An Abrupt Climate Change Scenario and Its Implications for United
States National Security
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Pentagon report prepared
By Peter Schwartz and Doug Randall
Imagining the Unthinkable
The purpose of this report is to imagine the unthinkable � to push the boundaries of current
research on climate change so we may better understand the potential implications on United
States national security.
We have interviewed leading climate change scientists, conducted additional research, and
reviewed several iterations of the scenario with these experts. The scientists support this
project, but caution that the scenario depicted is extreme in two fundamental ways. First,
they suggest the occurrences we outline would most likely happen in a few regions, rather
than on globally. Second, they say the magnitude of the event may be considerably smaller.
We have created a climate change scenario that although not the most likely, is plausible, and
would challenge United States national security in ways that should be considered
There is substantial evidence to indicate that significant global warming will occur
during the 21st century. Because changes have been gradual so far, and are projected
to be similarly gradual in the future, the effects of global warming have the potential
to be manageable for most nations. Recent research, however, suggests that there is a
possibility that this gradual global warming could lead to a relatively abrupt slowing
of the ocean�s thermohaline conveyor, which could lead to harsher winter weather
conditions, sharply reduced soil moisture, and more intense winds in certain regions
that currently provide a significant fraction of the world�s food production. With
inadequate preparation, the result could be a significant drop in the human carrying
capacity of the Earth�s environment.
The research suggests that once temperature rises above some threshold, adverse
weather conditions could develop relatively abruptly, with persistent changes in the
atmospheric circulation causing drops in some regions of 5-10 degrees Fahrenheit in
a single decade. Paleoclimatic evidence suggests that altered climatic patterns could
last for as much as a century, as they did when the ocean conveyor collapsed 8,200
years ago, or, at the extreme, could last as long as 1,000 years as they did during the
Younger Dryas, which began about 12,700 years ago.
Download the report in PDF format (940k)
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