Fact check: Climate change theory compatible with laws of thermodynamics

·5 min read

The claim: Laws of thermodynamics say CO2 can’t contribute to climate change

Significant and immediate worldwide carbon dioxide emissions reductions are necessary to avoid the worst effects of global climate change, scientists say.

However, a claim has been circulating online that CO2 can’t contribute to climate change because of the laws of thermodynamics.

“As the attached diagram shows CO2 plays no role in generating the heat that warms the earth,” states a version of the claim in an Oct. 23 Facebook post. “No one ever mentions this fact when discussing climate change because they don’t understand what they are talking about.”

The attached diagram does not illustrate the behavior of CO2 molecules in the Earth's atmosphere, however. It depicts a nuclear fusion reaction that takes place on the sun.

The Facebook post, which garnered dozens of shares in a month, misrepresents climate change science in multiple ways. Climate theory is compatible with the laws of thermodynamics, according to experts. Further, climate change scientists do not claim that carbon dioxide generates heat.

The existence of climate change driven by human greenhouse gas emissions, including CO2, is supported by multiple lines of evidence.

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Post misinterprets climate change theory

Researchers say the post misstates a basic principle of climate change theory.

"No one's claimed, ever, that CO2 generates heat," Josh Willis, a climate scientist at NASA Jet Propulsion Laboratory, told USA TODAY. "CO2 traps heat, it doesn't generate heat."

The heat that causes climate change is actually coming from the Earth, in the form of radiation or energy. The Earth emits radiation because it is heated by radiation from the sun.

However, the sun and the Earth emit most of their radiation at different wavelengths.

A wavelength is a measure of the distance between the crests of an energy wave. This measurement is important because different wavelengths of radiation behave differently.

For instance, much of the sun's radiation does not interact with CO2 molecules as it passes through Earth's atmosphere.

However, the outgoing radiation from Earth is "just the right wavelength to interact with the CO2," said Willis. "And that's the whole problem.”

When the Earth's radiation strikes CO2 molecules, it causes them to release radiation.

Some of this radiation is directed back down toward the Earth again, heating the planet.

“The ultimate thing that happens is more heat stays on the Earth and less gets out to space,” said Willis.

The Facebook page, Climate Truth, did not offer evidence that the laws of thermodynamics are incompatible with climate change theory. However, they challenged the idea that CO2 could drive climate change.

"No empirical CO2/Temperature data set showing CO2 driving the climate on any statistically significant historical time scale even exists," they told USA TODAY in a direct message.

But Willis said this principle can be verified by a simple lab experiment in which one tank is filled with CO2 and another is filled with oxygen. The tanks are then exposed to radiation.

"The one with the CO2 traps more heat," said Willis. That experiment has "been done for hundreds of years."

The post also references an attached diagram, saying it “shows CO2 plays no role in generating the heat that warms the earth.”

The diagram, which includes images of hydrogen and helium atoms, depicts a nuclear fusion reaction, according to Willis.

"There’s no CO2 in the entire diagram," said Willis. It "has nothing to do with climate change."

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Climate theory compatible with laws of thermodynamics

The post misuses the first law of thermodynamics, which states that energy can neither be created nor destroyed, to support its claims.

The post states that this basic principle of physics doesn't allow for heat to get "trapped in Carbon Dioxide."

This is true.

But climate scientists aren't saying energy is being trapped in CO2 or spontaneously created by CO2. They are saying CO2 is slowing the escape of energy into space by directing some of it back to the Earth, Becky Alexander, a professor of atmospheric sciences at the University of Washington, told USA TODAY.

The post later mentions the second law of thermodynamics, but the particular passage is nonsensical, and researchers USA TODAY spoke with couldn't tell what point the author was intending to make.

However, the theory of the greenhouse effect and climate change are “completely compatible” with the laws of thermodynamics, Sukrit Ranjan, a planetary photochemist and postdoctoral fellow at Northwestern University, told USA TODAY.

The post is "not actually addressing the core argument or the core mechanism by which the greenhouse effect or climate change is being proposed to proceed,” said Ranjan. “The mechanism (that creates) the greenhouse effect is being misunderstood to some degree.”

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Our rating: False

Based on our research, we rate FALSE the claim that the laws of thermodynamics say CO2 can’t contribute to climate change. Climate change theory isn't related to CO2 trapping heat itself, it's asserting that CO2 directs radiation to earth that would otherwise escape into space. The laws of thermodynamics are completely compatible with climate change theory, according to experts.

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This article originally appeared on USA TODAY: Fact check: Laws of thermodynamics compatible with climate change

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