The planet has been warming for decades, but an extraordinary surge in global temperatures over the past two years has baffled scientists. While the long-term warming trend is clear, the sudden and extreme heat from 2023 to 2024 has taken global climate conditions into uncharted territory.
Over this period, temperature records were shattered, defying even the most advanced climate models. Scientists agree that burning fossil fuels has driven long-term warming, while natural climate variability plays a role in yearly temperature changes. However, they are still investigating the specific causes of this unusual and intense heatwave.
The Heatwave: What We Know So Far
Experts suggest that factors like changes in cloud patterns, reduced airborne pollution, and Earth’s carbon storage capacity might have contributed to this extreme warming. However, clear answers may take a year or two to emerge.
According to Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, “Warming in 2023 was head-and-shoulders above any other year, and 2024 will be as well.” He added, “I wish I knew why, but I don’t.”
The burning of fossil fuels releases greenhouse gases, such as carbon dioxide, which trap heat near the Earth’s surface. Record-high emissions in 2023 pushed both air and sea surface temperatures upward. From June 2023 to September 2024, global temperatures broke historical records, marking 2023 and 2024 as the hottest years ever recorded.
Climate Models Struggle to Explain
Scientists are debating why this heatwave is so intense. Climate expert Sonia Seneviratne from ETH Zurich explained, “The long-term warming trend is expected due to fossil fuel emissions, but what we’re seeing now is at the edge of what climate models predict.”
Climate variability might explain part of the anomaly. The rare, three-year La Niña event (which cools the planet by storing excess heat in deep oceans) ended in 2023. It was followed by a warming El Niño event, which brought the heat back to the surface. While El Niño’s peak ended in January 2024, temperatures have not dropped as expected, with November still ranking as the second-warmest on record.
Robert Vautard, a member of the UN’s climate panel IPCC, noted, “If temperatures don’t drop sharply in 2025, we’ll need to reassess the causes.”
Uncovering New Climate Clues
Scientists are exploring other possibilities. For instance, a global switch to cleaner shipping fuels in 2020 reduced sulphur emissions, which may have made clouds less reflective, allowing more sunlight to reach the Earth’s surface. Additionally, research suggests a possible decrease in low-lying clouds, further amplifying the heat.
At the recent American Geophysical Union conference, experts considered theories including solar cycles, volcanic activity, and changes in Earth’s carbon sinks. For example, forests and oceans — critical for absorbing CO2 — experienced a significant decline in their capacity to act as carbon sinks in 2023.
The Arctic tundra, once a reliable carbon store, is now emitting CO2, according to the US National Oceanic and Atmospheric Administration. Meanwhile, the oceans, which have historically acted as climate regulators, are warming at a rate scientists cannot fully explain.
Johan Rockstrom from the Potsdam Institute for Climate Impact Research expressed concern: “Could this be a sign of the planet losing resilience? We cannot exclude it.”
The Road Ahead
The exceptional heat over the past two years raises urgent questions about how the climate system is evolving. While long-term warming from fossil fuel emissions is expected, the intensity and persistence of recent temperature surges are pushing scientists to reevaluate their models.
The planet’s climate system may be undergoing profound changes that are not yet fully understood, highlighting the importance of continued research and global climate action.
