Dr. Jeremy Leggett
temperatures rise, the tundra begins to melt faster than expected. More carbon
dioxide and now huge quantities of methane, a more potent greenhouse gas, are
emitted from the spreading wetlands and the increased oxidation of organic
matter. However, much depends on the behavior of water tables, for flooded soils
are capable of releasing 100 times more methane than dry soils. [ECES note: widespread melting of Arctic tundra and permafrost has indeed begun - see a
number of the articles at Global Warming: Arctic.]
the reorganization of global cloud cover also works against us, creating a new
positive feedback factor. More high-altitude (noctilucent) clouds form than do
at the present time. They contain ice crystal distributions that trap more heat
in the atmosphere. According to the IPCC, this feedback could go either way in a
warming atmosphere, as much depends on the physics of ice in clouds. In the
worst-case analysis, luck is not with us. [ECES note: In 1993, scientists began
reporting the unprecedented appearance of noctilucent clouds - formerly only
seen above 40 degrees latitude - as far south as Colorado and Utah. See this
Meanwhile, profound aridity has begun to develop at many latitudes.
Though one might expect that vegetation would prosper from the carbon dioxide
"fertilization effect," in fact it suffers because of other factors
such as decreasing soil moisture, increasing forest fires, multiplying plant
pests, and increased exposure to ultraviolet-B radiation. Hence, land plants are
less able than expected to absorb carbon dioxide from the atmosphere. Even
higher concentrations of the gas build up, driving temperature levels higher
than previously projected.
By now, today's children are in their 50s and 60s, some of them the
policy-makers of the day. Some regions, as would be expected from the
variability of climate, have warmed only slightly. Most, however, are suffering
profound ecological trauma. Warming effects are such that the "short-term
winners" - areas where the climate has become more temperate and crop
yields have risen - are now deteriorating as a result of a drastically blighted
world economy. Cuts in greenhouse gas emissions have long since been
internationally implemented, but they are still not deep enough to stabilize
atmospheric concentrations. Net economic savings from energy-saving measures and
enhanced energy independence have been lost in the bill for environmental
Bad luck continues. Tropospheric chemistry has started to work against
humankind. The hydroxl reservoir (the atmosphere's cleansing agent, oxidizing a
host of polluting gases), has come under stress from excess quantities of
hydrofluorocarbons, carbon monoxide, and nitrogen oxides in the atmosphere. The
quantities of these gases increase by default, as do their lifetimes, boosting
global warming still further. [ECES note: In May 2001, scientists reported that
hydroxl levels declined 10 to 24 percent between 1979 and 2000. See this article
in Pollution: Air for more.]
Meanwhile, the pollution assault continues. Still more carbon monoxide
and nitrogen oxides are emitted by the ever-expanding global automobile fleet.
These gases are precursors for tropospheric ozone, a powerful greenhouse gas.
By now, the Arctic is appreciably warmer. The ice around the fringes of
the ice cap is beginning to retreat, reducing the Arctic's albedo and providing
more positive feedback. The Arctic ocean warms still further and the ice cap
begins to show signs of thinning. At this stage, one of the worst feedbacks is
awakened. On the Arctic continental shelf, submarine methane hydrates start to
destabilize. Methane hydrates are ice-like solids comprising a network of water
crystals with methane gas trapped under pressure. Geologists have shown that an
unspecified but apparently huge quantity of methane is isolated from the
atmosphere in these hydrates. Warming can destabilize them under the permafrost
and in shallow high latitude seas.
The measurements of the World Climate Monitoring System detect
unprecedented acceleration of atmospheric methane concentrations. In emergency
session the United Nations votes sweeping measures for worldwide greenhouse-gas
reductions. But it is too late. A runaway greenhouse effect has been generated.
The point is not that a worst-case scenario will happen, but that it
could happen. Consider some of the
reservoirs in the planet's carbon cycle. The
pre-industrial atmosphere contained around 580 billion tons of carbon for
thousands of years. Now it contains 750 billion tons. The coal and oil reserves
waiting to be burned total 4,000 billion more tons of carbon. We cannot afford
to burn more than a small fraction of this, yet oil and coal companies are
looking for still more.
Carbon in soils amounts to 1,500 billion tons, a good proportion of it at
risk of positive feedback. Nearly 90 billion tons is exchanged each year between
the atmospheric reservoir and the 39,000 billion-ton reservoir in the oceans.
Approximately 100 billion tons of carbon circulates between the atmosphere and the approximately 750 billion-ton reservoir in land plants. Almost
a quarter of all atmospheric carbon is cycled down into the terrestrial and marine
biota each year. Even small changes in this quantity could have huge
implications for atmospheric concentrations.
Though not yet addressed in the IPCC science-advisory process, the
worst-case scenario is central to formulating a policy response. In evaluating
military threats throughout history, policy response has been predicated on a
standard military yardstick must also apply to environmental security.
The Japanese government's report, "Action Program to Arrest Global
Warming," released in October 1990, refers on its first page to the
potential magnitude of the stakes. "It is essential," it says,
"to steadily promote feasible measures so that damage from global warming
may not become prominent and give birth to irreversible situations." The
tension here between the "feasible" and the "irreversible"
is clear, and it reflects the fact that 13 ministries and agencies are
represented by the committee planning the Japanese government's response to
What seems "feasible" to the Ministry of International Trade
and Industry is not very far outside the present energy-industrial status quo.
In contrast, what seems "irreversible" to scientists of Japan's
environment agency is made clear in several of its publications. For example,
the April 1991 report from Japan's Advisory Panel on Environment and Culture
notes "expansionism consists of damaging the environment without
replenishing it. If we refuse this definition of expansionism, we run the risk
of creating a crisis which will not stop with the ruin of one country, but will
cause the destruction of the entire planet and every living thing on it."
Worst-case analyses can creep into the language of governments, not just the
language of environmentalists.
But such examples are far fewer than the instances of governmental
rhetoric stressing the difficulties and economic costs involved in cutting
emissions. Unfortunately, policy-makers
see the risks of responding to the threat of climate
change as equal to, or even greater than, simply waiting to see what
happens in a business-as-usual world. A sad potential epitaph for humankind thus
emerges: "We wanted to save the world. But our leaders told us it would be
The Intergovernmental Panel on Climate Change (IPCC) did not deal with
the influence of biological feedbacks on global warming in its 1992 report. One
sentence in the report read, "Biological feedbacks have not yet been taken
into account in simulations of climate change." Unfortunately, the
implications of this omission, one way or the other, were not elaborated for the
This was not the case two years ago, when the 1990
IPCC report was
finalized in Windsor, England. There, several eminent ecologists and
paleoecologists contributed. The section on confidence in simulated models
included the following:
"Because natural sources and sinks of greenhouse gases are sensitive to a change in climate, they may substantially modify future concentrations [of greenhouse gases]. ... It appears likely that, as climate warms, these feedbacks will lead to an overall increase rather than a decrease in natural greenhouse gas abundances. For this reason, climate change is likely to be greater than the estimates we have given." In other words, the panel's "best estimate" of global warming is likely to be an underestimate.
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