It's not too late
OP-ED By James Hansen
International Herald Tribune, Dec. 13, 2005
SAN FRANCISCO -- The Earth's temperature, with rapid global warming over the past 30 years, is now passing through the peak level of the Holocene, a period of relatively stable climate that has existed for more than 10,000 years. Further warming of more than one degree Celsius will make the Earth warmer than it has been in a million years.
Business-as-usual scenarios, with fossil fuel (CO²) emissions continuing to increase at 2 percent per year as in the past decade, will yield additional warming of two or three degrees this century. That implies practically a different planet.
The Earth's climate is nearing, but has not passed, a tipping point beyond which it will be impossible to avoid climate change with far-ranging undesirable consequences. These include not only the loss of the Arctic as we know it, with all that implies for wildlife and indigenous peoples, but losses on a much vaster scale due to rising seas.
Ocean levels will increase slowly at first, as losses at the fringes of Greenland and Antarctica due to accelerating ice streams are nearly balanced by increased snowfall and ice-sheet thickening in the ice sheet interiors.
But as Greenland and West Antarctic ice is softened and lubricated by melt-water, and as buttressing ice shelves disappear because of a warming ocean, the balance will tip toward the rapid disintegration of ice sheets.
The Earth's history suggests that with warming of two to three degrees, the new sea level will include not only most of the ice from Greenland and West Antarctica, but a portion of East Antarctica, raising the sea level by 25 meters, or 80 feet. Within a century, coastal dwellers will be faced with irregular flooding associated with storms. They will have to continually rebuild above a transient water level.
This grim scenario can be halted if growth of greenhouse gas emissions is slowed in the first quarter of this century. That requires two things: first, flattening out and then decreasing the rate of growth of CO² emissions, primarily through improvement in energy efficiency; second, an absolute decrease in emissions of non-CO² gases that also affect warming, particularly methane and carbon monoxide, and therefore tropospheric ozone and black carbon (soot) aerosols.
The action must be prompt. Otherwise, CO²-producing infrastructures that may be built within a decade will make it impractical to keep further global warming under one degree. Of top concern is the large number of coal-fired power plants that China, the United States and India are planning to build without CO² sequestration (the process whereby CO² is separated and stored in the ground).
CO² is a greenhouse gas. It absorbs the Earth's infrared radiation, reducing the emission of heat to space. This causes a temporary imbalance between the amount of solar energy absorbed by the Earth and the energy emitted to space, so the Earth will warm up until it restores energy balance.
The good news is that about 40 percent of annual fossil fuel emissions continue to be soaked up. And if we decrease CO² emissions and improve reforestation and agricultural practices, we could probably increase that percentage.
The bad news is that to stabilize the amount of CO² in the atmosphere may require reducing emissions by 60 to 80 percent. Yet, emissions have increased at the rate of 2 percent per year in the past decade.
In the long run, satisfying energy needs while decreasing CO² emissions will require developing renewable energies, sequestering CO² produced at power plants and perhaps a new generation of nuclear power. But emissions can already be reduced now with improved energy efficiency.
It is important that the United States, as a leader in technology and as the largest producer of CO² in the world, take the lead.
In general, industrial emissions of CO² are declining. The problem is emissions from power plants and vehicles. The solution in both cases depends on efficiency. We need to avoid building fossil fuel power plants unless and until sequestration is a reality. For vehicles, efficiency is critical because of the rapidly growing global number of vehicles.
In the United States, even though the number of vehicles on the road increases every year, we could stop increasing emissions by accepting even modest improvements in efficiency of about 30 percent by 2030. This could be done with available technology, and there's ample time to phase it in.
The accrued benefit in 35 years, even without the introduction of hydrogen-powered vehicles, is a savings of oil equal to more than seven times the estimated amount of oil in the Alaska National Wildlife Refuge.
Keeping the rise of global temperature below one degree Celsius is technically within reach. Everything depends on an informed public to bolster the political will of leaders across this warming globe.
(James Hansen is director of the NASA Goddard Institute for Space Science. This article was adapted from a presentation given Dec. 6 to the American Geophysical Union.)