Recent reductions in aerosol pollutants in the atmosphere have increased Earth's energy imbalance, accelerating global warming
By: Kevin Miller
News article: “Weatherwatch: how reducing air pollution adds to climate crisis”
Research paper: “Recent reductions in aerosol emissions have increased Earth’s energy imbalance”
Background
Air pollution due to the emission of aerosols from industrial sources, vehicles, biomass burning, etc. is a known cause of death in humans from inhalation, and has a score of negative environmental impacts associated with it (1). Health problems in humans from breathing in particulate matter (PM) include but are not limited to respiratory and cardiovascular diseases (2). Environmentally, pollutants in the air affect ecosystems across the planet as well (2). These health-related and environmental impacts of aerosols in our atmosphere are important, but notably different from the results of large concentrations of greenhouse gases in the atmosphere, also caused by human activities (3). Greenhouse gases in the atmosphere are involved with creating the EEI, or the Earth’s Energy Imbalance. This imbalance results from more solar energy entering the Earth’s boundaries (known as top-of-atmosphere, or TOA) than other energy exiting the TOA, causing the Earth’s temperature to gradually rise (global warming) (3). The total solar energy coming in through the TOA can be referred to as the net downward shortwave radiative flux (SW) and the total heat energy emitted by the Earth can be referred to as the longwave radiative flux (LW). LW can be downward (going towards the Earth’s surface) or outgoing into space (3).
The EEI is related to effective radiative forcing (ERF) in that the ERF determines how influential different factors like greenhouse gases are in advancing global warming and increasing the EEI (3). CERES, or clouds and the Earth’s radiant energy system, uses satellites to directly measure the SW and LW radiative fluxes impacting the EEI by observing clouds in the atmosphere (3). Until recently, research had not been completed concerning aerosol pollutants and their impacts on global warming and the EEI in contrast to greenhouse gases. The research paper and related news article here discuss this new comparison.
News Article
The news article from The Guardian, “Weatherwatch: how reducing air pollution adds to climate crisis” by Paul Brown, is extremely brief, and mainly discusses the research paper’s most important conclusion. While informational, the article does not get into any real details of the research. It talks about how aerosol pollutants in the atmosphere, though harmful for humans to breathe in, actually increase cloud formation in the sky and change the weather to reflect solar energy back into space. This cools the Earth, inducing the opposite effect of greenhouse gases, which trap solar energy inside the TOA. One of the main conclusions of the research paper is that increased global efforts to remove aerosol pollutants from the atmosphere and prevent further aerosol emissions have actually accelerated global warming because more solar energy gets trapped in the atmosphere (by greenhouse gases which have not been removed) rather than being reflected back into space (by aerosol-formed clouds). The article captivates the audience well by stating this conclusion and clearly addressing the problem that arises from it (accelerated global warming). However, it glosses over the fact that atmospheric aerosol pollution is detrimental to human health and should still be avoided, making this research seem more hopeful than it actually is. I give this news article a 4 out of 10, because it gave enough information about the research paper and the importance of the topic for the general public. I feel that this made me more interested in looking into the research paper. However, the article was very short and undetailed, with nothing in particular standing out to me to raise my rating. All the article served to do was (hopefully) bring people to read the research paper.
Research Paper
The attached research paper, “Recent reductions in aerosol emissions have increased Earth’s energy imbalance” by Hodnebrog et al, is extremely dense with data and statistical analysis of trends in EEI levels through the last ~20 years, though mainly focusing on EEI trends from the years 2005 to 2019. The paper uses measurements in the SW and LW fluxes from satellites around the globe (CERES) to calculate the EEI for 2005-2019, and then compares the rising EEI values to trends in the concentrations of different atmospheric aerosols globally. The goal is to determine whether the EEI is rising in agreement with the amount of aerosol emissions mitigated by societal changes around the world. The paper also compares EEI levels to a calculated average of five different global climate models (GCMs), and concludes that the EEI rise is related to there being lower atmospheric aerosol levels globally, as is clear in figure 1.
Figure 1 - Trends in net downward radiative flux (SW and LW) from CERES compared with five global climate models. Each model uses different scientific strategies to compare aerosol cloud formation in different parts of the world (including above the oceans) to radiation into the atmosphere. The top graph compares the climate models’ representation of radiation (in W m-2 decade-1) with all forces evolving, meaning everything that could impact the radiation is represented by the models. The middle graph keeps the effects on the radiation from aerosols constant. The bottom graph keeps the effects from all forces constant.
There is a lot of information to digest in figure 1, but there are a few key takeaways that the paper focuses on. First, even when aerosol cloud levels were kept constant (no decrease in aerosol levels), there was still an increase in downward radiation levels through the years in every single one of the GCM models. CERES downward radiation levels are the same in each graph because the satellites measure the same levels of downward radiation through the TOA every time, while the other GCMs use other strategies (some similar, some different) to determine radiation levels. For example, certain GCMs might not be able to determine the effects of aerosol clouding on downward radiation as well as others, resulting in some inconsistencies between models.
What the researchers gleaned from the data is that even if aerosol levels stayed relatively high in the atmosphere and humans around the world continued to pollute the air with aerosols, global warming would still advance steadily because the levels of different greenhouse gases in the atmosphere continue to rise. In fact, the researchers confirmed that even if greenhouse gas emissions stopped and we were left with only what is already in the atmosphere, global warming would still advance for a time because the greenhouse gases take years to go away.
When all forces (greenhouse gases, lowering levels of aerosols, etc.) were taken into account in the top graph, the researchers concluded that lowered levels of aerosol clouds due to human anti-pollution action resulted in confidently higher measured levels of downward radiation in all of the models. In some models, measurements were noticeably higher than the CERES measurements during certain years. This directly leads to the researchers’ later conclusion that these lowered aerosol levels accelerate global warming because there are decreasing aerosol cloud levels to reflect downward radiation back into space.
Figure 2 - Separation of contributions to EEI from LW and SW downward radiation. These graphs depict the influence on the effective radiative forcing (ERF) from aerosols alone compared to the influence on the ERF from other factors like greenhouse gases. These effects are summed up in each graph (LW, SW, and net influence on EEI) in order to find out exactly what aerosols are influencing when it comes to downward radiation. This data, like in figure 1, is taken from the years 2001-2019 and uses the same GCMs.
Figure 2 confirms in the net EEI trend that reduction of aerosols in the atmosphere leads to a positive addition to net EEI on top of greenhouse gases and other pro-climate change factors. However, the separate SW and LW graphs tell an interesting story. Summed together, SW and LW downward radiation lead to an ERF positive enough to result in a high and positive EEI level, but individually, it is really just the SW downward radiation contributing to the higher EEI. Based on the LW graph, LW downward radiation due to reduction of atmospheric aerosols actually helps to decrease the ERF contribution to the EEI when looking at the mean energy levels for each GCM. It is mainly the SW downward radiation that leads to the overall accelerated effects of global warming because it outweighs the effects of the LW radiation when aerosol levels in the atmosphere drop. This leads to increased aerosol ERF levels added to the ERF from other sources, resulting in a higher EEI. Though there are additional figures and models that the research paper analyzes, figures 1 and 2 here highlight the main takeaways from the research and their explanations.
Most importantly, the researchers ultimately conclude that human reduction of aerosol emissions results in an accelerated rate of global warming, added to what is already known to be caused by greenhouse gases and other anthropogenic factors.
This research paper was very hard to follow, partially because of a host of new terminology being introduced, but mainly because it statistically analyzed all of the data found to an excruciating extent. There is no inherent problem with this, but it seemed to take away from the researchers’ ability to explain the meaning of the results. Because of this, I had to spend a lot of time interpreting the data myself and reading back to the paper to make sure I was getting all of the information. While I think it could have been made easier to digest, I really enjoyed analyzing this paper and I think the researchers involved did a fantastic and accurate job of gathering and interpreting their data to reach their conclusions.
References
Pozzer A, Anenberg SC, Dey S, Haines A, Lelieveld J, Chowdhury S. Mortality Attributable to Ambient Air Pollution: A Review of Global Estimates. Geohealth. 2023 Jan 1;7(1):e2022GH000711. doi: 10.1029/2022GH000711. PMID: 36636746; PMCID: PMC9828848.
Manisalidis I, Stavropoulou E, Stavropoulos A, Bezirtzoglou E. Environmental and Health Impacts of Air Pollution: A Review. Front Public Health. 2020 Feb 20;8:14. doi: 10.3389/fpubh.2020.00014. PMID: 32154200; PMCID: PMC7044178.
Hodnebrog, Ø., Myhre, G., Jouan, C. et al. Recent reductions in aerosol emissions have increased Earth’s energy imbalance. Commun Earth Environ 5, 166 (2024). https://doi.org/10.1038/s43247-024-01324-8
Hi Kevin, great analysis on breaking down such a dense paper! You explained the core concepts and background so clearly. I agree with your grading of the Guardian news: it was oversimplified. The article, especially the title, focused almost entirely on the idea that reducing aerosols speeds up global warming but left out the crucial point that aerosols are extremely harmful to human health and ecosystems. This omission creates a misleading narrative that could be misinterpreted as pollution having a climate "benefit." The key takeaway shouldn’t be a paradox; it’s that greenhouse gases are the dominant driver of warming, and cutting them is the most urgent priority. Cleaner air and climate protection need to happen together, not separately.
ReplyDeleteWhile the research paper was far more comprehensive, it raised my questions about uncertainties regarding inter-model variability. As you noted in your review of Figure 1, the models all exhibited a positive trend in the EEI; however, the spread in their magnitudes was considerable, and in some cases, the models were higher than the CERES satellite data. Which model is actually more realistic, and how do we know? If policymakers base decisions on model averages, could that mask important uncertainties? Furthermore, future aerosol reductions will likely be geographically and temporally heterogeneous. How well can these models capture such complex regional scenarios? These questions made me realize the complexity of turning scientific data into action more deeply.
Thank you for your thoughts, Siyu! I completely agree that clean air and climate protection both need to be addressed as important issues that deserve our attention. While there are continued (and controversial) efforts to research the injection of aerosols into the atmosphere to control weather patterns and the EEI, I believe the best way to solve these issues is to simply cut down on emissions.
DeleteAs for the variation in the magnitudes of the models, there are a few factors that could have influenced it. As you can see in figure 4 of the paper, global distributions of aerosol emissions and regional radiative fluxes are incredibly uneven. This might explain why the models exhibit the same general trends, but with different magnitudes. Though the paper mentions the CERES model much more often than any of the other models, it is not clear if any of the models are more reliable than the others. After all, they take an average of all of the global climate model data in order to make their final conclusions, so I would say policymakers basing decisions off of the model averages would likely lead to the most favorable result. Future aerosol reductions definitely will be heterogeneous if they happen, but since the models provide global averages and extensively use and verify data with satellites, I would not be worried about model accuracy in future regional scenarios. Furthermore, though I did not mention this in my analysis, 90% of the energy absorbed by Earth which contributes to the EEI is absorbed by the oceans. Knowing this, the heterogeneity of aerosol reductions in the atmosphere is further complicated. I appreciate your insight on the relationship between research like this and policymaking.
Great job Kevin, this is a very interesting topic that poses a difficult question. The background information you gave, especially the detailed explanation of all the acronyms involved in the research paper was very informative. I agree with your rating of the news article. The article is very short and skims over most of the important data from the research article, and severely downplays the immediate, negative health effects of aerosol pollutants. Without discussing these adverse affects, the news article presents the idea that aerosol pollution has a net positive effect on the environment which isn't the case.
ReplyDeleteThe research article was very informative and you did a great job summarizing it in your blog post. The large dip in the EEI right after 2010, which was recorded in all models was very intriguing to me. Do you know what caused this?
Thanks, Seth! I agree that the news article was very misleading in terms of a call to action. It definitely skims over the data and almost makes it seem like we should be polluting the air more. I spent a lot of time trying to find out what might have caused that large dip around 2010-2011 you mentioned, and as far as I can tell, it doesn't seem to be discussed in the paper. However, I read part of a separate 2011 publication from NASA (https://www.giss.nasa.gov/pubs/abs/ha06510a.html) that discusses how the aerosols released in the Mount Pinatubo eruption in 1991 caused a delayed rebound effect, resulting in lower-than-normal heat energy uptake from the ocean around 2011. It is possible that this anomaly caused such a drastic drop in the model data.
DeleteThe news article was definitely very short and lacks a lot of details. One thing I noticed is how interchangeably they use the words pollution, particulate matter, and aerosols, making it hard to follow what they are saying leads to worse climate change when removed (although I followed it due to reading your review on it first, when I read it myself I tried following it grammatically and had trouble). I'm sure it's even worse for the average reader without a scientific background. The research paper was very dense, but you can tell how much effort was put into it (which stuck out after just reading the brief and disjointed news article). While the data and detail were a large part of it being hard to follow, like you and another commenter both had said a bit about, it was really all the acronyms that was hard for me. Even though I just read what one stood for I found myself constantly scrolling up to check again and the sheer number of acronyms and how often they were used didn't help.
ReplyDeleteThanks, Zackary! I agree that the research paper was extremely difficult to follow. I also took an uncomfortable amount of time scrolling back and forth to make sure I understood all of the acronyms and other scientific language being used. I think it would've been much easier to follow if they had just written out all of the little phrases each time, though that might've resulted in a much longer paper. It seems that the authors were very detail-oriented and worked very hard on their research, but likely that came at the expense of fewer people reading it due to lower attention spans and lack of interest.
DeleteThis is an interesting paper, and your review was very well-written and did a good job summarizing the research paper and drawing to attention some of the shortcomings of the article. I agree with your rating for the article, and I think the article should have made more of an effort to include more data from the paper. The article just saying that air pollution helps cool the planet is an oversimplification of the issue, and it would have been more productive for them to go into the dangers of aerosols, as well as describing the mechanisms for this phenomenon in a little more detail. Since both the paper and the article are from a year and a half ago, I'm curious as to whether there has been more research done on this topic. Have there been any suggestions on how to deal with this issue?
ReplyDeleteI agree that the article oversimplified the paper greatly and was very misleading at times. There has definitely been more research related to this topic, including but not limited to a study done this July at UT Auston linking lower aerosol levels in cities around the world to increased yearly numbers of heatwaves (https://www.jsg.utexas.edu/news/2025/07/decline-in-aerosols-could-lead-to-more-heatwaves-in-populated-areas/). I believe the general concensus among scientists is that humans need to both reduce aerosol emissions and greenhouse gas emissions in order to combat climate change while also lowering death rates due to air pollution. This is a difficult problem to solve with seemingly no quick answer. There has been (though very controversial) an effort by some to inject certain aerosols into the atmosphere strategically in order to combat climate change, but research on the effects of this is still being done and many (including me) are frightened by the idea of polluting the air more to solve a problem that probably needs a different solution. Thank you for your input, Teresa!
DeleteNice work Kevin! I agree the news article was very weak and not very convincing. It could be used as a short read to understand the gist of the article but it doesn't get close to explaining the chemistry behind how reducing aerosols has added to the climate crisis. The research paper, on the other hand, was incredibly in depth and almost impossible to follow. The sheer amount of information was overwhelming, I had to take a break while making my way through it. I wish they made it more manageable of a read because even though it is an important topic, the article is too intimidating for the average reader.
ReplyDeleteHi Mira, thank for the input! I wish the article was longer and went into more of the basic concepts from the paper. I think that would've made the paper a bit more manageable to follow, though I agree that the amount of information was crazy! It definitely hurt my brain trying to figure out even just the terminology they used. However, the information in the paper is very interesting to me which is why it is frustrating to me that they didn't simplify things a bit more for a more average audience, and also that the article did not help to simplify things.
DeleteHi Kevin! I think you made some really good points here. It brings up what I think is is an interesting conversation of what should news articles focus on when discussing research papers. I'd be curious to know if the author of the news article when reading the research article just purposely left out that atmospheric aerosol pollution is detrimental to human health or when reading the research article from a non scientist viewpoint that point was communicated well.
ReplyDeleteThe news article certainly brings you in with its title, as it seems counterintuitive that reducing air pollution could add to global warming. I definitely agree with the fact that the news article was quite brief, and while that's not necessarily a bad thing, I do think that it did a poor job at giving an effective conclusion about how aerosol pollutants are inherently bad for human health. I also think it would have been nice to compare and contrast the detriments of global warming to the detriments of aerosols. I know it's difficult to model/estimate, but would be interesting to see the mortalities attributed to climate change without aerosols vs mortalities attributed to aerosols to compare the trade-offs.
ReplyDeleteHi Kevin! This is a really interesting topic. I think it's really interesting to explore the nuances of air pollution and air quality, especially when some solutions may actually cause different problems. This study of aerosols reminds me of learning about the effects of ozone in different layers of the atmosphere. Although the general public isn't super familiar with aerosols, I could see this becoming a misunderstood point of contention if there were conflicting information that didn't give the full story, like you mentioned with this news article.
ReplyDeleteI agree that the news article equating aerosols as almost the opposite of air pollution leaves out how these interventions to improve air quality overall are protecting public health. Although it's difficult to really compare the dangers of aerosols in terms of public health vs. global warming, it seemed like the paper itself didn't really explore the human health element.
Do you think that short articles like this that might only present one side of the story could be potentially dangerous? I can imagine people unfamiliar with academic papers who might not read the study accepting that we should increase aerosols to prevent climate change, without actually understanding what that would mean to human health.
Hi Kevin, great job on your analysis. I am very interested in the nuance of this issue, because it makes sense why a news article would latch on to the most attention-grabbing aspect of the scientific article but it is also very detrimental to only present that one aspect of the complicated environmental situation. I am curious to know if there is any form of aerosol that we could intentionally promote for the sake of preventing further global warming which is not as detrimental to human health, however I assume such an option is unlikely to exist given the nature of aerosol inhalation. Without the context of the health complications that aerosols cause, presenting the main point of the scientific article is misleading and I wonder how intentional the omission of more detailed and unbiased content in the news article was.
ReplyDelete