The Case for Climate Change is Growing

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http://pubs.acs.org/cgi-bin/cenmaster.cgi?hotartcl/cenear/cen

ENVIRONMENT

August 9, 1999

Volume 77, Number 32

CENEAR 77 32 pp. 16-23

ISSN 0009-2347

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CASE GROWS FOR CLIMATE CHANGE

New evidence leads to increasing concern that human-induced global warming

from CO2 emissions is already here

Bette Hileman

C & EN Washington

In 1995, the United Nations Intergovernmental Panel on Climate Change

declared: " The balance of evidence suggests a discernible human influence on

global climate. " This conclusion set off a major battle among policymakers,

scientists, and industry over the connection between greenhouse gas

emissions and global climate change.

That battle has continued, but in the four years since the UN report was

released, evidence for anomalous warming has become more compelling, and as

a result scientists have become more concerned that human-induced climate

change has already arrived.

Data from many different fields now indicate that Earth is warming and that

significant shifts are occurring in climate and in the biosphere, at least

in part because of human activities. However, major uncertainties remain

that make it difficult to predict the extent of warming or its consequences

over the coming century.

Globally, almost every year since 1990 has been hotter than the preceding

year, according to analysis from many studies. The average global surface

temperature in 1998 was higher than in any year this century and was in fact

higher than it has been at any time in the past 1,000 years. The tundra,

which for millennia has stored large amounts of carbon in the form of peat,

now seems to have become a net source of carbon dioxide emissions across

vast areas of the Arctic.

Ocean temperatures during El Niño events since 1980 have been high enough to

bleach corals in many regions, and much of that coral is diseased or dying.

Because of strong warming, large sections of the ice shelves on the

Antarctic Peninsula—ice that has been stable for at least 400 years— have

broken up recently.

Few scientists who publish research in the field of global warming believe

these changes are entirely due to natural fluctuations in Earth's climate.

Only a handful would say that human activities—in particular, burning fossil

fuels—have played no role in the global average 0.7 °C (1.2 °C) warming at

ground level that has taken place since the late 1800s.

It is highly probable that the greenhouse gases added to the atmosphere

since the start of the Industrial Revolution have directly acted to heat up

the planet and will heat it further over the coming century, says Jerry D.

Mahlman, director of the National Oceanic & Atmospheric Administration's

(NOAA) Geophysical Fluid Dynamics Laboratory in Princeton, N.J.

Mahlman

However, scientists fall into two camps when they consider what society's

response to global warming should be. Some believe Earth's climate is

already showing strong signs of instability and is causing alarming changes

in sea ice and the biosphere. Consequently, they say governments and

individuals need to take immediate action to curb emissions.

" Given the time frame over which these things, such as coral bleaching, are

expressing themselves—decades, not centuries—we don't have time to take

anything other than the precautionary principle as our appropriate role, "

says W. Porter, a professor of ecology and marine sciences at the

University of Georgia, Athens. ``The precautionary principle says, if the

scientific evidence is incomplete, you shouldn't do anything to make the

situation worse. " The alternative, he says, should not be " if you don't

understand everything, you should shut up and do nothing.''

Other researchers believe there are some large uncertainties in global

warming science that need to be eliminated or reduced before governments

mandate strong, potentially expensive, measures to reduce emissions. ``We

need to take the steps now to make the political agreements and develop the

technological capabilities to substantially lower emissions if and when the

science shows that to be necessary,'' says G. Prinn, director of the

Center for Global Change Science at Massachusetts Institute of Technology.

Several major questions dominate the unknowns of global warming science.

These concern what effect clouds, aerosols, ocean circulation, and

vegetation (its uptake or emission of carbon dioxide) will have on global

warming over the coming century. Another important question is: What kinds

of regional changes in climate might be expected as Earth warms? Satellite

and ground-based instruments for the Earth Observing System that the

National Aeronautics & Space Administration will deploy over the next 15

years are designed to help resolve these questions.

In recent international negotiations, the U.S. has advocated using

reforestation and the incorporation of carbon in agricultural soils as a

carbon dioxide sink to achieve a substantial part of the greenhouse gas

emissions reductions agreed to under the 1997 Protocol to the United Nations

Framework Convention on Climate Change—known as the Kyoto protocol. But many

scientists and the European Union are skeptical about depending heavily upon

this approach.

Evidence of warming

Evidence pouring in from many different fields indicates a speedup in the

rise of Earth's surface temperature. Globally, 11 of the past 16 years have

in turn been the hottest of the century, according to a NASA report. The

average global temperature in 1998 exceeded the previous record set in 1995

by 0.25 °C—a huge jump. The average global temperature in 1995 was already

about 0.75 °C above temperatures during the late 1800s. Some of the warming

in 1998 can be explained by the El Niño phenomenon that year, but not most

of it, says E. Hansen, director of NASA's Goddard Institute for Space

Studies in New York City. (El Niño is the periodic, marked warming of the

central and eastern tropical Pacific Ocean that can spawn droughts and

floods worldwide.)

Hansen [Photos by Bette Hileman]

In addition, the rapid temperature rise of the past 25 years exceeds the

rise seen in any previous period of equal length during the past century

since reliable instrumental data have been available. This accelerated

warming has been occurring just as models have predicted—during the time

when greenhouse gases in the atmosphere (about 80% carbon dioxide) have

increased most rapidly, Hansen says.

When " proxy " records—such as tree rings, pollen, sediments, and gases

trapped in glaciers—are used to estimate global temperatures in the distant

past, 1998 stands out as a record hot year for the millennium, says

E. Mann, adjunct assistant professor of geosciences at the University of

Massachusetts, Amherst. The average global temperature last year exceeded

temperatures in the so-called medieval warm period, he says.

" The notion of the medieval warm period is really outdated,'' Mann says.

Temperatures in Greenland were unusually high from about 900 to 1100,

allowing the Norse colonization, but that was a regional phenomenon, he

explains. Europe warmed a few centuries later, but that warming was also

confined to a small part of the planet. ``There is no evidence of any period

of warmth at the hemispheric scale that rivals the late 20th century,'' he

explains.

Global temperatures in the late 20th century are a cause for concern, Mann

says. " Any time a scientist sees a system exhibit very anomalous behavior

all of a sudden, it is reason to be very cautious about whatever it is that

might be perturbing that system, " he says. " There could be obviously

deleterious and relatively unpredictable effects because we're changing the

system so quickly. "

As Earth's temperature has risen, most polar regions have warmed much more

than the global average. Alaska, for example, has been as much as 6 °C(10

°C) warmer recently than it was 35 years ago, and this causes the Alaskan

tundra to melt more in the summer than it used to.

It also means that vast areas of the tundra that formerly were a sink for

carbon dioxide now have become net sources, according to Walter C. Oechel,

director of the Global Change Research Group at San Diego State University.

The tundra has deep layers of peat that decay and release carbon dioxide

when warm.

Oechel has been measuring carbon dioxide emissions and absorption (flux)

over an area about the size of the Netherlands on Alaska's North Slope.

Using towers, chambers, and aircraft, he has found that essentially all of

this area is now a net carbon dioxide source on an annual basis.

Measurements in the 1960s and early 1970s show that the Alaskan tundra was a

carbon dioxide sink at that time, Oechel says. ``The first year when we saw

areas of the Arctic become sources during the summer was 1982,'' he says.

From carbon-14 data for the peat, he concludes that " the tundra was

basically a sink going back 9,000 years before present. "

Oechel and several other research groups are extending flux studies to the

Seward Peninsula in western Alaska and to the adjacent Chukota Peninsula in

Russia. They are finding that the Russian tundra also is a source. " The

overall pattern is that the extrapolar Arctic tundra is a source to the

atmosphere, " he says. " The two vegetation types we've looked at—tussock

tundra and wet tundra—are emitting about ;5>0.7 billion metric ton of carbon

dioxide a year [measured as carbon], " he estimates, compared with about 7

billion metric tons released annually from burning fossil fuels and from

deforestation.

In addition to tundra, scientists are measuring how much CO2 is emitted or

absorbed by forests. L. Goulden, an assistant professor of earth

system science at the University of California, Irvine, and his

collaborators have been using gas-exchange chambers; radiocarbon analysis;

and wood, moss, and soil inventories to measure the carbon balance of a

120-year-old black spruce forest in Manitoba. They found that the site has

lost ;5>0.3 metric ton of carbon per hectare per year from 1994 to 1997

[science, 279, 214 (1998)]. The gain in wood carbon was more than offset by

losses from the soil. " The soil remained frozen most of the year, and the

decomposition of organic matter in the soil increased 10-fold upon thawing, "

he writes.

C. Wofsy, a professor of atmospheric and environmental science at

Harvard University, has been measuring carbon fluxes in a variety of

forests. Measurements made by Wofsy show that certain types of boreal

(high-latitude northern) forests are definitely not taking up any carbon, he

says. But there aren't enough measurements yet to give a comprehensive

picture of how much carbon dioxide boreal forests are absorbing or emitting

overall, he says. " The atmospheric data, though, would suggest the boreal

zone is not a very strong sink and may be a source today, " Wofsy notes.

Wofsy

All this research shows that as climate warms in the tundra or in the boreal

forests, it can transform them from sinks to sources.

Ice shelf breakup

Average summertime temperatures on the Antarctic Peninsula have risen 2.5 °C

(4.5 °C) since the 1940s and are now just above 0 °C, according to data from

the British Antarctic Survey. This strong warming seems to have led to

increased colonization by plants at certain sites in the region and to have

accelerated the breakup of ice shelves on the peninsula. Two ice shelves,

Larsen B and Wilkins, lost nearly 3,000 sq km (1,200 sq miles) of their

total area of 24,000 sq km in the past year, according to Vaughan, a

British Antarctic Survey researcher.

" We have evidence that the shelves in this area have been in retreat for 50

years, " with cumulative losses amounting to about 7,000 sq km, he says. So

retreat of 3,000 sq km in a single year is clearly an escalation, Vaughan

says. The recent breakup was also unusual because the ice shelves calved

thousands of small icebergs at once, while normally they release only a few

relatively large icebergs in any single year.

Sidebar: New satellite network will aid climate-change research

" Within a few years, much of the Wilkins Ice Shelf will likely be gone, "

Vaughan predicts. Although the breakup and melting of an ice shelf does not

contribute to sea level rise because the shelf is originally floating on

water, this phenomenon has an important effect. When an ice shelf is gone,

the ice sheet (the huge glacier resting on land) behind the ice shelf would

tend to melt faster because there is nothing to stop it from flowing out

over the ocean, in what a NASA report calls an irreversible process.

The Greenland Ice Sheet, the world's second largest glacier, has begun to

thin by up to a meter per year when losses are averaged over the whole ice

sheet, according to NASA surveys completed this year. In 1994, NASA

researchers using aircraft equipped with laser altimeters measured the

profile of the 10 million-sq-km ice sheet. This year, researchers flew on

the same path and found that the ice sheet had lost up to 5 meters in

thickness. The west side of the ice sheet had lost no net ice, but the east

and south sides had thinned substantially, leading to an overall loss.

Significant melting of ice sheets would contribute to a sea level rise.

However, because snowfall could be increasing in polar regions, researchers

still do not know whether the overall mass of all the world's polar ice

sheets is growing or shrinking, NASA reports. There is no evidence yet that

the huge ice sheet that covers the Antarctic continent is thinning.

Coral bleaching

Another effect believed to be caused at least in part by the recent rise in

global temperatures is that record seawater temperatures have triggered the

largest die-off of coral ever observed. " Worldwide episodes of coral

bleaching, coral disease outbreaks, and macro algal overgrowth of coral are

increas-ing in frequency, intensity, and range, " says the University of

Georgia's Porter. Bleaching occurs when coral becomes stressed and expels

its microscopic plant life, which provides it food.

These events are occurring in all reef-supporting regions, including the

Indo-Pacific, the western Atlantic, and the Caribbean, and are affecting

reefs near both inhabited and uninhabited regions. Scientists attribute the

coral decline to seven causes--coastal development, global warming, oxygen

starvation, sediment loading (including dust from the Sahel, the semiarid

fringe of the Sahara, in Africa during drought years), destructive fishing

practices, overfishing of plant-eating fish, and increased ultraviolet

radiation from stratospheric ozone depletion.

But only global warming and enhanced UV radiation are ubiquitous enough to

affect coral globally in remote as well as inhabited areas, Porter says.

Another clue to causality is that changes in the coral ecosystems started

abruptly in the mid-1970s, just when global temperatures began rising

rapidly, he says.

Coral bleaching has been particularly pronounced in El Niño years,

especially during severe events, such as the one in 1998, Porter says. Since

the mid-1970s, a number of very intense El Niños have occurred when seawater

temperatures have been unusually high, Porter says. If the water temperature

rises to 31.5 C, only 1.5 C above the summertime seawater average in the

tropics, corals are bleached.

Coral can often recover from short bleaching episodes, but it becomes

diseased or dies when subjected to prolonged or repeated bleaching.

Bleaching weakens coral's ability to resist pathogens or competitors, Porter

says. " We are now seeing at least 14 diseases in coral, some of which appear

to be new in that they have not been described before, " he says.

Porter currently is collaborating with the Environmental Protection Agency

on long-term monitoring of coral reefs. In just three years, he has found a

huge increase in the number of monitoring stations in the Florida Keys with

diseased coral. In 1996, there were 26 out of 160 EPA monitoring stations

with disease. In 1998, 131 stations exhibited disease. Furthermore, the

number of coral species affected by disease in the Florida Keys has tripled

over those three years. " No coral reef in Florida could have grown with the

rates of loss now being seen, " Porter says.

Reefs are threatened not only by rising temperatures but also by the

modified chemical composition of the surface ocean water. Higher atmospheric

concentrations of carbon dioxide result in enhanced absorption of carbon

dioxide by the surface ocean. This, in turn, lowers the concentration of

carbonate ion, reducing the ability of corals to build their skeletons (made

of calcium carbonate in the form of aragonite).

Joan A. Kleypas, a chemist at the National Center for Atmospheric Research

(NCAR), Boulder, Colo., has found that the addition of extra carbon dioxide

to surface ocean water has already reduced calcification rates on some reefs

by 6 to 11% [science, 284, 118 (1999)]. She estimates that calcification

rates would decrease by an additional 8 to 17% if the carbon dioxide

concentration in the atmosphere were to rise from its current level of 360

ppm to double the preindustrial level (about 550 ppm) as some models predict

will happen by 2050.

Coral reefs are important because they are biologically diverse and

beautiful marine ecosystems. They are important for tourism in many areas

and provide food, coastal protection, and new medications for drug-resistant

diseases. For example, Caribbean countries derive half their gross national

product from reefs, and the coral reefs of Southeast Asia harbor one-quarter

of the world's fish species. The World Resources Institute, Washington,

D.C., estimates that the world's reefs provide $375 billion each year in

goods and services.

An unstable climate

At the same time that changes have been taking place in coral, weather

patterns have been shifting in ways that lead some scientists to believe

that climate has become unstable.

R. Karl, director of NOAA's National Climatic Data Center, Asheville,

N.C., has analyzed weather records for the past century and found much

evidence of an enhanced hydrological cycle. From his analysis, he concludes

that precipitation has increased about 10% across the contiguous U.S. since

1910, with much of the increase occurring in winter. Also, the proportion of

total precipitation coming in very heavy events has risen relative to more

moderate episodes, he says. For example, the frequency of extreme daily

rainfall events (specifically, days with rainfall exceeding 2 inches) has

increased by about 10% during the past century. Analyses of precipitation in

Canada, Japan, Russia, China, and Australia show similar trends [bull. Am.

Meteorol.Soc., 79, 231 (1998)].

Another sign of an enhanced hydrological cycle, Karl says, is that the

moisture in the lower atmosphere in the U.S. has increased 5% per decade

over the past 20 years. This is a consequence of simple physics: As

temperatures rise, more water evaporates. Enhanced water vapor and increases

in sulfate aerosols lead to more clouds, which tend to reduce temperatures

during the day and raise them at night. As a result, daily low temperatures

in the U.S. have increased at nearly twice the rate of the daily highs.

Similar trends can be seen in most other parts of the world.

Karl

Further evidence of an enhanced hydrological cycle has been an increase in

the number of intense storms over the North Atlantic and North Pacific

Oceans, Karl says. This number has doubled since 1900.

In contrast, the frequency of tropical cyclones has decreased overall. This

is not surprising, says E. Trenberth, chief of the climate analysis

section at NCAR. " With increases in sea-surface temperatures, there is a

potential for stronger, bigger hurricanes, " he says. On the other hand, he

explains, groups of thunderstorms can substitute for a hurricane as a

mechanism to transport heat upward. So there is always a trade-off between

the two. However, it is very difficult to detect trends in hurricanes

because they fluctuate so much from year to year.

Trenberth

For El Niño events, which are a major cause of widespread floods and

droughts around the world, the trend is more clear-cut. There have been more

frequent and more intense El Niños since the late 1970s, Trenberth says. The

two most severe El Niños on record occurred in 1982-83 and in 1997-98, and

the longest on record persisted from 1990 to mid-1995.

There are reasons to think that global warming increases both the frequency

and intensity of El Niño events, Trenberth explains. " The timescale of El

Niño is determined by the time required for an accumulation of warm water in

the tropics to essentially recharge the system, plus the time for the El

Niño itself to evolve. Because El Niño is involved with movement of heat

around, it is conceptually easy to see how increased heating from the

buildup of greenhouse gases can interfere. " As yet, however, there is no

scientific consensus on how El Niños are affected by rising global

temperatures.

Along with changes in the hydrological cycle and in the El Niño phenomenon

has come a sharp rise in the incidence of and damages from severe weather

events around the world. Munich Re, a reinsurance company based in Munich,

Germany, estimates that global losses from weather-related natural disasters

have increased from between $7 billion and $10 billion annually in the 1980s

to about $90 billion annually in 1998.

Part of the reason damage costs have risen so much is that governments and

insurers in developed countries have made inexpensive insurance widely

available and this has encouraged people to build near the seacoast. But at

the same time the sheer number of severe weather events has also escalated.

Because of the ongoing climate changes, Karl says, effective future

government planning needs to account for a nonstationary climate. " We cannot

rely on the past climate to guide us into the future, " he says.

Models mimic reality

There is no " smoking gun " in global climate research that provides a

near-absolute link between carbon dioxide emissions and climate change. But

the newest general circulation models give results that, in the opinion of

many scientists, come close to being a smoking gun. These models are very

similar to those used for long-range weather forecasts.

In 1990, when general circulation models were used to project temperature

rises resulting from increasing greenhouse gases in the atmosphere, the

modeled temperatures for the past century were not very close to the

observed data. The models predicted a temperature rise of 1.2 C from

greenhouse gases during the 20th century, when the actual rise was about 0.7

C.

But in 1995, when data on the cooling effects of sulfate aerosols and

changes in the sun's irradiance were added to the models along with

greenhouse gases, the model-predicted warming closely agreed with

observations. There was also a close correspondence between model-predicted

and observed patterns of temperature changes in the horizontal and vertical

planes, says Tom M. L. Wigley, senior scientist at NCAR. That is, the

model-predicted temperature and precipitation patterns on continental and

high-latitude/low-latitude scales were close to those seen in reality, he

explains. Also, the pattern of temperatures predicted for different levels

of the atmosphere was close to the measured pattern. " The skeptics' view

that the models are inconsistent with observations is just not correct, " he

says.

" If one takes off the shelf the best information about greenhouse gas

concentrations, the best information about sulfate aerosol forcing (the

warming or cooling result), the best information about solar forcing, and

the best estimate about climate sensitivity (that is, how many watts per

square meter of warming result from a given concentration of greenhouse

gases), then what you get " is very close to the observations, Wigley

explains.

Although the most sophisticated models give fairly realistic results for

temperatures in the past, model predictions of the temperature changes to be

expected in the next century vary widely. Models project average global

temperature increases of 1.2 to 4 C compared with the 1990 global average if

nothing is done to curb greenhouse gases. In Wigley's view, the best

estimates range between 1.9 and 2.9 C.

Some scientists say a global average temperature rise close to 1 C--the

lowest change projected for the next century--would have minimal effects.

But Mann disagrees. A 1 C global average rise could have very noticeable

effects on climate and the biosphere because the rise in polar regions and

even in the continental U.S. would be much greater than 1 C, he says.

One of the inputs that always makes temperature projections from climate

models for the next century vary over a wide range is estimating how fast

greenhouse gas concentrations will rise. That depends on many different

human factors, including choices people make affecting population, changes

in land use, and the structure of industry. It is impossible to eliminate

all the uncertainties associated with future human behavior.

Other large modeling uncertainties result from a lack of scientific

understanding about the physical effects of aerosols, clouds, and ocean

circulation in a warmer world.

Aerosols--tiny particles suspended in air--originate from sea spray,

volcanoes, dust storms, and wildfires, as well as fossil-fuel burning,

agriculture, and forestry. Scientists do not know where on Earth aerosols

are increasing or decreasing. Nor do they understand how the effects of

aerosols might change as greenhouse gas concentrations rise.

Preliminary results from a project to study aerosols over the Indian Ocean

have produced many surprises and illustrate how little is known about

aerosols, says V. (Ram) Ramanathan, director of the Center for Atmospheric

Sciences at Scripps Institution of Oceanography, La Jolla, Calif. In a

National Science Foundation-sponsored project, scientists from Scripps and

the Max Planck Institute for Chemistry, Mainz, Germany, used aircraft,

ships, balloons, satellites, and land stations to study aerosols and clouds.

The aerosol layer--consisting of soot, sulfates, nitrates, and organics--was

surprisingly persistent and thick and covered most of the Indian Ocean,

Ramanathan says. A second unexpected finding was that the reduction of

sunlight at the surface caused by the aerosols was three times as great as

the amount of sunlight the aerosols reflected into space. Usually, the

amount of sunlight reflected into space is the only measurement taken of the

radiative properties of aerosols, he explains.

Ramanathan

Another of the more important uncertainties in climate modeling is how the

cloud system reacts in response to increases in the levels of greenhouse

gases. In general, high clouds warm the climate while low clouds, by

reflecting sunlight back to space, tend to cool the system. Overall, clouds

averaged together globally now have a net cooling effect of -15 to -20 watts

per sq meter, Ramanathan says. However, scientists do not know how clouds

will respond to further increases in greenhouse gases, he says.

NASA's Earth Observing System, which consists of satellite-based and

ground-based instruments, is designed to reduce many of the uncertainties

concerning clouds and aerosols. Data obtained will be used in complex Earth

system models in climate projections for the next century and to help in

predicting regional changes in climate with increasing levels of greenhouse

gases. A minimum of 15 years of continuous monitoring is believed to be

needed to identify meaningful climate trends and to separate human effects

from naturally occurring ones.

Insistence on sinks

In the international negotiations over what to do about the potential

problems of global climate change, beginning with those in Kyoto, the U.S.

delegation has been advocating reforestation and the incorporation of carbon

in agricultural soils as a substitute for reducing emissions from burning

fossil fuels. The U.S. aims to use sinks to achieve a substantial part of

the 7% reduction in greenhouse gas emissions below the 1990 level by 2012 as

promised in Kyoto. Government statements submitted to the UN by the State

Department say that using sinks is often more economical than cutting back

on the use of fossil fuel.

Although research on carbon sequestration in forests and soils had been

going on for decades, the U.S. government did not seem to have an intense

interest in this topic until about the time of the Kyoto negotiations in

December 1997. At that time, a draft paper by a group at NOAA's Geophysical

Fluid Dynamics Laboratory was being circulated among the delegates. The

paper, which was later published in Science, concluded that the forests and

soils of North America, especially those below the 51st parallel, were

absorbing as much or more carbon than the U.S. was emitting from burning

fossil fuel [science, 282, 442 (1988)].

According to the paper, North American forests and soils were sucking up 1.7

billion metric tons of carbon dioxide (measured as carbon) annually--the

entire so-called missing sink--while the rest of the world was taking up

very little carbon dioxide. The paper was one reason U.S. policymakers came

to believe that enhancing forest and soil carbon sequestration had great

potential as an economical way to offset emissions reduction targets.

In Kyoto, delegates from the European Union believed that the U.S. interest

in sinks had come out of the blue; they were very skeptical about including

sinks in the protocol. At one point, the U.S. delegation threatened to walk

out of the negotiations if sinks were not included.

In the past year, two more groups--one in Australia and one in France--have

completed similar research and have come to different conclusions that show

U.S. vegetation is taking up much less carbon dioxide than the NOAA

researchers found. However, these new research results are not yet published

and have had no noticeable effect on climate-change policy.

The sinks issue has been dominating every negotiating session since Kyoto,

says R. Gurney, a research scientist in the department of atmospheric

science at Colorado State University, Fort , who served as an expert

at the negotiations. " A lot of the delegates are just perplexed " because the

issue is complicated and the science is not very mature, he explains. " It's

difficult for them to negotiate issues that seem very vague and fuzzy. "

When greenhouse gases, aerosols, and changes in solar irradiance are used as

inputs into general circulation models, predicted temperatures are very

close to those observed. When greenhouse gases are the only input, as was

done in the past, predicted temperatures are higher than those observed.

But many scientists favor using forest sinks as one way of reducing

emissions under the protocol. " The world would be a better place with more

forests for many reasons--preservation of biodiversity and production of

forest products, " says H. Schlesinger, a professor of botany and

geology at Duke University. He has been experimenting with 13-year-old

loblolly pine trees grown outside to see how they respond to enhanced levels

of carbon dioxide. After three years, trees nourished with enhanced carbon

dioxide grew 25% faster than controls [science, 284, 1177 (1999)].

Schlesinger

Schlesinger and his collaborators estimate that if atmospheric carbon

dioxide levels double to 560 ppm sometime in the next century as predicted,

the world's forests could absorb 50% of the fossil-fuel emissions as an

upper limit. But that would be an unrealistic goal, he says, achievable only

if all the trees were relatively young and all were as responsive to carbon

dioxide as the most responsive tree--the loblolly pine. Also, it is unclear

whether the enhanced growth of trees would be sustained for more than a few

years, he says.

Harvard's Wofsy also is in favor of using forests and soils as a way to get

credit for carbon dioxide reductions. But, he says, people need to decide

what the overall objectives are. These objectives should put the management,

stewardship, and ecological services of the forests and soils first and the

advantages of carbon reductions second, he believes. " A spreadsheet approach

will lead to a big push from Wall Street to plant short-rotation,

fast-growing tree plantations and ignore other environmental

considerations, " he says.

Widespread use of forests and soil sequestration as a substitute for

reductions in fossil fuel use can backfire, Gurney warns. " The problem is

that it's entirely possible every bit of carbon that goes into these systems

now will come right out " as temperatures rise. To use sinks, he says, " you

have to account for sink carbon forever, so if it comes out of forests or

soils, countries [should be] penalized for that. "

Climate politics

Some scientists believe Congress is taking an ostrichlike approach to

climate-change issues. Last month, 50 climate-change researchers met in

Washington, D.C., in an effort organized by the Union of Concerned

Scientists to try to convince Congress that global warming is a serious

issue and to urge the Senate to ratify the Kyoto protocol.

Since the Kyoto protocol was negotiated, Congress has for the most part been

opposed to doing anything that might eventually reduce greenhouse gas

emissions. There has been some funding for research on climate change and

for research on nuclear and renewable energy, however.

There is virtually no chance the Senate will ratify the Kyoto protocol

during the Clinton Administration. In fact, most members of Congress seem to

agree with the view of Rep. Jim Sensenbrenner (R-Wis.) that the Kyoto

protocol " poses a severe threat to the vitality of the U.S. economy in the

form of drastic energy price increases, job losses in key manufacturing

industries, and an overall decline in our standard of living. "

In March, Sen. H. Chafee (R-R.I.) introduced S. 547, a bill to

encourage companies to reduce their greenhouse gas emissions in return for

credits usable in any future climate-change program. But this bill also has

little chance of passage.

In April, Sen. Murkowski (R-Alaska) introduced S. 882, a bill that

would reduce and sequester greenhouse emissions through clean-coal

technologies, provide $2 billion over 10 years for R & D on various

technologies that would reduce greenhouse gas emissions, and consolidate

climate-change duties in one office at the Department of Energy.

Environmental activists oppose Murkowski's bill, saying that while R & D is

important, more immediate steps are necessary to reduce emissions.

Partly as a result of congressional inaction, the U.S. has made little

progress toward meeting its goal of reducing greenhouse gas emissions 7%

below the 1990 level by 2012. DOE's Energy Information Administration (EIA)

has reported that U.S. emissions last year were more than 10% above the 1990

level.

EIA's 1998 emission figures also show that U.S. industry made some

surprising progress last year in reducing carbon dioxide emissions. In 1998,

fossil fuel use in the industrial sector fell 1.4% from the 1997 level, even

as the gross domestic product grew 3.9%. This is the first time U.S.

industrial use of fossil fuel has fallen in a strong economy. Emissions from

1997 to 1998 for the U.S. as a whole grew only 0.4%.

Table: Worldwide carbon dioxide emissions fell in 1998

Lindstrom, EIA industry economist, says he does not know why

industrial emissions went down, nor does he know whether the trend will

continue. " Part of the downward movement has to be the result of a changing

structure in the U.S. economy, " he says.

Similar trends can be seen around the world. Worldwide carbon emissions fell

0.5% last year while the world economy expanded 2.5%, according to figures

from BP Amoco and the Worldwatch Institute, a Washington, D.C.-based public

policy research organization. This shows there is a disconnect between

economic expansion and carbon emissions, says Flavin, Worldwatch

senior vice president. If that falling trend continues, it may demonstrate

that cutting carbon emissions and maintaining economic growth may be easier

than previously thought.

Research that casts light on global climate change is now published every

week, and new data from NASA's Earth Observing System likely will provide

much information that will help eliminate uncertainties over the next 10 to

15 years. Although the data may build an increasingly stronger case that

greenhouse gases from the burning of fossil fuels are altering climate, they

may never prove it absolutely.

So policy debates over whether the government should mandate major

reductions in emissions now or wait for more scientific certainty may well

continue for a number of years. But eventually climate change and its

associated harm to ecosystems may seem so ominous that a consensus among

policymakers, scientists, and the general public will develop to take strong

measures to reduce greenhouse gases, even while important scientific

questions remain unanswered.

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