Could a global tree-planting programme really save us from climate change?

Trees are our friends. Image: Getty.

Restoring the world’s forests on an unprecedented scale is “the best climate change solution available”, according to a new study. The researchers claim that covering 900m hectares of land – roughly the size of the continental US – with trees could store up to 205 billion tonnes of carbon, about two thirds of the carbon that humans have already put into the atmosphere.

While the best solution to climate change remains leaving fossil fuels in the ground, we will still need to suck carbon dioxide (CO₂) out of the atmosphere this century if we are to keep global warming below 1.5˚C. So the idea of reforesting much of the world isn’t as far-fetched as it sounds.

Since the dawn of agriculture, humans have cut down three trillion trees – about half the trees on Earth. Already 43 countries have pledged to restore 292m hectares of degraded land to forest worldwide. That’s an area ten times the size of the UK. But what the new study advocates is reforesting something like ten times that amount.

Trees absorb CO₂ from the air and store the carbon as bark and other tissue. Image: author provided.

Rewilding habitats and reforesting may be easier in the future as the world is already becoming a wilder place in many areas. This may seem a strange prediction, given that the global population will grow from 7.7 billion to 10 billion by 2050, but by then nearly 70 per cent of us will live in cities and have abandoned rural areas, making them ripe for restoration. In Europe already, 2.2m hectares of forest regrew per year between 2000-2015, and forest cover in Spain has increased from 8 per cent of the country’s territory in 1900 to 25 per cent today.

Massive reforestation isn’t a pipe dream and it can have real benefits for people. In the late 1990s, environmental deterioration in China became critical, with vast areas resembling the Dust Bowl of the American Midwest in the 1930s. Six bold programmes were introduced, targeting over 100m hectares of land for reforestation.

Grain for Green is the largest and best known of these. It reduced soil erosion and stabilised local rainfall patterns. The ongoing programme has also helped to alleviate poverty by making payments directly to farmers who set aside their land for reforestation.

Better yet, the new study suggests that bringing back 900m hectares of forest wouldn’t impact on our capacity to reserve land for growing food. This is certainly possible, and in line with other estimates. Reforestation may even result in production from farmland increasing, as was found in China when more stable rainfall and fertile soil followed the return of forests.

Where the billion hectares of forest could be planted – excluding desert, farmland and urban areas. Image: Crowther Lab/author provided.

How all of that new forest would look, alongside what’s already there. Image: Crowther Lab/author provided.

No solution without emission cuts

There should be more scepticism about how much CO₂ 900m hectares of new forest could store though. The paper insists on 205 billion tonnes of carbon, but this seems too high when compared to previous studies or climate models. The authors have forgotten the carbon that’s already stored in the vegetation and soil of degraded land that their new forests would replace. The amount of carbon that reforestation could lock up is the difference between the two.

Mature forests can store a lot of carbon, but this capacity is only reached after hundreds of years, not a couple of decades of new forest growth as assumed in this study. The most recent estimate from the IPCC suggests that new forests could store on average an extra 57 billion tonnes of carbon by the end of the century. This is still a huge number and could absorb about one sixth of the carbon that’s already in the atmosphere, but reforestation should be thought of as one solution to climate change among many.

Radically reducing carbon emissions and absorbing the carbon that’s already in the atmosphere will be necessary to avert catastrophic climate change. Image: Mark Maslin/author provided.

Even if warming is stabilised at 1.5˚C, the study indicates that one fifth of the land proposed for reforestation could be rendered too hot for growing new forests by 2050. But this concern ignores the role of carbon dioxide fertilisation – when there are higher levels of carbon dioxide in the atmosphere, photosynthesis is more efficient, meaning plants need less water and can still be productive at higher temperatures. Today, the most immediate threat to tropical forests is deforestation by people and the fires they light which get out of control, not the more subtle impacts of higher temperatures.

Reforesting an area the size of the US will have massive benefits on local environments and will store a huge amount of man-made carbon emissions. It is not, however, a substitute for reducing those carbon emissions.


Even if the world reduces its carbon emissions to zero by 2050, there will still need to be negative global carbon emissions for the rest of the century – drawing CO₂ out of the atmosphere to stabilise global warming at 1.5˚C. Reforestation is essential for creating negative emissions – not reducing the amount of carbon that humans are still emitting.

There is another sting in the tail. Massive reforestation only works if the world’s current forest cover is maintained and increasing. Deforestation of the Amazon rainforest – the world’s largest – has increased since Brazil’s new far-right president, Jair Bolsonaro, came to power. Current estimates suggest areas of rainforest the size of a football pitch are being cleared every single minute.

It won’t be easy, but society needs to protect the forests we’ve got, and protect new forests in perpetuity to permanently keep carbon sequestered in trees and out of the atmosphere.

The Conversation

Mark Maslin, Professor of Earth System Science, UCL and Simon Lewis, Professor of Global Change Science at University of Leeds and, UCL.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 
 
 
 

The mountain in North Wales that tried to stop the UK’s blackout

Elidir Fawr, the mountain in question. Image: Jem Collins.

Last Friday, the UK’s National Grid turned to mush. Not the official term perhaps, but an accurate one after nearly one million people were left without power across the country, with hundreds more stranded at train stations – or even on trains (which isn’t nearly as fun as it might immediately sound). 

Traffic lights stopped working, back-up power failed in hospitals, and business secretary Andrea Leadsom launched an investigation into exactly what happened. So far though, the long and short of it is that a gas-fired power station in Bedfordshire failed just before 5 o’clock, followed just two minutes later by Hornsea offshore wind farm. 

However, amid the resulting chaos and inevitable search to find someone to blame for the outage, a set of mountains (yes, mountains) in North Wales were working extremely hard to keep the lights on.

From the outside, Elidir Fawr, doesn’t scream power generation. Sitting across from the slightly better known Mount Snowdon, it actually seems quite passive. After all, it is a mountain, and the last slate quarry in the area closed in 1969.

At a push, you’d probably guess the buildings at the base of the mountain were something to do with the area’s industrial past, mostly thanks to the blasting scars on its side, as I did when I first walked past last Saturday. 

But, buried deep into Elidir Fawr is the ability to generate an astounding 1,728 megawatts of electricity – enough to power 2.5 million homes, more than the entire population of the Liverpool region. And the plant is capable of running for five hours.

Dubbed by locals at the ‘Electric Mountain’, Dinorwig Power Station, is made up of 16km of underground tunnels (complete with their own traffic light system), in an excavation which could easily house St Paul’s Cathedral.

Instead, it’s home to six reversible pumps/turbines which are capable of reaching full capacity in just 16 seconds. Which is probably best, as Londoners would miss the view.

‘A Back-Up Facility for The National Grid’

And, just as it often is, the Electric Mountain was called into action on Friday. A spokesperson for First Hydro Company, which owns the generators at Dinorwig, and the slightly smaller Ffestiniog, both in Snowdonia, confirmed that last Friday they’d been asked to start generating by the National Grid.

But just how does a mountain help to ease the effects of a blackout? Or as it’s more regularly used, when there’s a surge in demand for electricity – most commonly when we all pop the kettle on at half-time during the World Cup, scientifically known as TV pick-up.

The answer lies in the lakes at both the top and bottom of Elidir Fawr. Marchlyn Mawr, at the top of the mountain, houses an incredible 7 million tonnes of water, which can be fed down through the mountain to the lake at the bottom, Llyn Peris, generating electricity as it goes.


“Pumped storage technology enables dynamic response electricity production – ofering a critical back-up facility during periods of mismatched supply and demand on the national grid system,” First Hydro Company explains.

The tech works essentially the same way as conventional hydro power – or if you want to be retro, a spruced up waterwheel. When the plant releases water from the upper reservoir, as well as having gravity on their side (the lakes are half a kilometre apart vertically) the water shafts become smaller and smaller, further ramping up the pressure. 

This, in turn, spins the turbines which are linked to the generators, with valves regulating the water flow. Unlike traditional UK power stations, which can take hours to get to full capacity, at Dinorwig it’s a matter of 16 seconds from a cold start, or as little as five if the plant is on standby.

And, designed with the UK’s 50hz frequency in mind, the generator is also built to shut off quickly and avoid overloading the network. Despite the immense water pressure, the valves are able to close off the supply within just 20 seconds. 

At night, the same thing simply happens in reverse, as low-cost, surplus energy from the grid is used to pump the water back up to where it came from, ready for another day of hectic TV scheduling. Or blackouts, take your pick.

Completed in 1984, the power station was the product of a decade of work, and the largest civil engineering project commissioned at the time – and it remains one of Europe’s largest manmade caverns. Not that you’d know it from the outside. And really, if we’ve learned anything from this, it’s that looks can be deceiving, and that mountains can actually be really damn good at making electricity. 

Jem Collins is a digital journalist and editor whose work focuses on human rights, rural stories and careers. She’s the founder and editor of Journo Resources, and you can also find her tweeting @Jem_Collins.