Past climate records do not contradict climate science


The claim: The Arctic was warmer 6,000 years ago and 90% of glaciers were smaller or absent

A recent blog post shared on social media platforms referenced a paper who reported evidence that summer temperatures in the Arctic were warmer around 6,000 years ago, and called the existence of past warm periods an “inconvenient fact” for “climate alarmists”.

“New study: Arctic was much warmer 6000 years ago…90% of glaciers, ice caps smaller than present or absent,” reads the blog link in a April 11 Facebook post.

The Facebook post received more than 200 interactions. Versions of the blog were also shared on Reddit and TwitterAlthough the The Twitter account was later suspended.

But, the message is misleading. Paleoclimatologists, who study the history of Earth’s climate, have documented periods of warming and cooling. The hot summer temperatures of the period referenced in the article – the early Holocene – were caused by the normal variation of the Earth’s orbit around the sun, while the current warming trend is due to human behavior . Thus, there are different long-term ramifications for the two different warming periods, according to the researchers.

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USA TODAY has reached out to social media users who shared the claim for comment. The blog author, who also posted the link on Twitter, could not be reached.

Past warming periods are useful for understanding modern and future climate patterns

Despite what the blog post implies, the existence of past warm spells does not contradict modern climate science, Laura LaroccaThe study’s lead author and a postdoctoral fellow at Northern Arizona University, told USA TODAY.

“Evidence of past warm spells from paleoclimate records is not ‘inconvenient fact,'” Larocca said in an email. “We learn a lot from past warm spells about our rapidly warming world and what we can expect in the future.”

In fact, one of the main goals of Larocca’s study was to put contemporary human-induced Arctic glacier retreat into a long-term context, she said.

His paper provides evidence that summer Arctic temperatures about 2° Celsius higher than today eventually caused significant land loss, ending mountain glaciers and ice caps. . Losses peaked around 6,000 to 7,000 years ago when more than 90% of glaciers disappeared or were reduced in size.

Other arctic ice masses such as Greenland ice sheet and sea ​​ice were not evaluated in the study.

Fact check: Warming varies by ocean and atmosphere, does not contradict climate change

Larocca pointed out that Arctic summer temperatures due to human-caused global warming are expected to be even warmer by the end of this century than they were thousands of years ago.

“Summer temperatures only moderately warmer … than today have resulted in major environmental changes in the Arctic, including widespread decline and loss of small mountain glaciers,” she said. “This is an important point because future end-of-the-century temperatures are projected to exceed early Holocene values ​​in most places, presaging the eventual loss of most small Arctic glaciers.”

Current warming has different causes and ramifications than past warming

Michelle Stirling, communications manager for Friends of Science, which posted the claim on Facebook, told USA TODAY that contemporary warming is not “extreme or unusual” when examined in the context of the geological records of Earth.

However, while the study claims that Arctic summers were warmer during the period referenced in the article, this warming was caused by predictable changes in Earth’s orbit that exposed the northern hemisphere to more than solar radiation in the summer, Larocca said.

As Earth’s orbit continued to change, arctic summers cooled and glaciers began to advance. Currently, the orientation of the Earth towards the sun in its orbit would favor the expansion of glaciers, she said. However, warming caused by human behavior is causing a setback.

Twila Moonresearcher at the National Snow and Ice Data Center, told USA TODAY that these disparate causes mean that ancient and contemporary periods of warming have different ramifications.

“The loss of ice from today’s glaciers is happening for different reasons than the loss that happened 6,000 years ago,” Moon said in an email. “Unfortunately, this means that we cannot expect natural changes to steer us toward glacier stability or growth in the centuries or millennia to come, let alone decades.”

Another difference is that contemporary human-caused warming is progressing at a much faster rate than in the past, Samantha Bovapaleoclimatologist and assistant professor at San Diego State University, USA TODAY told USA TODAY in an email.

“Modern carbon emissions rate and warming are faster than anything we have observed in Earth’s history for at least the past 65 million years,” she said. “Rapid rates of change mean, for example, that the biosphere (global ecosystem) does not have much time to adapt to new conditions.”

Moreover, the melting of modern glaciers, which partially causes sea level riseposes unique threats to modern human populations, Larocca said.

Fact check: false claim that Arctic and Antarctic ice has reached record highs

Unlike thousands of years ago, millions of people live in coastal towns under threat by rising sea levels. In addition, she says, millions of people depend on mountain glaciers for their water.

However, Moon pointed out that human behavior can still influence future outcomes for Arctic glaciers.

“In the same way that human activities are causing today’s rapid ice loss and temperature increase, human activity can also shift to reduce the current causes of warming and limit the loss of ice in the future,” she said.

Our opinion: Missing context

Based on our research, we assess MISSING CONTEXT to the claim that the Arctic was warmer 6,000 years ago and 90% of glaciers were smaller or absent. According to the researchers, the warm temperatures of the early Holocene were caused by the variation in the Earth’s orbit around the sun, while the current warming trend is due to human behavior. Thus, the ramifications of the two periods of warming are different.

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