It’s Actually a Huge Problem that Aerosol Pollution Is Plummeting

The latest report from the Intergovernmental Panel on Climate Change is out — and the news is both good and bad.

As Neel Dhanesha writes here at Heatmap, the report notes that significant progress has been made on reducing the expected future trajectory of carbon emissions. Prior reports predicting that a “business as usual” approach would lead to 6 degrees Celsius of warming by 2100 are now out of date. Simply proceeding along the status quo instead would lead to perhaps 3 degrees of warming.

The bad news is that 3 degrees is still far too much. So far we have warmed the planet by just 1.1 degrees, and the ensuing droughts, flooding, extreme weather, mass extinctions, and so on speak for themselves. Much more progress is needed to avert disaster.

Media coverage of the report has focused on the emissions question, naturally enough. Yet there’s another aspect to it that is also both good and bad: namely, human aerosol pollution. So far these aerosols have partially mitigated the effect of greenhouse gas emissions — but they are being reduced thanks to pollution controls. Given the fact that humanity is on a trajectory to transition away from fossil fuels, but is not getting there nearly fast enough; and that ending aerosol pollution might boost our warming by up to 73%, intentionally injecting aerosols into the atmosphere for a limited time (sometimes called “peakshaving”) might be our least bad option.

Some background: Aerosols are tiny particles of stuff like sulfur dioxide produced by diesel exhaust, coal-fired power plants, cargo ships, as well as dust storms and ocean spray. These reflect a small percentage of sunlight back into space, which reduces the amount of heat that the planet absorbs. IPCC scientists now estimate that manmade aerosols provide a cooling effect somewhere between nothing … and 0.8 degrees Celsius.

So it’s rather alarming aerosol emissions are falling fast. Coal power plants are in terminal decline in rich countries, and given the cheap and falling cost of renewable energy, they will be in poorer ones sooner or later. Electric vehicles will replace most carbon-fueled cars and trucks over the next few decades. And thanks to long-overdue international regulations, emissions from container ships — which hitherto used ultra-filthy “bunker fuel,” containing something like 3,300 times as much sulfur as modern diesel — are plummeting. All that is good in terms of air quality, because ground-level pollution causes all kinds of health problems, but it also raises the prospect of a sudden increase in warming of nearly a degree on top of what has already happened.

Now, one wouldn’t want to just go spray sulfur dioxide willy-nilly into the atmosphere. The first order of business would be to conduct careful research on just how much cooling aerosols are providing, how an intentional aerosol injection might disperse around the globe, how that might affect precipitation and weather patterns, what the cheapest, most effective, and least dangerous form of aerosol might be, and so on. The think tank SilverLining, which advocates for such research, estimates that it might cost about $2.6 billion per year.

Now, most people don’t know about this kind of technology yet — and might have understandable reservations about messing with the atmosphere. But the recent Heatmap Climate Poll of 1,000 American adults conducted by Benenson Strategy Group last month found that 51% of respondents favored conducting “a major research program into the feasibility of this technique” when it was explained to them, and 67% supported deploying it if the government found it to be “inexpensive, effective, and low-risk.”

An aerosol program would also have the advantage of being relatively cheap and easy to implement. Emissions reductions require massive changes to our energy system and economic structures which take years at least to implement. So far only a crisis event — like Vladimir Putin’s invasion of Ukraine drastically increasing the price of natural gas in Europe — can motivate nations to decarbonize at anything even close to the appropriate speed.

Moreover, the biggest climate problem by far today is China, which emits something like 63% more carbon dioxide than the U.S. and the EU put together. To be fair, China is investing heavily in renewable energy, but its economy remains heavily dependent on carbon, and it’s hard to imagine how America might bully or entice the Chinese leadership into accelerating the energy transition (at least without undermining the trade restrictions that were central to assembling the coalition behind President Biden’s big climate bill, the Inflation Reduction Act). China is simply too big and powerful to be pushed around.

It might theoretically be possible to compensate for Chinese emissions with carbon capture and sequestration, but that technology is barely out of the prototype stage, and even it weren’t, sucking up China’s emissions would require an industrial complex on the order of the size of the entire American auto industry. That is a decade off in a best-case scenario.

What we could do, however, is mask the effects of excessive emissions for a few decades, while nations build out zero-carbon industry and carbon capture technology can get up to speed. The cost would likely be in the tens of billions per year — outside of the reach of all but the richest countries, but a pittance compared to the American military budget.

Again, it’s important to note that an aerosol program is not a solution to climate change. It would be a flawed, temporary measure to buy us time. (It wouldn’t reduce ocean acidification, for instance.) The energy transition is happening, and every possible effort should be made to speed it up. But we have to be realistic about the space of political possibility, particularly when it comes to the limits of influence on the other global superpower.