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Humans are causing modern warming; other things caused past climate change | Fact check

Kate S. Petersen   Paste BN
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The claim: Past climate change shows modern climate change isn't caused by humans

A Jan. 17 Facebook post (direct link, archive link) shows two distinctly different images of Earth. One, labeled "now," features blue oceans and green-toned continents. The other, labeled "4.5 billion years ago," has what appears to be ice sheet-covered continents and red and yellow oceans.

"The environment of Earth has been continually changing for 4.5 BILLION YEARS!" reads some text surrounding the image. "The idea that 'Climate Change' is new or is caused by Humans is nonsense."

The post was shared more than 700 times in less than two weeks.

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Our rating: False

Earth's climate has changed throughout history for numerous reasons, but an abundance of evidence shows modern climate change is driven by human behavior. There is no evidence the post's depiction of ancient Earth is accurate.

'Overwhelming' evidence humans are changing Earth's climate

Earth's climate has varied significantly over its roughly 4.5 billion-year history, Taylor Perron, a geologist at Massachusetts Institute of Technology, told Paste BN.

"There were times when Earth was warmer than it is now and times when Earth was colder than it is now," he said in an email. "But the fact that Earth has been warmer and colder in the past doesn't mean that the current warming trend is not dangerous, and it doesn't mean that humans aren't the cause."

Humans are causing modern climate change through activity that releases greenhouse gases into the atmosphere − such as fossil fuel combustion and deforestation. The warming property of these gases, such as CO2, has been known since the 1800s.

Human activity has increased the amount of CO2 in the atmosphere by 50% since 1750, according to NASA.

Earth's average temperature has warmed over this same timeframe, and "the amount of warming we see matches what we expect based on the increased CO2 we've added," Josh Willis, a NASA climate scientist, previously told Paste BN. "The timing of the warming matches the timing of the CO2 increase caused by people."

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Researchers know the excess CO2 was contributed by humans because it matches the amount humans have produced (after natural processes are accounted for) and because atmospheric CO2 contains a disproportionate amount of the type of carbon found in fossil fuels.

"There are many different 'fingerprints' that have been clearly identified by scientists as evidence that industrial pollution is the cause of recent global heating," Dargan Frierson, an atmospheric scientist at the University of Washington, previously told Paste BN. "This is not exactly a 'whodunit' situation. The evidence is overwhelming that fossil fuel burning is the culprit."

Past climate change events driven by different phenomena

Earth's past climate changes were driven by a variety of events, including changes in Earth's orbit and orientation to the sun, fluctuations in the amount of solar radiation striking Earth, volcanic activity and changes in ocean circulation patterns, according to researchers.

"What's alarmingly different about the global warming happening now is how fast it's happening and how it's clearly associated with humans adding greenhouse gases like carbon dioxide to the atmosphere," Perron said. "Rapid warming in the geologic past, long before there were humans, led to mass extinctions. And times when it was only slightly warmer than now, like before the last ice age, had sea levels high enough to flood most of today's coastal cities."

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The post's depiction of Earth "4.5 billion years ago" is not supported by scientific evidence, Tanja Bosak, a geobiologist at Massachusetts Institute of Technology, told Paste BN.

When and how Earth's continents emerged is a subject of active research. However, there is no evidence that ice sheet-covered continents existed 4.5 billion years ago, Bosak said.

Paste BN reached out to the Facebook user who shared the post for comment but did not immediately receive a response.

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