depths. A major challenge to sequestering the greenhouse gas is to find ways to reduce the cost of such storage to about $10 a ton, a goal the Department of Energy has set for 2015.
Sorting out how to best inhibit the harmful effects of human activities on the atmosphere will take on a new urgency in the coming years. The problem has important international economic and social implications—such as coastal submersion from rising sea levels, increased storms and flooding, and disruptions in agriculture—that reinforce the need for excellent science. The Bush administration’s emphasis on the use of fossil fuels for electricity generation and combustion engines does not bode well for reducing greenhouse gases in the near term.
Studies of ice cores from Greenland and the Antarctic continue to elucidate evidence that Earth goes through periodic temperature shifts short of full ice ages. Recent data indicate that this warming—cooling cycle occurs poles apart: When it grows colder in the Arctic, the southern polar region warms and vice versa. Work correlating rises and falls in Earth’s temperature with ocean circulation patterns may further explain the intricate interconnection that shifts the climate on scales of hundreds and thousands of years.
Climate changes of shorter scales, such as the phenomena known as El Niño and La Niña, present a challenge of even greater human immediacy. El Niño is a movement of warm surface water from the western Pacific to the eastern Pacific off South America. It is propelled by the Southern Oscillation, an unstable interaction between the ocean and the atmosphere. During an El Niño, the trade winds weaken and the warm water rushes east and releases more water into the air, which results in heavy rainfall over Peru and Ecuador. Far to the west, places such as Indonesia and Australia suffer droughts. La Niña is the reverse phase of the oscillation. So expansive is the area of warm Pacific water that it affects climate over much of the globe in both phases. The two strongest El Niños in more than 100 years occurred in 1982 and 1997, and some scientists believe this intensification was a result of global warming.
The introduction and refinement of plate tectonics provided a unifying theory that in the broadest terms explained the pattern of earthquakes and volcanic activity observed globally, such as the so-called ring of fire around the rim of the Pacific Ocean. Yet knowing generally where a quake might strike does not say when, and plate tectonics itself did little to provide the information needed to accurately predict temblors by precise time and location.