The most shocking statement in the aftermath of Hurricane Katrina was US President George W. Bush's remark that "I don't think anybody anticipated the breach of the levees" that protect New Orleans from flooding. New Orleans is a city mostly below sea level, and must be protected by levees to keep water out. Concern that the levees might break in the midst of a powerful hurricane was widespread among scientists, engineers and emergency-preparedness experts. Yet Bush apparently did not know of these concerns, even days after the hurricane destroyed the levees and flooded the city.
There is a simple fact on display here, one that goes well beyond this particular hurricane, and even this particular president. There is a deep disconnect in US politics between scientific knowledge and political decisions. Bush bears much responsibility for this. He has proven to be one of the US' least knowledgeable presidents when it comes to science -- and one of the most ready to turn science into a political issue.
In recent months, Bush undermined biological theories of evolution in favor of Christian fundamentalist dogmas. He disdains climate science and public health science when it conflicts with the beliefs -- and interests -- of his core supporters. Simply put, Bush's record on science policy is miserable.
Climate scientists have warned for years that global warming caused by man-made emissions of greenhouse gases will generate more extreme storms. While there is no scientific way to link a particular hurricane such as Katrina to the long-term trend -- in the sense that Katrina might have been bad luck rather than a sign of man-made climate change -- the energy of hurricanes throughout the world has been rising markedly.
Bush, alas, led an aggressive effort to discredit climate science rather than to respond to its findings. He called for delays in reducing greenhouse gas emissions that cause global warming, which in turn causes the energy of hurricanes to rise.
According to the underlying science that Bush ignores, hurricanes take their energy from the warmth of seawater. That is why hurricanes occur in hot tropical regions, and at the end of the summer months, when the sea surface temperatures are at their annual maximum. Man-made global warming raises not only air temperatures, but sea-surface temperatures as well. Higher sea-surface temperatures translate into more powerful storms in the world's oceans.
Hurricanes are measured according to three dimensions: frequency, intensity and duration. The frequency of hurricanes has not changed much, if at all. The big changes are in hurricanes' intensity and duration.
Intensity measures a hurricane's force, which includes wind speeds, and there has been some recorded increase. The biggest change, however, has been in the duration of hurricanes: how many days each hurricane lasts.
Duration has risen markedly around the world. The total energy of a hurricane is found by multiplying the intensity of the hurricane by its duration. This, too, has risen sharply, and more is in store as temperatures rise.
Scientists and engineers who work on climate change stress that governments need to adopt two main responses. The first, called "mitigation," means reducing the amount of man-made climate change.
This can be done by changing the world's energy system to limit emissions of carbon dioxide into the atmosphere -- the main driver of man-made climate change. One option is a shift to non-carbon energy sources, renewable energy such as solar and wind power and nuclear energy. Another option is to combine carbon-based energy -- coal, oil and gas -- with new technologies that prevent the emission of airborne carbon.