Zero Emission Network

"Why fast action on climate change is needed"

Transcript of presentation

Slide 1
Title

Slide 2
I'd like to point out that there's a large gap between what is understood about global warming and what is known about global warming. I mean, what is understood by the relevant scientific community and what is known by the people who need to know, and that's the public [and] the policy makers. Part of the reason for this is that the climate problem differs from previous global pollution problems in the sense that we don't see the effect immediately upon the emission of the gases, partly because of the . . . thermal inertia of the ocean, which is four kilometres deep and has a response time of several decades before we see 50 or 60 per cent of the equilibrium response. So there's more global warming in the pipeline due to the gases that are already in the atmosphere: about half of that effect is still to occur.

We also realise that there are positive feedbacks. The climate system, it turns out, is very sensitive to forcings because positive feedbacks predominate and the result is, when you combine the fact that we have the infrastructure that has a long-time constancy (the power plants and vehicles), we're at a point where it really is a crisis because the danger is that we're close to passing tipping points. We're close to a point where the rest of the Arctic sea ice can disappear quite rapidly, and we're close to the point where the West Antarctic ice sheet and the Greenland ice sheet could become unstable and begin to disintegrate out of our control.

Slide 3
And this is a little hard for people to understand because this is the global warming to date which is in the last hundred years, which is about 0.8 degrees Celsius. Three-quarters of that warming has occurred in the last thirty years but that's small compared with weather variations - the temperature depends a lot more upon whether the wind is blowing from the north or whether it's blowing from the south, than it does upon the changes of these greenhouse gases.

Slide 4
But even if you average the temperature anomalies over a month - and these are maps of temperature anomalies relative to the base period 1951 to 1980, when many of us grew up - so reds and yellows are warmer than that base period and blues are colder than the average for that base period. You can see that at a given place it might be warmer or colder than normal, even when you average over a month. But if you go to the next chart . . .

Slide 5
. . . which shows the average temperature anomaly for the first six years of this century, then the patterns begin to make a lot more sense, from a scientific standpoint. The warming looks just like what we expect, it's larger over the land than it is over the ocean because the thermal inertia of the ocean makes the response there smaller to date. And the warming is larger at higher latitudes than it is a lower latitudes because of the positive feedbacks at higher latitudes, especially the ice/snow albedo feedback which is a positive feedback because as you melt the ice and snow the surface underneath is darker and absorbs more sunlight. And also the warming is larger in the northern hemisphere than it is in the southern hemisphere because you've got more ocean in the southern hemisphere and the ocean around Antarctica mixes quite deeply so that the warming there is rather small. And of course a person doesn't tend to average the temperature over the last six years but you can see that it makes a lot of sense.

Slide 6
Now I don't know how many of you are scientists and are used to looking at graphs and charts, but I'd like to show this one, which is a little complicated, because I think it's helpful. You know, recently the NASA administrators said that it was arrogant of us to think that humans could control climate when we know that in the past the natural world has had much larger variations of climate - and of course that's true, there have been very large changes of climate in the past. But nevertheless humans are now completely in control of global climate and I'd like to try to make that clear.

What this shows is the oxygen 18 isotope measured in ocean sediments at many different places around the world ocean and at the times before there were ice sheets on the planet, the O18 isotope provided a measure - this is the oxygen in foraminiferous shells, microscopic animals that lived in the deep ocean and when they died their shells sink to the bottom and you have these layers of sediments and by taking a core you can sample the composition of these shells for the last 65 million years, in this case. You can see that over that time period the ocean has been becoming colder; it's about 10 degrees Celsius colder now than it was 50 or 60 million years ago. When we get into this period beginning about 35 million years ago when the first ice began to appear on east Antarctica, then this oxygen isotope depends on how much water is locked in those ice sheets, so it becomes a little more complicated on the black part of the curve - there are two variables that affect it.

But the point is that what's happening here is that in this time period, normally there's a balance between the carbon dioxide put in the atmosphere by volcanoes going off, and carbon dioxide removed from the atmosphere by weathering which converts the carbon dioxide to carbonate rocks, and you have a balance of that. But what's happening in recent times - the last 50 or 60 million years - is there's been strong orogeny (mountain building) because of the motion of the continental plates. In particular, the Indian plate has been crushing up against the Asian plate and causing the Himalayan mountains to rise up; and the Andes have been rising at a rate of about 1 mm per year, which may not sound like a lot but that's one kilometre in a million years. So this rather rapid mountain building has caused CO2 in the atmosphere to decrease. We don't have a very accurate measure of what it was 50 million years ago but it was probably of the order of 1000 ppm; it's now about 380 ppm. But this is of course a long time period. Let's look at the right-hand piece of this diagram in the next chart.

Slide 7
In the most recent 3.5 million years, you can see the oxygen isotope continuing to increase during this time period, which means that the temperature has been decreasing, and sea level has been decreasing during that time period. And you can see very regular fluctuations; those are rather strong climate fluctuations and for most of that period they have a regular 41,000 year periodicity. It gets a little more complicated in the last million years for reasons that we understand - I don't have a lot of time to talk about this. Let's go to the next chart.

Slide 8
The time period for which we can analyse these climate changes very well is the last 400,000 years (actually 700,000 years with the new ice cores) but this is the time in which we can analyse from the ice cores on Greenland and Antarctica. The Antarctic ice sheet is formed by snowfall piling up year after year and being compressed into ice as it gets thicker, and when we drill a core through that, we can sample the composition of the ice and, from the isotopic composition of the age and the oxygen, we can deduce the temperature at which the snowflakes formed. But also when the snowflakes are compressed into ice, they trap bubbles of air, so we can sample the atmospheric composition that existed throughout this time period. And what we see is that the temperature between the interglacial periods - and on the far right we have the Holocene: homo sapiens existed for maybe 150,000 to 200,000 years, so that's the right half of this diagram, but civilisation only developed in the last several thousand years during the Holocene period which is now almost 12,000 years long. So we've lived in this period of climate stability; humans have existed in this period. About 20,000 years ago - the depth of the last ice age - it was 8 degrees Celsius colder than during the current interglacial. Typically [there is] a 10 degree variation between the warm interglacial periods and the depths of the ice ages at the poles. But at the equator the temperature variations from ice age to interglacial are about 3 to 4 degrees and on a global average they are about 5 degrees.

Slide 9
We can understand quantitatively what the direct cause of these temperature changes was. One of the causes is the greenhouse gases. You can see this graph shows the carbon dioxide and the methane, how they varied over this same time period and you can see there is a high correlation of these gases with the temperature, and nitrous oxide also varied in a similar way. And those are the long-lived greenhouse gases in our atmosphere. But in addition what was changing was the area of ice sheets on the planet, so too were the surface conditions, the vegetation distribution and even the coastline, because the sea level was changing between the glacial and interglacial times by about 100 metres.

Slide 10
We can tell how big the ice sheets were because we have measures of the sea level throughout this time period. So we can calculate quite accurately the climate forcing due to both the greenhouse gas changes and the surface changes on the planet. Climate forcing is an imposed change of the planet's energy balance with space which would tend to alter the earth's temperature. And the greenhouse gases work by making the atmosphere more opaque in the thermal region of the spectrum where the earth's heat is radiated. So if the atmosphere is more opaque, the radiation to space emerges from a higher level where it's colder, and therefore in effect these greenhouse gases trap the heat radiation and so they are a positive forcing and you get more greenhouse gases. And ice sheets, as they get bigger, reflect more sunlight. So from the size of the ice sheets and from the amount of the greenhouse gases we can calculate the forcings and if we just multiply these forcings by the climate sensitivity, which we obtain both from climate models and from just looking at two points in the earth's history - say, the current interglacial period and the depth of the last ice age - and we infer that the sensitivity of the system is about ¾ of a degree for each watt of forcing, and then what the bottom curve shows you is that that sensitivity - this bottom curve, called calculated temperature - is simply multiplying ¾ of a degree for each watt by the number of watts in the climate forcings due to these two mechanisms. And what we see is that those two mechanisms account for the global temperature changes.

Slide 11
However the interesting thing is that those two mechanisms are both slightly trailing the temperature change. They're virtually simultaneous, as you can see in this chart, where I've graphed the greenhouse gas forcing and the temperature. And you can see there a remarkable correspondence, but the temperature change leads the greenhouse gas change by several hundred years on the average, and the same is true with the ice sheets. So both of these mechanisms are feedbacks, but they are indeed the primary causes of the temperature change, but they're doing it as feedbacks. And what is instigating these fluctuations from ice age to interglacial period is very weak forcings due to the earth's orbital changes.

Slide 12
The next chart shows the earth's spin axis which is tilted by about 23.5 degrees to the plane of the earth's orbit about the sun. But that tilt of the spin axis fluctuates from 22.5 to 24.5 degrees, the perturbations being caused by the other planets - Jupiter and Saturn tug at the earth, they are very heavy, and Venus comes very close - and we can calculate the perturbations of the earth's orbit. This is one of the perturbations; also the orbit is sometimes nearly circular and sometimes it's elliptical up to about 6% eccentricity. But this variation of the spin axis orientation is very regular at about 41,000 year periodicity and it's exactly in the variations that I showed you on an earlier chart for the earth's temperature and the sea level. Let's go to the next chart.

Slide 13
This again is showing the variations of temperature in the last 3.5 million years and, as I was saying, these variations up until the last million years, they were at a 41,000 year periodicity. The point is that when the tilt is larger, you're exposing both Antarctica and the north pole to more sunlight, at six month separations. So when the tilt is larger, the ice melts and the sea level goes up, and that's exactly what we see in the record. And then we get closer to the recent times, it got a little more complicated because a big ice sheet grew in North America and there was no way that a similar ice sheet could grow in the southern hemisphere because you had no land at the same latitude. So it became asymmetric and then this eccentricity of the earth's orbit also comes into play, but we don't really have time to talk about that in detail.

Slide 14
Now this chart shows the current recent times expanded; the timescale is expanded on the right. It shows that carbon dioxide and methane are now increasing off the chart, almost. And of course these are the anthropogenic effects primarily from fossil fuel burning. But we've now driven the amounts of these greenhouse gases far outside the range that has existed in hundreds of thousands of years, and we're even approaching the amount of CO2 that existed during the Pliocene a few million years ago.

Slide 15
So the implications of the palaeoclimate information is that climate on long timescales is very sensitive, even to small forcings. But the human-made forcings are now dwarfing the natural forcings that drove the glacial to interglacial climate changes, so it's clear that humans are now in control of global climate, for better or worse.

Slide 16
We understand this reasonably well, quantitatively. If we make simulations of the earth's temperature for the last century and put in the changes in greenhouse gases, and over that time period there are other forcings that are not negligible - and I don't have time to go through all of the climate modelling business and all the forcings, but the volcanoes, we have quite accurate measurements of stratospheric aerosols by volcanoes and those cause a cooling effect whenever big volcanoes go off; there are also human-made aerosols in the troposphere which we don't have as good measurements of, but with our best estimates for that, and using the model that has a climate sensitivity that's consistent with the palaeoclimate evidence for climate sensitivity, we get good agreement with the observed temperatures in the last century, the observations being the green line.

We can then project into the future for different assumptions about increasing greenhouse gases: the dark blue lines, like A1B, that's a typical business-as-usual IPCC scenario consistent with the growth rates in CO2 emissions that we've had in recent decades. I have also there what I call an alternative scenario in which I assume that we will begin to slow down the emissions of the greenhouse gases and actually get methane to decrease substantially. And that scenario was designed to keep the additional forcing in the next century less than about 1.5 watts, and that would keep additional global warming less than 1 degree, which is a rough idea of what we thought might constitute dangerous human interference.

Slide 17
The reason for trying to understand what is the level of global warming that is dangerous . . . All countries, 160 nations or so, have agreed on this Framework Convention on Climate Change that we should stabilise emissions at a level that prevents dangerous interference with the climate system.

Slide 18
So what is dangerous? Well, I think that the two things that are perhaps most important in defining that are ice sheet disintegration - because that would be irreversible on any timescale of interest to humanity, it takes tens of thousands of years to regrow an ice sheet - and the other thing is the extermination of species, which is also irreversible. And not to downgrade the regional climate dangers, which can be very important in different places, and also things like acidification of the ocean are important.

Slide 19
So then the question is, well, what amount of global warming would be dangerous, and again I think the best information we have is to look at the history of the earth. And what we see is that the warming that has occurred in the last century, and especially in the last 30 years, has taken the temperature back up to perhaps the highest in the Holocene, at least comparable to the warmest time in the Holocene 6000 to 8000 years ago. And it's not as warm as the warmest interglacial period: there were prior interglacial periods that were warmer.

This particular graph is for the western equatorial Pacific because if you want to look at a single place on the planet, this may be the most important one to look at because it's the warmest ocean on the planet and it influences the heat transport to higher latitudes in both hemispheres, by both ocean and atmosphere. But we're within 1 degree of the warmest interglacial periods and if we want to find a time that's 2 to 3 degrees warmer we have to go back to the Pliocene when it was a very different planet. There was no sea ice in the Arctic and sea level was about 25 metres higher, so 2 or 3 degrees warming I think is clearly dangerous and it would be crazy for us to allow the system to go there if we can avoid that.

Slide 20
Of course in the case of ice sheets and sea level, there is big uncertainty in how long it takes them to respond. But again I think there's a lot of evidence that has come to the fore in the last several years, mostly from the palaeoclimate data, as we get more specific data, and also from what we actually see happening, beginning to happen on the ice sheets, which is surprising a lot of people. For one thing, the area with summer melt has been increasing both on Greenland and on West Antarctica, as shown in this chart.

Slide 21
This is a picture of the summer melt, and to some degree that's always been occurring. But the area on which it's occurring, and the amount of it, is increasing. But it doesn't go off the edge of the ice sheet: it finds a low spot and bores a hole all the way through the ice sheet to the base of the ice sheet and that lubricates the base of the ice sheet and helps it move downslope toward the ocean more rapidly.

Slide 22
The next chart shows these giant icebergs being discharged to the ocean. The speed of these ice streams has doubled on Greenland in the last 5 or 6 years.

Slide 23
There was disagreement as to whether the increased snowfall due to the warming atmosphere was more important than the increased melting. Well, we now have these fantastic measurements from GRACE, the gravity satellite, which measures the gravitational field of the earth with such high precision that we can measure the mass of the Greenland ice sheet and the Antarctic ice sheet. What we find is that while during the winter the ice sheet gets heavier and then during the spring and summer it loses mass, the net effect in the last few years since this satellite began to take measurements has been a decrease in mass of about 150 cubic kilometres per year, which is not a huge amount yet, but sea level is now going up at a rate of about 3.5 cm per decade or 35 cm per century. But that's double what it was a couple of decades ago and it's four times what it was a century ago, and the concern is that when ice sheets begin to disintegrate it's a very non-linear process and there are multiple positive feedbacks. So you could reach a point where you begin to have very rapid ice sheet disintegration. And again the palaeoclimate record tells us that when ice sheets have disintegrated in the past, sea level has gone up rapidly. The last time, 14,000 years ago, sea level went up 20 metres in 400 years, which is one metre every 20 years. So ice sheets can disintegrate rapidly once they get started.

Slide 24
The next chart shows areas that would be under water if we got the 25 metre change in sea level that existed 3 million years ago. There would be 250 million people in China that would be under water with 25 metres, and the entire nation of Bangladesh and almost the entire state of Florida. So it's really a big deal and in fact we wouldn't expect that big a sea level change even in a century. But you could get a sea level change of metres in a century and that alone is enough to be disastrous for tens of millions of people.

Slide 25
Species are already under stress for a number of reasons that humans are mainly responsible for. But climate change, if it followed business-as-usual, would be a tremendous additional stress on species. The rate of movement of an isotherm now in the northern hemisphere land areas is about 50 to 60 kilometres per decade and species will migrate to stay within the climatic zones that they can survive in, but there are limits if you continue to . . .

Slide 26
I'll just summarise by saying that the polar species we're tending to push off the planet because there's no place colder for them to go. And also alpine species: as the isotherms move up the mountain, we will be pushing off the planet those species that live at high altitudes. And this is a particular example of a species that's under threat.

Slide 27
In the next chart I have a polar bear, which is an example of a high latitude species. But again if you look at the palaeoclimate record there have been large warmings several times in the earth's history - and these were typically 6 to 8 degrees Celsius warming - which resulted in the extermination of more than 90% of the species on the planet. And that's probably larger warming than I hope we will get due to human gases, but the human forcing is actually much more rapid.

The other variable that's different now is that humans have erected barriers to the movement of species. And there are natural barriers also - for Australia, of course, you've got coastlines. So I think that global warming of a few degrees is going to cause the extermination of many species. And then there are regional things, but let's go to talking about the solutions.

Slide 28
An important point which is not realised by everybody is that when humans put a pulse of carbon dioxide into the atmosphere, the decay of that is initially quite rapid, so 50% of it will get taken up, mostly by the ocean, but it's taken up within about 25 years. But after a century, a third of the pulse is still in the atmosphere and after 500 years almost a quarter of it is still in the atmosphere. The reason is that the CO2 that goes into the ocean in effect exerts a back pressure on the atmosphere and doesn't let in more CO2 until you get deep mixing. But then even when the ocean has mixed, until the CO2 is taken out by sedimentation, which takes formation of rocks, sediments with carbon, which takes hundreds of thousands of years, you're going to have part of the human emissions still in the atmosphere. And 500 years is eternity for all practical human purposes.

So then this question of the size of the fossil fuel reservoirs becomes an important boundary condition because if you look at the amount of carbon in the oil and gas, that's enough to put us up to something of the order of 450 ppm, which is enough to put us up to I think the dangerous level . . . [where] we get more than a degree of additional warming. And you know it's going to be very hard to prevent the use of oil: you can't tell Saudi Arabia not to drill for its oil. And [oil] is used in mobile sources; it's impractical to capture the CO2. But what we could do is decide that we're not going to use coal except in power plants where we capture the CO2 and sequester it. And put the same constraint on these unconventional fossil fuels.

Slide 29
Repeated chart.

Slide 30
I think that technically it's possible to keep CO2 at 450 ppm or less. It would require that we phase out the old-technology coal use, and use it only where we capture it and sequester it. Or phase it out over the next few decades. Also, though, it's important to stretch the conventional oil and gas because otherwise, if we just keep burning more and more each year, there won't be time to develop the technology for going beyond the petroleum era. I mean, there's pressure then to make liquid fuels out of coal or out of unconventional fossil fuels.

So I think that it's essential to have a price on carbon emissions, as well as efficiency standards, and that would be a natural way to avoid the mining of these unconventional fossil fuels like tar shale, which is just incredibly energy intensive to cook the Rocky Mountains and drip oil out of them, and it results in such a high amount of carbon going into the atmosphere.

And then I think the other two points are that the other forcings are not negligible. Right now the CO2 forcing is about the same as the sum of all the non-CO2 forcings, and some of these we could reduce the absolute amount in the atmosphere and it would make a lot of sense because it would reduce air pollution; especially in places like China and India it would be a great boon.

I suspect that we're going to get to the point where we actually realise that we've overshot, that we've got too much CO2 in the atmosphere and that we're going to have to try to draw some of it out. If it's only a little bit of an overshoot then it's practical to do that by means of improved agriculture and forestry practices.

Slide 31
As a former resident of Iowa, I like the idea of the Mid West in the US coming to the rescue of the coastal states, but you could burn biofuels in power plants, capture the CO2 and sequester it, and in that way you would draw down the amount of CO2 in the atmosphere. And to a limited extent that could help.

Slide 32
There's one important point. Although China is now passing the US and may have caught us in 2006 and if they didn't they will in 2007, because their emissions are going up rapidly, but it's not the current emissions that determine the climate change, because of the long life of the carbon dioxide in the atmosphere. It's the cumulative emissions that count. So the US is responsible for more than 3 times the climate change of any other nation and that will continue to be true for decades, even when China is emitting more than the US. But as I show in a bar graph on the bottom, Canada and Australia are about equally as bad as the US in terms of per capita contributions to the climate problem.

Slide 33
So in summary, I think that technically it's still possible to avoid the disastrous changes that I think would accompany business as usual, but we're not on that path. Even though there's a lot of talk about this problem, the emissions are increasing every year and in the last few years by just as much as they have in the past few decades. So although I think it's technically feasible to get on this alternative scenario and keep warming less than one degree, it's not happening. If we stay on [the current] path for even another ten years, then by 2015 emissions will be 35% higher than they were in 2000. And this alternative scenario assumes that by the middle of the century you're a few tens of per cent less than in year 2000. So given the infrastructure that would be in place for power plants and vehicles and everything, it just would be impractical if not impossible to get back on this alternative scenario. So I think the problem is really becoming urgent. And that's the end of my story.

Questions from the audience
Q: In Australia, a lot of the green groups are protesting about so-called "clean coal", which involves sequestration, and nuclear. What would your thoughts be on the efforts going into that?

A: What President Bush describes as clean coal, I would protest against too, because there are a lot of bad things in coal beside CO2, [such as] mercury, and that's the problem with this. The Chinese plants are really dirty and they're polluting the whole ocean and are going to affect fish for everybody in the world. But it is possible, I think, to have clean coal. There was a paper last year by House et al at Harvard which makes the point that if you sequester the CO2 beneath ocean sediments, it's inherently stable there, so you don't have to worry about it leaking out. In effect we're putting it back under ground where it came from. So I think it's possible to have clean coal, but it does have to be really clean coal, so it depends on what you mean by that. But it should have to compete against efficiency and renewable energies and the way you do that is you put an appropriate price on carbon. And in that case I think renewables and efficiency - there is a tremendous potential in these and it's not being realised because right now we're not only not putting a price on carbon, we are subsidising these fossil fuels in many countries. So I don't see any inherent problem with clean coal, I would let it compete but it may not do so well in that competition if it has to pay its appropriate price. Now nuclear is another issue. I think that the new technology nuclear can be much safer as far as having release of radioactive materials due to accidents, but there are other problems with nuclear including the waste disposal problem and the fact that you don't want terrorists to get their hands on the material. So it becomes a matter of individual countries deciding on what they want to do. But what I object to is, for example in Germany, they decided they don't want nuclear but instead they're making coal-fired power plants that do not capture the CO2, so they still don't get it, even though their leaders supposedly understand this problem. We cannot burn all of the coal or we're done for. All of that [?] in the atmosphere for tens of millions of years - you'd be talking about a completely different planet if we burn the coal without sequestration.

Q: At the beginning of the presentation, there was the notion of the gap between what the scientists understand and what the public and policy makers know, and given, if you look at the political elite, for want of a better term, a lot of them either don't want to listen or they hear it but they think that there's nothing they can realistically do about it. Why don't scientists, like James [Hansen], form their own political movement, because you'd certainly get the moral high ground.

A: I do think we have to do a better job of informing them and I think that we have this special problem that politicians like to get re-elected and they tend to require donations - I don't know if it's true in Australia, but in the United States it certainly is true that special interests have undue influence. I think the public has got to make clear to the politicians that this is a high priority and then they may begin to respond. But I don't know, it's a hard problem. I think Al Gore's movie has done some good in trying to educate and reduce this gap, but then many people consider that political, so it's a hard problem. I don't know, I don't have the answers.

Q: You mentioned biofuels. Do you think that kind of thing is feasible, considering the obvious limits on the world's agricultural output?

A: That's a good question. I should make clear that, boy, there are some biofuels and then there are others. What's being planned in the US right now is a disaster. Corn-based ethanol, if they make the amount that they're talking about, it's going to take land that's been put out of production - marginal land that is starting to grow natural grasses and trees - then plough it up for corn and you fertilise that, and it has many problems, and it raises the price of food worldwide. It just doesn't make sense. What I was talking about was using natural grasses and cellulosic fibres, things which you could do with no-till agriculture and which would not compete with food. You could do a limited amount that way, but vehicles are going to have to find a non-petroleum, non-CO2 way of propulsion in the future. We've got to go beyond that - there's just not enough land area to provide all of that fuel for vehicles.