Secretary of Defense Donald Rumsfeld was widely ridiculed some time ago for wading into the realm of epistemology (the study of "the nature of knowledge," according to one dictionary). Rumsfeld described national security threats in three categories: "known knowns," "known unknowns," and "unknown unknowns." His point, briefly stated, was that the greatest risks in the years ahead may come not from threats we've identified, but from those we haven't.
For all the ridicule he received, Secretary Rumsfeld may be right. Evidence comes in a recent study on the national security implications of global warming, by the Defense Department's widely respected Office of Net Assessment.
The Pentagon study examines national security risks posed by abrupt climate change. It looks closely at a scenario in which changes in ocean currents cause sudden shifts in weather patterns, including droughts, persistent typhoons and sharp temperature increases in much of the developing world during the next two decades. The collapse of the Gulf Stream causes temperatures in the eastern United States and western Europe to plummet more than 5 degrees Fahrenheit by 2020.
The results are dramatic: Mass migrations, declining agricultural productivity, conflict over access to fresh water. Tens of millions of Bangladeshis are forced toward India, causing border skirmishes; famines cause chaos in parts of China; serious strains emerge within the European Union over food and water supplies; droughts and windstorms hurt farm productivity in much of the U.S.; tensions among the U.S., Mexico and Canada over water rights grow heated; refugees from Caribbean islands stream to U.S. shores.
As the Pentagon study states, this scenario is unlikely but "plausible." A more likely scenario is gradual warming in the decades ahead, generating serious but less dramatic consequences.
The Pentagon study inevitably raises the question: how much do we know about climate change? It makes a big difference whether New York will end up as a refrigerator or toaster in the year 2050. Which one will it be?
Or, as Secretary Rumsfeld would ask: When it comes to climate change, what are the "known knowns," what are the "known unknowns" and what are the "unknown unknowns"?
Fortunately, we have a rich body of scientific knowledge to help answer these questions. Ever since the late 1980's, thousands of scientists from around the world have compiled peer-reviewed research under the sponsorship of the Intergovernmental Panel on Climate Change (IPCC). The U.S. National Academy of Sciences weighed in on these topics in 2001, at the request of the Bush administration.
Based on this body of work, here are few examples of non-controversial facts—what Mr. Rumsfeld would call the "known knowns":
- Concentrations of heat-trapping gases in the atmosphere have been climbing steadily since the beginning of the Industrial Revolution;
- Human activities—such as the burning of fossil fuels and deforestation—are responsible for this increase;
- Global average temperatures have risen by roughly 1 degree Fahrenheit in the past century;
- If emissions keep growing at projected levels, concentrations of heat-trapping gases in the atmosphere will reach levels unknown since the time of the dinosaurs during the lifetimes of children born today.
- Impacts will include heavier rainfall and faster drying of soils, with significant consequences for semi-arid regions such as the U.S. Great Plains.
- Impacts will also include higher sea levels, threatening coastal regions with increased wind and flood damage.
- Developing countries—in particular some of the poorest developing countries—will suffer more from global warming than wealthier ones.
And here are examples of items we don't know—the "known unknowns":
- Exactly how much will temperatures increase? (Scientists predict the global average temperature will increase anywhere between 2.5 degrees F. and 10 degrees F. this century, if emissions keep growing at current levels. A 2.5 degree F. increase might cause only minor problems; a 10 degree F. increase would be much more serious.)
- How will the weather change at any one location on the planet?
What about the "unknown unknowns"? By definition these require speculation, but what if undiscovered feedback loops in the atmosphere turned out to protect us from global warming? (Wouldn't it be great!) Of course, undiscovered feedback loops might do just the opposite, accentuating the buildup of greenhouse gases and making global warming worse.
Additional research in these areas is vital, as the Pentagon study suggests.
Unfortunately, research into these topics is underfunded and, in some surprising ways, misguided. A panel of the National Academy of Sciences recently found that the Bush administration's climate change research plan "lacks a commitment to provide the necessary funds." It also criticized the plan for failing to pay sufficient attention to research on the potential effects of global warming in different parts of the United States.
These failings fit a broader pattern. Notwithstanding Secretary Rumsfeld's comments, the Bush administration often adopts a blinkered and quite traditional view of the threats facing the country today. Environmental degradation—a nontraditional security threat—is routinely minimized or ignored.
At the National Security Council, for example, senior positions established during the 1990's to address environment and health issues have been eliminated (including a position I once held). At the Defense Department, similar positions have been downgraded as well.
More significantly, President Bush's opposition to domestic measures to control greenhouse gas emissions and reluctance to propose an alternative to the Kyoto Protocol, even after three years in office, suggests an assessment that these environmental threats are either unimportant or too difficult to tackle.
To be sure, the threat of terrorism is more immediate, but the destructive potential of environmental degradation is as great as many other perils that command attention. Some might even call the environmental threat "grave and gathering."
The devastating impact of turning away from environmental problems is nowhere more evident than in Haiti, where deforestation during the past few decades left hillsides bare and countless thousands in abject poverty. The loss of Haiti's forests has robbed whole communities of livelihoods and contributed to the turmoil sweeping the country. In contrast, the lush forests of the Dominican Republic—which end so abruptly at the Haitian border—offer a reminder that paying attention to natural resource management can help promote stability and prosperity.
When it comes to global warming, however, we do not have the luxury of comparing two terrains—one well managed, the other not. The most important heat-trapping gases circle the globe and remain in the atmosphere for decades. By continuing to pump these gases into the atmosphere at record rates, we are conducting a long-term experiment with the planet as a whole. Decisions we make today shape each breath our children and grandchildren will take many years hence.
President Bush's approach to global warming stands in stark contrast to the growing bipartisan support for serious measures to address the problem. Supporters of such measures include the Republican governors of the nation's two largest states, George Pataki of New York and Arnold Schwarzenegger of California, and the chairman of the Senate Foreign Relations Committee, Senator Richard Lugar.
Global warming presents a paradigm case of decision-making under uncertainty. Our decisions will never be informed by perfect knowledge. But that is no reason to turn our eyes from the risks.
As Don Rumsfeld once said: "there are also unknown unknowns—the [threats] we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tend to be the difficult ones."