Question: What is a basic definition of climate change?
James Hansen: Yeah. Well, human-made global warming is caused by changes in the atmosphere which are due to burning fossil fuels, primarily. As we burn oil, gas and coal, this releases carbon dioxide to the atmosphere. And carbon dioxide absorbs heat radiation from the earth, and that traps the heat radiation and makes the planet a bit warmer. So we notice that the world has warmed up about one and one-half degrees Fahrenheit in the last century, with most of that warming in the last 30 years.
Question: What is the latest conclusion on CO2 emissions?
James Hansen: Yeah. Well, there's now 387 parts per million of CO2 in the atmosphere. A hundred and fifty years ago it was 280, so it's increased by 107 ppm. What we thought a few years ago was that it would probably be safe to let CO2 go as high as 450 parts per million. The reason we thought that was that we know that there were previous periods in the earth's history called interglacial periods -- we're now in a warm interglacial period, which we have been in for about 12,000 -- but there were prior periods when the earth was warmer than it is now, and the planet was still pretty much the way it is now. And we thought that -- it was then about a degree or so Celsius, which is about two degrees Fahrenheit, warmer than it is now -- and we thought that might be okay to be that warm. And 450 parts per million would probably take us to that sort of a climate.
But what we now realize is that during those prior warm periods, sea level was about six or seven meters higher than it is now. And also we see what's happening with the current 387 parts per million. That's already enough that the arctic sea ice is melting, mountain glaciers all around the world are melting, which is going to affect the fresh water supply for billions of people. The climate zones are shifting, so the southwest United States and Mediterranean region are becoming hotter and drier; likewise Australia. So you see increased forest fires and reduced water supplies in those regions. Coral reefs are already under stress; many of them are going to be lost if we continue with increasing greenhouse gases. So we realize already that 387 is actually too large. About 350 parts per million is a more realistic target, and that means we're going to have to phase out use of coal over the next couple of decades if we want to be able to get back to 350 parts per million.
Question: Are you critical of the use of fossil fuels?
James Hansen: We simply -- if we look at the fossil fuels and we see how much carbon there is in oil, gas and coal -- and by far the largest is coal -- and we know that we're going to use the oil and the gas; they're very convenient fuels. The big pools are owned by Russia and Saudi Arabia. They're certainly going to sell that gas and oil. If we want to be able to get back to 350 parts per million, it's this huge coal reserves that we're going to have to leave in the ground. Or we could burn the coal and capture the CO2 and put it back in the ground, but that's very difficult. We're going to have to move beyond fossil fuels sometime within the next century anyway, so why not do it now and preserve a climate that will allow our children and grandchildren to have the same sort of planet that we enjoyed, and with all of the species that are still on the planet? [00:05:09.00]