Lethal Heating: 07/06/19

06/07/2019

Climate Change Could Be Paused By Planting Trees, Researchers Say, As They Map Out Available Land

ABC Science - Nick Kilvert

Key points:

Researchers identified 0.9 billion hectares of land that is available to be reforested
That could buy us a 20 year pause in climate warming
Coastal ecosystems are capable of storing carbon up to 40 times faster than forests and should also be considered, expert says

Planting trees to reduce the amount of carbon dioxide in the atmosphere seems like a no-brainer in the fight against climate change.
But until recently it's not been clear how much land we'd need to make a tangible difference to warming, and whether we'd need to reclaim farm and residential land to do it.
Now new research published today in Science estimates there's enough suitable unused land on the globe for reforestation to store around 205 gigatonnes of carbon.
That's enough to buy us about 20 years in the fight against climate change, according to researcher Jean-Francois Bastin from the Institute of Integrative Biology in Zurich.
"This would definitely help to keep us at that maximum of 1.5 degrees by 2050," Dr Bastin said.
The researchers started by modelling the amount of tree cover the earth could sustain under current environmental conditions, if there were no humans on the planet.
They considered local climate factors like rainfall and temperature in their modelling.
Then they worked backwards, subtracting existing tree cover, urban environments and agricultural land.
They were left with 0.9 billion hectares of degraded land, which could be returned to canopy cover ranging from open savannah to dense forest.
The land they identified had been affected by things like logging, slash-and-burn fire regimes, intensive ongoing burning and clearing for grazing.
Other technological methods for combatting climate change, such as injecting sulphate aerosols into the stratosphere, have been proposed but most carry significant risks or are yet to be proven at scale.
The beauty of reforestation, according to Dr Bastin, is that it's win-win.
"When you think about tree restoration, it's not only about fighting climate change it's also about maintaining ecosystems," he said.
"The forests of the world protect 80 per cent of the biodiversity that exists on land."

Reforestation needs to happen before 'tipping point'

The researchers also modelled the effect that climate change will have on how much of the earth's surface will be able to support trees in future.
Their findings suggest that reforestation needs to happen soon if it is to be effective.
Under current forecasts, they project that global tree canopy cover will shrink by up to 223 million hectares by 2050.
The impacts will be most significant at the tropics, according to Dr Bastin.
"The tropics will be under a lot more climatic stress. There will be more severe droughts," he said.
"Forests are a little bit resilient. But at some point we are afraid that it might shift, hit a tipping point and we are going to lose a lot."
An argument often espoused by climate-change sceptics is that more carbon in the atmosphere will equal more plant growth.
But David Ellsworth, an expert in the response of forests to climate change from the University of Western Sydney, said that wasn't the case.
Instead, tree growth is limited by a range of factors, including water availability and how nutrient-rich the soil is.
"What we know is that phosphorous is very limiting [in places like Australia]," Professor Ellsworth said.
He has conducted experiments where plants are exposed to the levels of CO2 predicted in the future, and observed no significant changes in growth rate.
While today's research points to exciting possibilities, he warned that the amount of CO2 that could be absorbed should be treated with some caution.
He said that by not factoring in soil nutrients or the full range of carbon densities of different vegetation types, there was room for error.

Most potential reforestation land in Australia and five other countries

More than half of the land available for what the researchers call "tree restoration potential" was identified in just six countries.
Australia ranked fourth on the list, behind Russia, the United States and Canada, and was followed by Brazil and China.
Twenty million trees are expected to be planted in Australia by 2020 under a federal government program.
But critics say any reforestation efforts in Australia are being undermined by land clearing.
Deforestation in Australia in recent years has spiked, drawing comparisons with tree-clearing hotspots like the Amazon rainforest in Brazil.
In 2017 around 1,000 football fields were being cleared each day in Queensland, and more than a million hectares were cleared in that state between 2012 and 2016.
The Nature Conservation Council (NCC) claims around one football field of bushland was cleared in New South Wales every 10 minutes, in 2017-18.
"We are in an extinction and climate emergency. We must stop destroying wildlife habitat if we are going to stop more species disappearing," NCC CEO Kate Smolski said in a statement last week.
A million species worldwide are now under threat of extinction, according to a UN-backed report published in May this year.
In Australia, 121 species are listed as critically endangered by the IUCN, with 41 species having gone extinct.
A further 239 are endangered.
Numerous critically endangered and endangered species, including Leadbeater's possum, swift parrots and bettong could benefit from forest restoration in Australia.

'Armpits of the ocean' can store carbon 40 times faster

But forests aren't the only ecosystems that can help fight climate change.
While trees are able to draw down carbon dioxide from the atmosphere and store it for the duration of their lives, blue carbon ecosystems can do it up to 40 times faster, and can potentially lock away carbon for 1,000 years or more.
Blue carbon is the term referring to stored carbon in coastal ecosystems like mangroves, seagrass and salt marshes.
But according to Peter Macreadie from the Blue Carbon Lab at Deakin University, these systems which he calls the "armpits of the ocean" have an image problem.
"That's a big, big problem," Dr Macreadie said.
"I'm working on a program in the Maldives where they're ripping out seagrass because people don't like the look of the dark patches in the water."
Getting public support to conserve and restore habitats that might be muddy and smelly and home to mosquitoes and sand flies is a difficult ask.
But in terms of a carbon sequestration investment, blue carbon is better value for money than tree planting, according to Dr Macreadie.
"If you're a carbon offset provider you're going to think, 'I can store the same amount of carbon in a fortieth of the land area'," he said.
Like planting trees, restoring coastal ecosystems has other benefits as well like boosting fish stocks and buffering coastlines from storm surges and sea-level rise.
While we focus on decarbonising our economies, restoring natural ecosystems may buy us precious time, according to Dr Bastin.
"We cannot be too picky. We need to use every good idea we can develop to fight climate change."

Links

Climate Change: Trees 'Most Effective Solution' For Warming

BBC - Matt McGrath

Sutthipong4222

Researchers say an area the size of the US is available for planting trees around the world, and this could have a dramatic impact on climate change.

The study shows that the space available for trees is far greater than previously thought, and would reduce CO2 in the atmosphere by 25%.
The authors say that this is the most effective climate change solution available to the world right now.
But other researchers say the new study is "too good to be true".
The ability of trees to soak up carbon dioxide has long made them a valuable weapon in the fight against rising temperatures.
The Intergovernmental Panel on Climate Change (IPCC) said that if the world wanted to limit the rise to 1.5C by 2050, an extra 1bn hectares (2.4bn acres) of trees would be needed.
The problem has been that accurate estimates of just how many trees the world can support have been hard to come by.
This new report aims to show not just how many trees can be grown, but where they could be planted and how much of an impact they would have on carbon emissions.

A map showing only the potential for restoring forests and excluding desert, agricultural and urban areas. Crowther

The scientists from ETH-Zurich in Switzerland used a method called photo-interpretation to examine a global dataset of observations covering 78,000 forests.
Using the mapping software of the Google Earth engine they were able to develop a predictive model to map the global potential for tree cover.
They found that excluding existing trees, farmland and urban areas, the world could support an extra 0.9bn hectares (2.22bn acres) of tree cover.
Once these trees matured they could pull down around 200 gigatonnes of carbon dioxide, some two-thirds of extra carbon from human activities put into the atmosphere since the industrial revolution.
This is a quarter of the overall amount of CO2 in the air.
"Our study shows clearly that forest restoration is the best climate change solution available today and it provides hard evidence to justify investment," said Prof Tom Crowther, the senior author on the study.
"If we act now, this could cut carbon dioxide in the atmosphere by up to 25%, to levels last seen almost a century ago."
The researchers identify six countries where the bulk of the forest restoration could occur: Russia (151m hectares), US (103m), Canada (78m), Australia (58m), Brazil (50m) and China (40m).

Crowther Lab

But they say speed is of the essence because as the world continues to warm then the potential area for planting trees in the tropics would be reduced.
"It will take decades for new forests to mature and achieve this potential," said Prof Crowther.
"It is vitally important that we protect the forests that exist today, pursue other climate solutions, and continue to phase out fossil fuels from our economies."
The new study has been welcomed by Christiana Figueres, former UN climate chief, who was instrumental in delivering the Paris climate agreement in 2015.
"Finally an authoritative assessment of how much land we can and should cover with trees without impinging on food production or living areas," she said in a statement.
"A hugely important blueprint for governments and private sector."

What do the critics say?
However not everyone was as effusive about the new study.
Several researchers expressed reservations, taking issue with the idea that planting trees was the best climate solution available to the world right now.
"Restoration of trees may be 'among the most effective strategies', but it is very far indeed from 'the best climate change solution available,' and a long way behind reducing fossil fuel emissions to net zero," said Prof Myles Allen from the University of Oxford.

Planting trees is important say some scientists but cutting emissions is paramount. Getty Images

Others are critical of the estimates of carbon that could be stored if these trees were planted.
"The estimate that 900 million hectares restoration can store an addition 205 billion tonnes of carbon is too high and not supported by either previous studies or climate models," said Prof Simon Lewis from University College London.
"Planting trees to soak up two-thirds of the entire anthropogenic carbon burden to date sounds too good to be true. Probably because it is," said Prof Martin Lukac from the University of Reading.
"This far, humans have enhanced forest cover on a large scale only by shrinking their population size (Russia), increasing productivity of industrial agriculture (the West) or by direct order of an autocratic government (China). None of these activities look remotely feasible or sustainable at global scale."
The study has been published in the journal Science.

Links

Tree Planting 'Has Mind-Blowing Potential' To Tackle Climate Crisis

The Guardian - Damian Carrington

Research shows a trillion trees could be planted to capture huge amount of carbon dioxide

Redwood trees in Guerneville, California. Photograph: Gabrielle Lurie/The Guardian

Planting billions of trees across the world is by far the biggest and cheapest way to tackle the climate crisis, according to scientists, who have made the first calculation of how many more trees could be planted without encroaching on crop land or urban areas.
As trees grow, they absorb and store the carbon dioxide emissions that are driving global heating. New research estimates that a worldwide planting programme could remove two-thirds of all the emissions that have been pumped into the atmosphere by human activities, a figure the scientists describe as “mind-blowing”.
The analysis found there are 1.7bn hectares of treeless land on which 1.2tn native tree saplings would naturally grow. That area is about 11% of all land and equivalent to the size of the US and China combined. Tropical areas could have 100% tree cover, while others would be more sparsely covered, meaning that on average about half the area would be under tree canopy.
The scientists specifically excluded all fields used to grow crops and urban areas from their analysis. But they did include grazing land, on which the researchers say a few trees can also benefit sheep and cattle.
“This new quantitative evaluation shows [forest] restoration isn’t just one of our climate change solutions, it is overwhelmingly the top one,” said Prof Tom Crowther at the Swiss university ETH Zürich, who led the research. “What blows my mind is the scale. I thought restoration would be in the top 10, but it is overwhelmingly more powerful than all of the other climate change solutions proposed.”

Crowther emphasised that it remains vital to reverse the current trends of rising greenhouse gas emissions from fossil fuel burning and forest destruction, and bring them down to zero. He said this is needed to stop the climate crisis becoming even worse and because the forest restoration envisaged would take 50-100 years to have its full effect of removing 200bn tonnes of carbon.

Guardian graphic. Source: Bastin et al, Science, 2019

But tree planting is “a climate change solution that doesn’t require President Trump to immediately start believing in climate change, or scientists to come up with technological solutions to draw carbon dioxide out of the atmosphere”, Crowther said. “It is available now, it is the cheapest one possible and every one of us can get involved.” Individuals could make a tangible impact by growing trees themselves, donating to forest restoration organisations and avoiding irresponsible companies, he added.
Other scientists agree that carbon will need to be removed from the atmosphere to avoid catastrophic climate impacts and have warned that technological solutions will not work on the vast scale needed.
Jean-François Bastin, also at ETH Zürich, said action was urgently required: “Governments must now factor [tree restoration] into their national strategies.”
Christiana Figueres, former UN climate chief and founder of the Global Optimism group, said: “Finally we have an authoritative assessment of how much land we can and should cover with trees without impinging on food production or living areas. This is hugely important blueprint for governments and private sector.”
René Castro, assistant-director general at the UN Food and Agriculture Organisation, said: “We now have definitive evidence of the potential land area for re-growing forests, where they could exist and how much carbon they could store.”
The study, published in the journal Science, determines the potential for tree planting but does not address how a global tree planting programme would be paid for and delivered.
Crowther said: “The most effective projects are doing restoration for 30 US cents a tree. That means we could restore the 1tn trees for $300bn [£240bn], though obviously that means immense efficiency and effectiveness. But it is by far the cheapest solution that has ever been proposed.” He said financial incentives to land owners for tree planting are the only way he sees it happening, but he thinks $300bn would be within reach of a coalition of billionaire philanthropists and the public.
Effective tree-planting could take place across the world, Crowther said: “The potential is literally everywhere – the entire globe. In terms of carbon capture, you get by far your biggest bang for your buck in the tropics [where canopy cover is 100%] but every one of us can get involved.” The world’s six biggest nations, Russia, Canada, China, the US, Brazil and Australia, contain half the potential restoration sites.
Tree planting initiatives already exist, including the Bonn Challenge, backed by 48 nations, aimed at restoring 350m hectares of forest by 2030. But the study shows that many of these countries have committed to restore less than half the area that could support new forests. “This is a new opportunity for those countries to get it right,” said Crowther. “Personally, Brazil would be my dream hotspot to get it right – that would be spectacular.”
The research is based on the measurement of the tree cover by hundreds of people in 80,000 high-resolution satellite images from Google Earth. Artificial intelligence computing then combined this data with 10 key soil, topography and climate factors to create a global map of where trees could grow.
This showed that about two-thirds of all land – 8.7bn ha – could support forest, and that 5.5bn ha already has trees. Of the 3.2bn ha of treeless land, 1.5bn ha is used for growing food, leaving 1.7bn of potential forest land in areas that were previously degraded or sparsely vegetated.
“This research is excellent,” said Joseph Poore, an environmental researcher at the Queen’s College, University of Oxford. “It presents an ambitious but essential vision for climate and biodiversity.” But he said many of the reforestation areas identified are currently grazed by livestock including, for example, large parts of Ireland.
“Without freeing up the billions of hectares we use to produce meat and milk, this ambition is not realisable,” he said. Crowther said his work predicted just two to three trees per field for most pasture: “Restoring trees at [low] density is not mutually exclusive with grazing. In fact many studies suggest sheep and cattle do better if there are a few trees in the field.”
Crowther also said the potential to grow trees alongside crops such as coffee, cocoa and berries – called agro-forestry – had not been included in the calculation of tree restoration potential, and neither had hedgerows: “Our estimate of 0.9bn hectares [of canopy cover] is reasonably conservative.”
However, some scientists said the estimated amount of carbon that mass tree planting could suck from the air was too high. Prof Simon Lewis, at University College London, said the carbon already in the land before tree planting was not accounted for and that it takes hundreds of years to achieve maximum storage. He pointed to a scenario from the Intergovernmental Panel on Climate Change 1.5C report of 57bn tonnes of carbon sequestered by new forests this century.
Other scientists said avoiding monoculture plantation forests and respecting local and indigenous people were crucial to ensuring reforestation succeeds in cutting carbon and boosting wildlife.
Earlier research by Crowther’s team calculated that there are currently about 3tn trees in the world, which is about half the number that existed before the rise of human civilisation. “We still have a net loss of about 10bn trees a year,” Crowther said.

Links