The scariest thing about climate change? Global cooling.
By Eliza Cattaneo
News Article: https://www.washingtonpost.com/climate-environment/2024/06/25/climate-aerosols-shipping-global-cooling/
Research Article: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022MS003070
Background
The presence of aerosols in Earth’s atmosphere has pronounced climate impacts, specifically through the ability of particulate matter to offset the warming effect caused by greenhouse gas emissions. (1) Aerosols achieve this through two main pathways called the aerosol direct and cloud albedo effects. (1) The aerosol direct effect describes the phenomenon of particulate matter either reflecting or absorbing incident solar radiation before it reaches Earth’s surface. The cloud albedo effect describes how aerosol particles enhance cloud droplet formation, allowing clouds to reflect solar radiation for longer periods of time and with better efficiency. (1)
Aerosols can be categorized as a forcing agent, which describes any human or natural phenomenon that impacts the ratio of incoming solar radiation to outgoing radiative energy. (2) Forcing agents can be either positive or negative, meaning they will either increase or decrease the amount of incoming solar radiation reaching Earth’s surface respectively. (3) The aforementioned cooling effect of aerosols classifies them as negative forcing agents, whereas the ability of greenhouse gases to absorb outgoing radiative energy classifies them as positive forcing agents. These two forcing agents are perpetually in a changing equilibrium with each other as various environmental and human factors change their respective abundances. (2) When any one forcing agent overpowers another, the result is a net change in the surface temperature of Earth. (3)
News Article
The Washington Post article, “The scariest thing about climate change? Global cooling.”, describes how the reduction of polluting aerosols in the atmosphere is contributing to increased warming effects. The article starts by explaining how the creation of aerosols from air pollution produces a cooling effect by reflecting incident solar radiation and contributing to cloud formation. This effect has prevented the Earth’s surface from feeling the full impact of warming caused by greenhouse gas emissions: The article states that atmospheric aerosols have blocked up to 80% of warming since the 1980s. However, these aerosols consist of air pollutants that cause millions of deaths not to mention numerous public health crises. The global community has collectively been trying to reduce air pollution, with the largest efforts targeting sulfur aerosols that are emitted during global shipping. This reduction in air pollution, while necessary due to the extreme health impacts of harmful aerosols, is projected to reduce the shielding of solar radiation and lead to increases in global temperature. The article introduces competing scientific opinions on the extent to which warming will increase, but concludes that there will be an overall warming effect in response to reducing air pollution.
Research Article
The peer-reviewed article “The Turning Point of the Aerosol Era” by Bauer et. al. conducts a thorough analysis of the historical and projected trajectory of atmospheric aerosol composition and its impact on global warming using a combination of computation models and observational data. The study articulates the various sources of spikes in atmospheric aerosol, namely industrialization, modernization, and changing agricultural practices. Sulfate is identified as the most potent contributor to aerosol forcing, allowing trends in atmospheric sulfate concentrations to dictate trends in aerosol forcing. This study also emphasizes the significant impact of aerosol forcing compared to other negative forcing agents, making its relationship with greenhouse gases the key deciding factor in the extent of global warming. This study employs two main algorithms called MATRIX and OMA to assess changes in aerosol forcing over the 20th and 21st century. These algorithms are part of a computation model called the NASA Goddard Institute for Space Studies (GISS) ocean-atmosphere ModelE version 2.1 (GISS-E2.1-G), which draws data from a larger model called the Coupled Model Intercomparison Project Phase 6 (CMIP6). The CMIP6 model assembles forcing and emission estimates from 1750-2014 and makes future predictions based on that data. The observational data for this study was collected mainly from satellite and ground-based measurements. The study uses GISS-E2.1-G to measure the impact of the aerosol direct effect (RFari) and the cloud albedo effect (RFaci) across the entire globe over the 20th and 21st centuries, and project the extent of aerosol impact on global warming in the future. The main goal of this study was to identify when the peak activity of aerosol negative forcing occurred and generate predictions for its trajectory through the end of the 21st century. While the two algorithms provided multiple results for the year in which peak aerosol forcing occurred, an overall trend of maximum forcing occurring during the 1980s was identified. Aerosol forcing was calculated to counterbalance 80% of warming from greenhouse gases during this time period and currently counterbalances only 20%– making aerosol forcing impact now similar to time periods before industrialization. This percentage is projected to further decrease to as little as 0% by the end of the 21st century.
An important aspect of this study is the lack of globally universal aerosol forcing trends. The study emphasizes that although the 1980s can be identified as an overall maximum in aerosol forcing, trends in aerosol forcing are dependent on geographic factors. In fact, the model expects aerosol forcing to still be increasing in Southeast Asia and East Africa in modern times, whereas most mid-latitude continents have been experiencing a decrease since the 1980s.
Analysis
Overall, the article did a fine job at presenting the issue of declining aerosols in the atmosphere and explaining its potential impacts. The science behind the cooling effect of aerosols is complex and the article breaks it down in a simple, accessible, and accurate manner. The article also references multiple conflicting studies aside from the Bauer et. al. paper, which captures the amount of uncertainty involved in taking atmospheric measurements and making predictions. Finally, the article accurately identifies sulfur to be the most influential compound on aerosol forcing. However, the article is also misleading in several ways. First, the article states that “since the 1980s, [aerosol] particles have offset between 40 and 80 percent of the warming caused by greenhouse gases.” (4) While this statistic is true for the duration of the 1980s, this leads the reader to think aerosol forcing has been at a constant level since that time, when the peer-reviewed article concludes that the 1980s were a peak and aerosol forcing has been steadily decreasing since. Next, the peer-reviewed study emphasizes regional differences in aerosol forcing and how peaks in aerosol impacts are not universal. The article makes it seem like the entire world experiences impacts of aerosol forcing equally, which glosses over the importance of the connection between region and the source of aerosols. Finally, the article states that atmospheric aerosols are purely the result of particulate matter released during the burning of fossil fuels. This is inaccurate, as the study clearly states that agricultural practices and sea salt are not insignificant contributors to aerosol forcing. I overall think the article and peer-reviewed study agree fairly well, and that the aforementioned disagreements are not so misleading that I would categorize them as being factual inaccuracies. I would appreciate it if the article took a more of a stance on the future of aerosol forcing instead of simply stating the many conflicting opinions and speculating that it will be difficult to predict. I do think the article is engaging and has a nice flow to it, which is a positive factor given how difficult it is to get the general public to engage with scientific material. The title reads a little like clickbait, but the statement is not false. The subheading “We’ve been accidentally cooling the planet– and it’s about to stop” is definitely misleading because aerosol forcing has already been in decline, but I don’t consider this to be seriously misleading. I give the article a 7/10, because although it does not translate the research provided in the study entirely accurately, it communicates the most important points about aerosol forcing and draws attention to the increased importance of reducing greenhouse gas emissions in the face of the necessity to reduce air pollution.
References
1 Aerosols and Climate. Geophysical Fluid Dynamic Laboratory, 2012, https://www.gfdl.noaa.gov/aerosols-and-climate/.
2 Smith, C. J. et. al. Understanding Rapid Adjustments to Diverse Forcing Agents. Advancing Earth and Space Sciences. 2018, 45, (21), 12023-12031. 3 Climate Change Indicators: Climate Forcing, United States Environmental Protection Agency. 2025, https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing. 4 Bauer, S. E.; Tsigaridis, K.; Faluvegi, G.; Nazarenko, L.; Miller, R. L.; Kelley, M.; Schmidt, G. The Turning Point in the Aerosol Era. Journal of Advances in Modeling Earth Systems. 2022, 14, (12)
Hi Eliza! This was a really interesting article. I appreciate that the Washington Post author emphasized that reducing aerosol concentrations is crucial for improving public health, and that they made it clear the solution needs to be decreasing greenhouse gases in tandem with air pollution (rather than no longer reducing air pollution). I agree with your assessment that the article does a good job of breaking down portions of the complex science in the Bauer et al. paper into something accessible to a general audience, but that it leaves out some important nuance, such as the regional differences in aerosol effects. Although the Washington Post article is already pretty long, I do think it would have been useful for the author to briefly discuss why there are so many uncertainties in terms of aerosol forcing effects, to provide context for the wide range of estimates on how much warming they have masked. For example, acknowledging that aerosol can contain a variety of different molecules and that some of these compounds (like black carbon) can have cooling effects could possibly help readers understand the challenges in this field and why it's hard to make exact predictions.
ReplyDeleteHi Claire! Thanks for your comment. I agree that the author of the Washington Post article is fighting against an issue of length-- generally more attention goes to shorter news articles. However, I completely agree that it would have enhanced the article to add what the different uncertainties are in the context of aerosol forcing, specifically what the relative contribution to overall forcing effects from different aerosol soures, not just fossil fuel pollution.
DeleteI do think it would have been beneficial for the author to include molecules like black carbon, or even list the main components and sources of common aerosols. The Bauer et. al. article does reference this (the model factors in ammonium, nitrate, water vapor, dust particles, and sea salt among other compounds), and I agree that including this information adds nuance to how reducing atmospheric aerosols is not just a question of reducing pollution.
Nice job, Eliza! I agree with you that the news article was easy to understand and relatively impactful for these issues. I believe that the article does a good job of introducing a complex topic like aerosol forcing in a way that’s understandable to a broader audience. I especially appreciated your point about how it captures the relationship between reducing aerosol pollutants for public health and the unintended consequence of potentially accelerating global warming. I thought that the observation by the peer reviewed article about regional differences in aerosol trends was an important reminder that climate impacts vary by region, and refusing to acknowledge those regional differences can negatively impact the development of effective, localized solutions. Even though climate change is a global issue the disproportionate regional effects need to be addressed. Like you, I found the article engaging and relatively easy to follow and I agree that a stronger stance on the future of aerosol forcing would have given readers a clearer understanding of the issue’s urgency, that could help to bridge the gap between presenting the science and inspiring action.
ReplyDeleteHi Sarea! You mentioned how effective, localized solutions to climate change often get overlooked, and I think this is an excellent point to articulate. The disproportionate impact that climate change has on different regions is a massive factor in how emissions are regulated (or not regulated), and should be instrumental to policies moving forward. However, global change is often incredibly slow and never as radical as it needs to be, requiring local change to be at the core of policy shifts. Without generally accessible information about how different regions are impacted by climate change, communities have a much harder time figuring out the smaller (but often extremely effective) ways to address climate change. If this article included information about the varying production/lifetimes of aerosols in different regions, it could become one of those very sources! After all, it is like you said: The best articles find the balance between presenting science and inspiring action.
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ReplyDeleteGreat analysis, Eliza! I thought you provided very thorough background information. Your explanation made the complex science behind aerosols and their climate impacts much easier to understand. I was not aware of the reduction of pollutants causing an increase in Earth’s surface temperature. Did the authors of the journal mention any strategies to reduce harmful pollutants while also minimizing the warming effect? I’m curious what this balance might look like in terms of future legislation. How do we combat both at the same time? You mention that data was collected with satellite and ground-based measurements, were there any significant differences in the data? I agree with your rating of the news article, it seems as though they missed key details important to the findings. These details, such as the regional differences, the source of these aerosols, and the decline in pollutants since the 80s, affect how the reader interprets the findings. Overall, I think your analysis was very insightful!
Hi Talia! Thanks for your questions :) The authors of the journal mostly focus on predictions of future aerosol forcing and the timing of its maximum effects, not as much mitigation efforts. However, they do address how much of the aerosol forcing comes from aerosols composed of pollutants like sulfate, ammonia, nitrate, and black carbon; implying there are not many approaches that would both reduce pollution and minimize warming.
DeleteSimultaneously combatting both of these effects is a large undertaking, and the release of non-harmful UV blocking compounds into the atmosphere is a highly relevant area of research. In terms of legislation, I know currently one of the significant roadblocks is testing the effectiveness of new compounds without knowledge of how it will impact public health when the compounds eventually descend. I am far from an expert on this topic though, there is likely an entire branch of science policy dedicated to this subject.
The major differences in data collected with different sources was identifying the year that maximum aerosol forcing was occurring. However, all of these time frames had accompanying confidence intervals that allowed them to overlap enough so data was fairly consistent.
Great post, Eliza! I agree that the news article did a good job of communicating the science to a broader audience, but misrepresented some of the findings of the scientific article. I liked their emphasis on the fact that the decrease in aerosols is a net positive for public health, and that this effort to reduce pollution should be extended to other types of emissions, such as greenhouse gases. Because forcing by atmospheric aerosols has peaked, it is even more important that we reduce planet-warming emissions. I did have one question: was there any mention by the authors of either article about what specifically caused a decrease in atmospheric aerosols? Was it a result of air pollution reduction strategies, the changing climate, or something else?
ReplyDeleteHi Sophie! Yes, both of the articles indicate causes for the decrease in aerosol forcing. The Washington Post article states that human-driven efforts to reduce sulfate pollution is the primary cause of reduced aerosol pollution. The article specifically mentions legislation that targets the emission of sulfate pollutants in shipping traffic. The peer-reviewed article also mentions human-driven anti-pollution efforts (like shipping regualtions) as a cause of reduced aerosol forcing, but it also addresses how changes in agricultural and industrial practices has impacted aerosol formation. For example, changing irrigation systems for agricultural practices altered the amount of dust produced during farming.
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ReplyDeleteI think the article did quite a good job overall. I was a little skeptical at first given the clickbait title, but they accurately described the situation, talked about the pros and cons of reducing aerosol pollution, and gave some good background information. There definitely were some inaccuracies as you pointed out, but none which were too egregious or seemed intentionally misleading to favor a certain viewpoint. One thing I noticed is that they could have benefited by including an informational graphic from the research article, of which there were many, instead of the random picture of 2 ships which needs the subtext explaining they are moving a low carbon source to be relevant at all.
ReplyDeleteI agree that the article could have included more data and that more scientific graphics would have been an effective way to do that. I do think the informational graphics in the peer-reviewed article are pretty dense and require context for the methods used, but I would definitely also appreciate some more scientifically-geared visualizations in the article. I also agree with you that the clickbait title made me more skeptical that this article would contain factual inaccuracies. I think the article would actually be improved with a more straightforward title-- I'm sure you are not the only person to read it and assume there is misinformation involved.
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