Human greenhouse gas emissions, not El Niño, drive climate change | Fact check

Kate S. Petersen, USA TODAY
Updated ·8 min read
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Steam rises from a coal-fired power plant in Niederaussem, Germany, on Nov. 2, 2022. CO2 emissions from coal use are expected to grow 1.1% in 2023, reaching a record high and exceeding the temporary peak in 2014.

The claim: Emissions-driven global warming is a hoax because El Niño is driving recent warming

A July 5 tweet (direct link, archive link) claims the cause of modern global warming has been misidentified.

"Just in from NASA: June 2023 was cooler than June 1998 – despite 66% more industrial era CO2," reads the tweet. "Recent El Ninos have been driving recent warming. Emissions-driven warming is a hoax."

The tweet features a graph labeled "UAH Satellite-Based Temperature of the Global Lower Atmosphere." The graph appears to show that some global average temperatures were warmer in 1998 than in 2023.

The tweet was shared more than 80 times on Facebook, according to Crowdtangle, a social media analytics tool. It was retweeted more than 5,000 times.

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Our rating: False

This is wrong on multiple fronts. June 2023 was the hottest June on record, according to NASA. And human greenhouse gas emissions drive modern global warming. There is no mechanism by which the El Niño-Southern Oscillation – natural climate variability that causes short-term cycles of warming and cooling − could cause the sustained global warming that has been observed over more than a century.

Global warming driven by greenhouse gas emissions

Multiple lines of evidence show that greenhouse gas emissions caused by human activity are driving modern global warming.

These gases, which include CO2, warm the planet through a process that begins when solar radiation strikes the Earth. When this happens, the Earth heats up and releases infrared radiation upward.

This infrared radiation is absorbed by CO2 and other greenhouse gas molecules, which then release radiation in turn. However, some of this radiation is released back down toward the Earth, further warming the planet.

The more greenhouse gas molecules there are in the atmosphere, the more heat will be "trapped" in this way. The physics of this process is well understood by scientists and has been verified experimentally and through observations.

Researchers can tell that the excess CO2 in the atmosphere is due to human emissions because a significant proportion of the CO2 is composed of a type of carbon that matches the carbon found in fossil fuels, Josh Willis, a NASA climate scientist, previously told USA TODAY.

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."

Fact check: April 1895 v. April 2023 temperature comparison does not disprove climate change

El Niño doesn't cause sustained warming

There is no mechanism by which the El Niño-Southern Oscillation could drive the sustained global warming that has been observed since the late 1800s, Willis said in an email.

Instead, the El Niño-Southern Oscillation "rearranges the heat within the ocean," he said.

The El Niño-Southern Oscillation has a "warm phase" called El Niño, in which the surface layer of the ocean gets warmer and the layer just underneath it gets cooler. Since the surface layer of the ocean is in contact with the atmosphere, El Niño tends to bring higher global temperatures.

During the "cold phase" of the El Niño-Southern Oscillation − called La Niña − the surface layer of the ocean cools and the layer below it warms. This causes cooler average global temperatures.

"El Niño does not introduce new heat into Earth's system," Howard Diamond, a National Oceanic and Atmospheric Administration climate scientist, told USA TODAY. Instead, it "works off a baseline of temperature that the planet's climate provides, and that baseline is higher due to the emission of CO2 and other greenhouse gases."

"When an El Niño comes around, it is going to increase temperatures in line with that higher baseline, but it does not cause the higher baseline," he added.

Willis said that some scientists are researching whether there could be a "small uptick" in the amount of heat absorbed by the planet during an El Niño year. However, even if that turned out to be the case, it would still be dwarfed by – and in addition to – the amount of heat absorbed due to increasing greenhouse gases.

"El Niño can't drive sustained uptake of heat by the oceans," Willis said. El Niño has "been going on for thousands of years, and human-caused warming has only been happening for the last 150."

However, human-emitted CO2 has trapped more than 1 quadrillion watts of energy in Earth's climate systems, Dargan Frierson, an associate professor of atmospheric sciences at the University of Washington, told USA TODAY.

NASA reported that June 2023 was hottest on record

Despite the claim made in the tweet, June 2023 was warmer than June 1998, according to NASA data.

The data in the tweet was "not produced by NASA, and the claims made about NASA are incorrect," Peter Jacobs, a climate scientist working in the NASA Goddard Space Flight Center Office of Communication, told USA TODAY in an email. "June 2023 was the hottest June in our record."

Fact check: Humans are responsible for a significant amount of CO2 in the atmosphere

Instead, the graph matches one posted on the website of a climate scientist associated with the University of Alabama in Huntsville Earth System Science Center. The Center converts microwave data from satellite instruments to arrive at atmospheric temperature estimates, Jacobs said.

Some of the instruments utilized by the Earth System Science Center have been located on NASA satellites, Gavin Schmidt, a NASA climate scientist, told USA TODAY. But NASA's reported data is "based on tens of thousands of readings of near-surface air temperature measurements taken from weather stations on land as well as ocean temperature measurements from thermometers on ships and buoys in the ocean," Jacobs said.

Unlike NASA, Earth System Science Center reports a lower average global temperature for June 2023 than June 1998. However, Remote Sensing Systems, which uses the same satellite instruments as the Center, but processes the data differently, reports that June 2023 was hotter.

NOAA also reports that June 2023 was warmer than June 1998.

Regardless, comparing the average temperatures of two random months neither proves nor disproves global warming.

"To identify climate trends it is necessary to examine long-term observational records, not just recent months or seasons," Sean Birkel, an assistant professor at the University of Maine and the Maine state climatologist, previously told USA TODAY.

NASA reports that average global temperatures have increased nearly 2 degrees since the late 1800s.

USA TODAY reached out to the Twitter user who shared the post for comment but did not immediately receive a response.

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This article originally appeared on USA TODAY: No, El Niño isn't the reason we have climate change | Fact check