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Governments should not rely on risky “nature-based” climate solutions to solve global warming, such as planting trees, a report led by King’s College London (KCL) has found.
Many countries are banking on being able to remove carbon dioxide from the atmosphere in the future as a way to delay or avoid significant emission cuts.
During his tenure as US president, Donald Trump even launched the ‘One Trillion Trees Initiative’, designed to mitigate emissions from one of the highest carbon per capita nations on the planet.
But the KCL report found that little consideration has been given by the feasibility of such schemes, with various social, cultural, environmental and institutional factors often overlooked.
All the pledges made worldwide to use land-based carbon dioxide removal (CDR) techniques would require around 1 billion hectares of land, not far off the total area of the planet’s cropland, 1.5 billion hectares.
“Land use change on this scale overlooks the fact that we now inhabit a ’used’ planet: there is little land that can be used for CDR without some difficult decisions,” said lead author Oliver Perkins.
These decisions include converting huge swathes of land to forestry away from its current uses such as livestock rearing or crop production.
In addition, the world’s farmland is divided into 600 million farms, most of them smaller than 1 hectare, and many with either insecure or disputed ownership. This makes it very difficult to achieve coordinated attempts to change their usage.
Another danger the team outlines is that storing so much captured carbon in trees creates a high risk of re-release. This danger is even greater as climate change progresses, as the threat to forests from disease, droughts and wildfire increases.
“When you think of fire and climate change, you might think of images from last summer’s fires across Greece or northern Canada. Rightly so – these represent an important and growing climate adaptation challenge. However, fire also has another important interaction with climate change: by restricting our ability to mitigate it through reforestation,” Perkins added.
“A worst-case scenario for fire and carbon removal would see large areas dedicated to planting new forests, only for them to go up in smoke.”
Other types of land-based carbon removal that could be used instead include increasing the carbon stored in soils, and BECCS – bioenergy with carbon capture and storage.
BECCS makes use growing plants’ natural absorption of carbon dioxide from the atmosphere. Its proponents suggest wide-scale farming of bioenergy crops, such as willow, and burning them to produce energy – with the carbon dioxide that is also produced safely captured and stored.
