Sometimes it is almost impossible not to feel hopeless and broken,” says the climate scientist Ruth Cerezo-Mota. “After all the flooding, fires, and droughts of the last three years worldwide, all related to climate change, and after the fury of Hurricane Otis in Mexico, my country, I really thought governments were ready to listen to the science, to act in the people’s best interest.”

Instead, Cerezo-Mota expects the world to heat by a catastrophic 3C this century, soaring past the internationally agreed 1.5C target and delivering enormous suffering to billions of people. This is her optimistic view, she says.

“The breaking point for me was a meeting in Singapore,” says Cerezo-Mota, an expert in climate modelling at the National Autonomous University of Mexico. There, she listened to other experts spell out the connection between rising global temperatures and heatwaves, fires, storms and floods hurting people – not at the end of the century, but today. “That was when everything clicked.

“I got a depression,” she says. “It was a very dark point in my life. I was unable to do anything and was just sort of surviving.”

Cerezo-Mota recovered to continue her work: “We keep doing it because we have to do it, so [the powerful] cannot say that they didn’t know. We know what we’re talking about. They can say they don’t care, but they can’t say they didn’t know.”

In Mérida on the Yucatán peninsula, where Cerezo-Mota lives, the heat is ramping up. “Last summer, we had around 47C maximum. The worst part is that, even at night, it’s 38C, which is higher than your body temperature. It doesn’t give a minute of the day for your body to try to recover.”

She says record-breaking heatwaves led to many deaths in Mexico. “It’s very frustrating because many of these things could have been avoided. And it’s just silly to think: ‘Well, I don’t care if Mexico gets destroyed.’ We have seen these extreme events happening everywhere. There is not a safe place for anyone.

“I think 3C is being hopeful and conservative. 1.5C is already bad, but I don’t think there is any way we are going to stick to that. There is not any clear sign from any government that we are actually going to stay under 1.5C…”