Climate scientists urge countries to adopt split gas approach

// Climate Change

In a paper published in the prestigious Nature journal, 33 leading climate scientists call for countries to take a split gas approach when setting targets for greenhouse gas emissions reduction, such as New Zealand did in our Climate Change Response Act (Zero Carbon Bill).

The paper also encourages countries to use a split gas approach when determining their Nationally Determined Contributions (NDCs) under the Paris Agreement. 

The natural extension is that countries should report on warming rather than just emissions, something B+LNZ has been asking for for some time.  

The paper is an important and valuable contribution to conversations about reporting and targets. We’ll be using it as part of our ongoing advocacy efforts, alongside like-minded organisations such as the Meat Industry Association, DairyNZ, Federated Farmers, Deer Industry New Zealand and others. This means sharing it with Government officials and providing information to media outlets to build understanding.  

What it all means

In the Climate Change Response Act, the Government has set a legislated target of net zero for carbon dioxide and nitrous oxide by 2050, and a 10 percent reduction in methane by 2030, climbing to between 24-47 percent by 2050. 

A number of commentators have continued to claim this approach lets agriculture off the hook, however the article in Nature rejects this.

All 33 co-authors (who include Professor Myles Allen of Oxford University and Professor Adrian Macey of the Victoria University of Wellington) unanimously supported taking a split gas approach when determining reduction targets.

They also referred to the recent Intergovernmental Panel on Climate Change (IPCC) conclusions that while carbon dioxide emissions must be brought to net zero, short-lived gases like methane need to be reduced and stabilised but not go to net zero.

The IPPC report noted that GWP100 overstates the warming impact of methane by a factor of 3-4, if methane is stable and understates the warming impact of an increase in methane by 4-5 times over a 20-year period. GWP100 is even more inaccurate if methane is reducing.  

If countries don’t differentiate between the different types of greenhouses gases well, countries could vastly over or underestimate the impact of their emissions reductions on the changes to our climate overall.

“Using the current GWP100 metric, agriculture in New Zealand accounts for 48 per cent of emissions, but because methane has been stable for over a decade, agriculture has not contributed 48 per cent of annual new warming for a long time, says B+LNZ chief executive Sam McIvor.

“We would like to see the Government start to report on annual warming, alongside annual emissions, in order to help build understanding of the contribution the different gases are having on the climate.  

“An alternative metric, GWP*, scales emissions over time and better accounts for the different warming behaviours of short-lived gases. We would like to see this metric, or the underlying science behind it, used in the review of the methane reduction targets in 2024. 

“Farmers are absolutely committed to playing our role to address climate change. Through He Waka Eke Noa, we are working to progress an emissions pricing approach that can better address our agricultural emissions and ensure farmers get credit for the sequestration happening on their farms.

“Countries, including New Zealand, have already started to make decisions about how much to limit their emissions in the future to limit their impact on warming. But these decisions are not always being made based on what warming impacts different greenhouse gases are likely to have. That must change.”

The Nature paper can be found here: