Geoscience Reference
In-Depth Information
13.1 Pioneers of climatic change research
In the late nineteenth century, it was widely accepted that climate conditions were described by
long-term averages (sometimes termed normals). The longer the record, the better would be the
approximation of the long-term mean. The standard interval for computing climate means from
instrumental records adopted by the World Meteorological Organization is 30 years: 1971-2000,
for example. Geologists and a few meteorologists were aware that climates of the past had been
very different from the present and sought explanations of Ice Ages in astronomical and solar
variations. Two classic works by C. E. P. Brooks - The Evolution of Climate(1922) and Climates of
the Past(1926) - provided a remarkably comprehensive picture of variations through geologic time
and set out the possible forcing factors, external and internal to the earth's climate system. It was
not until the 1950-1960s, however, that awareness grew of substantial decadal-century-scale
climatic fluctuations. Historical weather records and proxy climatic data began to be assembled.
Pioneers in historical climatology included Gordon Manley and Hubert Lamb in England, Herman
Flohn in Germany, Emmanuel LeRoy Ladurie in France, and J. Murray Mitchell and Reid Bryson in
the United States.
In the 1970s attention turned initially to the possibility of a renewed Ice Age and then to concern
over the effect of increasing carbon dioxide concentrations in the atmosphere. The possibility of
global cooling arose from two main sources; the first was paleoclimatological evidence that
previous interglacial conditions lasted for only about 10,000 years and that the post-glacial Holocene
period was already of that length. A conference titled 'The Present Interglacial - how and when will
it end?' took place at Brown University, Providence, RI, in 1972 (G. Kukla, R. Matthews and J. M.
Mitchell). The second source was concern over the role of aerosols in reducing incoming solar
radiation. Adding to concern over potential cooling, the early 1970s saw an increase in the extent
of Northern Hemisphere snow cover (Kukla and Kukla, 1974). Almost simultaneously, however, the
first conferences on carbon dioxide and greenhouse warming were taking place! The occurrence
of abrupt climatic shifts during the last Late Pleistocene and Holocene began to be identified in the
1970s-1980s. Most notable is the 1000-year-long severe cooling known as the Younger Dryas that
occurred around 12,000 years ago.
Interest in past climates was driven by the concept that 'the past is the key to the future'. Hence,
efforts were made to document and understand conditions during historical times and the remote
geological past, when global climate varied over a much wider range of extremes. As a final note,
recent calculations of orbital forcings indicate that the present interglacial will last for another 30,000
years.
location, or the surroundings of the instrumental
site, or even errors in transcribed data. Proxy
records may suffer from errors in dating or
interpretation. Even when climate signals are real,
it may be difficult to ascribe them to unique causes
owing to the complexity of the climate system, a
system which is characterized by myriad inter-
actions between its various components on a suite
of spatial and temporal scales (
Figure 13.1
).
What is the distinction between climate
variability and change? Climate variability, as
defined by the Intergovernmental Panel on
