What will happen over the coming century, with temperatures rising? The standard story is that our world will become a very unpleasant one. Famously, the chief scientific advisor to the British government, Sir David King, even envisions that an ice-free "Antarctica is likely to be the world's only habitable continent by the end of this century if global warming remains unchecked."

Nearly all discussions of the future impacts of global warming use the 2003 heat wave in Europe as their prime example. In Al Gore's words: "We have already begun to see the kind of heat waves that scientists say will become much more common if global warming is not addressed. In the summer of 2003 Europe was hit by a massive heat wave that killed 35,000 people."

Yet while we will see more and hotter heat waves, talking only about heat waves means we leave out something even more important.

The International Panel on Climate Change finds that the trends we have seen over the 20th century will continue, with temperatures increasing more over land, more in the winter and especially in the high northern latitudes: Siberia, Canada and the Arctic. In the wintertime, temperatures might increase 9F in Siberia compared to perhaps 5F in Africa. There will be an increase in heat waves and a decrease in cold spells.

Models show that heat events we now see every 20 years will become much more frequent. By the end of the century, we will have such events happening every three years. This confirms the prospect that we could be seeing many more heat deaths -- a tragedy that will indeed be caused by global warming.

But cold spells will decrease just as much as heat waves increase. In areas where there is one cold spell every three years, by the end of the century such spells will happen only once every 20 years. This means fewer deaths from cold, something we rarely hear about. It might seem callous to weigh lives saved versus those lost, but if our goal is to improve the lot of humanity, then it's important to know just how many more heat deaths we can expect compared to how many fewer cold deaths.