Heatwaves across Europe and South Asia have dominated the news recently. But these events are really a surface expression of more fundamental changes affecting our planet: 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, Earth’s energy imbalance would be zero. But since the 1970s, 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.