When trees burn, they release particulate matter, as millions of people on the East Coast of North America were reminded in June 2023. The sky turned orange in New York City when
the tiny particles in wildfire smoke blocked shorter wavelengths of light—the yellows, greens, and blues—while letting through the longer-wavelength reds and oranges. More important than the color of the sky were the effects on human health. Those tiny particles can damage lungs and hearts, and even affect cognition.
Aerosols, the blanket term for the tiny particles in the air, are a big part of our climate story. Particulate matter in the air is at once a deadly side effect, a useful sunscreen, and a potential emergency solution.
Deadly, but Not Without Benefit
Particulate matter is truly deadly. The World Health Organization estimates that air pollution causes seven million premature deaths a year. The smoke from the Canadian wildfires made New York City’s air quality the worst in the world—but only briefly. Cities like Lahore, Pakistan, routinely have days as bad as New York’s worst. The release of these tiny aerosols, whether from burning wood, coal, or oil, is a nasty, deadly side effect of the ways we humans produce our energy and food. The European Environment Agency reports that chronic exposure to fine particulate matter caused 275,000 premature deaths in Europe in 2020, with Italy and Poland reporting the most polluted air, due to the burning of fuel for domestic heating and industry.
And yet they are also a useful sunscreen. Coughing East Coasters had plenty of problems, but extreme heat and sun were not among them. Dense wildfire smoke can block incoming sunlight, causing regional temperatures to drop a few degrees; the smoke severely reduced the effectiveness of solar panels in the New York area. Some of it drifted as far as Norway.
Missing Particles
In the spring of 2023, climate scientists sounded the alarm about extreme, record-breaking temperatures in the north Atlantic Ocean. Major causes include the warming of the planet as a whole due to climate change and the El Niño weather pattern, which tends to increase global temperatures. The World Meteorological Organization expects El Niño to push global average temperatures more than 1.5 degree Celsius over their pre-industrial average in the next five years.
But in explaining why Atlantic Ocean temperatures are setting records, scientists are also pointing to the absence of tiny particles in the air. The weather expert Michael Lowry notes that mineral dust from the Sahara desert usually drifts over the Atlantic Ocean at this time of year, significantly lowering temperatures. This year, however, the dust has failed to materialize. And the water is so hot that thousands of suffocated fish are washing up on Texas beaches—warmer water holds less oxygen. Scientists fear that extreme temperatures in the waters off of Western Europe could trigger a “mass mortality” of fish and oysters.
Others, like the Dutch researcher Leon Simons, are highlighting how a switch to cleaner shipping fuels is allowing more sunlight to get through to the ocean. The turn of the calendar to 2020 brought with it a new International Maritime Organization regulation mandating sharp reductions of the sulfur content in ships’ fuel oil, which means fewer tiny particles in the air above the Atlantic Ocean. Simons, alongside co-authors such as the pioneering climate scientist James Hansen, has published papers warning of the side effects of reducing emissions of the tiny particles that serve as our toxic sunscreen. Indeed, IPCC-backed research has found that anthropogenic aerosols are masking about 0.5 degree Celsius of warming, no minor effect in a field concerned with every tenth of a degree. The fact that limiting the burning of certain fossil fuels can increase local temperatures in the short-term is one of the ironies of our climate crisis.
Solar Geoengineering
When people talk about “solar geoengineering” or “solar radiation management” (SRM), they are talking about taking advantage of the potential cooling effect of particulate matter. By intentionally releasing tiny particles into the stratosphere, humans could reflect more sunlight back into space and keep temperatures down. Of course, this desperate response to the climate crisis couldn’t be a substitute for cutting emissions, and it would do nothing to address other climate-related problems, such as ocean acidification caused by the oceans taking up CO2 from the atmosphere. But the fact that scientists and governments are researching it is a measure of the direness of our times. An expert panel convened by the UN Environment Program “considers that a near and mid-term large-scale SRM deployment is not currently warranted and would be unwise.” However, they add, “this view may change if climate action remains insufficient.”
If humans did intentionally use tiny particles to block the sun, they would be mimicking the effects of major volcanic eruptions throughout history, like the 1991 eruption of Mount Pinatubo in the Philippines, which caused average global temperatures to fall by about 0.5 degree Celsius over the ensuing year.
Back in 1815, the eruption of Mount Tambora in Indonesia led to “the year without a summer,” when crops failed across Europe and North America, and New York got heavy snow in June. Those dark days left their mark on literature too: Mary Shelley spent the summer of 1816 in Geneva, where she wrote her dark novel Frankenstein. The introduction to the book recalls the “wet, ungenial summer” that inspired it.
The same cooling mechanism is at play in the dreadful idea of a nuclear winter, where gargantuan explosions and fireballs from nuclear weapons would create so much smoke, soot, and dust that sunlight would be unable to reach the Earth’s surface—although humans would have much more pressing problems than cool temperatures in this scenario.
Smoke is no longer blanketing the East Coast of North America. But over the next few decades, people in North America, Europe, and beyond will learn more about the interplay between smoke, sunlight, and heat than they would have liked.
Noah J. Gordon is INTERNATIONALE POLITIK QUARTERLY’s climate columnist and acting co-director of the Sustainability, Climate, and Geopolitics Program at the Carnegie Endowment for International Peace in Washington, DC.
