Seas and Soils Emerge as Keys to Climate
Published: May 16, 2000
(Page 2 of 2)
This much warming, the experts say, would bring rising seas, more severe droughts, rainstorms, heat waves and floods, along with broad shifts in climatic and agricultural zones that would benefit some regions but seriously harm others.
Environmentalists and some parties to the Kyoto Protocol, especially the European Union, strenuously object to allowing any country to meet all or most of its emissions reduction goal by expanding carbon sinks.
''Sucking carbon out of the atmosphere is not the same as preventing it permanently from leaving the exhaust pipe or power plant,'' said Jennifer Morgan, director of the World Wildlife Fund's climate change campaign.
Environmentalists argue that since forests can always be cut down as well as planted, and soils can always be plowed up as well as conserved, the terrestrial biosphere is not nearly as secure a carbon reservoir as the underground reservoirs where coal, oil and gas are contained. So, they say, why remove them from that secure spot in the first place?
They also fear that reliance on sinks to meet the Kyoto targets could delay the adoption of measures to reduce fossil fuel use and replace it with other energy technologies.
In any event, scientists say, carbon sinks will eventually probably reach a saturation point, at which they will be unable to absorb any more carbon dioxide. The dominant view therefore remains that if the world is serious about reducing and stabilizing the atmospheric concentrations, emissions must be cut at the source by burning fossil fuels more efficiently, switching from relatively high-carbon fuels like coal to lower-carbon natural gas, and replacing fossil fuels altogether by alternatives like hydrogen fuel cells.
Given the slow progress in that direction, though, proponents of the carbon sink idea argue that it could be a valuable interim measure.
In many ways, however, human activity has been shrinking carbon sinks rather than expanding them. Deforestation and farming have obliterated great stretches of forest and grassland that once absorbed carbon dioxide. Farming has also chopped up soils in ways that cause them to give off carbon dioxide rather than to sequester it.
In fact, said the scientific report issued in Montreal, human use of the terrestrial biosphere, including the burning of wood, has released some 135 billion tons of carbon into the air since 1850 -- about half as much as has been emitted by fossil fuel burning.
The net result of all this is that overall atmospheric concentrations of carbon dioxide are about 30 percent higher now than at the start of the industrial revolution.
A de facto counterattack has been under way for some time in the Northern Hemisphere, where the replanting of forests on deforested lands has made headway in recent decades. One provision of the Kyoto Protocol allows for industrialized countries to gain credit toward their reduction targets for tree planting since 1990 -- but also to incur debits for any deforestation since then. To reap meaningful credit, a country would have to show a net gain.
The protocol also allows countries to gain credit for reductions through a variety of other ways of expanding terrestrial carbon stocks should the parties to the agreement so decide. These include, for instance, expanding carbon stores in soil through no-till agriculture, in which no plowing takes place and seeds are sown in the carbon-rich detritus of the previous year's harvest.
Other possibilities include conversion of cropland into grassland, fertilization of pastureland and forest management practices designed to increase carbon stocks -- for example, lengthening the period between harvests of a forest's timber, or promoting faster tree growth and thicker stands of trees, plantation-style.
Estimates suggest that these kinds of measures might allow some countries to achieve large cuts in net carbon dioxide emissions. The potential of such measures in the United States, Canada and Russia is great, according to a recent calculation made for the World Wildlife Fund by Kevin Gurney, an atmospheric researcher at Colorado State University who studies the carbon cycle.
Mr. Gurney estimated, for example, that without planting any trees, the measures would potentially enable the United States to remove about 150 million tons of carbon a year from the atmosphere. This exceeds its Kyoto emissions reduction target by tens of millions of tons. ''They're pretty big,'' Mr. Gurney said of the estimates.
The Montreal report estimated that in theory, measures other than tree-planting by the industrialized countries could remove nearly 290 million more tons of carbon a year from the atmosphere by about 2010 than are removed by such measures now. By comparison, the Kyoto Protocol would require the rich countries to cut emissions by about 200 million tons a year below 1990 levels by about 2010.
The report also raised caveats about how much of this estimated potential might be achieved. Even with ''an ambitious policy agenda,'' it said, the estimates were ''likely to be on the high side.''
Far smaller gains could be achieved by the rich countries by planting trees and slowing deforestation, the report concluded. It said that a 20 percent increase in forest planting would probably offset no more than 3 million tons of carbon emissions a year, while slowing deforestation by 20 percent could offset about 18 million tons.
Even if the potential for carbon sequestration can be realized to a substantial degree, many headaches still present themselves. For instance, forest growth is spurred -- and terrestrial carbon stocks are increased -- by a warming climate, and by rising levels of carbon dioxide and of atmospheric nitrogen deposited on forests as a result of industrial emissions.
In assessing a country's carbon stocks for purposes of assigning credit, how can these effects of human activity be separated from the growth in carbon stocks brought about by tree-planting efforts alone? It is almost impossible to make such a separation, Dr. Watson said.
Another difficulty for some kinds of carbon sequestration efforts is that of monitoring and accounting for carbon stocks. Although there are well-established means of measuring the increase of carbon in a stand of growing trees, other sinks may present problems. One way to get around the difficulty in the case of agricultural soils might be to set up a business-as-usual control plot, in which conventional farming methods are used, against which to measure the change in carbon stocks as a result of no-till farming.
Then there are ecological concerns. For instance, managers of carbon-sequestration projects might be tempted to replace naturally functioning forests with tree plantations, which in biological terms are comparatively poor and sterile, with little of the biological richness and variety of the wild woods. Likewise, managers might be tempted to cut down mature forests so as to plant new, faster-growing ones that sequester carbon at a higher rate.
It is on questions of detail like these that the success or failure of the Kyoto Protocol may ultimately hinge.
Photo: A United Nations convention on climate change in Kyoto in 1997 led to an agreement to reduce emissions of carbon dioxide and other gases. (Associated Press)(pg. F4); (Angel Franco/The New York Times); (Linda Kahlbaugh for The New York Times); (Fred Bernstein for The New York Times); (Hannah Fairfield and Al Granberg/The New York Times); (Will and Deni McIntyre/Photo Researchers)(pg. F4) Chart: ''Manipulating the Carbon Cycle'' Scientists believe that more than half the carbon dioxide put into the atmosphere by the burning of fossil fuels is absorbed by the earth's oceans, plants and soils. The rest of the carbon dioxide remains in the atmosphere, trapping the sun's radiation and warming the earth. Researchers are now exploring ways to reduce atmospheric carbon dioxide further by expanding plant and soil carbon reservoirs, or sinks, on land. THE GLOBAL CARBON CYCLE Carbon atoms -- many in the form of carbon dioxide, organic compounds, fossil fuels or carbonate rocks -- cycle through the earth among air, water and land. Ocean MARINE PLANTS, ANIMALS Carbonate shells fall to the ocean floor when an animal dies. Respiration and Decomposition A carbon atom, on average, will remain in the ocean for 350 years as aquatic life uses it in photosynthesis and respiration. Land and the Living Earth The average residence time for carbon on land is 35 years, but atoms can be buried for millions of years, becoming fossil fuels if subjected to high temperatures and pressures Atmosphere On average, an atom stays in the air only five years before it gets cycled. Carbon taken up by plants may return to the air through decomposition and other processes, or it may be buried. Combustion For 10,000 years, the amount of carbon in the atmosphere was stable. But since the advent of industry in 1850, levels have been rising. The Route to a Cleaner, Perhaps Cooler, Earth: Pulling Carbon Out of the Atmosphere . . . Scientists on the United Nations' Intergovernmental Panel on Climate Change suggest that increasing plant and soil sinks in industrialized countries may help those countries meet quotas for emissions reduction. SOME RESEARCHERS PROPOSE TO: Plant forests and lengthen the period between timber harvests to extract carbon from the atmosphere. Convert cropland into grassland because plowed land releases carbon dioxide rather than absorbs it. Use no-till agriculture, in which seeds are sown in the unplowed soil of the previous harvest. ... Or Not Putting It There at All? Some environmentalists question this strategy, arguing that added carbon sinks are a less reliable approach and that they have limits in their capacity to store carbon. SOME ENVIRONMENTAL GROUPS WOULD RATHER ENCOURAGE: Using nonfossil fuel energy sources like solar power and hydrogen fuel cells. Switching from high-carbon coal to lower-carbon natural gas. Finding greater efficiency in burning fossil fuels. (Sources: Biology of Plants, by Peter H. Raven, Ray F. Evert and Susan E. Eichhorn; William H. Schlesinger, Duke University)(pg. F1)