With Speed and Violence Fred Pearce - Global Commons Institute

into the entire climate system. Occasionally that causes cooling and other
weird weather, but mostly it causes strong warming.
To summarize the current state of affairs: the global trends are real. No
known natural effect can explain the global warming seen over the past
thirty years. In fact, natural changes like solar cycles would have caused a
marginal global cooling. Only some very convoluted logic can avoid the
conclusion that the human hand is evident in climate change. Indeed, to
think anything else would be to flout one of the central tenets of science. The
fourteenth-century English philosopher William Ockham coined the
principle of Ockham's razor when he argued that, if the evidence supported
them, the simplest and least convoluted explanations for events were the
best. Changes in greenhouse gases are the simple, least convoluted
explanation for climate change. And those changes are predominantly
man-made.
This is not the end of the story, however. While we can be fairly certain that
more greenhouse gases in the air will push the atmosphere to further
warming, big uncertainties remain about how the planet will respond. An
assessment of the sensitivity of global temperatures to outside forcing
—whether to changes in sunlight or the addition of greenhouse
gases—mostly revolves around disentangling the main feedbacks: the things
changed by an altered climate that influence the climate in turn. Positive
feedbacks reinforce and amplify the change, and run the risk of producing a
runaway change—the climatic equivalent of a squawk on a sound system.
Negative feedbacks work in the other direction, moderating or even
neutralizing change.