Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 344

in north-west India with the Cretaceous-Tertiary extinction. As stated, whereas these
eruptions were not the sole cause of the mass extinction, it is now well established
(especially with regards to the Cretaceous-Tertiary event) that species were declining
at the time of the eruptions. So, by this standard alone a large Yellowstone eruption
may have roughly a five-hundredth the impact of Cretaceous-Tertiary vulcanism.
Current global warming might actually help a little in offsetting the cooling effect of
the eruptions. Even so, an eruption at Yellowstone would most likely have a climatic
impact far greater than that of large eruptions of normal volcanoes that do not have
large volcanic traps (a trap is the magma chamber of a volcano).
So, what of a large eruption of a standard-type volcano? The eruption of Huayn-
aputina in February 1600 (see Chapter 4 and Figure 2.1) was not the biggest eruption
in the Little Ice Age. Nonetheless, the following few years saw very low temper-
atures. In Europe the summer of 1601 was cold, with freezing weather in northern
Italy extending into July and overcast skies for much of the year, while in parts of
England there were frosts every morning throughout June. Yet despite this the eco-
nomic impact of this climate change was marked, although not as clear cut as one
might expect. The eruption happened to follow some years of the late 1590s that also
saw climate-related food shortages. By 1601 people were adapting (as they will in
the future once they have experience of global warming in their area). In England
in 1600-10 documented wheat prices were not high. However, the purchasing power
of non-agricultural workers, as revealed by English builders' wages, not only dipped
due to the earlier shortages of the 1590s but failed to rise significantly throughout
much of the first half of the 17th century, after which there was a steady recovery
and upward trend lasting a century (Burroughs, 1997). Builders' wealth is a useful
indicator of societal economic well-being, as building is inevitably associated with a
wealthy society, but builders themselves do not generate food. Consequently builders'
wealth is in no small part an indicator of a society's agricultural surplus. So the Huayn-
aputina eruption during the Little Ice Age, while not having a devastating effect on the
economy, does coincide with a period of little food surplus (if anything, a marginal
food deficit).
While the economically discernable effect on agricultural systems from standard
(as opposed to super-) volcanoes lasts only a few years, their thermal impact on the
biosphere lasts longer. Evidence comes from today's computerised climate models
that are sufficiently good to simulate at least most continental-scale climate events of
which we have knowledge (be it through direct measurement or from several sets of
palaeoclimatological data). Of course, there is still work to be done regarding mod-
elling of high latitudes and increasing the level of spatial resolution, not to mention
in reducing uncertainty relating to, and increasing the number of, the various climate
forcing factors. Nonetheless, that many of today's global models do successfully cap-
ture past climatic change suggests that, even if much refinement is still possible, they
do have a very meaningful role to play in informing us about likely climate factors
(and indeed policy). There is some evidence that volcanic eruptions, such as Krakatau
in 1883, have a small, but clearly discernable, impact on deep-ocean temperature that
lasts for between 50 and 100 years.
Twelve state-of-the-art global climate models were analysed, both including and
omitting the impact of the Krakatau eruption and its injection of particulates, gases