CONCLUSIONS
The fact that we are having profound and far-reaching effects Stabilising greenhouse gas concentrations can be achieved
on the world’s climate is no longer in serious doubt. As a result either by reducing the rate of emission, or by increasing the
of human activities concentrations in the atmosphere of so- rate of absorption of the gases or both. Reduction in emissions
called greenhouse gases, chiefly carbon dioxide (CO
2
), methane from fossil fuel use is clearly of paramount importance. Car-
(CH4) and nitrous oxide (N
2
O) are currently at levels unseen bon capture technologies that store the greenhouse gases pro-
for at least the last 650,000 years, and are rising at unprec- duced at concentrated emission points such as power stations
edented rates. Around two-thirds of the increase in greenhouse offer some hope for reducing rates of increase in emissions
gases in the last 150 years or so can be ascribed to the burning although their likely overall impact in the short or medium
of fossil fuels. Most of the rest is a result of changes in land-use term remains uncertain.
and a small proportion is the product of burning calcium car-
bonate to produce cement. Land-use change – most notably de- But the management of fossil fuel use and adoption of car-
forestation – results in an increase in greenhouse gases chiefly bon capture technologies will not in themselves be sufficient
through the release of carbon stored in biomass. to prevent serious climate change in the next few decades. The
management of carbon in living systems has a vital role to play:
The greenhouse gases emitted as a result of human action en- even with drastic cuts in fossil fuel emissions, current land-
ter the carbon and nitrogen cycles. As a result of these cycles, use practices would still lead to significant increases in green-
not all the greenhouse gases produced through human action house gas concentrations. Such management has two funda-
remain in the atmosphere: it is estimated that nearly 30% of mental components: ensuring that existing carbon stocks held
these emissions over the past 150 years have been absorbed by in natural ecosystems and in agricultural areas remain secure;
the oceans and just under 30% by terrestrial ecosystems. and attempting to increase the rate at which carbon is seques-
tered in these systems.
The Intergovernmental Panel on Climate Change believes that
in order to avoid the worst effects of climate change, at the very Some aspects of the carbon cycle are at present effectively be-
minimum greenhouse gas concentrations need to be stabilised yond direct policy control or technological intervention – nota-
at 445–490 parts per million carbon dioxide equivalent. The bly the behaviour of the oceans in mediating the carbon cycle
current concentration is around 430 parts per million CO
2
e. and global climate (large-scale fertilisation experiments are be-
At current rates of CO
2
emission alone, the threshold of 445 ing undertaken to try to improve carbon fixing through oceanic
parts per million CO
2
e will be reached in a mere seven years, photosynthesis, but there can be little human influence on the
even sooner if the accelerating output observed in the first few physical and purely chemical role of the ocean in the carbon
years of the present century continues. cycle). Similarly, warming at high latitudes will lead to at least
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