Climate Science Is Not Settled
We are very far from the knowledge needed to make good climate policy, writes leading scientist Steven E. Koonin
There is little doubt in the scientific community that continually growing amounts of greenhouse gases in the atmosphere, due largely to carbon-dioxide emissions from the conventional use of fossil fuels, are influencing the climate. There is also little doubt that the carbon dioxide will persist in the atmosphere for several centuries. The impact today of human activity appears to be comparable to the intrinsic, natural variability of the climate system itself.
Rather, the crucial, unsettled scientific question for policy is, “How will the climate change over the next century under both natural and human influences?” Answers to that question at the global and regional levels, as well as to equally complex questions of how ecosystems and human activities will be affected, should inform our choices about energy and infrastructure.
But—here’s the catch—those questions are the hardest ones to answer. They challenge, in a fundamental way, what science can tell us about future climates.
Even though human influences could have serious consequences for the climate, they are physically small in relation to the climate system as a whole. For example, human additions to carbon dioxide in the atmosphere by the middle of the 21st century are expected to directly shift the atmosphere’s natural greenhouse effect by only 1% to 2%. Since the climate system is highly variable on its own, that smallness sets a very high bar for confidently projecting the consequences of human influences.
A second challenge to “knowing” future climate is today’s poor understanding of the oceans. The oceans, which change over decades and centuries, hold most of the climate’s heat and strongly influence the atmosphere. Unfortunately, precise, comprehensive observations of the oceans are available only for the past few decades; the reliable record is still far too short to adequately understand how the oceans will change and how that will affect climate.
A third fundamental challenge arises from feedbacks that can dramatically amplify or mute the climate’s response to human and natural influences. One important feedback, which is thought to approximately double the direct heating effect of carbon dioxide, involves water vapor, clouds and temperature.
Read the full article: http://online.wsj.com/articles/climate-science-is-not-settled-1411143565