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and aerosols into the atmosphere. Each of these models differed in its physics, resolu-
tion, initialisation and ocean-atmosphere coupling as well as different combinations
and strengths of forcing factors. However, each successfully captured the principal
climate features of the past couple of centuries, albeit coarsely and within certain
margins of error. However, the analysis did show that simulations that included a
Krakatau-type eruption noticeably differed from those that did not. The eruption's
thermal fingerprint is clearly seen in the simulated oceans, with a small but clear
temperature difference of around 0.01 C in the top kilometre of the ocean column
that lasted for about 50-100 years. This analysis also revealed that present-day (non-
super-) volcanoes have a smaller cooling event. The simulated heat-content recovery
after the 1991 Pinatubo eruption (which was comparable to Krakatau in radiative
climate forcing terms) was far quicker: this was actually measured by satellite mon-
itoring data. The reason for this more speedy oceanic thermal recovery was that at
the time of Pinatubo (and more so now) there were rising greenhouse gas emis-
sions and global warming taking place. Anthropogenic greenhouse gas emissions
at the time of Krakatau were roughly a tenth of those at the time of Pinatubo. The
thermal impact on the oceans of each volcano may be small, and shorter-lived in
today's faster-warming planet than the past, but taken together over time they do
have a more pronounced effect. The importance of this work is that it helps val-
idate components of climate models; in this case the inclusion of volcanic activity
(Gleckler et al., 2006). Including volcanic eruptions in models also helps current
forecasts, as there are different likelihoods of global warming depending on whether
or not there is a run of volcanic activity. Remember that much of the 20th century
up to the 1960s was largely free of major (standard) volcanic eruptions, whereas the
period from the 1960s to the mid-1990s saw considerable climate forcing volcanic
activity.
Although standard-sized volcanic eruptions do seem to impart a discernable
thermal fingerprint on the oceans and large volcanoes may impact on food prices
for a couple of years, a super-volcanic eruption has a different order of impact that
noticeably affects biological systems. By comparison today, should the Yellowstone
trap erupt, it would impart a much greater level of impact than a standard Huayn-
aputina-type volcano, so that there would almost certainly be significant food-security
implications. These would be global, so there would be no major bread-basket coun-
try from which to import food. Furthermore, eruption size aside, the lack of food
security would be far worse than the European food shortages experienced periodic-
ally during the Little Ice Age, due to the 21st century's high population density (and
the concomitant smaller areas of woodland in which to forage for alternatives) and
the lack of recent experience of such conditions.
In 2005 the Geological Society of London established a working group to examine
the probability and likely global effects of a super-eruption. Its report's conclusions
called for the completion of a database of super-eruptions over the past 1 million
years. It also recommended that the UK Government establish a task force to con-
sider the environmental, social and political consequences of large-magnitude vol-
canic eruptions and that this involve international collaboration (Geological Society,
2005).
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