May 16, 2000
Seas and Soils Emerge as Keys to Climate
By WILLIAM K. STEVENS
ver the last 150 years, the burning of
coal, oil and natural gas has released some
270 billion tons of carbon into the air in the
form of heat-trapping carbon dioxide.
that had stayed in the atmosphere, much of
the substantial global warming predicted
for a century from now might have already
Luckily, more than half the carbon dioxide emitted by fossil-fuel burning is absorbed from the air by the oceans, by plants
(which use it in converting sunlight to chemical energy) and by soils.
Fewer than half
the emissions, scientists believe, remain airborne to warm the earth.
All of this is part of one of nature's grand
and endlessly complicated global recycling
In it, carbon is constantly exchanged among the air, the terrestrial biosphere, the oceans and the solid rock of the
earth at varying rates on time scales ranging from hours to millions of years.
Now, as the economic and political difficulty of reducing carbon dioxide emissions
at the source becomes ever more obvious, a
broad-based move is under way to manipulate the carbon cycle so that it will remove
more of the heat-trapping gases from the
It is an ambitious idea, but on closer
inspection one surrounded by questions, potential risks and obstacles.
In one approach, researchers are investigating ways to remove carbon chemically
from industrial and automotive emissions
before they are released to the atmosphere,
then to sequester it at some other way
station in the natural carbon cycle -- by
injecting the removed carbon back into underground reservoirs or into the ocean, for
The United States Department of Energy
has expanded research into carbon-removal
technologies at eight of its national laboratories.
But this option, the department said in
a recent study, is "truly radical" and most
experts believe it is some distance from
providing a practical alternative.
More promising in the near term, many
scientists believe, are prospects for increasing the absorption of atmospheric carbon
dioxide by what is called the terrestrial
biosphere: that is, the whole complex of
living things on land, mainly plants and
various tiny inhabitants and detritus of the
Every time a plant sprouts and grows to
maturity, it absorbs carbon dioxide from
the atmosphere, breaks it down chemically
and uses carbon as construction material
for roots, stem, branches, flowers and
leaves. When the plant dies, some of the
carbon goes back into the atmosphere, but
some is also released into the soil as the
dead plant decays. Decomposing animals,
including people, further add to the carbon
reservoir in the soil.
Globally, soil contains
about five times as much carbon as vegetation.
The expansion of these carbon reservoirs,
or "sinks," in vegetation and soil has been
sanctioned as one way industrialized countries might meet their obligations
under the 1997 Kyoto Protocol, which
is aimed at reducing emissions of
carbon dioxide and other heat-trapping greenhouse gases.
Lately, intense argument has developed over the degree to which
countries like the United States,
which may have great potential for
expanding its carbon sinks, ought to
be allowed to meet their emissions
reduction targets under the protocol
by means like planting trees, improving forest management and conserving soils rather than reducing
carbon dioxide emissions from cars,
factories and power generating stations.
Delegates from more than 100
countries are to grapple with the
issue when they meet in November
in The Hague for what is widely seen
as a make-or-break effort to make
the Kyoto Protocol operational.
The rules governing carbon sinks
are among the many sets of yet-to-be adopted regulations necessary to
put the protocol into effect, and only
a few countries have ratified the
agreement pending action on them.
The United States, where the protocol has encountered strong opposition in Congress on several grounds,
is one of those holding back.
In preparation for the critical November meeting, scientists of the
Intergovernmental Panel on Climate
Change, created by the United Nations more than a decade ago to
advise the world's governments, issued a report on the carbon issue at a
meeting last week in Montreal.
analysis suggested that expansion of
terrestrial carbon sinks in the industrialized countries could potentially
more than enable them to meet their
entire combined emissions reduction
quota under the protocol.
But experts associated with the
report questioned how much of that
potential could be achieved, given
the difficulty of actually expanding
the world's carbon sinks in practice.
"Judging the technical potential is
easy," said Dr. Robert T. Watson,
chairman of the intergovernmental
panel, who is also the chief atmospheric scientist and environmental
adviser of the World Bank. "The real
question is, what is the likelihood of
realizing that technical potential?"
Under the Kyoto Protocol, the rich
industrial countries as a group are
obligated to reduce their greenhouse
gas emissions 5 percent below 1990
levels by about 2010.
are widely seen as a first step in
eventually stabilizing atmospheric
If emissions are not
reduced, prominent scientists say,
the average global temperature will
rise by about 3.5 degrees Fahrenheit
by the year 2100.
the world is now 5 to 9 degrees warmer than in the depths of the last ice
age 18,000 to 20,000 years ago.)
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
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
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
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
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.
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
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
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.
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.
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
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
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.
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