The scariest climate statistic

The world’s top weather agency just added a new number to the climate story — and it may be the most fundamental one of all.

It’s not 1.5 C. Not 2 C. Not the carbon loading of the atmosphere or the string of record-breaking annual temperatures. For the first time, the World Meteorological Organization's (WMO) annual assessment includes the “Earth's energy imbalance” as a key climate indicator.

It sounds arcane but it’s powerfully simple. It’s the difference between the energy hitting the Earth and the energy going back out into space. If the balance between what comes in and what goes out still sounds abstract, maybe cast your mind back to your last bout of constipation.

The whole planet is bunged up. Increasingly swinging out of balance. That means heat is getting trapped, unable to discharge. And what the planet’s weather gurus desperately want policymakers to understand is that the amount of pent-up heat isn’t just growing steadily but accelerating. We are lurching ever further out of balance, and the Earth’s energy imbalance paints the clearest picture of where we’re headed. It is, says the WMO's deputy chief, Ko Barrett, a “dire picture.”

It is impossible to truly wrap our heads around the amount of energy and heat we’re talking about. The Earth’s energy imbalance had been increasing by about 11 zettajoules per year over the last two decades. But last year, it was more than twice that much.

You may not be used to measurements in zettajoules. Very few people are. Even the scientists who study this stuff find a “zetta” hard to grasp. They have been searching for analogies but even those sound surreal.

Over the past two decades, the Earth has been absorbing excess energy equivalent to roughly 18 times all of humanity’s annual energy use — every single year, according to the WMO. And here’s the part that should stop you mid-scroll: we feel almost none of that heat directly. More than 91 per cent of it is being soaked up by the oceans. 

Another three per cent melts ice at the poles and glaciers, five per cent gets absorbed by the land. Just one per cent heats the atmosphere and causes the temperatures that we feel. Which means the warming we experience — the heat domes, the storms, the fiery summers — are just a tiny fraction of a much larger energy buildup that is mostly intangible, so far.

The amount of heat absorbed by the oceans leads to analogies that are absolutely mind-boggling. In 2025, ocean energy imbalance reached a new record high of 23 zettajoules, breaking the record set in 2024 and doubling the average of the last 20 years. If it helps to write it out, that would be 23,000,000,000,000,000,000,000 joules.

In that context, the summaries from scientists sound distinctly understated. “Human activities are increasingly disrupting the natural equilibrium and we will live with these consequences for hundreds and thousands of years,” said WMO Secretary-General Celeste Saulo.

Climate politics has long revolved around surface temperature targets. But as those targets slip by and the consequences become more severe, we need to prioritize other ways to measure and forecast planetary risk.

Carbon pollution from burning fossil fuels is still the primary cause of the heat-trapping blanket around the Earth. Burning oil, gas and coal has driven carbon dioxide concentrations to the highest level in the last 2 million years, according to the WMO. Concentrations of the other main greenhouse gases — methane and nitrous oxide — are higher than any time in at least 800,000 years. 

But we are triggering other dynamics that upset the energy balance as well. As the ice shrinks, the planet gets darker and reflects less energy. Cuts in smokestack pollution have been removing an unintended sunshade. And one of the biggest uncertainties in climate science has long been the behaviour of clouds. For the past 20 years, low-level cloud cover has been declining. That increases the amount of sunlight absorbed by Earth and amplifies global warming.

“The energy imbalance gives you the full picture,” said Karina Von Schuckmann, an author of the WMO report and senior adviser at Mercator Ocean International. 

UN Secretary-General Antonio Guterres was more blunt. Speaking alongside the release of the WMO annual assessment, he said: "The global climate is in a state of emergency. … Every key climate indicator is flashing red. 

“And in this age of war, climate stress is also exposing another truth: our addiction to fossil fuels is destabilizing both the climate and global security. … Now more than ever, we must accelerate a just transition to renewable energy.”