Heatwaves across Europe and south Asia have dominated the news recently. But these events are really a surface expression of more fundamental changes that are affecting our planet: the Earth itself is accumulating heat faster than ever before.
We lead a large international team of scientists who come together every year to provide an update on the state of the climate system. This year, we find that Earth’s energy imbalance- the difference between the amount of energy entering and leaving the planet- has doubled in recent decades, and is now at record levels.
This extra heat is a key indicator of the pace and scale of human-caused climate change. In a climate unaffected by human greenhouse gas emissions, the Earth’s energy imbalance would be zero. But, since the 1970s, the Earth has become increasingly out of balance. This rate of increase is faster than expected, and work is underway to understand exactly why this is happening.
Where the extra heat goes
Most of this excess heat doesn’t stay in the atmosphere. Around 90% of it is being absorbed by the oceans, which act as a vast heat sink, but the consequences are playing out across the entire Earth system. The oceans are warming, ice sheets and glaciers are melting, and permafrost is thawing.
Sea levels are rising too, driven by thermal expansion of the warming ocean (a physical increase in the volume of seawater as it absorbs heat) and melting of land-based ice.
The rate of sea level rise is also speeding up. Between 1901 and 2018, it rose by around 1.7mm per year. In the past decade (2006-25), this rate has more than doubled to over 3.6mm per year.
The oceans themselves, warmed by all that stored energy, are also increasing the odds of more extreme events. Marine heatwaves- prolonged periods of unusually high ocean temperatures – are now around three times more frequent than they were in the early 1990s. In 2025, an average area in the ocean would have experienced about 65 marine heatwave days- nearly one day in five -although some regions saw far more and others far fewer.
This is substantially higher than in previous decades and without human intervention, we would only expect to see around three to four days of heatwaves a year. Marine heatwaves can devastate marine life, disrupt fisheries, and weaken the natural coastal protections that many communities rely on.
The impacts of the energy imbalance also don’t stay at sea. Warmer oceans lead to stronger evaporation and a moister atmosphere, making weather extremes such as continental heatwaves, intense rainfall and droughts more likely too.
A warming world meets El Niño
On top of the changes caused by human activity, the energy imbalance combines with natural climate patterns such as El Niño- a periodic warming of the tropical Pacific Ocean that shifts weather patterns across the globe. While El Niño events themselves are natural, today’s are happening in a world that already has a warmer baseline.
Scientists are currently watching for the development of a particularly strong “Godzilla” El Niño, driven by exceptionally warm ocean conditions. As UN Secretary-General António Guterres put it, El Niño can “pour fuel on the fire of a warming world”.
Whatever our experiences of the upcoming El Niño, the underlying driver of longer-term climate change remains the same. Both the Earth’s energy imbalance and global wtemperatures are increasing due to record greenhouse gas emissions.
The prospect of a strong El Niño in the future is a stark reminder of how natural variations in the climate system can combine to produce particularly intense impacts.
As more heat enters the Earth system than leaves it, temperatures will continue to rise. Until we bring the planet back into balance – by drastically reducing greenhouse gas emissions and ultimately reaching net zero- that heat will keep building. (The Conversation)
