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Calspace Courses
Climate Change · Part One
Climate Change · Part Two
Climate Change 2 Syllabus
1.0 - The Ice Ages: An Introduction
2.0 - Discovery of the Ice Ages
3.0 - Ice Age Climate Cycles
4.0 Climate: Last 1000 Years
· 4.1 - The Last Millennium
· 4.2 - Tale of Viking Exploration
· 4.3 - The Riddle of the Little Ice Age
5.0 - Determining Past Climates
6.0 - Causes of Millennial-Scale Change
7.0 - Climate and CO2 in the Atmosphere
8.0 - Recent Global Warming
9.0 - Climate Change in the Political Realm
10.0 - The Link to the Ozone Problem
11.0 - Future Energy Use
12.0 - Outlook for the Future
Introduction to Astronomy
Life in the Universe
Glossary: Climate Change
Glossary: Astronomy
Glossary: Life in Universe
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The Last Millennium
The time series shows the combined global land and marine surface temperature record from 1856 to 2000. Data from Jones et al., 1998; and from the Climate Research Unit at the University of East Anglia ( Climate Research Unit; compilation by Phil Jones). |
There was a time, not so long ago, when scientists assumed that
climate is a more or less unchanging condition on the planet, perhaps punctuated
by catastrophic events. (The concept of "punctuated equilibrium" in paleontology
is reminiscent of this concept; see the glossary.) First Louis
Agassiz's discovery of the "Great Ice Age" and subsequently the idea of multiple
ice ages, in the middle of the 19th century, destroyed the idea of unchanging
background conditions: climate changes all the time.
At the end of the 19th century, the first reconstructions of climate change over
the last 1000 years were published by the Austrian climatologist Eduard Brückner.
In recent decades, the role of climate history as a means toward understanding
the Earth has received increasing attention, following the monumental work of
the British meteorologist Hubert H. Lamb (1913-1997).
The chief benefit of climate history is the expansion of our horizons even beyond
imagination. Without the historical perspective we are trapped within the limited
wisdom provided by physics and the experience of individual observers. It is perhaps
surprising that the various expert opinions in the climate-related sciences regarding
the problem of man-made global warming can diverge as much as they do. But it
will also surely come as a shock to realize that many of these opinions are not
especially relevant to the question of how much of the warming experienced
over the last several decades can be ascribed to human impact.
The reason for this is actually quite simple. Physics can tell us a lot about
how the climate machine works. We are in great need of that knowledge, and we
should vigorously pursue such studies. However, only climate history, that is,
long-term experience, can tell us whether we are witnessing highly
unusual conditions or not. In some ways, only the scientists studying long time
series of climate change have anything worthwhile to say about whether the Earth
is warming or not. Their data show that the Earth is warming, and it is doing
so at a highly unusual rate and toward highly unusual conditions. Concerning
the future, the balance between physics and history is a bit more difficult to
assess. We definitely need to generate mathematical simulations of the climate
machine using computer programs, and ask how these artificial climate systems
would react if we were to change the trace-gas content in the atmosphere, or the
amount of aerosol, or
the number of hurricanes, or any number of other conditions. (After all, we cannot
do these experiments any other way.)
But we also need to check somehow whether our machines perform realistically,
or whether they are too constrained (from a lack of understanding) to give what
we consider "reasonable" responses. To make the artificial machines into more
realistic performers, they need to be constructed in such a fashion as to be able
to simulate the past. In this sense, the past performance of the climate
system is a guide to its future behavior.
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