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Ever spent time in Dubai airport, on the shores of the Persian Gulf? You might have reflected that human beings can live quite well when temperatures exceed 50°C. All they need to do is stay behind plate glass, with the air conditioning on maximum.

No doubt you looked out through the glass at the dust and sand. If you’re unusually reflective, you might then have asked yourself: if this is what global warming has in store for huge stretches of the Earth, what’s everyone going to eat?

Modern capitalist society seems to be doing its best to turn this horror-movie script into reality.

In May, the International Energy Agency reported that human-caused greenhouse emissions in 2010 were back close to trend, just under the UN’s worst-case scenario.

Scientists say that would push global average temperatures 4°C above pre-industrial levels sometime in the 2070s.

On land areas like southern Australia, the rise would be around 6°C, with summer temperatures much like in today’s Dubai.

The message for food supplies is not good — and worse if you reflect that for billions of people, nutrition levels are already inadequate or precarious.

Strictly speaking, there’s no food deficit; all of humanity could be adequately fed if food grains were diverted from feeding livestock.

Nevertheless, the said in 2010 that 925 million people around the world experience actual hunger, while perhaps a further billion lack essential nutrients.

Higher temperatures will multiply the nutrition challenges. About three billion people live in tropical regions, where crops are often close to their limits of heat tolerance.

US environmental writer : “Crop ecologists have their own rule of thumb: for each 1 degree Celsius above the optimum during the growing season, we can expect a 10% decline in grain yields.”

Adding to the problems will be more frequent extreme weather, and especially, “hot droughts”.

Last October, the US National Center for Atmospheric Research published a review called   (archived by 28/09/2011) that predicted dust-bowl conditions in many of today’s global “food baskets”.

The review used a familiar tool of agricultural experts, the Palmer Drought Severity Index (PDSI), which combines measures of precipitation and temperature.

“Severe drought”, seen during Australia’s “Big Dry” from 1997 to 2009, has a PDSI rating of minus three; “extreme drought” is minus four.

Modelled PDSI outcomes for 2060-2069 show severe to extreme drought (or worse) in the US west and great plains; Mexico, the Caribbean, and Chile; the Mediterranean region, Ukraine and southern Russia; southern China and southeast Asia; west Africa and southern Africa; and southern Australia.

Of today’s major food-exporting regions, the only one predicted to have reasonable conditions for rain-fed agriculture in 50-60 years’ time is in South America — Uruguay, much of Argentina, and parts of southern Brazil.

Conditions for agriculture in Australia are predicted to deteriorate swiftly. The review’s 2030-2039 map indicates PDSI figures of minus six along most of the southern and eastern coastline, and minus 10 in the south-west of Western Australia.

Most rain-fed agriculture would cease. Australia’s food surpluses may not have much more than 20 years to run.

But perhaps the assumptions underlying the modelling are unduly pessimistic? Rather the reverse: the review used the United Nation’s A1B emissions scenario, considerably milder than the worst-case scenario that humanity has tracked for most of the past decade.

Surely, though, there’s an upside? After all, higher carbon dioxide levels raise the efficiency with which plants use water. But field experiments suggest that the boost to crop yields from this “carbon dioxide fertilisation” would be marginal.

Warmer temperatures in sub-Arctic regions, meanwhile, will lengthen growing seasons. Couldn’t the world’s great cropping regions migrate to the north and south poles? Most sub-Arctic soils, though, are thin and acidic — no substitute for the threatened farmland.

Might not technology come to the rescue? New irrigation methods, perhaps? But fresh water in key areas is already heavily overexploited.

In India, the World Bank reports, 175 million people are being fed with grain produced through pumping groundwater faster than it is being replenished.

Rational food policies, vigorously implemented, could effectively end malnutrition over the next decade or so. But hopes of adapting to the effects of climate change, if it takes hold, are fanciful.

As an NCAR press release observes, the threatened changes are “beyond catastrophic”.

One of Britain’s most distinguished climate scientists, Professor Kevin Anderson of the Tyndall Centre for Climate Change Research,  (archived by  10/01/2010): “I think it’s extremely unlikely that we wouldn’t have mass death at 4°C. If you have got a population of nine billion by 2050 and you hit 4°C, 5°C or 6°C, you might have half a billion people surviving.”

Ultimately, the only way humanity can cope with climate change is not to go there in the first place. That means far-reaching action to cut greenhouse gas emissions — starting now.