Now, the growth of China is part of a dramatic change, fundamental change, in the structure of the world economy. Just 25 years ago, the developing countries, the poorer countries of the world, were, notwithstanding being the vast majority of the people, they accounted for only about a third of the world's output. Now it's more than half; 25 years from now, it will probably be two thirds from the countries that we saw 25 years ago as developing. That's a remarkable change. It means that most countries around the world, rich or poor, are going to be facing the two fundamental transformations that I want to talk about and highlight.
Now, the first of these transformations is the basic structural change of the economies and societies that I've already begun to illustrate through the description of Beijing. Fifty percent now in urban areas. That's going to go to 70 percent in 2050. Over the next two decades, we'll see the demand for energy rise by 40 percent, and the growth in the economy and in the population is putting increasing pressure on our land, on our water and on our forests.
This is profound structural change. If we manage it in a negligent or a shortsighted way, we will create waste, pollution, congestion, destruction of land and forests. If we think of those three areas that I have illustrated with my numbers — cities, energy, land — if we manage all that badly, then the outlook for the lives and livelihoods of the people around the world would be poor and damaged. And more than that, the emissions of greenhouse gases would rise, with immense risks to our climate. Concentrations of greenhouse gases in the atmosphere are already higher than they've been for millions of years. If we go on increasing those concentrations, we risk temperatures over the next century or so that we have not seen on this planet for tens of millions of years. We've been around as Homo sapiens — that's a rather generous definition, sapiens — for perhaps a quarter of a million years, a quarter of a million. We risk temperatures we haven't seen for tens of millions of years over a century. That would transform the relationship between human beings and the planet. It would lead to changing deserts, changing rivers, changing patterns of hurricanes, changing sea levels, hundreds of millions of people, perhaps billions of people who would have to move, and if we've learned anything from history, that means severe and extended conflict.