Greenhouse gases, not Milankovitch cycles, drive modern global warming | Fact check
The claim: Modern climate change caused by Milankovitch cycles and solar inertial motion, not human CO2 emissions
A July 18 post (direct link, archive link) on X, formerly Twitter, features an illustration of the sun.
"THE REAL REASON FOR CLIMATE CHANGE: The distance of where you are from the Sun is constantly changing because the Earth's orbit around the Sun is VERY irregular," reads the post. "Start by learning the three Milankovitch Cycles, then look into Solar Inertial Motion. None of this has anything to do with humans. None of this has anything to do with CO2."
The post was shared more than 100 times on Facebook, according to Crowdtangle, a social media analytics tool. It was also reshared on X more than 6,000 times.
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Our rating: False
Modern climate change is driven by greenhouse gas emissions released by human activity, according to researchers. While Earth's position with respect to the sun can influence global temperatures, Milankovitch cycles and the movement of the sun around the solar system's center of mass (called solar inertial motion) cannot explain modern climate change.
Milankovitch cycles and solar inertial motion can't explain modern global warming
Milankovitch cycles are long-term changes in the orbit and orientation of the Earth as it moves around the sun. These include changes to the shape of Earth's orbit around the sun, the angle of the Earth's axis and the direction the Earth's axis points when an imaginary line is drawn through the Earth's rotational center.
These changes unfold over periods of tens of thousands to 100,000 years, Alex Young, the associate director of science in NASA's heliophysics science division, told USA TODAY. And because the cycles affect solar irradiance ? the amount of energy the Earth receives from the sun ? they also affect Earth's climate.
"Climate modelers and related scientists are well aware of this," Young said.
However, Milankovitch cycles cannot be responsible for modern global warming.
"Over the last 150 years (in which modern climate change has occurred), Milankovitch cycles have not changed the amount of solar energy absorbed by Earth very much," NASA reports.
In fact, the energy the Earth receives from the sun has decreased over the last 40 years, Young said. Over this same timeframe, however, the rate of global warming has more than doubled, according to National Oceanic and Atmospheric Administration.
Additionally, "Earth is currently in an interglacial period ? a period of milder climate between Ice Ages," NASA reports. "If there were no human influences on climate, scientists say Earth’s current orbital positions within the Milankovitch cycles predict our planet should be cooling, not warming."
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The post is also wrong to blame modern climate change on solar inertial motion, according to researchers.
Solar inertial motion refers to the movement of the sun around the solar system's center of mass, also known as a"barycenter," Rona Oran, a Massachusetts Institute of Technology plasma physicist, told USA TODAY. Because of the mass and gravitational pull of the planets, the solar system's center of mass is not actually in the center of the sun, but is offset.
The sun moves around this barycenter, which is constantly changing position as the planets move in their orbits.
However, "the variation of the barycenter and distance between Earth and the sun is very small so the irradiance varies a small amount," Young said.
Ken Rice, an astrophysicist at the University of Edinburgh, agreed.
"The main reason for the solar inertial motion is the influence of Jupiter, which causes both the sun and the Earth to move around the solar system barycenter in such a way that the average distance between the sun and the Earth" changes only an insignificant amount, he told USA TODAY in an email. "The solar inertial motion has essentially no impact on the Earth’s climate."
Multiple lines of evidence show that modern global warming is caused by humans, not Milankovitch cycles
There are multiple lines of evidence that show modern global warming is caused by CO2 and other greenhouse gases emitted by human activity, Josh Willis, a NASA climate scientist, previously told USA TODAY.
The physical process by which CO2 delays the escape of heat into space and warms the planet is well understood and has been verified through observations and experiments.
Additionally, "the amount of warming we see matches what we expect based on the increased CO2 we've added," he said. "The timing of the warming matches the timing of the CO2 increase caused by people."
Researchers can also tell that the excess CO2 that has accumulated in the atmosphere is due to human behavior because a significant proportion of the gas contains the type of carbon atoms found in fossil fuels, he said.
"Scientists have looked for other sources of heat, cycles of the sun, volcanos on the sea floor and pretty much everything else you can think of," Willis said. "Nothing besides humans burning fossil fuels can explain all of these things."
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The user who posted the claim could not be reached.
The claim was also debunked by Logically Facts.
Our fact-check sources:
Alex Young, Aug. 11, Email exchange with USA TODAY
Rona Oran, Aug. 8, Interview with USA TODAY
Ken Rice, Aug. 15, Email exchange with USA TODAY
NASA, Feb. 27, 2020, Why Milankovitch (Orbital) Cycles Can't Explain Earth's Current Warming
NASA, Feb. 27, 2020, Milankovitch (Orbital) Cycles and Their Role in Earth's Climate
NASA, March 25, 2021, Direct Observations Confirm That Humans Are Throwing Earth's Energy Budget off Balance
NASA Vital Signs of the Planet, accessed Aug. 14, Global temperature
NASA Science Space place, accessed Aug. 14, What is a barycenter?
The Conversation, July 31, 2020, John Tyndall: the forgotten co-founder of climate science
NOAA, Sept. 1, 2009, Climate Change: Incoming Sunlight
NOAA, Oct. 12, 2022, How do we know the build-up of carbon dioxide in the atmosphere is caused by humans?
NOAA, Jan. 18, Climate Change: Global Temperature
Australian Government Department of Climate Change, Energy, the Environment and Water, accessed August 6, Understanding Climate Change
Bloomberg, June 24, 2015, What's really warming the world?
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This article originally appeared on USA TODAY: No, Milankovitch cycles don't cause modern global warming | Fact check
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