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MYTH #24: It’s cosmic rays


Cosmic rays from outer space seed clouds here on Earth. We’re seeing fewer cosmic rays, so we’re also seeing fewer clouds that block sunlight — that's the reason we have global warming.


Let's get serious. Global warming has nothing to do with cosmic rays — or anything else from outer space. 

Some scientists believe cosmic rays (high-speed particles from outer space) are one of the reasons clouds form in the Earth's lower atmosphere. Hypothetically, if fewer cosmic rays were bombarding Earth, fewer clouds would form and the planet would warm. But here’s the thing: The number of cosmic rays hasn’t changed much in recent decades, and scientists have failed to find a consistent relationship between cosmic rays and clouds. There is overwhelming evidence that the Earth has been steadily warming since the Industrial Revolution, and the reason for this warming is pollution from dirty energy like coal and gas.

More info from The Climate Reality Project

Cosmic rays are particles that constantly stream into Earth’s atmosphere from outer space. Most of us don’t come into regular contact with cosmic rays unless we live at high elevations or travel by air.

The cosmic ray myth goes something like this:
a. The number of cosmic rays hitting the planet has declined.
b. Because there are fewer cosmic rays, there are fewer clouds blocking the sun.

Let’s take each of these pieces in turn.

Has the number of cosmic rays declined?

Not recently. Scientists have been able to directly count cosmic rays since 1953. In fact, you can plot data from stations around the world yourself. If you do that, you’ll see up-and-down cycles over the last few decades, but no long-term increase or decrease. The planet, on the other hand, has been steadily warming since the late 1800s.

Is there a link between cosmic rays and clouds?

Good question. After at least a half-century of research, the answer increasingly looks like “no.”

One problem with the hypothesis linking cosmic rays and clouds is that there are different kinds of clouds — and they don’t all have the same effect on our climate. Low-altitude clouds tend to reflect more sunlight to space, so they have a cooling effect. But high-altitude clouds trap outgoing heat (just like carbon dioxide!), so they have a warming effect. In other words, cosmic rays would only have a potential impact on climate change if the rays seeded more low-altitude clouds than high-altitude clouds. But this seems unlikely — after all, the uppermost layers of the atmosphere intercept most of the incoming cosmic rays.

Does that mean scientists have given up on the idea that cosmic rays might help form clouds on Earth? No. In fact, there’s a lab in Europe with an ongoing experiment to address this very thing. But as one expert writes about the cosmic ray-cloud link: “For each piece of evidence in its favor, an equal or greater number of studies fail to find the effect.”

We don’t need to look to outer space to answer the question “what has caused recent changes in climate?” Because the answer is right here on Earth: It’s us.