As leaders leave Brazil and the 2025 UN climate summit draws to a close, it’s worth reflecting on what science says about Earth’s climate – what’s changing, why it’s happening, and where we’re heading next.

The 2025 United Nations Climate Change Conference (COP30) has just concluded in Brazil.

Amid all the talk with politicians, policy experts and scientists, it’s worth reminding ourselves of the state of Earth’s climate – a kind of long-term average of weather conditions – what’s driving the changes we’re seeing, and where we’re heading next.

We have understood the fundamentals of Earth’s climate for many decades, but scientists like us are constantly working to extend our knowledge.

In 2025, we have seen plenty of advances, including the ability to more clearly link individual greenhouse gas emitters with the impacts of their emissions.

The how and why of Earth’s changing climate

The planet we inhabit is changing. That change, especially since the start of the industrial revolution in the 18th century, is largely due to human activities.

Many different forms of data allow us to observe changes to the climate. We have long-running weather stations we can use to track temperature and rainfall changes, as well as newer technologies such as satellite imaging, which helps us see how sea ice is changing in the Arctic and Antarctic.

We can also make estimates of changes over much longer timescales using environmental indicators linked to temperature, such as tree ring growth, the air bubbles in ice cores, and coral formation.

Taking all these lines of evidence together, we can see major changes in the Earth system. These changes have accelerated in recent........

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