- Climate
No, marine emissions study didn’t find that climate change is ‘greatly overestimated’, contrary to recent claims
Key takeaway
A scientific study was published in Science Advances, detailing new findings on ocean emissions and their potential climate implications in the Southern Ocean. As explained by one of the paper’s authors, the discovery of higher sulfur emissions has regional climate implications (e.g., potential cooling due to more aerosols); however, the findings do not not suggest that predicted global warming has been ‘overestimated’. The author also explained that the paper’s findings are unlikely to change the expected rate or magnitude of global warming that climate models have projected. Studies have shown that past climate models have been fairly accurate when compared to direct temperature observations over the same time periods. The recent findings presented in the Science Advances paper do not overturn those past studies, but instead offer new data that may help improve climate models through better modeling of clouds over the Southern Ocean (i.e., Antarctic ocean).
Reviewed content
Verdict:
Claim:
New study shows that climate change is greatly overestimated because oceans are cooling Earth far more than we thought
Verdict detail
Factually inaccurate:
This claim is a misinterpretation of the research findings; as explained by one of the authors of the paper, these findings have regional climate implications (i.e., in the Southern Ocean), but do not overturn the well-established evidence of global warming, nor the projections of future warming.
Misleading:
Studies show that climate models have been fairly accurate; the temperatures that climate models fit well with temperatures that later occurred. However, it is misleading to claim that climate scientists consider current climate models as ‘settled’ and ‘final’ – they clearly state model uncertainties and work to improve them.
Full Claim
New study shows that climate change is greatly overestimated because oceans are cooling Earth far more than we thought. This shows that climate models are, and continue to be, inaccurate – they are not ‘settled science’ like we are told.
Review
In late November 2024, a paper was published in Science Advances – a reputable scientific journal of peer-reviewed papers – detailing new findings about emissions from marine organisms and their impact on Earth’s climate[1]. Articles began springing up in the weeks that followed, claiming these research findings suggest that ‘climate change has been greatly overestimated’ or that ‘climate models are, and continue to be, inaccurate – they are not settled science’ (linked here and here).
However, these claims are not conclusions drawn by climate science experts, nor by the authors of the Science Advances paper, but rather interpretations from people online.
As we will explain below, the study’s findings are far more nuanced than those claims imply. In this review, we will compare these recent claims to the paper’s findings and scientific evidence from reputable sources. Stay tuned to read the comments we received from one of the paper’s authors when we asked about these claims.
Findings from ocean emissions study have regional climate implications, but do not suggest climate change has been ‘greatly overestimated’
A paper titled ‘Marine emissions of methanethiol increase aerosol cooling in the Southern Ocean’ was published in Science Advances on 27 November 2024. The study found that ocean emissions of biogenic sulfur (i.e., produced by marine organisms) are higher than previously known, which has potential implications on Earth’s climate.
After a careful review of the paper’s findings, Science Feedback found no evidence to support the recent claims that reference this study. However, to confirm this, we reached out to the paper’s authors and another climate scientist with relevant expertise to get independent feedback.
One of the paper’s authors, Dr. Rafel Simó, Research Professor at Institut de Ciències del Mar, CSIC, provided helpful responses confirming that the claims we are reviewing are not supported by their research findings. Dr. Simó explained, for example, that:
Research Professor, Institut de Ciències del Mar, CSIC
“Our paper shows indeed that Earth System Models, and Climate Models in general, so far did not take into account a missing source of sulfur from the ocean, which introduces some extra cooling in [the] current climate […] This does not mean that current warming has been overestimated, because it is based on observations. Warming is real and accountable. Does it mean that climate projections (predicted warming) is overestimated? This would be too brave a statement, if not false”
Dr. Simó explained that this is an overstatement – or potentially false – because there are still uncertainties about these marine emissions, which is why it is a subject of ongoing research. For example, Dr. Simó pointed out:
Research Professor, Institut de Ciències del Mar, CSIC
“We do not know yet if the emissions of gaseous sulfur from the oceans, both the already known and the newly discovered, will increase or decline into the coming decades, in response to global warming. Therefore, we do not know if they will slow down or accelerate climate warming.”
Dr. Simó also explained that there are other trace elements emitted from the ocean that require further research to fully understand how they affect radiative forcing (i.e., incoming vs. outgoing radiation that drive Earth’s temperature changes).
Receiving comments directly from one of the paper’s authors offered helpful context, which showed that the claims we are reviewing are inaccurate. However, to gain outside perspective, Science Feedback also reached out to a climate scientist who was not part of this project, but has relevant expertise. We asked Dr. Mark Zelinka, Atmospheric Scientists at Lawrence Livermore National Lab, whether or not these claims are supported by the Science Advances paper and received the following response:
Research Scientist, Lawrence Livermore National Laboratory
“I see nothing in this paper that could lead one to conclude that ‘climate change has been greatly overestimated’, either in models or in observations […] It simply shows that accounting for marine biogenic sulfur emissions in a model helps alleviate a well-known model bias in which there is too little reflection of sunlight back to space at high southern latitudes. The one open possibility is that, if marine emissions depend sensitively on surface temperature, it could lead to a dampening feedback wherein higher temperatures lead to more emissions, which reduce solar heating. The existence of such a feedback has not been established, let alone its sign or strength. As this paper states in the conclusions, this would be worthwhile to investigate further.”
We asked Dr. Simó more about what potential impacts their findings could have on regional and global climate models, including any changes to the current projections of future climate. As Dr. Simó explained*:
Research Professor, Institut de Ciències del Mar, CSIC
“We [argue] that our “discovered” extra sulfur emissions should be incorporated in climate models for a more accurate simulation of global climate and better climate projections. Will this incorporation change much [the] current climate projections? [O]ur estimate is that not too much on a global scale: they will not change the order of magnitude of the projected warming, nor the warming rate.”
As explained by one of the paper’s authors – and by another climate scientist with relevant expertise – these recent claims are inaccurate and mischaracterize the research findings. However, one of the recent articles making these claims, also suggests that climate scientists as a group consider climate models ‘settled science’. In the next section we will review that claim and provide more context on the accuracy of climate models.
Note:
*The full quotes from Dr. Simó and Dr. Zelinka can be found at the bottom of this review.
Climate models have generally performed well over the years, but climate scientists still don’t call it a ‘settled science’
Contrary to recent claims, it is not the consensus among climate scientists that climate models are 100% accurate or a ‘settled science’ – this is evident by the fact that they state the uncertainties associated with each model. Uncertainty is an inherent part of modeling because it is nearly impossible to know all variables at all times. However, this does not mean that models are useless or inaccurate, nor that climate models are ‘perfect’ or ‘settled’.
As we’ve shown in past reviews, climate models have held up relatively well compared to the direct observational record of global temperatures. As explained in one of our past reviews, a 2019 study found that climate models published between 1970 and 2007 “were generally quite accurate in predicting global warming in the years after publication, particularly when accounting for differences between modeled and actual changes in atmospheric CO2 and other climate drivers”[2] (Figures 1, 2, and 3).
In other words, climate scientists have found that our direct observational record (i.e., temperatures we’ve directly recorded) have tracked relatively well with what climate models had predicted years prior for that same time period. So, in regards to the past, climate change has not been ‘greatly overestimated’ as evidenced by the climate models being quite accurate in predicting the temperature changes.
However, despite the fairly accurate performance of these models, it is incorrect to suggest that climate scientists have a consensus that climate models are a ‘settled science’. This claim is a mischaracterization of the field of climate science – one that, like other scientific fields, grows and evolves as new evidence is found. New scientific evidence allows climate scientists to refine their understanding of our variables and processes affecting Earth’s climate, and thus improve climate models.
Scientists’ Feedback
Science Feedback reached out to several climate scientists and posed questions to gather insights about the findings presented in the recent Science Advances paper. We received two responses: one from Dr. Rafel Simó, who was an author of the paper, and another from Dr. Mark Zelinka, a climate scientist with relevant expertise who was not affiliated with this research.
Below are the questions we asked, followed by their responses:
- Some people have claimed that ‘climate change has been greatly overestimated’, based on the recent paper published in Science Advances (linked here). Do you think that this claim is accurate or inaccurate based on the findings in that paper?
- What impact or relevance do you think the findings in this paper have to regional and global climate simulations? For example, do you think the “amplified aerosol radiative cooling effect” outlined in the paper could significantly change the current climate projections presented in the most recent IPCC reports (e.g., IPCC AR6 Synthesis Report) if incorporated into those models? If not, how would you better characterize/summarize the findings from this study and their implications in climate science?
Rafel Simó
Research Professor, Institut de Ciències del Mar, CSIC
“1. Our paper shows indeed that Earth System Models, and Climate Models in general, so far did not take into account a missing source of sulfur from the ocean, which introduces some extra cooling in [the] current climate. Meaning an extra element or piece that should allow models reproduce better the observed energy balance. The energy balance is one of the foundations of climate, probably the most important. Current models simulate (or reproduce) quite well the observed energy balance, because they are built to do so, but they can do better. Especially in some regions like the Southern Ocean. This does not mean that current warming has been overestimated, because it is based on observations. Warming is real and accountable. Does it mean that climate projections (predicted warming) is overestimated? This would be too brave a statement, if not false, for two reasons:
(a) We do not know yet if the emissions of gaseous sulfur from the oceans, both the already known and the newly discovered, will increase or decline into the coming decades, in response to global warming. Therefore, we do not know if they will slow down or accelerate climate warming. This is the aim of current research.
(b) It is true that climate projection models hitherto did not consider this extra cooling element but, likewise, they did not consider other elements whose cooling or warming effects are yet to be figured out. That is, other trace gases also emitted by the oceans or the biosphere in general whose impact on the radiative forcing is unknown. Depending on the magnitude and sign of their impacts, they will bring further warming or cooling.
2. We [argue] that our “discovered” extra sulfur emissions should be incorporated in climate models for a more accurate simulation of global climate and better climate projections. Will this incorporation change much [the] current climate projections? [O]ur estimate is that not too much on a global scale: they will not change the order of magnitude of the projected warming, nor the warming rate. One of the reasons is that the “added” marine sulfur emission occurs on top of large sulfur emissions from anthropogenic activities, especially combustion of fossil fuels. But note anthropogenic sulfur emissions are declining worldwide as a result of emission regulations. Hence, the relative impact of natural emissions is expected to increase with time.
The impact at the regional level is more remarkable. In the Southern Ocean, we estimate that the disclosed extra sulfur emission increases sulfate aerosols by 20-50%. This is a remarkable increase, given that sulfate aerosols are an important cooling agent as they reflect solar radiation by themselves and by making clouds brighter. Current climate models struggle to simulate the clouds right in this region, and our findings may help out. In other words, our findings may help get model clouds brighter, i.e., closer to real clouds.”
Mark Zelinka
Research Scientist, Lawrence Livermore National Laboratory
“I see nothing in this paper that could lead one to conclude that ‘climate change has been greatly overestimated’, either in models or in observations (not sure which one the statement is referring to exactly). It simply shows that accounting for marine biogenic sulfur emissions in a model helps alleviate a well-known model bias in which there is too little reflection of sunlight back to space at high southern latitudes. The one open possibility is that, if marine emissions depend sensitively on surface temperature, it could lead to a dampening feedback wherein higher temperatures lead to more emissions, which reduce solar heating. The existence of such a feedback has not been established, let alone its sign or strength. As this paper states in the conclusions, this would be worthwhile to investigate further.”
Note: Scientists comments were lightly edited for clarity (i.e., information was added in brackets for context and minor punctuation changes were made).
References:
- 1 – Wohl et al. (2024) Marine emissions of methanethiol increase aerosol cooling in the Southern Ocean. Science Advances.
- 2 – Hausfather et al. (2019) Evaluating the Performance of Past Climate Model Projections. Geophysical Research Letters.
