NEW YORK (BLOOMBERG) - What's so scary about climate change?

The term is not scary - at last not in a visceral, skin-crawling sense. Scientists have shown that the likely 2 degrees Celsius of global average warming to come this century will be extremely dangerous, but, you know, "2 degrees" is hardly a phrase from nightmares and horror films.

How about "rat explosion"?

As the climate warms, rats in New York, Philadelphia and Boston are breeding faster - and experts warn of a population explosion.

Like rats, humans are hardy animals, and we've adapted to all kinds of climates. So it can be tempting to brush off the prospect of 2 degrees of warming. Especially for Americans, who mostly use Fahrenheit. That 2 degree warming is Celsius. Think of 3.6 degrees Fahrenheit. Still not scared? Fine.

The physics of climate change doesn't have the same fear factor as the biology. Many living things are sensitive to small changes in temperature, so warming of 2 degrees Celsius will transform the flora and fauna that surround us in a big way.

Other life forms are also very sensitive to moisture, and so populations will crash or explode as anthropogenic climate change continues to make wet areas more sodden and dry areas, more parched.

And while extinctions may inspire a sense of tragedy, it's the creatures multiplying in outbreaks and infestations that generate horror.

As rat expert Bobby Corrigan of Cornell University has told various media outlets, rats have a gestation period of 14 days. The babies can start reproducing after a month. That means that in one year, one pregnant rat can result in 15,000 to 18,000 new rats.

Warmer winters will continue to dial up rat fecundity. People in urban areas such as New York and Boston are already noticing a lot more rats, not just in downtown alleyways, but even in the posh suburbs.

Rats are just the beginning. Biologists have calculated that with the expected warming this century of 2 degrees Celsius, populations of dangerous crop-eating insects are likely to explode as temperate areas warm, reducing crop yields by 25 to 50 per cent.

Similar horrors lurk offshore, where biologists have found that a population explosion of purple sea urchins - "cockroaches of the ocean" - is choking out other denizens of Pacific kelp forests. There's something deeply troubling about a single species taking over what was a diverse ecosystem.

In recent years, psychologists have accused conservatives of being more innately fearful than liberals, but that never quite squared with the fact that conservatives express less fear over environmental problems.

Some social scientists are finally starting to question the broad equation of political preferences with fear, recognising that different people fear different things depending on their upbringing, education and surroundings. But we're all sharing this warming planet, and at the very least surely we can unite against a future filled with rats.