Carbon removal to slow climate change vital but hurdles remain

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It seems almost certain that the world will be unable to limit global warming to 1.5 deg C above pre-industrial levels, a major goal of the United Nations' Paris climate agreement.

The global economy is simply pumping too much carbon dioxide (CO₂) and other greenhouse gases into the air, heating up the planet more and more.

The UN climate panel says the world needs to reach zero emissions by 2050. But it says this will not be enough to limit warming to 1.5 deg C.

Just how much warmer the world becomes will increasingly be determined by how much CO₂ - the main driver of global warming - can be removed from the air and how quickly.

By 2050, huge amounts of CO₂ will be in the atmosphere, plus residual emissions from some industries that find it challenging to go completely emissions-free.

That means going to net negative emissions - taking out more CO₂ than is being emitted and scaling this up to try to bring global average temperatures back to 1.5 deg C or below.

"Net zero will not be enough. You need net negative emissions," Dr Oliver Geden, a carbon dioxide removal (CDR) expert, told The Straits Times Green Pulse podcast yesterday.

Already, investment is growing in CDR techniques, with scores of start-ups vying for the prize of being able to remove large quantities of CO₂ cheaply and efficiently.

Many of the techniques are new and expensive - the cost of removing a tonne of CO₂ varies from about US$200 (S$280) a tonne to more than US$1,000.

The ultimate goal is to get the cost down to less than US$100 a tonne.

Right now, the amount of CO₂ removed by these methods is tiny - to date, less than 10,000 tonnes, according to the Frontier fund, a US$925 million initiative by some of the world's largest companies to support CDR start-ups.

This compares with the 36.3 billion tonnes of CO₂ from burning fossil fuels emitted globally last year, a record, the International Energy Agency said.

The key is to ensure that the CO₂ that is removed is stored for a very long time, Dr Geden said.

It can be in soils and vegetation, such as trees, or in geological formations, in the ocean, or even wooden building products.

Dr Geden is senior fellow at the German Institute for International and Security Affairs. He is also a lead author for the UN's top climate science body, the Intergovernmental Panel on Climate Change (IPCC), and he co-wrote a chapter on CDR for the IPCC's recent report on mitigation, or cutting emissions.

The IPCC looked at more than 10 methods to remove CO₂. These included direct air-carbon capture and storage, which involves machines that capture CO₂ and store it deep underground.

Other methods involve turning plant waste, such as forestry trimmings or city garden waste, into a type of charcoal that locks in the carbon and also acts as a fertiliser for soil and crops.

Tree plantations and forest restoration are also effective - and cheaper - methods but they carry risks such as loss from wildfires or illegal logging, he said.

Research has also shown that there is not enough spare land available to plant sufficient trees to soak up the billions of tonnes of CO₂ that the IPCC said will need to be removed annually by mid-century.

Plus, large-scale tree planting can compete with food production and harm biodiversity, such as planting vast stands of a single species.

Another method is enhanced weathering, which involves speeding up the natural weathering of certain types of rocks that naturally capture CO₂. The material is spread onto fields and then washed into the ocean via rivers, locking away the carbon.

But to be truly effective, there needs to be ways to carefully track where the carbon is going.

"More research is needed on all these methods, (and) also on policy incentives," said Dr Geden.

"That (research) will really be important if you want to deploy them at very large scales. There also has to be robust methods for monitoring, reporting and verification of that CO₂ that has been drawn down.

"Somehow you need to follow that CO₂, and to have robust methods for that."