Current climate models predict that global warming will cease once the world achieves “net zero”: a phenomenon expected to occur when the amount of carbon dioxide (CO₂) that human activities emit into the atmosphere equals the amount of CO₂ that we remove from the atmosphere. 

Not so fast, assert the authors of “The Zero Emissions Commitment and climate stabilization,” a recent Frontiers in Science article that challenges those modeling estimates. Co-authored by 21 international climate experts, including IBES Fellow and DEEPS Professor Baylor Fox-Kemper, this article offers the first comprehensive analysis of the diverse factors controlling global temperatures and provides a framework for improving warming predictions. 

Significance of new research lies in uncertainty 

The article, explained Fox-Kemper, is a trailblazing review of the Zero Emissions Commitment (ZEC) — a commitment that, of course, has yet to be achieved.

“Our research evaluates what changes will occur after emissions zero out; describes the underlying physical, chemical, and biological processes and model estimates; and identifies the key sources of the uncertainty of our current understanding of these complex issues,” said Fox-Kemper, whose contributions to the article primarily focused on how the ocean’s physical processes affect the ZEC. 

While climate models have become very accurate under strong emissions scenarios, Fox-Kemper explained that there is less certainty about how ZEC will impact future scenarios. “If we intend to stay under a particular temperature threshold, such as the Paris Agreement’s 2°C, these changing ZEC trends will affect how much carbon dioxide we can emit and still meet our threshold goal,” he noted. 

Temperature changes expected to continue 

Global temperatures are regulated by myriad natural processes in the ocean, land, and atmosphere. CO₂ emissions have influenced many of these processes and triggered long-term changes that could continue for centuries after net-zero is achieved. 

“We know that global warming will slow – but not cease – after zero emissions, but we don’t know whether temperatures will continue to rise (albeit more slowly), remain stable for a long time, or begin to slowly decline,” said Fox-Kemper.  

“As we have observed in the Arctic Ocean, and recently in the Antarctic, a thin layer of floating ice helps reduce global temperatures by reflecting the sun’s energy back into space,” Martin Sieger, professor at the University of Exeter and a co-author of the article, said in a press release. “However, once this ice melts, this reflection is replaced by absorption of solar energy, which drives temperatures even higher.” 

Such phenomena will persist in the wake of net zero, driving temperatures higher even in a CO₂ -neutral world. Subsequent warming would worsen major climate risks across the world, added Siegert, particularly in the most vulnerable regions.

Accurate climate models needed to reduce future risks

“I hope this article highlights the important research gaps in our current understanding of ZEC,” said Fox-Kemper, “and I’m especially hopeful that it will motivate key climate scientists to continue to improve and refine climate models.” 

Acknowledging that such models have been critical tools in establishing how human activities affect the world’s climate, Fox-Kemper added, “Now that climate change is really underway, we need these models to be far more accurate, refined, and reliable.” 

To that end, the Frontiers in Science article urges climate experts to develop a host of scientific tools that will enable scientists to comprehensively study and understand the level of global temperature increases we can expect, even after net-zero emissions are achieved. Further research and climate modeling is essential to reduce the risks and dangers of catastrophic climate crises.

Fox-Kemper warned, “As we transition off fossil fuels and prepare for ZEC, there will be continued global warming. As such, we need these climate models to become planning tools as we adapt for these transitions.”