beetles – all of which send stored carbon straight back to the sky. And even while the greening goes on, all the other downsides of climate change mount – such as sea level rise and more frequent extreme weather.

So if you’re out for a walk and find yourself marvelling at the unusually lush foliage, remember that Eden was only a fable.

Journal reference: Nature Climate Change, DOI: 10.1038/NCLIMATE3004

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