Climate could warm another 0.5°C if we fail to capture far more CO2

The world would have to remove hundreds of billions of tonnes of carbon dioxide from the atmosphere to limit the rise in global temperatures to 1.5°C this century. Even the less ambitious 2°C climate target is now virtually out of reach without large volumes of carbon capture and carbon dioxide removal (CDR), alongside aggressive cuts to emissions.

The role that such carbon-management technologies have to play in meeting climate targets has long proved controversial. The Intergovernmental Panel on Climate Change has said some amount of carbon management will be “unavoidable” to reach the net-zero emissions required to stabilise global temperatures. But others have pointed out that technologies that could achieve this haven’t yet been proven to work at the scale needed, and relying on them risks providing an excuse to continue emitting as usual.

There is a “debate across scientists that CDR is both essential and impossible”, says Candelaria Bergero at the University of California, Irvine. “There are some people saying that without CDR, we are doomed,” she says, adding that others say ”we are banking on some almost fictional technology that we think we will have, and we’re putting future generations at risk”.

To get a better handle on what is at stake, Bergero and her colleagues used a simple climate model to estimate the consequences of failing to manage CO2 across hundreds of different emissions scenarios consistent with the Paris Agreement target to keep the rise in global temperatures well below 2°Cs. These scenarios included carbon dioxide removal technologies, such as direct air capture and nature-based approaches like tree planting. They also included varying amounts of carbon capture and storage applied to emissions from power plants and other industrial sources.

They found that failing to capture or remove any CO2 added about 0.5°C to global average temperatures at the end of the century, while failing to deliver half of the carbon management assumed in the scenarios added about 0.28°C of warming. This would make it nearly impossible to limit the rise in temperature to 1.5°C, even in a scenario where temperatures breach 1.5°C but then are brought back down.

The 2°C warming target might still be just about possible without any carbon management. However, the researchers found it would require extremely steep emissions cuts equivalent to 16 per cent per year from 2015 through 2050. Such a rapid decline seems unlikely given that global emissions have increased over the past decade, says Bergero.

Efforts to expand carbon management aren’t moving anywhere near fast enough either. Steve Smith at the University of Oxford says the world now captures and stores just 40 million tonnes of CO2 from emissions sources and removes about 1 million tonnes directly from the air each year.

“As with other emissions reductions, countries are often talking a good long-term game, but not putting in place the near-term measures to actually deliver the multibillion-tonne scale of action involved in these pathways,” he says.