Climate Change is Worse Than You Thought

Posted April 13, 2016

MP3 Excerpt of a talk by climate scientist Dr. James Hansen, delivered at Yale University on April 7 recorded and produced by Melinda Tuhus


Former NASA climate scientist James Hansen is one of the world's leading experts on climate change. He testified before Congress back in 1988 that global warming was already occurring due to the burning of fossil fuels, becoming one of the first scientists to go on record. He now works at Columbia University's Earth Institute, and in late March published an important paper in the journal Atmospheric Chemistry and Physics titled, "Ice Melt, Sea Level Rise and Superstorms: evidence from Paleoclimate Data, Climate Modeling, and Modern Observations that 2C Global Warming Could be Dangerous."

The paper posits that sea level rise is on track to occur faster and at higher levels than more conservative estimates, like that of the Intergovernmental Panel on Climate Change, or IPCC, have predicted. An agreement signed by 195 countries in Paris last year seeks to cut greenhouse gas emissions, but it's not remotely ambitious enough to limit global warming to the degree Hansen regards as necessary. Hansen is party to a lawsuit against the federal government filed by the group, Our Children's Trust, for not protecting young people and future generations from the ravages of climate change. On April 8, a judge ruled in favor of the 21 youthful plaintiffs, which moves their lawsuit one step closer to a trial.

Hansen visited Yale University April 6 through the 8 as the Yale Climate Change and Health Initiative's "Climate Change Leader in Residence." What follows are excerpts from his April 7 talk at Yale, where Hansen discussed his new study. He uses the term "paleoclimate" to refer to studies of the climate dating back hundreds of thousands of years. The term "forcing" refers to anything that forces the climate system to go out of equilibrium, resulting either in an increase in temperature, or a decrease, which is called a "negative forcing."

JAMES HANSEN: One of the other issues that I've wanted to raise and have tried to raise several years ago, but have not gotten any response from the [scientific] community, so I'll raise it again. And I raise it in this paper, I think, more clearly. And that is that I think the climate response function of climate models is too lethargic compared to the real world. You know, the paleoclimate evidence tells us that when ice sheets disintegrate they can disintegrate quite rapidly and give you several meters of sea level rise in a century, even though the forcings that caused those p changes were much weaker than the human-made forcing. I argue that when the ice sheets disintegrate it's going to be a very non-linear process, and is probably better characterized by a doubling time than it is by a more linear assumption.

But we don't know what the characteristic time would be, so I just say let's assume that there's up to five meters of sea level rise; there's ice equivalent to that, which is vulnerable to contact with the ocean, because the threat of rapid sea level rise is caused by the fact that parts of the ice sheets are in contact with the ocean, and that ocean water can cause relatively rapid melting of ice shelves, and once ice shelves are melted then the ice sheets can discharge icebergs to the ocean much more rapidly. And there's at least five meters of sea level rise in the West Antarctic, plus parts of East Antarctica and parts of Greenland, that is vulnerable to rapid change.

So it depends on what we do with our fuel use. If we stay on business as usual, and right now, as long as fossil fuels are allowed to be the cheapest energy, then regardless of these statements, that were made in Paris in December, those are practically worthless. If we stay on that path, I think we would get several meters of sea level rise this century. We say 50 to 150 years. But we have to keep our eye on Greenland and Antarctica the next several years and see how that rate continues to change. But, the question is, have we passed a point at which it's inevitable that we're going to lose the West Antarctic ice sheet? I'm not sure about that, but this amplifying feedback in the southern ocean has to make one very concerned.

We have to restore the planet's energy balance. As long as there's more energy coming in than going out, then ice is going to keep melting, and to restore the energy balance requires that we get CO2 to go down. And that's very hard, but that's what we're asking in the lawsuit that we filed against the federal government – or Our Children's Trust has filed against it. We're asking the government to give a plan for how they're going to reduce emissions at a rate that would be consistent with restoring the planet's energy balance in a century. And if we did that I think we could minimize sea level rise. We're not going to avoid it altogether.

BETWEEN THE LINES: An audience member asked what is the role of methane in Dr. Hansen's climate modeling. Natural or fracked gas is composed mostly of methane, which creates 86 times more global warming, unit for unit, than CO2 in the first 20 years after release.

JAMES HANSEN: Methane is actually quite important. The human-made methane increase also causes tropospheric ozone to increase and stratospheric water vapor to increase. So when you include those indirect effects of methane, the forcing is about 7/10 of a watt of meter squared, which is at least as large as the planet's energy balance. So if we would just stop the human-made emissions of methane, we could restore the planet's energy planets, if CO2 stayed the same. The reason you could restore it is that the methane lifetime is only about 10 or 12 years, so it would go back to its pre-industrial level. So it's a big factor; it has to be part of the plan for how we're going to restore the planet's energy balance. But unless we get CO2 under control, that methane knob is just not powerful enough, so I don't emphasize it. We've got to make policy makers think of the major knob, and that's the CO2 knob.

For more information, download James Hansen's paper "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 degrees ℃ C global warming could be dangerous" at

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