No, sea level rise over past 20,000 years doesn't prove climate change is a 'scam' | Fact check

Isabella Fertel, USA TODAY
·5 min read
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The claim: Sea level rise over the last 20,000 years shows climate change is a 'scam'

A July 22 Instagram post (direct link, archive link) shows a screenshot of a post from X, formerly Twitter, with a chart of global average sea levels over the past 20,000 years.

“Sea level has risen 400 feet over the last 20,000 years, but climate experts say the last three inches are your fault,” reads the post. “#ClimateScam.”

The X post garnered more than 2,000 reposts in a month. Other versions continue to circulate on X.

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Our rating: False

The chart is correct that sea levels have risen more than 300 feet over the past 20,000 years, according to climate scientists. However, experts say the rise was triggered by the end of the last ice age and does not contradict the fact that human activities are warming the planet and causing modern sea levels to rise.

Human-caused climate change is driving modern sea level rise

The chart used in the posts seems to have been made by a Wikimedia Commons user and appears on the Wikipedia page for Early Holocene sea level rise. It is purportedly based on data from various studies on sea level rise since the last glacial maximum, which is when the polar ice sheets were at their largest size during the last ice age.

At that time, sea levels were more than 300 feet lower than today, said Marcus Sarofim, an environmental scientist at the Environmental Protection Agency’s Climate Science and Impacts branch.

That’s because a “giant mass of water” was “locked up in the ice sheets covering Canada and much of northern Europe and the northern U.S.,” Sarofim told USA TODAY in an email.

As temperatures warmed and the glaciers and ice sheets melted, sea levels began to rise starting about 15,000 years ago, as the chart in the post shows.

But this historic fluctuation in sea level “does not prove that modern sea level rise is or is not caused by human-driven climate change,” said John Callahan, a climate scientist at NOAA.

The average global sea level has gone up by about 6 to 8 inches over the past century, according to NASA. The rate of sea level rise continues to increase and has more than doubled since 2006.

Fact check: Ample evidence the Earth is round and sea levels are rising

This rate of rise is “unprecedented in the last 3,000 years,” Callahan said, pointing to the United Nations Intergovernmental Panel on Climate Change’s sixth assessment report.

The acceleration is unequivocally linked to increasing global temperatures due to human activity, according to NASA. The ensuing melting of ice sheets and glaciers and physical expansion of warming seawater mean sea levels will continue to rise as the Earth continues to warm.

Average surface temperatures around the globe have increased by an average of about 0.1 degrees per decade since 1880, or about 2 degrees in total, according to data from multiple climate agencies. The rate of warming since 1981 has nearly doubled since the 1980s, with global temperatures continuing to increase at a rate of more than 0.3 degrees per decade.

Both Sarofim and Callahan said the scale of the chart obscures how global mean sea levels have stayed “relatively stable” over the last several thousand years prior to the Industrial Revolution.

During that time of stability, Callahan noted that many coastal cities and infrastructures were built at low elevations and close to shorelines.

So, while the 6 to 8 inches of sea level rise from 1901 to 2018 may “look insignificant” in the graph, Sarofim said this amount of increase in the global average sea level “actually results in a lot of human-relevant impacts.”

As a result of this rise, storm surges have increased in intensity, flooding events have become more frequent and more intense, and coastal areas are rapidly eroding.

USA TODAY reached out to the Instagram user who shared the post for comment but did not receive an immediate response.

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This article originally appeared on USA TODAY: No, climate change is not disproven by past sea levels | Fact check