PARIS: If Earth heats by 4°C the planet we call home would become a very unwelcoming place.

Even as some world leaders tamp down expectations for the December 7-18 UN climate conference, experts say the threat of a 4°C warming over pre-industrial times is all too plausible. Once that threshold is crossed, what might a four-degree world look like?

Brace yourself.

Oceans have risen by at least 3.25 feet, drowning several island nations and driving hundreds of millions of people in Bangladesh, Thailand and Vietnam and other delta nations to scramble for higher ground. Polar bears are a folk memory, starved to extinction in an Arctic where temperatures have soared by 15°C, nearly four-fold the global average.

Australia is routinely swept by white-hot fires of the kind that claimed 170 lives last February.

Asia’s eternal fountain, the Himalayan glaciers, are running dry. South Asia’s precious monsoon, once reliable as clockwork, has become fickle, dumping too little or too much rain.

“A 4°C increase in global mean temperatures has the potential to threaten human security and quality of life in a manner unprecedented in recent history,” says Arizona State University professor Pamela McElwee.

Britain’s Met Office, a leading centre on climate change, said the 4.0°degree rendezvous could come as early as 2060 — in time for you or your children to experience first-hand. Crossing that threshold, they conclude, would send the misery index into unchartered territory.

In 2080, three billion people would struggle to find adequate water. Yields of the major crops that feed most of the planet today would shrink, some dramatically, resulting in chronic hunger for tens, possibly hundreds, of millions.