May 2025 was world's second-hottest on record amid Arctic heatwaves

May 2025 was the second-hottest May globally since records began, driven by climate change and marked by unprecedented heatwaves in Greenland, scientists reported.

According to the European Union’s Copernicus Climate Change Service (C3S), only May 2024 was warmer. This month concluded the second-warmest spring (March–May) ever recorded in the northern hemisphere.

Global surface temperatures in May averaged 1.4°C above levels from the pre-industrial era (1850–1900), when large-scale fossil fuel use began. This contributes to an ongoing stretch of extreme heat, with 21 of the past 22 months registering global average temperatures at or above 1.5°C above pre-industrial levels. However, scientists caution this may not be a permanent state.

“This may bring a short-lived reprieve, but we anticipate the 1.5°C threshold will be breached again soon, as the climate system continues to warm,” said C3S Director Carlo Buontempo.

Fossil Fuels at the Heart of Warming

The main driver of global warming is greenhouse gas emissions from burning fossil fuels. 2024 was officially the hottest year ever recorded.

In a related study released by the World Weather Attribution (WWA) group, human-induced climate change was found to have triggered extreme heat events in Greenland and Iceland last month. These temperatures were around 3°C higher than they would have been without climate change, causing extensive ice melt in Greenland.

Between May 15 and 21, ice in Greenland melted 17 times faster than the historical average, according to the WWA. In Iceland, temperatures soared above 26°C on May 15 — a first for the island nation situated on the edge of the Arctic.

Iceland Sets Temperature Records

“Iceland’s May temperatures broke all previous records, surpassing the 1991–2020 average of maximum daily highs by more than 13°C,” the WWA study reported.

Nearly 94% of Iceland’s weather stations recorded new temperature highs in May, the country’s meteorological institute confirmed. In eastern Greenland, the warmest day was 3.9°C above pre-industrial norms.

“A 20°C heatwave may not seem extreme globally, but in this region, it's a major concern — with far-reaching consequences worldwide,” said Friederike Otto, study co-author from Imperial College London.

Rapid Arctic Warming with Global Effects

The Arctic is now warming four times faster than the global average, as highlighted in a Nature journal study. “Even traditionally cold regions are facing unprecedented heat,” noted Sarah Kew, a researcher at the Royal Netherlands Meteorological Institute and co-author of the study.

Greenland’s accelerating ice loss has global consequences, as its ice sheet holds enough water to raise sea levels by about seven meters if fully melted.

Climate experts stress that while some months may temporarily fall below the 1.5°C benchmark, the long-term trend remains upward due to persistent greenhouse gas emissions.

C3S climate records, which began in 1940, are analyzed alongside global temperature data dating back to 1850, offering over 175 years of comprehensive climate insight.