The world warmed to a new monthly heat record this January, despite cooling factors like a La Nina event and an abnormally chilly United States, according to the European climate service Copernicus. This surprising temperature rise is sparking debate among scientists, with some arguing that global warming is accelerating.
Copernicus reported that January 2025 was 0.09 degrees Celsius warmer than January 2024, the previous hottest January on record. It was also 1.75 degrees Celsius warmer than pre-industrial levels. This marks the 18th month out of the last 19 in which the world hit or surpassed the 1.5-degree warming threshold set by the Paris Agreement. However, scientists only consider the threshold breached when temperatures stay above it for 20 consecutive years.
Copernicus has tracked temperature records since 1940, but older records from the U.S. and Britain date back to 1850. Some scientists, using proxies like tree rings and ice cores, suggest that Earth is now experiencing its warmest period in about 120,000 years—essentially since human civilization began.
Greenhouse Gases Are the Main Culprit
The primary cause of record-breaking global temperatures is the buildup of greenhouse gases from the burning of fossil fuels like coal, oil, and natural gas. However, natural factors influencing temperature changes haven’t behaved as expected, according to Samantha Burgess, climate strategy lead at Copernicus.
One of the most significant natural factors is the cycle of warming and cooling in the equatorial Pacific Ocean. When the central Pacific is warmer, it leads to an El Nino event, which typically pushes global temperatures higher. Last year’s substantial El Nino ended in June 2024, but the year still became the hottest on record.
Conversely, La Nina El Nino’s cooler counterpart typically dampens global warming effects and reduces the likelihood of record temperatures. A La Nina event began in January, and climate experts initially predicted that 2025 would be cooler than both 2023 and 2024.
“Even though the equatorial Pacific isn’t creating warming conditions, we’re still seeing record temperatures,” Burgess said. She attributed much of the rise to record warmth in other parts of the world’s oceans.
Usually, after an El Nino ends, temperatures drop significantly, but “we’ve not seen that,” Burgess explained.
Extreme Arctic Warmth and Sea Ice Loss
The record-breaking heat in January may feel surprising to Americans who experienced a colder-than-average month. However, the United States makes up only a small portion of the planet’s surface. Globally, a much larger area experienced extreme warmth, Burgess said.
The Arctic saw especially mild conditions in January. Parts of the Canadian Arctic were 30 degrees Celsius warmer than average, causing some sea ice to melt prematurely. Copernicus reported that Arctic sea ice levels tied the lowest-ever January record, while the U.S. National Snow and Ice Data Center ranked it as the second-lowest on record, trailing 2018.
Accelerating Warming? Scientists Are Divided
Former NASA scientist James Hansen, now at Columbia University, recently co-authored a study in the journal Environment: Science and Policy for Sustainable Development. He argued that global warming has accelerated over the last 15 years, with the planet warming at roughly twice the rate seen over the previous 40 years.
“I’m confident that this higher rate will continue for at least several years,” Hansen said. He suggested that 2025 could rival 2024 as the hottest year on record.
Hansen also pointed to new international shipping regulations that have reduced sulfur pollution, which previously reflected sunlight and helped mitigate some warming. With less sulfur in the atmosphere, temperatures could rise even further, Hansen said.
“The persistence of record warmth through 2023, 2024, and now into the first month of 2025 is jarring,” said Jonathan Overpeck, environmental dean at the University of Michigan. “There seems little doubt that global warming and the impacts of climate change are accelerating.”
However, not all scientists agree. Gabe Vecchi of Princeton University and Michael Mann of the University of Pennsylvania cautioned against jumping to conclusions. Vecchi argued that there isn’t enough data to confirm whether the recent warming spike is part of a long-term trend or just random variation. Mann noted that the observed temperature increases are still within the range predicted by climate models.
What’s Next for the Global Climate?
While February has started cooler than last year, experts warn against counting 2025 out as a potential record-breaker. Even if temperatures dip slightly, the world remains on a trajectory of sustained and potentially accelerating warming.
As global temperatures rise, the effects of climate change ranging from extreme weather events to shrinking ice caps are becoming more evident. Scientists are committed to closely monitoring temperature changes and updating climate models to ensure that humanity can adapt to a rapidly changing world.