Geology Reference
In-Depth Information
90% chance of being correct) that “the globally averaged net effect of human activities
since 1750 has been one of warming”. The IPPC predicted that doubling the carbon di-
oxide content of the atmosphere as compared to pre-industrial levels would be likely to
produce an average surface warming between 2.0 to 4.5°C (where “likely” means a 66%
or more chance of being correct), a situation that would probably be reached by 2050.
Commentators have noted that this amount of warming would constitute the “biggest
temperature increase in the history of civilization”. An even higher maximum average
surface warming was not ruled out by the IPCC, although, in their view, the scientif-
ic bases for this possibility were less reliable. The IPCC cautioned that there would be
“substantial global impacts such as species extinctions and millions of people at risk
from drought, hunger and flooding” if the warming is not kept below 2.0°C, but they
considered it “very unlikely” (less than a 10% chance) that we would be able to hold
down the warming to this level since this would involve the difficult task of allowing
carbon dioxide emissions to peak by 2015 followed by a 50-85% reduction by 2050 re-
lative to the level in the year 2000.
That we have drastically changed our climate was indisputably confirmed in Febru-
ary 2005, in the week when the Kyoto Protocol was at last ratified, when American and
British scientists announced a dramatic warming of the world's oceans over the pre-
vious 40 years that could only have been caused by our pollution of the atmosphere
with greenhouse gases. Other data show that global average temperature had increased
to about 0.7°C during the 20th century—the warmest century for a millennium. Such a
small increase may not sound very important, but it masks much greater regional tem-
perature changes. Furthermore, the warming has happened unbelievably fast compared
to previous pre-industrial changes, even though the biotic communities of both land and
ocean have absorbed about 60% of our emissions in roughly equal proportions. The
mean global temperature graph from the 2007 IPCC report covering the period from
1000 to 2005 shows a clear downward trend until about 1900, when the planet's temper-
ature began to climb rapidly to today's high level. This suggests that before our interfer-
ence Gaia was headed for the next ice age, possibly in about 15,000 years. Greenhouse
gas emissions have risen in step with the temperature increase. We now have about 385
parts per million carbon dioxide in our atmosphere, about 30% above the ceiling of 279
parts per million to which Gaia has returned during each of the previous four interglacial
periods.
Despite the usefulness of its work in reporting current and historical levels of green-
house gases and global average temperatures, there are good reasons to believe that the
IPCC has underestimated the severity of climate change over the next century. This is
in part because the 'panel' in the IPCC is composed of government representatives from
about 140 countries to whom scientists must report their findings. It is these politicians
