Geoscience Reference
In-Depth Information
Present climate and biological change
5
5.1 Recentclimatechange
5.1.1 ThelatterhalfoftheLittleIceAge
The 17th century was not just the time of the Little Ice Age, it is also noted (and
for some better noted) for the Renaissance, which saw the gathering of scientific
understanding that in turn was to drive the Industrial Revolution of the 18th and 19th
centuries. In Britain in the 1640s and 1650s scientists sought what they termed 'a great
insaturation', which drew on the philosophies exposed by the likes of Francis Bacon.
Among these, Bacon's principles of exact observation, measurement and inductive
reasoning provided the intellectual tools for scientific advance. These advances had
yet to percolate through to day-to-day application in technology, so life, society and
its economy were still largely powered by humans and animals together with the
burning of wood. Major global impacts from human activity were not yet manifest
(although, of course, trace global signatures such as metals in Greenland ice cores
can be found dating to thousands of years earlier).
In terms of climate and weather, 1659 - within the Little Ice Age - is an import-
ant date. Before that date we rely solely on the proxy indicators (see Chapter 2) for
climatic information. After 1659 there began a source of new information: direct met-
eorological measurement. The first significant series of measurements began in 1659
and (much later) were compiled into a monthly series of temperature readings for
rural sites in central England by Gordon Manley (1974). This is the longest homogen-
eous record and is still kept up to date by the UK Meteorological Office. The earlier
measurements were varied but increasingly included, and were soon dominated by,
instrumental measurements. The Central England Temperature (CET) records were
soon accompanied by others to ultimately be built into a series such as those for De
Bilt in The Netherlands from 1705. Such records are fundamentally important. As
we have seen, although we can use a variety of proxies to build up, piece by piece,
quite a good picture of past climate, deep-time climatic proxy indicators simply are
either not sensitive or representative enough to tell us what was going on. This is
especially true with regard to finer changes. For example, ice-core isotopic records
are very fine for charting regional glacial and interglacial transitions of a few degrees
but are less useful for discerning trends in changes of fractions of a degree within
our current interglacial. For instance, Figure 5.1 is a portrayal of seven centuries of
Greenland deuterium up to the late 20th century. That it only represents the deuterium
evapo-fractionation from the ocean surrounding Greenland restricts its usefulness.
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