November 14, 2023

expert reaction to study of climate change after net zero

A study published in Frontiers in Science looks at climate change after net 0. 

Dr Karsten Haustein, Climate Scientist at Leipzig University, said:

“The press release discusses the implications of the findings in a comprehensive, honest and rigorous way. They highlight the risks we are facing even in the best case scenario, i.e. a world in which we manage to swiftly transition to net zero emissions.

“They analyse state-of-the-art model intercomparison data (ZECMIP as part of the DECK framework) as well as key Earth (sub)system processes in order to estimate the range of potential temperature change either way once net zero has been achieved. They introduce the concept of ‘Zero Emission Commitment’ to narrow down the range of uncertainty linked to Earth system components that respond very slowly to (in this case human-induced) warming.

“Their work reviews and discusses the existing literature and strengthens the evidence that net zero brings us closer to stabilising global temperatures. Yet, they underscore that the uncertainty associated with very slow Earth system processes such as sea level rise, ice sheet changes or biological processes remain rather large, potentially setting us (certainly future generations) up for major upheaval with uncontrollable societal consequences.

“There are no limitations beyond what are very well known issues with regard to coarse resolution modelling, gaps in our understanding of very slow feedback processes (e.g. melting Greenland or Antarctica ice sheets), or the response of the biosphere to drastically increased levels of carbon in the atmosphere.

“The paper highlights that the risks owing to longer-term climate feedback processes are substantial, especially since they are not adequately represented in most state-of-the-art climate models. Worryingly, their assessment does show that uncertainties point more toward a higher ‘Zero Emission Commitment’, i.e. the remaining carbon budget is considerably smaller than thought in order to avoid manyfold planetary and societal disturbances. In that sense, the paper is a very timely plea to COP28 delegates to ponder what’s really at stake.

“If all of that isn’t enough, the very recent and unprecedented spike in global temperatures should be more than enough reason to be alarmed and to rally for a ramping up of our universal ambitions to reach net zero as quickly as we possibly can!”

Dr Declan Finney, Research Fellow in Cloud Physics, University of Leeds, said:

“It’s helpful to have clearly marked net zero as a waypoint, not a finish line. From that waypoint, as scientists, it will be about understanding how the Earth system will approach a steady state, opposed to how it responds as it is forced away from steady state with greenhouse gas emissions. For decision-makers, this study should be a reminder that climate change won’t stop when we reach net zero. For example, sea-level rise will continue for decades and centuries. The political measures that are brought in to adapt to climate change will need to be robust to a changing climate well after emissions are brought under control.

“Unfortunately, we do not know where the net zero waypoint is. That is a political challenge, not a scientific one. A pertinent point from the study is that the higher the cumulative emissions before we reach the net zero waypoint, the more uncertain we are about the warming that may follow. Yet, I’m personally most concerned about tipping points. These are very difficult to represent in climate models which is why there is limited mention of them in this study. There is a lot of work to be done to understand how the risks of tipping points can be considered in decision making, and how they fit into the uncertainty framework presented here.”

Prof Richard Allan, Professor of Climate Science, University of Reading, said:

“Cutting our carbon dioxide emissions effectively down to nothing is the only plausible way of halting the inexorable human caused warming of climate. But the devil is in the detail so it’s important to know how and when Earth’s air, land, ice and oceans reach their new equilibriums after this zero emissions commitment is attained. Building on the recent Intergovernmental Panel on Climate Change, this important and comprehensive new study begins the pathway for further research that will help us better adapt to an unseen future climate.”

‘The Zero Emissions Commitment and climate stabilization’ by Sofia Palazzo Corner et al. was published in Frontiers in Science at 10am UK time on Tuesday 14 November.

DOI: 10.3389/fsci.2023.1170744

Declared interests

Declan Finney: I have no conflicting interests

Karsten Haustein: No conflict of interests

For all other experts, no reply to our request for DOIs was received.