Photograph by Timothy Archibald. Earth's rising temperatures are starting to affect plants and animals around the planet. Territories have moved, breeding seasons have shifted, and some organisms may already have gone extinct. Ken Caldeira of Lawrence Livermore National Laboratory in California takes the long view in understanding how to respond. Using computer models, he simulates Earth's climate into the distant past and far future. He also uses modeling to evaluate techniques that might stem the rising thermometer. Caldeira spoke with Discover associate editor Kathy A. Svitil.
What are the consequences of rising carbon dioxide levels? Researchers say Earth might warm two to five degrees Celsius [roughly three to nine degrees Fahrenheit] over the next century. A two-degree increase is like moving the climate bands 250 miles poleward in 100 years, or around 30 feet each day. Squirrels might be able to move at those kinds of rates, but an oak tree can't.
There have been reports that mountain glaciers are retreating. There are signs in Canada of tree diseases resulting from warm temperatures. There is some danger of peat bogs drying out and releasing methane to the atmosphere, thereby accelerating global warming. On the long-term scale, there is the possibility of destabilizing methane hydrates on the continental shelf, which will also accelerate global warming. So there is an array of effects. While the warming is global, the effects are local. With warming in California, for example, we'll lose snow in the Sierra Nevada mountain range. Here, it rains mostly in the wintertime, and the water is stored as snow. As it melts, it's distributed to farmers and homes and so on. If we lose that snow, we'll need to greatly expand the reservoir system, but dams are highly controversial here. So warming will cause ecosystem movements, changes to human infrastructure, unknown effects on agricultural systems.
Are there good ways to remove carbon dioxide from the air? The most benign one is to grow more forests, but the amount of land available is too small. Our simulations suggest that by fertilizing the oceans you might be able to pull 1 billion tons of carbon per year out of the air. Later in the century, carbon emissions are predicted to range upwards of 20 billion tons a year, so ocean fertilization might be able to take care of 5 percent of that.
You've also looked at injecting carbon dioxide into the deep ocean. How would that help? Some 70 or 80 percent of the carbon dioxide that humans release into the atmosphere will eventually be absorbed by the oceans, but the transit time is several hundred years. One idea is to get the carbon into the deep ocean right away. The downside is that we don't completely understand the impact of carbon dioxide on marine organisms such as coral, mollusks, and plankton, which make their shells or skeletons out of calcium carbonate. When water is enriched with CO2, it forms carbonic acid. Carbonic acid is corrosive to calcium carbonate. Studies suggest that coral reef growth might be reduced by 50 percent through the century because of the chemical effects of enhanced CO2. Plankton could also be seriously affected.
If you put more CO2 into the atmosphere, the ocean is going to eventually become more acidic anyway, but the acid will be distributed fairly evenly over the surface of the ocean. When you inject into the deep ocean, however, CO2 is put in as a concentrated fluid, and the effects will be localized.
What about ambitious proposals, such as using giant mirrors in space to deflect sunlight? My colleagues and I did computer simulations and found the engineering schemes worked well. They canceled most of the climate change and actually made plants grow more vigorously. But I think Earth is more complicated than our models and more complicated than our understanding of it. If humans attempt large-scale disruptions of the natural system, we're likely to screw things up. What we really need are strong, long-term reductions in carbon emissions.
Most of these plans would cost billions of dollars. Why should we be responsible for paying for something that won't be a big environmental problem for 100 years or more? There's no purely rational argument for why we should do something to help future generations. From an ethical point of view, however, we're the stewards of our environment, and we have an obligation to hand over a planet that is in at least as good a shape as it was when we got it.
What is the most promising alternative energy source? The key is having a portfolio of energy options. Wind is promising, and it would be helpful if it was coupled with a nationwide electrical distribution system. Fission power could be playing a much larger role, and I say that as somebody who used to demonstrate against it, in front of nuclear power plants.
You've criticized the Kyoto Protocol, the international accord to reduce greenhouse-gas emissions. Why? It's not enough to restrict emissions to several percentage points below the 1990 level, which Kyoto requires. Strong, long-term reductions in emissions are needed. Also, the Kyoto Protocol restricts emissions in industrialized countries but not in developing countries. Lastly, the amount that countries are allowed to pollute is based on historical patterns--how much those countries polluted in the past--so people who polluted a lot historically get to continue polluting a lot.
I would like to see a per capita emission allotment. That would give an incentive for everybody around the world to reduce emissions. With a per capita system, people from Botswana could sell their emission allotment to people from the developed world, giving them capital. Unfortunately, what I would like would never fly politically.
The Bush Administration, which hasn't ratified Kyoto, says it is instead committed to cutting greenhouse-gas intensity by 18 percent over the next decade. Will that help? It will help, but it's not enough. Greenhouse-gas intensity is the amount of greenhouse gases emitted per unit of gross domestic product, and we're expecting to grow GDP by more than 18 percent. So the Bush plan basically involves increased U.S. emissions. We need to decrease them.
Some researchers argue that Earth's climate is self-regulating. Do you see support for that idea? I do believe that there are feedbacks, many of them involving biological systems, which tend to stabilize the climate. But I don't think there is regulation in the sense that there is some special temperature, a set point, that Earth will keep itself at.
Life thrived when Earth was much warmer in the past. Why would it be bad if our planet warmed up again? What is unprecedented is the rate of change. When the dinosaurs were around, the carbon dioxide level was as high as we are likely to make it in the next century, and global temperatures were also high. But that earlier increase occurred over millions of years, so ocean chemistry and ecosystems could adapt to the new climate conditions. We're asking Earth to make the same kinds of transformations in a few hundred years.
What does Earth's long-term climate future look like? The sun, which is 30 percent brighter than it was early in Earth's history, will continue to get hotter and hotter. At first, carbon dioxide levels will drop and compensate for the brighter sun. Within a billion years there will be virtually no carbon dioxide left in the atmosphere. From then on, Earth will start heating. The oceans will evaporate more quickly, sending more water into the upper atmosphere, where it will be bombarded by cosmic radiation and split into hydrogen and oxygen. The hydrogen will escape into space, so we will eventually lose our oceans. At that point, Earth will be uninhabitable.