Forests and oceans shouldn't count toward emission reductions, study warns

The world will keep heating after net zero is achieved if countries include natural carbon sinks in their emission targets, a new study warns.

Net zero refers to an overall balance between emissions produced and emissions removed from the atmosphere. Most countries signed up to the 2015 Paris Agreement have net zero targets, including the UK which aims to achieve net zero emissions by 2050. 

Countries should not include the natural absorption of carbon dioxide from forests and oceans in their emission reduction goals as they work toward net zero, the paper published today in Nature argues.

When the science of net zero was established in the 2000s, these natural carbon sinks were never intended to count toward overall emission reductions, but identified as critical for helping stabilise warming after net zero.

However, countries are increasingly turning toward them to meet their emission targets, without taking meaningful steps to phase out oil, gas and coal, which are the root cause of global warming. This would result in warming continuing after global net zero has been achieved, the scientists say.  

Every country signed up to the Paris Agreement must announce a new 2035 emission reduction target by February next year. These short-term targets, called Nationally Determined Contributions, or NDCs, act as important stepping stones to get to net zero.  

Professor Joeri Rogelj, Director of Research at the Grantham Institute and Professor of Climate Science and Policy at the Centre for Environmental Policy at Imperial, and a co-author of the paper says it has “clear implications” for NDCs.  

“Targets should distinguish between emissions reductions, geological removals that effectively put CO2 away forever, and any climate mitigation action that draws on forests or storing carbon in nature.

“Failing to do so muddies the waters and our understanding of whether and when we could stop global warming."

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To achieve net zero, fossil fuels need to be replaced with renewable energy, like wind and solar. However, some fossil fuels are expected to be used for industries that are difficult to decarbonise, like the production of steel.

The authors of the paper call for geological net zero, which involves offsetting every tonne of these fossil fuel emissions with one tonne of underground carbon storage using carbon capture and removal technologies

Professor Myles Allen, Head of Atmospheric, Oceanic and Planetary Physics at the University of Oxford and lead author of the study, says:

“We are already counting on forests and oceans to mop up our past emissions, most of which came from burning stuff we dug out of the ground.

“We can’t expect them to compensate for future emissions as well. By mid-century, any carbon that still comes out of the ground will have to go back down, to permanent storage. That’s geological net zero.”

Dr Glen Peters, of the CICERO Centre for International Climate Research in Oslo, Norway and a co-author of the study, says:

“Countries report both emissions and removals, but using all removals in climate targets is a recipe for continued warming.

“Natural carbon sinks currently clean up around half our annual emissions for free, but this ecosystem service must be kept separate from the fossil emissions driving climate change. Relabelling things will not stop global warming.”