Global warming is like a human fever, influential scientist says

Global warming is like a fever, says well-known climate scientist Katharine Hayhoe — even a small rise is serious.

Why it matters: Adapting to the warming already underway is a top focus at the United Nations climate talks underway now in Belém, Brazil.

• Hayhoe has one of the world's largest social media followings of climate scientists, with nearly a quarter-million followers on LinkedIn alone.

Where it stands: The planet is on track to warm around 5°F (just under 3°C) by the end of the century, according to the International Energy Agency's annual outlook released last week.

• If governments enact current policy proposals, that increase could drop slightly — by roughly half a degree Celsius.
• Reaching net-zero emissions by 2100 would keep the rise to about 2.7°F (1.5°C) — the goal set under the Paris Agreement, though such a goal is already largely out of reach, scientists say.

Between the lines: To many people, a two- to five-degree change sounds insignificant — just normal weather variation. But weather isn't the right frame.

• The better comparison is the human body, says Hayhoe, chief scientist at The Nature Conservancy, in the latest episode of the "Shocked" podcast.

How it works: "If our body temperature spiked by 2 degrees Fahrenheit in a very short period of time, which is exactly what the Earth's temperature has done, then we'd be feeling really achy," said Hayhoe, who's also a Texas Tech professor.

• "Imagine if your body is running a 5, 6, 7-degree fever," she said. "That is life-threatening."

Catch up fast: Last year was the hottest on record, and 2025 is likely to rank among the hottest as well.

• Hotter temperatures trigger a cascade of impacts — from melting ice caps and worsening floods, to more intense heat waves and stronger storms that strain infrastructure, economies and human health.

Flashback: A decade ago, the world was on track to warm closer to 9°F (5°C) by the end of the century, but efforts to scale cleaner energy have helped temper that.

What we're watching: "The most important thing anyone needs to know about future scenarios is that the No. 1 source of uncertainty in terms of what will happen in the future is us," said Hayhoe, referring to humanity collectively.

Cover photo:  Data: International Energy Agency; Note: Increase relative to 1850–1900 baseline; Chart: Kavya Beheraj/Axios