Climate may warm 25% faster than thought as cleaner air removes natural cooling

This past July, as Britain sweltered through record heat, a politician on social media claimed that cleaner air—not carbon dioxide—was driving the warming. He was wrong about the main cause, but the science he was mangling points to something genuinely unsettling: the planet may be far more responsive to greenhouse gases than climate models have assumed.

The confusion starts with a basic fact about industrial pollution. Burning coal and oil releases two very different things into the air. Carbon dioxide traps heat in the atmosphere—that much is well known. But sulphur dioxide, less discussed, does something else entirely. It forms tiny particles that float high in the sky and bounce sunlight back toward space, creating a cooling effect that has partially offset the warming from carbon dioxide for more than a century. It's like dust on a greenhouse window, dimming the light before it can heat the interior.

For decades, this cooling effect went largely unnoticed because it was doing its work quietly. But starting in the 1990s, countries began passing clean-air laws. The United States cracked down on pollution from power plants. Europe and China followed. Ships were required to burn cleaner fuel. The goal was simple: protect human lungs and forests from acid rain. It worked. Sulphur emissions plummeted across the developed world. The problem is that sulphate aerosols, unlike carbon dioxide, vanish from the atmosphere within weeks. Remove the source, and the cooling stops almost immediately. It's as if someone wiped the dust from those greenhouse windows, letting in more light all at once.

Climate scientists have begun to suspect this shift explains part of why the past three years have been the warmest on record. A team at ETH Zurich, led by climate physicist Reto Knutti, stripped away the noise of natural variations like El Niño to reveal the underlying trend. The warming rate has accelerated. One study estimates that falling aerosol pollution alone has added roughly half a degree of warming to summer temperatures in western-central Europe since 1980. A researcher at the University of Leeds calculates that declining aerosol pollution is now contributing between 0.05 and 0.1 degrees of warming per decade—a significant amount, though still dwarfed by the roughly 0.2 degrees per decade from greenhouse gases themselves.

But here is where the story darkens. If cleaner air is only part of the acceleration, what accounts for the rest? Scientists have begun to notice something troubling in their measurements of Earth's energy balance—the difference between how much solar energy the planet absorbs and how much heat it radiates back to space. That imbalance has roughly tripled over the past two decades. Some of the extra warming appears to come from clouds. As oceans warm, low-lying clouds that reflect sunlight are disappearing, allowing more heat to be absorbed by the dark water below. This creates a feedback loop: warming reduces clouds, which allows more warming, which reduces more clouds.

When Knutti's team compared their observations against computer models of the climate, they found something striking. The models that best predicted both the recent warming and the rising energy imbalance were also the ones that assume the climate is more sensitive to greenhouse gases than previously thought. In other words, the models predicting the most warming are now looking like the most accurate. His analysis suggests that the same amount of emissions could produce roughly 25 percent more warming than earlier estimates indicated. A separate study published in Science reached a similar conclusion. Under current government policies, the world is headed for approximately 2.8 degrees of warming by the end of the century. If this new evidence holds, the same emissions path could instead produce warming closer to 3.5 degrees—a difference that translates into more severe heatwaves, floods, droughts, and wildfires.

Scientists urge caution. The satellite record is short. Natural variations are large. These new studies do not overturn previous estimates so much as suggest they may be conservative. A researcher at the University of Leeds notes that observations spanning only one or two decades must be interpreted carefully. But the pattern is becoming hard to ignore. The cleaner air that protects our lungs may have inadvertently revealed a climate system more volatile than we thought. If that turns out to be true, the case for cutting emissions quickly becomes not just important but urgent.