The news is bad, and it’s coming in fast. Turn tens of thousands of scientists loose on a problem for two decades, and the results will seem pathetic for the first few years, because it takes time to gather the data — even to build the equipment with which you gather the data. But slowly the flow of data will grow, and at the end of 20 years you can expect major new insights every month or so.

That’s where we are now with climate change. September’s unwelcome news, from the Hadley Centre for Climate Prediction and Research in Britain, was that if fossil fuel use continues on the present trend line, the planet will be an average of 4 degrees centigrade warmer by the 2060s. This contrasts with the prediction of the Intergovernmental Panel on Climate Change, published in 2007, that we might see 4 degrees centigrade, at the most, by 2100.

This month’s bad news came from the drilling ship Joides (Joint Oceanographic Institutions for Deep Earth Sampling) Resolution, which brought up cores from the ocean bottom containing sediments dating back 20 million years. The news was that when the carbon dioxide in the atmosphere was last at 450 parts per million, the average global temperature was 3-6 degrees centigrade hotter than now. That is bad news because 450 ppm is where we are hoping to halt the rise in carbon dioxide in the atmosphere this time around. All the world’s major governments have agreed that the warming must never be allowed to exceed 2 degrees centigrade, because beyond that we risk runaway warming.

Not so, or at least not for long. The leader of the JOIDES research team, Aradhna Tripati, of the University of California, put it bluntly: “What we have shown is that in the last period when CO2 levels were sustained at levels close to where they are today, there was no icecap on Antarctica and sea levels were 25-40m higher.” Suspicions that the 450 ppm target is much too high have been growing for some time. Late in 2007 James Hansen, the director of Nasa’s Goddard Institute for Space Studies, made a public appeal at a meeting of the American Geophysical Union to move to a 350-ppm target.

Listen carefully

Hansen’s study of ancient climates had led him to the conclusion that the first time permanent ice appeared on the planet was when the amount of carbon dioxide fell to 425 ppm some 35 million years ago. His calculations had a possible error of plus or minus 75 ppm, so for safety’s sake he settled on 350 ppm as the long-term target for human stewardship of the atmosphere.

Hansen even thought that 350 ppm might still be too high, because the ‘normal’ level of carbon dioxide during the 10,000 years of human civilization was only 280 ppm. Now Joides has given us a more accurate measure of ancient climate, from closer to the present. By 20 million years ago, almost all the ice on the planet had been lost again, due to a prolonged period of volcanic activity in the Columbia river basin of North America. The carbon dioxide emitted by that activity had raised the average global temperature to 3-6 degrees centigrade above the current level. But the actual level of carbon dioxide that caused all that was only 400 ppm.

We will be there in five years, but we must not stay there for very long or history will repeat itself. In reality, we are going to go to at least 450 ppm before we get our emissions under control, and then we will have to commence the long and arduous task of getting the carbon dioxide in the atmosphere down to a level that will preserve our present climate. And all through that time, we must prevent the warming from exceeding 2 degrees centigrade, which means that the various methods of geo-engineering to keep the heat down are unavoidable. That is what these numbers are telling us, and we would be wise to listen.