Abstract
Why is there still doubt about the human contribution to climate change?
Is it too late to change people's minds?
The president of the American Association for the Advancement of Science and the Teresa and John Heinz Professor of Environmental Policy at Harvard's Kennedy School of Government, John P. Holdren focuses on the causes and consequences of environmental change, and energy technologies and policies. He is also director of the Woods Hole Research Center, which applies scientific and policy initiatives to environmental issues. The Bulletin's executive director Kennette Benedict recently spoke with Holdren in Chicago.
We have changed that composition with emissions of carbon dioxide, principally from fossil-fuel burning (75-80 percent) and deforestation (20-25 percent). We have changed it with additions of methane, nitrous oxide, and halocarbons, which like carbon dioxide are greenhouse gases that warm the surface of Earth. We have changed it with black soot from inefficient engines and burning biomass, which absorbs sunlight and thus warms the atmosphere. And we have also changed the composition of the atmosphere in some countervailing ways–namely with the addition of reflective and cloud-forming particles that tend to cool the Earth, partly canceling the warming effects of the greenhouse gases and soot.
The really striking thing is that the observed pattern of changes in the climate–not just the changes in global-average temperature, but greater warming at high latitudes than near the equator; greater warming at night than during the day; greater warming in winter than in summer; cooling in the stratosphere (the upper part of the atmosphere) while warming in the troposphere (the lowest region)–all match what would be expected to result from the measured increases in the atmospheric concentrations of these particular gases and particles.
A few have argued that variations in the sun's output, rather than human influences on the atmosphere, have been responsible for the observed changes in climate. But there are two powerful reasons we know that the sun is not the culprit.
First, for the last 25 years we've been able to measure directly, from satellites, the solar energy reaching the top of Earth's atmosphere, and the variation in this has been far too small to have produced the observed changes in climate over that same time period. The second reason is that if the sun were responsible, the pattern of change would be different than what has been observed and what is expected from greenhouse gases. For example, increased input from the sun warms the stratosphere as well as the troposphere, unlike greenhouse gases, which cool the stratosphere while warming the troposphere. The latter is what is observed.
People who claim that climate change is not being caused by human activities but by some other phenomenon need to meet a very large burden of proof. They need to explain what culprit other than greenhouse gases would be able to produce the observed changes, and they need to explain how it could be that greenhouse gases are not having the effects that theory and models predict they should have. No skeptic has done either thing.
And, more importantly, our understanding of what's going on in the climate is not based on the models alone. The ways in which climate has changed over Earth's history in response to natural influences–such as changes in Earth's orbit and tilt–augment solid theoretical understandings of how climate works and tell us much about what we can expect from the less gradual changes that humans are now imposing. Understanding of past climates is based on “reconstructions” from multiple lines of evidence including tree rings, corals, ice-core samples, layered sediments, and fossil pollens. Today's computer models of how climate will respond to human influences are consistent with what the paleoclimatological record tells us about the response of the climate to natural changes over geologic time.
On this basis we know that the so-called sensitivity of the climate is about three-fourths of a degree Celsius per watt per square meter of change in energy flow. And we can estimate quite well how much the human-caused increases in carbon dioxide, methane, soot, and so on have changed the energy flow. When you add it all up–taking into account the countervailing effects of reflecting and cloud-forming particles and the measured rate of heat storage in the ocean–you get the right answer for the observed rate of increase in global-average surface temperature over the last 120 years, which is the period when thermometer records have been good enough to tell us what that average temperature has been.
That observed increase is about 0.8 degrees Celsius, most of it having occurred since 1970. And because of the thermal lag of the oceans, we are in for another 0.6 degrees Celsius increase even if we don't change the atmospheric concentrations of greenhouse gases and particles any further. So the consequence of what humans have done to the atmosphere up until now is an eventual temperature rise of something like 1.5 degrees Celsius, which may already be enough to mean the end of coral reefs all over the world. It might also be enough to eliminate the Arctic sea ice in summer altogether, which would cause drastic changes in the climate of the Northern Hemisphere.
Two degrees, just a hair more than the 1.5 degrees Celsius to which we're already committed, might be enough to initiate irreversible melting of the Greenland ice sheet. No one knows for sure how rapidly this melting could occur, but a resulting rate of sea-level rise of as much as 2, 3, or even 4 meters per century cannot be ruled out. Until recently, most scientists thought sea-level rises of this magnitude would take thousands of years. But there is now evidence indicating that there have been earlier periods in Earth's history when the sea level went up by 4 or 5 meters in a century as a result of natural influences on climate no stronger than what humans are doing today. This new understanding indicates that the great ice sheets on Greenland and Antarctica have “tipping points” and that we may be close to one.
Another potential catastrophe is wildfires, which are very sensitive to humidity, soil moisture, temperature, and winds. We've had numerous instances of big wildfires in California and Colorado that did huge amounts of damage and could have done far more except that the weather changed just enough, just in time, to finally make them controllable. There's a real danger that wildfires will become a completely unmanageable, terribly devastating environmental problem for those places where they naturally occur now in milder form.
Another issue is heat waves. The 2003 heat wave in Europe that killed 35,000 people was estimated, based on statistics of the last few hundred years, to have been a 1-in-250-year event. By the time that it occurred, however, it had become a 1-in-100-year event. Under the “business as usual” rate of climate change, it will be a 1-in-2-year event by 2050. That's stunning.
Tropical forests and coral reefs, the two biggest reservoirs of biodiversity on the planet, are both acutely at risk from climate change. The coral reefs are at risk from a combination of heat stress–from the warming of the surface layer of the ocean–and increased ocean acidity. This acidity occurs because the part of human-produced carbon dioxide that doesn't stay in the atmosphere goes mostly into the ocean. The acidity effect alone, never mind the heat stress, could wipe out corals all over the world by 2030 or so. As for the tropical forests, the combination of partial deforestation and global climatic changes–which are, in part, a result of deforestation–is causing drying and periodic burning in forests that previously were too wet to burn.
Yet another prospective tipping point–one that has the potential to accelerate everything else we worry about–is the possibility of very large releases of carbon dioxide and methane from northern soils as they get warmer. There is about as much carbon stored under the tundra and the permafrost as there is in the atmosphere. If initial warming were to reach the point that, say, half of that carbon came out in the form of carbon dioxide and methane, we'd have a pulse of greenhouse gases in the atmosphere that would drastically amplify the greenhouse effect experienced up until that point. There are, in fact, already signs of increasing carbon dioxide and methane fluxes from far northern soils.
This drumbeat of science has contributed to a change in attitudes in the U.S. Congress. In 2005, a “sense of the Senate” resolution on climate change–calling for a mandatory, economy-wide approach to greenhouse gas regulation–passed with 54 votes. Support for this was led by Sen. Pete Domenici of New Mexico, the Republican chairman of the Senate Energy Committee, and Democratic ranking member Sen. Jeff Bingaman, also from New Mexico. It would have been unimaginable five years ago that such a resolution could pass in a Republican-controlled Senate.
Part of the reason that it happened is that the corporate sector has, remarkably, been clamoring for it. You have this extraordinary situation where many of the biggest and most successful energy-related companies in the country–General Electric, Exelon, Duke Energy, DuPont–are arguing for government regulation to curb greenhouse gas emissions.
Another remarkable indicator of the changing political climate was when the United Mine Workers (UMW) endorsed the climate-change proposal in the December 2004 report of the independent, bipartisan National Commission on Energy Policy, which I had the privilege of co-chairing. I believe the reason for the UMW's endorsement was that the commission proposed a two-pronged approach. It didn't simply recommend constraints on greenhouse gas emissions, but also endorsed a massive effort to develop and deploy the technologies that will enable coal-burning power plants to capture and sequester their carbon dioxide. The UMW understood that embracing this new technology, not hiding their heads in the sand, was the way that the coal industry was going to survive.
Initially, they wouldn't even take on an energy strategy, never mind the climate part. I and others on the President's Committee of Advisers on Science and Technology (PCAST) pushed in that direction, but we didn't really get anywhere until the very end of the first term and the beginning of the second. At that point, the administration did start to take on the task of developing an energy-technology innovation strategy for the challenges of the twenty-first century and also began serious work on a climate policy.
I don't know of any politician on the horizon who is willing to level with people and tell them what is necessary to curb climate change. It's almost like closing military bases; you probably need a bipartisan commission that looks at the evidence and sets the policy that we need and makes it acceptable. Right now, no politician is willing to enact a tax on carbon emissions.
Al Gore, who I have a lot of respect for, might do something, even though he and President Bill Clinton didn't do much when they held office from 1992 to 2000. The United States actually went up in its carbon emissions, from 22 to 23 percent. But if Gore were running now and elected, he may be able to do something since today the problem is widely recognized. There's some movement in Congress, but there are also dinosaurs in Congress who completely deny the science of climate change.
Those who deny climate change are clearly going to make fools of themselves in the long run. But that's little consolation if they're allowed to delay this for another decade, because we're running out of time.
The price on carbon emissions has to get up to around $100 per ton, because that's about how much it's going to take to make it economic to capture and sequester carbon dioxide from coal-burning power plants. If we don't do that, we can't solve the problem. The world's coal-burning power plants, all by themselves, are likely to push us past the 3 degrees Celsius level in global-average surface temperature if most of their carbon dioxide emissions are not avoided. And if we go that far–that is, beyond 3 degrees Celsius, I think we're cooked, literally. So we've got to get to $100 a ton, whether it's done with a carbon tax or emissions caps that are implemented through tradable permits. It would be easier in some ways to do it through a tax, since taxes are much easier to design, administer, and monitor than cap-and-trade systems. But we probably won't do it that way because “tax” is a dirty word in U.S. politics.
The current world energy system represents a replacement cost of about $12 trillion when you add up the value of all of the power plants, drilling rigs, oil refineries, pipelines, transmission lines, and so on. The average lifetime of these facilities is 30-40 years. That means we don't have the option of changing it overnight. If you want the energy system to look different in 2050 than it looks today, you have to start changing it now. And we need to invest substantial amounts of money now to get that change to happen in time.
The third thing is to do something about automotive fuel economy. One clever idea is “feebates”–a system in which you choose a level of fuel economy that you're shooting for, say 40 miles per gallon. Every car sold that gets more than 40 miles to a gallon gets a rebate in proportion to how much more it gets. Every car that's sold that gets fewer than 40 miles a gallon has to pay a fee in proportion to how much more fuel it uses. This generates a powerful set of economic incentives for people to buy more fuel-efficient cars. And you keep adjusting it to promote further improvements in fuel efficiency.
Some years ago, by the way, I suggested that the penalty for a country missing its Kyoto target should be a commitment to increase the amount of money to be invested in carbon-free energy technologies in proportion to the amount by which the target is missed. In other words, make the punishment fit the crime and make it palatable, because it's what the countries should want to do anyway if they're figuring out that climate change is threatening them. I still think this feature would be a useful element of the approach that needs to be devised to follow Kyoto.
One of the most interesting recent developments in the global arena is that the Chinese are figuring out that climate change is directly threatening them. They have estimated that the glaciers on the Tibetan Plateau that feed the great Chinese rivers are disappearing at a rate of 50 percent per decade. This means that the cycle of flood and drought that's always plagued China is going to get worse. Chinese scientists also believe that the monsoon disruptions that have been plaguing them for the last decade or so are being driven by global climate change. And these insights are changing the position of the Chinese leadership on climate policy. The old position was, “This might be an interesting problem, but our willingness to participate is going to depend on how much you pay us.” The new position is, “Climate change is harming China now, and we're going to have to participate in the solution, no matter what.”
The scientific, technological, and economics communities need to continue to strive for more comprehensive, more interdisciplinary, more accessible analyses of these matters, making clear what the economics, technology, and environmental science add up to when taken together. Of course, the world will continue to need lots of specialists in all the relevant disciplines, but it's increasingly important that a share of our brightest people become specialists in putting the pieces together and in communicating the big picture to policy makers.
There also needs to be a much larger effort in science education. In the end, what the public knows and can absorb is of real consequence for getting the policies right. It's interesting that in this country something like 90 percent of the public believes that climate change is happening and that humans have something to do with it. That doesn't mean that the whole 90 percent wants to do something about it. Still, 90 percent understanding that there is an issue here is a far higher number than the roughly 50 percent who believe evolution is a fact, so maybe there's hope.