All scientific indications suggest that the Earth is fast reaching a tipping point, a point of irreversible damage to life on the planet. Already animals and plants are becoming extinct at never before seen rates, some at 1,000 times more than before, and oceans are becoming too acidic and warm to sustain coral reefs, which are considered the lungs of the oceans. Maria Armoudian spoke with world-renowned climate scientist James Hansen about the science and politics of climate change.

James Hansen is head of the Program on Climate Science, Awareness and Solutions at the Earth Institute at Columbia University. He is an expert in climate science and is the author of Unprecedented Crime: Climate Science Denial and Game Changers for Survival.


This interview has been edited for clarity and length 

Maria Armoudian: Let’s try to cover both the science and the politics and let’s start with the science. You have looked at Earth temperatures from as far back as 1880, how are these temperatures measured and verified from that far back?

James Hansen: Well, we have to rely on measurements that were made by weather stations for much of that period and of course, those were not designed for measuring small long-term climate change. But they are good enough that we can infer with reasonably high accuracy how temperature has changed. And of course, there are many other ways to verify that, for example, by looking at ice melting and by looking at temperature profiles within the ground because a temperature change at the surface does move into the ground and you can actually measure in these bore holes that have been made by oil companies and mining operations, you can measure how the temperature changes as a function of depth. So there are various ways that you can get the temperature and we know that the world has warmed up by about 1.5 degrees Fahrenheit over the last century and over land areas it is about 2.5 degrees. But you know, that is not very large compared to weather fluctuations that can happen from day to day or even season to season, year to year. And that is one of the confusions in trying to inform the public about the reality of this change…So things are happening scientifically we can see, but communicating this to the public is still a challenge.

MA: And is it because when you look at 1.5 degrees or 2.5 degrees people generally think oh well you know it is not that big of a deal?

JH: Yeah, that is a big part of it because it would be true if that was the only thing changing, your local temperature by that amount, it wouldn’t be a big deal. But the problem is that the climate system we have had for the last ten to twelve thousand years has been a fairly stable climate and civilisation has adapted to that. And we can pass tipping points in the climate system where we begin to get dynamical changes occurring that could be outside of the ability of humans to control. For example, you mentioned one of them and that is species extinction. Because as we drive some species to extinction that affects other species because of the interdependencies of them. And that situation can become nonlinear and you can get ecosystems that just collapse and you get a very much larger number of extinctions. And likewise ice sheets: Greenland and Antarctica are beginning to lose mass at a substantial rate of a couple of hundred cubic kilometres per year and that rate is increasing. If it gets to a certain point, those ice sheets can begin to collapse quite rapidly and we could get sea-level rise of several metres and we just don’t want to pass that kind of tipping point.

MA: What is the likelihood of that?

JH: If we stay on business as usual, the likelihood is practically certain. We know that from looking at the Earth’s history. If we go back to a time when it was 2-3 degrees Celsius warmer, the sea level was 25 metres higher. Now we don’t know exactly how long it takes the ice sheets to disintegrate and cause a large sea level rise, but they would certainly start to disintegrate and once that happens then you don’t have a stable sea level for a very long time and there is going to be enormous economic and social consequences of that.

MA: Speaking of the Earth’s history, if we go and look way back and we see that the Earth had an ice age, that has allowed some people to argue ‘Well these things are cyclical’. What is the reality with regards to the Earth’s history with an ice age, what caused that and the cyclical nature of temperatures?

JH: Yeah, that is absolutely right, the temperature of the Earth over the last two million years has been oscillating between glacial and interglacial times where temperature changes are five to ten degrees Fahrenheit on average. But what that actually shows us is how sensitive the climate system is. Those changes are driven and instigated by small perturbations in the Earth’s orbit. There is a very strong correlation of these changes in the Earth’s orbit with the changes in climate. When you get more sunlight at the high latitudes then it will tend to melt the ice sheets and expose darker ground underneath which causes more warming. And as the planet gets warmer, the ocean releases carbon dioxide. The temperature changes are primarily caused by the changes in the atmospheric composition and the reflectivity of the surface of the planet and we can use that information to see how sensitive the climate is to changes in atmospheric composition. And what it actually tells us is the climate system is very sensitive, it takes its time to respond and that is what makes this problem very difficult because the planet has only partly responded to the atmospheric gases that we have introduced, primarily by burning fossil fuels. There is more climate change that is in the pipeline. And we know this from looking at the planet’s energy imbalance because what greenhouse gases do, like carbon dioxide, they reduce the thermal emissions to space. So we have more thermal energy coming in from the sun then we have heat energy being radiated to space. Most of that energy is going into the ocean, so if we measure the ocean’s internal temperature very accurately we can tell how far the planet is out of balance. And what it tells us is there is approximately as much warming that is still in the pipeline even without any more greenhouse gases, approximately as much as has occurred already. So that is what tells us that we are already into the dangerous zone and we really are going to have to reduce the amount of CO2 in the atmosphere if we want the climate to stabilise.

MA: Now some of the people who have argued against the model that you have talked about which incidentally has been verified time and again, and the scientific journals have been arguing that the Earth would be able to heal itself, bring itself back into balance. Is it unlikely and if so why?

JH: Well the Earth would certainly come back into balance. The way it went out of balance is its absorbing more energy than it is radiating so it is going to warm up until it gets into balance. The problem is that that balance is going to be at a climate which is very different than the one that has existed the last ten to twelve thousand years.

MA: Now talking about this argument in terms of bringing it back into balance, it sounds like what you are saying is ‘Sure that could happen but it will probably happen in a long time from now?’

JH: Right, that is right. And it will happen with enormous consequences. Irreversible on any time scale that humans would care about and that is the changes in the ice sheets and sea level and the extinction of species.

MA: You have talked about climate-forcing agents. What are these climate-forcing agents both natural and manmade and how do they work?

JH: Natural ones include things like volcanoes. Another natural climate-forcing is the sun itself. It is not a constant star, it is a variable star, only slightly variable, its energy output varies by about a tenth of a percent over a decade. But now humans have come into the equation in a very big way. We have added enough CO2 to the atmosphere, increasing it from 280 parts per million which had existed the last several thousand years to about 389 parts per million. And so you can compare that with the solar variations and you see it is much larger than the natural solar variability. Volcanic variability can be as much as a few watts, but it is only there for a couple of years. In addition to CO2, we are also adding methane, nitrous oxide so the total greenhouse gas forcing by humans is about three watts. Humans however are also doing things that cause a cooling. We are putting aerosols like sulfuric acid, aerosols that volcanoes put out into the atmosphere in several different ways by burning fossil fuels. It is the air pollution that you can see. When the air pollution is enough that you can see a smoggy effect, that is due to small particles not to gases which you can’t see. Those small particles reflect sunlight so they have a cooling effect. But now, because the greenhouse gases have a much longer life and they just continue to accumulate we are now at a point where the human-made greenhouse gases are causing a substantially larger forcing than the cooling effect of these aerosols. So in understanding what is going on we have to look at all these different forcings, but the bottom line is that the greenhouse gas forcing is the largest one and it is the one that is increasing the most and that is why the planet is continuing to get warmer and warmer.

MA: You have talked about this tipping point before federal government bodies. What might a tipping point look like?

JH: Well that is a difficult issue to say exactly when you have passed a tipping point. Perhaps one of the most important ones and one that we can now identify and monitor quite accurately is the ice sheets because we have had this satellite called Grace which is a gravity satellite. It measures the gravitational field of the Earth with such a high precision that you can see changes in the mass of the Greenland ice sheet and the Antarctic ice sheet. And what we see is that the Greenland ice sheet initially during the first few years, 2002-2007, was losing mass at a rate of about 150 cubic kilometres per year. In the last few years that has accelerated to more like 250 cubic kilometres per year. In Antarctica, which was initially losing mass at about 75 cubic kilometres per year, is now losing it at a rate of about 150 cubic kilometres per year. Well if that curve continues to bend down and become more rapid, that will be a tipping point where it will signify that the ice sheets are beginning to rapidly disintegrate. And as I have mentioned that is a tipping point we don’t want to pass because once the ice sheets do begin to disintegrate rapidly, humans will have lost control. You can’t tie a rope around these ice sheets – they are of continental scale. So there is nothing you can do about it if they begin to disintegrate rapidly.

MA: And the consequences as they disintegrate rapidly are?

JH: Enormous for our children and grandchildren. We are not going to see big sea level changes in the next few years or even the next decade or two, although we can now measure how sea level is changing and it is going up about 3cm per decade, that is a little more than an inch. But if this rate of ice loss doubles a few more times then you are starting to talk about sea level rise that will become very important. And we know from the Earth’s history when the ice sheets do disintegrate the changes can be of the order of five metres in a century, which is one metre every twenty years.

MA: So in terms of the things that we have been seeing a little bit more of over the past decade, things like more intense storms and more frequent fires, are these related to climate change?

JH: If you look at the statistics then, yes there is a relationship there. You can’t blame any single event and say this one was caused by global warming, but we can see a lot of things happening. You know the Arctic sea ice is decreasing in area very rapidly and we are likely to have an ice-free Arctic within a few decades if we stay on business as usual. And we do see that the subtropics have expanded, that is an expected effect of global warming the expansion of this circulation cell which has rising oceans in the tropics and subsidence in the subtropics which gives rise to the dry subtropical conditions and on the average that cell has expanded by about four degrees of latitude. And we can see that in the southern United States and in the Mediterranean region, in Australia where the hot, dry conditions and resulting forest fires have increased in frequency and intensity and area, partly because of that climate change. Storms [are] a difficult topic, except that we can say that the stronger storms are going to get stronger. That includes both the storms that are driven by latent heat, that is energy and evaporated water, and that includes hurricanes, tornadoes, and thunderstorms. The strongest ones will get stronger because there is more water vapor in the atmosphere which provides more fuel for the storms. We will also see stronger frontal storms, the cyclonic storms because as the ice sheets begin to melt faster they will cause the high latitude oceans to remain relatively cool just because of the iceberg injection into the ocean. But the tropics are going to get warmer and warmer so we will have stronger temperature gradient and stronger frontal storms.

MA: You have been telling this to policymakers for thirty years. What has been your experience of this?

JH: In many cases the politicians are learning to accept the reality of climate change and the fact that it should have implications for policies. And those implications actually are consistent with things that we should be doing anyway to reduce our energy dependence on oil and other energy. But what we find is that policies that are proposed are not really successful, are not significant in actually addressing the problem. What began to be clear to me about ten years ago is the special interests are really driving the proposed policy changes. And the politicians have said to me ‘You are a good scientist, you should stick to talking about the science and not stick your nose into politics’. But what I have found is that if scientists don’t help connect the dots then the dots are connected in a way which is convenient for business as usual, for the fossil fuel industry which doesn’t solve the problem. Because the fundamental issue is that as long as fossil fuels are the cheapest energy then we are just going to continue to use them, somebody will use them.

MA: Now they are primarily cheap because we subsidise them, isn’t that the case?

JH: That is part of it. But also, we do not make them pay for the damage that they do. For example, to human health, air pollution due to fossil fuels has enormous consequences on human health globally but those costs are worn by the public, there is no cost at all to the fossil fuel industry. And so we have to put a gradually rising price on carbon emissions. The money that is collected in this fee, which should be a flat fee at the mine or the point of entry on oil, gas, and coal, that money should go to the public. That way the public would have the ability to adapt to the changing energy structure and invest in more efficient vehicles or changes to their heating system.

MA: I would actually like it if you could talk about your experiences, like what happened after your presentation to some of these entities like the task forces?

JH: That censorship has been occurring for decades all the way back to when I first started speaking in the 1980s. The first thing I realised was when I testified to Congress I found that my testimony had to be approved by the White House, which is true in both Democratic and Republican administrations. The constitution has the congress as controlling the purse strings and they need to get the best information that they can. But the other censorship is related to the public affairs offices which are headed by political appointees. Again, the purpose of public affairs should be to inform the public about the best available science, not about a political agenda.

MA: You are saying this as a result of having seen the censorship within two different administrations?

JH: Within several different administrations, yeah. It was in the middle of the Bush Administration when I gave a talk which really caused some annoyance at the White House, there were calls to NASA headquarters, public affairs tried to completely constrain me, I had to tell them what was on my calendar and I could not speak to any media without prior approval. And if they didn’t want me to speak to that media they would send somebody else. So there has been a variation in how intensely they tried to control the information that goes through the media. But to some degree it exists in all administrations.

MA: How have the media been in terms of explaining the science to the public?

JH: I have been around a long time and I can remember back to some times when we had reporters like Walter Sullivan at the New York Times who was really super. But the ability of the media to have a staff that can report science well has decreased a lot with time. And what has happened in the last few years is just remarkably bad. Just look at the situation now where a good fraction of the public now believe that global warming maybe a hoax.

MA: Where did that come from?

JH: Part of it is scientists are being hammered by the shock jocks in the media who promote this perspective and scientists are just not very good at hitting back in an equivalent fashion. Scientists tend to lose in such a confrontation.

This interview originally aired on the Scholars’ Circle. To access our archive of episodes and download this interview, click here.

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Disclaimer: The ideas expressed in this discussion reflect the views of the guest and not necessarily the views of The Big Q. 

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