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A bleak article in New York magazine headlined 鈥溾�� has created a storm among the climatorati. It describes how global warming will lead to famine, economic collapse and 鈥渁 sun that cooks us鈥�.

The piece has provoked two main criticisms. The first is to say it isn鈥檛 helpful, that frightening people leads to despair rather than action. Maybe, but that鈥檚 a ludicrous criticism of any piece of reporting.

In my view, the job of journalists is to tell it like it is, not to spout feel-good propaganda. If an asteroid is about to hit the planet, should all articles have to focus on NASA鈥檚 efforts to deflect it rather than on where it will strike if they fail and what will happen as a result?

The second criticism is to say the article has got the science wrong, along with . For instance, it implies that methane released from the melting Arctic will hugely add to warming. But most climate scientists say we don鈥檛 need to lose much sleep worrying about this.

Many of the doomsday scenarios outlined in the magazine will only come about if we see extreme warming of 6掳C or more, and there鈥檚 a very good reason this is unlikely to happen: physics.

What it gets right

More on that shortly. First, it is also worth pointing out that the article gets many things right. Indeed, on the most certain impact of warming 鈥� sea level rise 鈥� it mostly understates the case. It says correctly that some scientists now predict seas could rise 3 metres by 2100, but that鈥檚 not the full story.

In fact, we鈥檝e already emitted enough carbon dioxide to raise sea level 5 metres over the coming centuries. Over the new few decades, we鈥檙e likely to produce enough to make the seas rise 20 metres or more. Many coastal cities and low-lying places like Florida really are doomed.

It is also true that if the world warms by about 7掳C, parts of the planet could get so hot and humid that it becomes impossible to survive without air conditioning.

The good news is that it is very unlikely the world will warm that much 鈥� because the more CO₂ we put into the atmosphere, the less effect it has. So while limiting warming to 2掳C may now be practically impossible, keeping it to 3掳C is doable.

Simply put, global average surface temperatures will rise roughly 3掳C with every doubling of CO₂ in the atmosphere. The preindustrial level was 280 parts per million, and we鈥檝e just zoomed past 400 ppm, about halfway to the first doubling. But to double CO₂ levels again, from 560 to 1120 ppm, will require us to add twice as much CO₂ to the atmosphere as we already have.

In other words, emissions have to grow exponentially to produce a steady temperature rise. This means really extreme warming would only occur if we pump out really extreme quantities of greenhouse gases, far more than we have already. And for the past couple of years, at least, emissions from industry haven鈥檛 been increasing. It鈥檚 far too soon to leap to any grand conclusions about the long-term trend, but it is at least a hopeful sign.

Risks ahead

There are, of course, some . Firstly, half the CO₂ we have emitted has been soaked up by the land and seas. If they stop absorbing as much, atmospheric levels will rise much faster.

Secondly, while 3掳C of warming is the most likely response to a doubling of CO₂, higher values are possible. There is a small chance that climate sensitivity, as the response to doubled CO₂ is known, could reach 6掳C or more.

If our emissions keep rising, climate sensitivity turns out to be high, and the land and seas become net emitters of greenhouses gases rather than absorbers, our grandchildren will be in very serious trouble indeed. But this is not the most likely scenario.

And this is perhaps the main problem with the New York article. It claims at the beginning that it will set out 鈥渙ur best understanding of where the planet is heading absent aggressive action鈥�. But it then proceeds to confuse worse-case scenarios with the most likely scenarios.

Still, at least it has got people talking. That may be no bad thing.