If you drop a frog in a pot of boiling water, so they say, it will hop right out again. Frogs aren't stupid. Well, OK, but they're not THAT stupid.
However, if you put a frog in a pot of cool water, and gradually turn the heat up under it, the frog will not notice what's happening. It will happily sit there until the water boils, and it dies.
Now, I have never carried out this experiment personally — I prefer my frogs' legs fried — so I can't vouch for the truth of it. It's just a story the environmentalists like to tell. Besides, I already knew that human beings have trouble in detecting slow-moving threats. You can watch us failing to do it every day: we persistently ignore the fact that we are running into trouble at a civilizational level, even though the evidence is all around us.
The foundation of every civilization is an adequate food supply: human beings simply cannot live at the density of population that civilization implies without a reliable agriculture. But the supply of good agricultural land is limited, and the number of human beings is not.
You can postpone the problem for a while by increasing the yield of the available land: irrigate it, plant higher-yielding crops, fertilize the soil artificially, use pesticides and herbicides to protect the crops as they grow. But even these techniques have limits, and in many cases we have reached or exceeded them. So we are running into trouble. Why isn't anybody taking action?
Governments everywhere are well aware of the problem: we are now seven billion people, heading for an estimated 11 billion by the end of this century, and the food situation is already getting tight. So tight, in fact, that the average price of the major food grains has doubled in the past ten years. But everybody finds local reasons to ignore that fact.
The developing countries know that they are under the gun, because the standard predictions of global warming suggest that it is the tropics and the sub-tropics where the warming will hit food production first and hardest.
A (still unpublished) study carried out by the World Bank some years ago concluded that India (all of which is in the tropics or sub-tropics) would lose 25 per cent of its food production when the average global temperature is only two degrees C higher. China would lose an astounding 38 per cent, even though most of it is in the temperate zone. And all that is before their underground water sources are pumped dry.
Most governments in the developing countries know the facts, but the short-term political imperative to raise living standards takes precedence over the longer-term imperative to curb the warming. So headlong industrialization wins the policy debate every time, and we'll worry about the food supply later.
The developed world's governments do nothing, because until recently they secretly believed that the catastrophe would mostly hit countries in the former Third World. That would unleash waves of climate refugees, plus local wars and a proliferation of failed states, but the rich countries reckoned that they would still be able to feed themselves — and their military could hold the other problems at bay.
But what is becoming clear, just in the past few years, is that the developed countries will also have trouble feeding themselves. Part of the problem is that many of them depend heavily on underground aquifers for irrigation, and the water is running out.
It's running out even faster in China, India and the Middle East: for example, grain production has dropped by a third in Iraq and Syria in the past ten years. But it is hitting the big producers in the developed countries, too, and especially the United States.
For example, the amount of irrigated land in Texas has dropped by 37 per cent since 1975. The amount in Kansas has fallen by nearly 30 per cent in the past three years. And now it is becoming clear that the impact of warming will also be much greater than anticipated in the developed countries.
In these countries, the problem is extreme weather causing massive floods and prolonged droughts — like the heat wave that hit grain production in the U.S. Midwest last summer, or the coldest spring in 50 years in England, which has cut wheat yields by a third.
Combine the steep fall in irrigation, the crop losses to wild weather, and the diversion of large amounts of cropland to grow "biofuels" instead of food, and it is not at all certain that the developed world will be able to grow enough food for its own citizens in five or ten years time. So are the leaders of these countries launching crash programs to stop the warming, cut down on water losses and end the lunacy of biofuels?
Of course not. The smarter ones just reckon that since their countries will still be rich, they will buy up whatever food is available elsewhere and feed their own people that way. It will be other people, in other countries, who go hungry.
And the slower ones? They're just frogs.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries.