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Maps shows US having exceptional reabsorption of CO2 through new tree growth associated with reformation of forests removed in the 19th century

Fuel's Paradise NS 24 Oct 98 3

AMERICAN producers of fossil fuels must be rubbing their hands in glee. Forests appear to be soaking up virtually all of the carbon dioxide spewed out by American cars, power plants and factories (see p 5). With the help of a few trees from southern Canada, the US is declared innocent of greenhouse pollution. Global warming is no longer an American problem. What a gift to the fossil fuel lobbyists and what timing. On 2 November, representatives of the world's governments will meet in Buenos Aires to thrash out the finer details of the Kyoto climate treaty, which will oblige the US and others to reduce their C02 emissions. The US is already wrangling with the European Union, and the next step will be to try to squeeze the treaty past a hostile Congress. These are delicate times, and the new research looks set to upset the balance. Is the paper credible? In some ways, yes. it was published in a leading journal (Science), and by researchers who are universally respected. The results, however, are riddled with uncertainties. It is extremely hard to quantify how much carbon trees are absorbing, and whether they will subsequently release it through decomposition or fire. What's more, the researchers were forced to rely on data that-especially around Eurasia-are sparse, and on models whose assumptions are largely untested So although the researchers' best guess is that the US annually soaks up around 1.5 billion tonnes of carbon compared with Eurasia's 0.2 billion tonnes, their own large error estimates would allow an even split between the two continents, letting no one off the hook. And that's not counting tropical rainforests, which could be taking up large amounts of carbon, according to a paper in the same issue of Science. What, then, are we to make of all this? The researchers' eagerness to publish their findings in a high-profile journal is understandable, but unfortunate. Much more research is needed before these findings are nearly strong enough to inform policy. Yet reactionary forces out to destroy the Kyoto agreement will surely seize this tentative result and proclaim it from the rooftops. But they should first consider this: while many scientists doubt the size of the American carbon sink, most agree that some carbon is being taken up. Why? Because last century, the US, like Europe, chopped down its forests and flooded the atmosphere with C02 In many of those old, devastated sites, new trees are growing. But they are just making up for the excesses of the past. The effects of global warming will be everyone's problem, but the fault lies with some more than others.

Nov 98 Thriving rain forest absorb missing gas NZ Herald.

However another team reporting in Science have discovered that undisturbed rainforests are apparently growing faster indicating they may be absorbing more CO2 than indicated in the map at the top of this page. Tean member Dr. Yadvinder Malhi says there should be twice as much CO2 build up from fossil fuel and forest burning as we actually find.

A Perfect Excuse NS 24 Oct 98 5

THE US pumps around 1.6 billion tonnes of carbon dioxide into the atmosphere every year. But a new report claims that the nation's trees could be sucking up just about all this pollution. Critics say the results are unreliable. But their publication in a leading journal could be seized on by politicians who don't want to meet the US's commitment to reducing CO, emissions. Fossil fuel burning and deforestation bump up CO, levels in the atmosphere, but around 2 billion tonnes of CO, disappears every year into an unknown sink. To try to locate it, a team of American researchers called the Carbon Modeling Consortium divided the world into four regions-Eurasia, the southern continents and North America above and below 510 N. They used models to work out how atmospheric C02 should be distributed between these regions, based on the known carbon sources and sinks and estimates of how air moves between sites. To see where the extra carbon goes, they compared their simulations with measurements Of C02 taken between 1988 and 1992 from 63 sites around the world. To the researchers' surprise, almost all the carbon was being taken up by North America south of 51' N (Science, vol 282, p 442). They suspect that some of it is being absorbed by young trees in areas cleared in the Victorian era that have since been reforested. The rest could be due to improved fire prevention. But Stephen Schneider of Stanford University in California cautions that neither of these sinks would be long-term: when a forest matures, its emissions of carbon can grow to exceed the amount it absorbs. Another concern is that some of the new results conflict with other measurements. The researchers found that continents in the southem hemisphere appeared to be emitting carbon, which conflicts with a paper in the same issue of Science (p 439) reporting that Latin American tropical forests seem to be absorbing large amounts of carbon. David Schimel of the National Center for Atmospheric Research in Boulder, Colorado, adds that the researchers used data from a time when the global carbon sink was fluctuating wildly. He is also dubious about the size of the reported sink. "It suggests that the forests are storing carbon at rates close to their net photosynthetic rate," he says. "That's just not credible." Steve Pacala of Princeton University in New Jersey, a leading member of the Carbon Modeling Consortium, admits that it's hard to understand why American forests should take up so much carbon. He points out that there are many uncertainties; in particular, data for Eurasia are more sparse than those for America. "I will be very surprised if at the end of the day the sink turns out to be all in North America." However, with negotiations about emissions reductions between the European Union and the US at a delicate stage, the paper could throw a spanner in the works. Adam Markham of the World Wildlife Fund in Washington DC fears it will reduce the chances of the US Congress ratifying the Kyoto climate treaty. "There's a big potential for this paper to be misinterpreted and abused," he says. Gabrielle Walker

Growing Pains NS 24 Oct 98 20

IN COSTA RICA, money grows on trees. Thanks to a deal struck by the government, American and Norwegian businesses are about to pay farmers there to plant forests on their land. The farmers do not even have to produce timber-they just have to let the trees grow. The companies will pay the farmers $10 for every tonne of carbon that their trees absorb from the atmosphere and convert to plant tissue during photosynthesis. In return, the companies will get certificates declaring that they have paid for C02 to be removed from the atmosphere, or "sequestered". They are hoping that these certificates, known as carbon credits, will soon become valuable commodities. The deal will help fulfill the aims of the UN summit on climate change in Kyoto last December, which set targets for industrialised countries to reduce their emissions of C02 and other so-called greenhouse gases. The Kyoto protocol allows countries to meet part of their targets by planting forests to soak up C02 instead of making cuts. It also sets the scene for nations and businesses to trade in carbon credits. The Costa Rican government and its partners, which include the Norwegian industrial giant ABB and a Chicago com pany called Environmental Financial Prod ucts, believe they are in at the start of a multibillion dollar business. Whether or not they are right could be decided next month, when representatives of more than a hundred governments will meet in Buenos Aires to fill out the small print of the deal struck at the Kyoto summit. Costa Rica has already sold credits for more than 200 000 tonnes of carbon. Many analysts believe that once the system is up and running, carbon credits could change hands for $100 a tonne or more. If so, the companies that are buying credits in Costa Rica today for $10 a tonne could make vast profits. "The price is right," says Richard Sandor, the chief executive of Environmental Financial Products and a longstanding advocate of trading in environmental resources. But there is a host of practical problems with carbon sequestration. Most importantly, there is no way as yet to accurately measure how much carbon is absorbed or released by forests as they grow, die or burn. Even the European Union is unsure how much its forests are soaking up. After three years of examining satellite images and measuring the flow Of C02 above 17 forests, the EU's best guess is somewhere between 120 and 280 million tonnes a year (This Week, 3 October, p 20). John Lanchbery, who analysed the Kyoto agreement for the Verification Technology Information Centre in London, says it is inherently difficult to estimate how much CO, is produced or absorbed by biological activity. "The uncertainty can be well in excess of 50 per cent." For instance, different species grow at different rates. And trees assimilate carbon fastest when they are young and slow down as they get older.

To complicate matters further, the growth rates of trees depend on the cli mate, itself made increasingly uncertain by global warming. A drought could drasti cally slow the uptake Of C02, or even put it into reverse if the forest caught fire. Most of the carbon can be released from burning forests within a few days or weeks. And plant diseases, which themselves become unpredictable with climate change, can kill off vegetation, with similar effects. John Moncrieff of the institute of Ecology and Resource Management at the Univer sity of Edinburgh, who has been carrying out detailed studies of the Griffin forest in Scotland, points to other factors that affect carbon sequestration, such as the forest canopy closing as the trees grow, and the impact of other pollutants. Nitrogen oxides in acid rain, for instance, have a considerable effect on a forest's capacity for absorbing carbon. With no way of knowing exactly how much carbon trees take from the atmosphere, a reliable scheme to trade in carbon credits looks impossible. Yet new forests have a big potential as carbon sinks. In optimum conditions, tropical plantations can absorb up to loo tonnes or more of C02 per hectare in 50 years. if the UN's scien tific think-tank, the Intergovernmental Panel on Climate Change (IPCC), is correct in its 1995 estimate that a global reforesta tion programme could cover 350 million hectares-an area slightly larger than the EU-then this would lead to the seques tration of up to 35 billion tonnes of carbon in 50 years. That is equivalent to soaking up around 6 per cent of projected C02 emis sions between now and 2050 (see Figure). But ideal conditions seldom exist. And apart from the scientific uncertainty, there are other problems with sequestration.

Many conservationists believe that carbon credits could be disastrous for the world's surviving forests. Adam Markham of the World Wildlife Fund (WWF) in Washington DC fears that foresters will chop down existing natural forests to make way for fast-growing carbon-guzzling trees. In the process, the millions of people who rely on these forests will lose out. In addition, for maximum impact most carbon-sink forests would have to be in the tropics, where trees grow fastest. But there are huge competing pressures there. The UN's Food and Agricultural Organization estimates that an extra 90 million hectares of new agricultural land will be needed, mostly in the tropics, within the next decade alone. Carbon credits would have to offer higher profits than cash crops such as rubber and palm oil. Then there is the problem of what to do with carbon-sink forests once they have matured and are emitting, through decomposition, as much carbon dioxide as they absorb. These trees must then be removed or managed to ensure that the carbon they have locked up is not simply released again into the atmosphere. Others claim that carbon sinks will allow industrialised nations to simply put off the more difficult task of cutting pollution at home, or to wriggle off the hook of their emissions targets. For instance, foresters might sell carbon credits for forests they had always intended to plant, thereby reducing their targets without the environment gaining anything. Last year, the US government proposed that a scheme to pay Bolivian peasants to grow orchids should qualify for carbon credits on the grounds that it would discourage them from chopping down forests. Clearly, the rules by which countries can establish carbon sinks will be vital. But the Buenos Aires meeting will have to deliberate in a scientific fog-in June, the Kyoto protocol's science advisory committee referred crucial questions about carbon sequestration to the IPCC, which will not report until late in 2000. On the face of it, there is no hurry. The Kyoto protocol's targets do not come into force until 2008. But countries need to know what they are signing up to-without a clear programme for carbon sinks, the Clinton administration will find it much harder to sell the Kyoto protocol to a hostile Congress. Despite the uncertainties, the Kyoto pro tocol is already having a major influence on the shape of forests, says Nigel Dudley, editor of the WWF forest conservation newsletter. Many corporations are starting to plant trees and seek partnerships with conservation organisations Strong envi ronmental and social guidelines are ur gently needed, he warns. Without them, countries and businesses will pour money into projects that are at best useless, and at worst harmful. Fred Pearce

IN THE HEAT OF THE NIGHT Warmer nights may be slowing tropical forest growth and raising carbon dioxide levels

Researcliers working in Costa Rica have discovered disturbing evidence that increasing temperatures have markedly slowed the growth of tropical trees over the past decade. The slowdown may explain calculations suggesting that tropical forests, which are uaually considered to take up carbon dioxide, have actually added millions of tons of the greenhouse gas to the atmosphere each year during the 1990s, making them a huge net source, comparable iii size to the combustion of fossil ftiels. The trend could exacerbate global warming: as the mercury rises, tropical forests inay dump yet more carbon dioxide into the atmosphere, causing still more warming. In 1984 researchers Deborah A. Clark and David B. Clark of the University of Missouri, collaborating with Charles D. Keeling and Stephen C. Piper of the Scripps Institution of Oceanography in La jolla, Calif., began measuring the growth rates of scores of adult tropical rain-forest trees at La Selva Biological Station in central Costa Rica. The sample includes six different tree species, with both fast and slow-growing types represented. Using special measuring collars, the scientists obtain reliable data on aboveground growth each year. Deborah Clark presented the team's findings in August at a meeting of the Ecological Society of America in Baltimore. The group found that growth of all the trees fluctuated considerably from year to year. Moreover, the year-to-year changes correspond strikingly with the results of separate calculations of the size each year of a colossal unexplained tropical terrestrial source of carbon dioxide. In years when this theoretical source was large, the trees had grown slowly; in years when it was small or negative, the trees had grown faster. The apparent lesson is that the varying annual growth rate of trees in tropical forests could account, in large part, for a calculated increase in carbon dioxide released from land in the tropical zone in the 1980s and 1990s (although other sources, such as soil microbes, probably also contribute). Although trees take in carbon dioxide and release oxygen during photosynthesis, they also release some carbon dioxide as a by-product of respiration, as most organisms do. When growing vigorously, plants take up more than they produce. But if growth slows, the balance shifts. The annual excess of carbon coming from tropical forests, according to a preliminary calculation by Keel ing and his associates, has been more than four billion tons in some recent years. many researchers regard such estimates as provocative but not ironclad. The new data on tree growth "increase con fidence in Keeling's work," Clark says. For comparison, worldwide carbon release into the atmosphere from the combustion of fossil fuels is estimated to be about 6.5 billion tons each year. In an effort to understand what was causing the year-to-year variations in the rate of tree growth in Costa Rica, Clark and her colleagues evaluated climatic factors. They found that rate of growth was strongly linked to average temperature, slowing down in warmer years. The negative link was even stronger between growth rate and daily minimum temperature. "Tropical trees are being increasingly stressed through higher nighttime temperatures," Clark concludes. She thinks higher nighttime temperatures force the trees to respire more, thus promoting release of carbon dioxide. Yet warming does not increase photosynthesis, leading to a growing imbalance. The new information from Costa Rica has not yet been published in a peer-reviewed journal, so it remains to be seen whether the scientific community will accept it. Globally, daily minimum temperatures have been increasing faster than average temperatures, so the data suggest that tropical forests might become an even bigger net source of carbon dioxide in coming years. On the other hand, studies of trees in temperate regions indicate that artificially increased levels of carbon dioxide cause trees there to grow faster, which in principle might counter the heat-induced suppression of tree growth. But Clark's observations seem to suggest that the growth-slowing effect of increased temperatures in tropical regions is now stronger than any beneficial fertilizing effect from rising carbon dioxide. Lest anyone get the mistaken idea that destroying tropical forests would help, James T. Randerson of the Carne gie Institution of Washington notes that clearing a forest adds much more of the gas to the atmosphere than does leaving it be. Researchers believe that tropical forests account for about one third of all carbon dioxide taken out of the at mosphere by photosynthesis on land, making them a crucial part of the glob al atmospheric equation. The newly de tected slowing effect of temperature on tropical forest growth "could be a positive feedback" that will speed global warming, Clark warns. -Tim Beardsley in Washington, D.C.


Growth of atmospheric methane might soon abate

At December's climate talks in Kyoto, japan, helped to keep the world's attention firmly focused on the threat of greenhouse warming posed by emissions of carbon dioxide. And to good effect: if industrial nations can meet the targets they established, the heat-trapping veil of carbon dioxide should thicken less swiftly. But another, more subtle, event occurred last December that might also bode well for future climate. Researchers from the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado reported that methane, another potent greenhouse gas, appears to be accumulating in the atmosphere more slowly than anticipated. If this trend continues, the concentration of methane might soon stabilize, miraculously stemming some 20 percent of the burgeoning greenhouse problem. This news from NOAA's Edward J. Dlugokencky and his colleagues (delivered at the last meeting of the American Geophysical Union) represents a departure from previous conceptions. Researchers had known that the growth of atmospheric methane had been ebbing since comprehensive measurements began in the early 1980s. And they were aware of an abrupt decrease in the rising tide of methane and several other trace gases that occurred in 1992. But many, including members of the influential Intergoverrunental Panel on Climate Change (IPCC), regarded that sudden downturn as a short-term "anomaly." After all, the main sources of methanewetlands, rice paddies and livestockhad not gone away. According to their best guesses, the 1992 decline was caused, perhaps, by the drop in natural gas production (and, presumably, methane leakage from pipes) in the former Soviet Union. Or it came from the eruption of Mount Pinatubo the previous year, which reduced stratospheric ozone and allowed more ultraviolet light to reach the lower atmosphere, where it breaks up methane. So Dlugokencky's observation that the growth of methane has remained comparatively low for years after the atmospheric effects of Pinatubo subsided has sparked some rethinking. Inez Y. Fung, an expert on atmospheric methane at the University of Victoria in British Columbia, regards the new findings as "spectacular data," yet she emphasizes that most scientists are so far at a loss to understand what is behind the cliange. "Ed has presented for us a tremendous challenge," she notes. But Dlugokencky and his colleagues did more than just offer up data. They suggested that the slowing growth rate of methane can be explained by viewing the atmosphere as a chemical system approaching equilibrium on a timescale that is on par with the lifetime of methane-about a decade (it is broken down both by ultraviolet light and by certain chemical reactions). Asiam K. Khaiii, aii atmospheric scientist at Portland State University, has a different interpretation. He believes that methane is accumulating more slowly now because the long-standing link between methane sources and human population is weakening. But whatever the cause, if the current pattern holds, then stabilization between production and destruction is not far off. In contrast, the IPCC had projected that atmospheric methane would continue to rise, roughly doubling (in one typical forecast) by 2100. Thus, many of the scenarios for global warming provided in their last assessment may have been overly gloomy. Nevertheless, Fung thinks it is premature to celebrate, because this slowing in the rise of methane might not persist. When pressed for liow tong one must wait to be optimistic, she answers: "If it goes on for another 10 years, I would be ecstatic." David S. Schimel of the National Center for Atmospheric Research, one of the authors of the 1995 IPCC report on the topic, admits that the assumptions used at that time were "based on an understanding of methane that was five to 15 years old." He, too, notes that climate researchers are disquieted by their inability to forecast such changes. Still, he regards the recent downturn in the growth of this greenhouse gas as "definitely good news." -DavidScbneider

A Hole in the Greenhouse NS 17 Oct 98 3

WEARY science journalists have spent year trying to convince their public that the thinning ozone layer and the greenhouse effect are different phenomena, caused by different gases. Would that life were so simple. For the evidence of their interconnectedness grow by the month. This year's ozone hole over Antarctica is the biggest on record. And forms part of a pattern of longer-lasting holes that are now accompanied by a year-round thinning of Antarctic ozone. And on the other side of the globe, the Arctic ozone layer, to is continuing to deteriorate. This is perplexing. Concentrations ozone-eating chlorine compounds such CFCs reaching the ozone layer have stopped rising. We ought to be contemplating the start of repairs to the ozone layer. What has go wrong? The answer seems to be temperature rather than chemicals. The stratosphere is cooling. Over the poles, it increasingly dips below the threshold temperature of about 80 'C at which polar stratospheric clouds the centres of ozone destruction, form. Why so? The stratosphere is cooling because of the greenhouse effect. Greenhouse gases trap radiated heat close to the ground and stop it rising into the stratosphere. Additionally warming in the tropics is strengthening jet streams in mid-latitude and trapping the cold air above the poles. It cannot mix with warmer surrounding air NASA warns that, as a result, the ozone hole would continue to worsen. It turns out that to repair the ozone layer we have to tackle the greenhouse effect, too.