LONDON — My youngest daughter is 17, so she will have lived most of her life before the worst of the warming hits. But her later years will not be easy, and her kids will have it very hard from the start. As for their kids, I just don’t know.

It is the Met Office’s job to make forecasts, and its forecast for the 2060s is an average global temperature that is as much as 4 degrees (Celsius) warmer. Speaking last week at a conference called “4 degrees and beyond” at Oxford University, Dr. Richard Betts, head of Climate Impacts at the Meteorological Office’s Hadley Center, one of the world’s most important centers for climate research, laid it all out.

“We’ve always talked about these very severe impacts only affecting future generations,” said Betts, “but people alive today could live to see a four-degree (C) rise. People will say it’s an extreme scenario, and it is an extreme scenario, but it’s also a plausible scenario.”

All we have to do is go on burning fossil fuels at the rate we do now, and we’ll be there by the 2080s. Keep increasing our carbon dioxide emissions in pace with economic growth, as we have done over the past decade, and we’ll be there by the 2060s. “There” is not a good place to be.

At an average of 4 C warmer, 15 percent of the world’s farmland would become useless due to heat and drought, and crop yields would fall sharply on half of the rest: an overall 30 to 40 percent fall in global food production. Since the world’s population will have grown by 2 billion by then, there will be only half the food per person that we have now. Many people will starve.

In western and southern Africa, average temperatures will be up to 10 C higher than now. There will be severe drying in Central America, on both sides of the Mediterranean, and in a broad band across the Middle East, northern India, and Southeast Asia. With the glaciers gone, Asia’s great rivers will be mostly dry in the summer. Even one meter of sea-level rise will take out half the world’s food-rich river deltas, from the Nile to the Mekong.

So there will be famines, and massive waves of refugees, and ruthless measures taken to hold borders shut against them. The bitter irony is that the old-rich countries whose emissions did the most to bring on this disaster will suffer least from it, at least in the early stages. By and large, the further away you are from the equator, the less you are hurt by the changes.

In Britain, at 4 C hotter, there would doubtless be severe food rationing, but the country could still just feed itself if it farmed every available piece of land: the heat would not be lethal, and it would still be raining. That’s one advantage of being an island surrounded by sea; the other is that it’s easier to avoid being completely overrun by refugees. Britain would be almost unrecognizable, but it would be seen as one of the luckiest places on the planet.

The trouble is that 4 C is not a destination. It is a way station on the way to 5 C or 6 C hotter, where all the ice on the planet melts and the only habitable land is what’s still above sea level around the Arctic Ocean. Once the average global temperature rises more than 2 C, we are at ever-greater risk of triggering the big “feedbacks” that take control of the warming process out of our hands.

At the moment, we are in control of the situation if we want to be, for it is our excess emissions of greenhouse gases that are causing the warming. But if melting permafrost and warming oceans begin to give up the immense amounts of greenhouse gases that they contain, then we find ourselves on a climate escalator that inexorably takes us up through 3 C, 4 C, 5 C and 6 C with no way to get off.

The point where we lose control, most scientists believe, is when the average global temperature reaches between 2 C and 3 C warmer. After that, it hardly matters whether human beings cut their emissions, because the natural emissions triggered by the warming will overwhelm all our efforts. If we don’t stop at 2 C, our civilization is probably doomed.

That’s why the leaders of all the world’s big industrial and developing countries, meeting in Italy last summer, adopted 2 C as their joint “never-exceed” goal. (Interestingly, they didn’t explain the reasoning behind that goal to the rest of us. Mustn’t frighten the children, I suppose.)

Meanwhile, the people tasked with negotiating a new climate treaty at Copenhagen in December struggle bravely onward, but show no signs of coming up with a deal that will hold us under 2 C. Global emissions must start dropping by 3 percent a year right away, but over the past decade they have been rising at 3 percent annually.

Everybody involved in the process understands the stakes and agrees on the goal. Almost everybody knows what the treaty will eventually look like, but they don’t believe they can yet sell that deal to the folks back home, so it probably won’t happen this year. Or next. Tick tock.

Gwynne Dyer is a London-based independent journalist whose articles are published in 45 countries.