Why are September’s record temperatures causing scientific concern?

Global temperatures are abnormally high and El Niño appears to be playing a role. But research fears human influences may also play a role.

WASHINGTON, DC – After months of unprecedented global warming, temperatures have become even more erratic in recent weeks – briefly averaging nearly 2 degrees Celsius above pre-industrial levels, a threshold that those responsible for global warming want to avoid.

“I thought we were already seeing exceptional temperatures in July,” said Zeke Hausfather, head of climate research at payments services company Stripe. “What we saw this week is far beyond that.”

This trend is certain to contribute to 2023 being the warmest year on record and increases the risk of extreme conditions that heat could create around the world.

The El Niño phenomenon could cause temperatures to rise next year

Scientists said the warmth is likely a signature of a worsening El Niño climate pattern and a sign that temperatures will continue to rise above old standards next year. The El Niño phenomenon, which occurred this spring, is known to increase global temperatures by releasing large amounts of heat from the Pacific Ocean into the atmosphere.

“El Niño won’t peak until later this year, and there’s plenty of warmth ahead of us,” Michael McFadden, a senior scientist at the National Oceanic and Atmospheric Administration, said in an email. “So we expect to set more records in the coming months.

Climate analyzes show that September temperatures have always been one degree too warm

Scientists’ assessments are based on near-real-time climate analysis that uses weather observations to estimate global averages, similar to a weather prediction model — except it looks to the past rather than the future. Confidence in such analyzes has increased because they are consistent with routine assessments of global climate conducted by NASA and the National Oceanic and Atmospheric Administration (NOAA) weeks and months after events.

Such an analysis by the Japan Meteorological Agency shows that global temperatures this month have consistently deviated by 1 degree Celsius (1.8 degrees Fahrenheit) from the 1991-2020 averages.

According to Hausfather, the 1991-2020 average is about 0.9 degrees higher than the values ​​observed before the Industrial Revolution and the widespread burning of fossil fuels. This means that temperatures are approaching, at least in the short term, the temperature rise thresholds that world leaders have committed to avoiding.

A temperature rise of 2 degrees Celsius could have irreversible consequences

Scientists have warned that a long-term rise in average global temperatures of 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels could have irreversible consequences for all life on Earth. It would take years for this sustained global warming to lead to its worst and most widespread consequences, although the effects would be catastrophic in the hottest places on Earth where such warming has already occurred.

The planet is on the cusp of achieving the most ambitious climate goal of limiting temperature rise to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above the pre-industrial average. However, scientists said this goal is not out of reach and the recent heatwave underscores the importance of climate action.

“Experience the fury of heat as it enters the atmosphere.”

“Decades of burning fossil fuels and deforestation have pumped greenhouse gases into the atmosphere, and the oceans are absorbing most of that heat. We are now experiencing the wrath of That heat when it returns to the atmosphere.” “We must act quickly and boldly to reduce emissions of these gases to prevent as much warming and the effects of this heat as possible.

The temperature anomalies are notable because they are more distant than the extreme heat observed worldwide in July and August. European climate researchers said earlier this month that by a “wide margin” of 0.71 degrees, this summer was the warmest three-month period on Earth in records dating back nearly two centuries.

Hausfather called it “a foregone conclusion” that September will mark the third month in a row in which global average temperatures set records.

Temperature anomalies increased

If temperatures remain unusually warm as they are now, the global average could exceed 1.5 degrees Celsius of warming compared to pre-industrial temperatures on an annual basis for the first time, according to Housefather’s calculations, though he called that “unlikely.” Extremely”.

Temperature anomalies increased even as the planet’s temperature cooled in absolute terms before the September 23 equinox, which marks the beginning of autumn in the Northern Hemisphere. Conditions in the Northern Hemisphere have a greater impact on planetary averages because the land area there is larger than that in the Southern Hemisphere, and the land heats and cools faster than the oceans.

The El Niño phenomenon is said to be the main cause of rising temperatures

However, El Niño is likely a major cause of the warming trend, as it creates trade winds in the Pacific Ocean that cause more heat to be released from the ocean and trap greenhouse gases in the atmosphere. With the El Niño pattern expected to intensify and peak during the winter in the Northern Hemisphere, this warmth could become even more erratic next year, according to Michael Mann, a climate scientist and professor at the University of Pennsylvania.

The El Niño phenomenon is known to cause temperatures on Earth to rise by one to one tenth of a degree Celsius. The recent strong El Niño caused a new record for average global warming in 2016, and also increased extreme heat and storms.

According to Hausfather, other factors are also contributing to rising temperatures: reduced emissions from cargo ships, allowing more sunlight to reach the oceans; the eruption of the Hunga Tonga underwater volcano in the South Pacific in 2022, which sent large amounts of water vapor into the atmosphere; And a continuous increase in solar activity, which slightly increases the effect of the rising temperature of the sun on Earth.

However, the recent increase in temperature anomalies could be a sign that human influences and natural variability are working together to increase global temperatures, said Claudia Tibaldi, a geoscientist at the Pacific Northwest National Laboratory.

During a period in the early 2000s, when global warming appeared to be slowing, natural fluctuations had a cooling effect that dampened human-caused global warming, Tebaldi said. This seems to have changed now. “It is not surprising that the pendulum is now swinging in the other direction,” she wrote in an email.

We are currently testing machine translations. This article was automatically translated from English to German.

This article was first published in English on September 23, 2023 on “washingtonpost.com” was published as part of the collaboration, and is now also available in translation for readers of the IPPEN.MEDIA portals.