Cilmate Control

In the last century or so, humankind has re-scripted its role in the natural world. We have learned to treat many dread diseases, feed billions of people, cut canals between continents, and harness the power of the atom. We've bent much of nature to our will.

But we still can't do a darn thing about the weather.

Though we are clearly learning to adapt to extreme weather, it still killed 19,000 people per year on average between 2000 and 2004, according to data gathered at the Center for Research on the Epidemiology of Disasters at the Universite Catholique de Louvain, in Brussels. In the United States, just one huge storm, Hurricane Katrina in 2005, killed at least 1,600 people and caused damage estimated at $81.2 billion.

Climate change, the alteration in the established weather patterns, is likely to bring still more economic, political and social havoc. Even the less extreme climate-change scenarios predict stronger and more frequent storms leading to more deaths and greater damage to property. In the more severe scenarios, cities -- even entire nations -- could disappear under rising oceans; once-productive farmlands parch; and vast swathes of ocean become increasingly acidic, sending out ripples of extinction.

Overwhelming scientific evidence indicates that the Earth has warmed noticeably over the past century and a half. Eleven of the last 12 years were among the warmest since global records began in 1850. The global average temperature is up almost 1 degrees C since that time. Sea level is rising by about 1 centimeter every three years, in part because the oceans absorb much of the increased heat and expand.

What is less clear is the extent of humankind's role in the change. The latest consensus of climate scientists, summarized in last February's report of the Intergovernmental Panel on Climate Change, is that by far the biggest component of the forces currently warming the Earth is the increasing concentration of carbon dioxide, and the source of that carbon dioxide is us.

Even if you differ with the panel's conclusion, you undoubtedly agree that variations in climate don't occur without a reason. Briefly, the observed global warming prior to 1950 is best explained by natural variations in the sun's brightness and volcanic activity. In contrast, the warming since 1950 defies explanation by any known natural cause. Yet it fits quite closely with what we would expect from the well-documented human contribution to increased carbon dioxide.

Among the strongest evidence is that the climate is changing with a geographic and altitude-specific pattern consistent with explanations based on greenhouse gases but not with other possible explanations -- including such oft-suggested alternatives as variations in the sun's brightness and intensity of cosmic rays.

Our influence on climate may be inadvertent, but it is a milestone in civilization's progress. We have, for the first time, the technological capacity to noticeably alter climate on a global basis within a person's lifetime. History suggests that our expanding population and increasing technological ability will cause this capacity to grow with time, not decline.

If not because of greenhouse gas emissions, it will be because of something else, such as changes in land coverage or the acidification of the ocean. The question now is: Should we strive to channel this capacity to our benefit, or should we struggle perpetually to avoid having any impact, for better or worse?

I believe the choice is clear. Whether we start today or in a decade, it is inevitable that we will begin to apply our new found capabilities to actively manage -- even engineer -- climate. In fact, it could be argued that our limited efforts to reduce greenhouse gases through the Kyoto Protocol represent a primitive form of engineering. It may be many decades before we have sufficient confidence in our skills to apply them more broadly, but there are moral as well as practical reasons to begin doing so.

We are wise to invest in technologies that will help us adapt to a changing climate. But by themselves, they will still leave us vulnerable. Engineering the climate could help transform the remaining risks into benefits: increasing global crop yields through longer and more predictable growing seasons, altering large-scale weather patterns to deliver rainfall where it is needed, and limiting the frequency and magnitude of deadly floods and other natural disasters.

Such engineering might also mitigate the natural climate change that has been a large and sometimes destructive force in human history -- such as the Little Ice Age that is linked to many famines in Europe between the 14th and 19th centuries. Providing food and water to a growing global population and shielding them to the greatest extent possible against the ravages of severe weather is both a moral and a practical obligation. If society has the tools to do this within acceptable risk levels, it should apply them.

Still, you may think the idea of intentionally modifying the climate is frightening or even repellent. If so, you're not alone -- it would be a high-risk endeavor and raises the ire of environmentalists and atmospheric scientists alike.

Some of our feelings about intentional modification -- climate management -- stem from the noble but naive expectation that all human influence on the climate can be eliminated. In truth, today we have likely already introduced irreversible ecological changes around the world. Among other things, as warming drives species northward, those in the polar regions have nowhere to go and may be long extinct before our efforts can cool the planet enough for them to survive.

The real debate is not how to eliminate all human influence -- that is an unrealistic and perhaps even meaningless endeavor. The more relevant issue is how much human influence our planet and its inhabitants can tolerate. Surprisingly, the "less is better" conventional wisdom on this point is overly simplistic.

Suppose we accept, as many climate experts have, that a realistic goal for the next few decades is to halt the growth of greenhouse gas levels rather than reduce it. In choosing the carbon dioxide level to stop at, it is quite possible that we will find that an atmospheric carbon dioxide level of 550 parts per million -- about twice the pre-industrial amount and a level we're likely to surpass before the end of this century -- will alter precipitation patterns over some huge swath of the globe to the relative benefit of farmlands, population centers, and globally important ecosystems, as compared to a little less or a little more carbon dioxide, say, 500 ppm or 600 ppm. Or we might find something else entirely. The point is, we won't know unless we ask the question and do the research.

Becoming climate managers will be one of the most difficult things human beings have ever done. It took relatively simple technology -- cars and fossil-fuel power plants -- to get to this point. It will take far more sophisticated stuff to get us to where we can confidently start deliberately altering climate.

Such "geoengineering" technologies are mostly just fantasy now. The roster of possibilities ranges from the aeronautical to the agricultural: putting up space shields that cover billions of square meters; using chemicals to reflect sunlight or increase Earth's cloud cover; stimulating massive growth of phytoplankton in the oceans; and huge reforestation projects. These sound far fetched, but as is true of most multi-generational technology development efforts, our early ideas probably offer only a glimpse of what will eventually unfold.

There is now a small but growing will to support geoengineering research, despite entrenched reservations about the idea. Yet, as difficult as it would be to develop geoengineering technologies, deploying them would be a hugely more challenging affair, requiring not just the engineering technologies but breakthroughs in climate forecasting, systems management, global politics, economics and social sciences.

Our tools and skills are clearly insufficient for climate management today. The consequences of mismanaging climate would certainly be global and could be catastrophic. We lack the scientific understanding to accurately predict the results of intentionally modifying the climate. And today we are missing the political system even to decide what sort of climate we want to strive for. But now is the time to commit to developing the tools we'll need.

One of the hidden dangers of delaying such a commitment is that gaining too much knowledge about the coming climate may be an impediment to making a better one. Our current scientific understanding is just beginning to support reliable climate predictions at spatial scales needed to determine which nations will benefit overall from the climate we are heading for, and which will suffer.

But within a decade or two -- perhaps sooner -- advances in our understanding of climate and the inevitable increase in computational power will likely let us predict who wins and who loses in considerable detail. At that point, those nations that believe they are winners will lose the incentive to support climate management efforts that lessen their advantage.

Any international consensus for action will dissolve. And progress toward global solutions will cease. The upcoming 10- or 20-year time frame may well provide us our last opportunity to establish a long-term international agreement on how to manage climate. It is a grace period we mustn't squander.