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I thank Sean O. for his contribution, even though I disagree with it.

Here's why: Sean disputes that there is a scientific consensus on the causes of global warming by citing one survey: "a recent study of scientists only 39% felt that carbon dioxide reductions were a priority."

First we need to separate the issue of science from politics and policy. In this particular survey of some group of scientists, only 39% say CO2 reduction is a priority. Whether it is a priority is a political and policy decision, not a scientific conclusion.

But to get to Sean's main question: Is there a scientific consensus?

The best way to answer that question is to examine the way the current consensus came about. It came about in the same way as scientific consensus always does. Scientists published their findings, and other scientists challenged their findings or suggested others. They allowed the evidence and analysis to speak for itself.

Over time, several climate models gained credibility by their ability to match the data to new observations. They were shown to have good predictive ability. None was perfect, and each had its set of climate conditions in which it proved quite valuable. Collectively, they are a phenomenal resource for helping us to figure out what lies ahead.

By changing the inputs to these models to reflect more or less CO2 in the atmosphere, researchers were able to compare what the climate of the past decades would have been without anthropogenic CO2. The results were striking—even compelling. They all revealed that the most of the recent warming can be attributed to human activities.

That finding has political implications, which is why the United Nations created the Intergovernmental Panel of Climate Change that includes leading scientists from around the world. The IPCC put the scientific consensus in terms that policy makers could use. The IPCC did not fund the research or create the consensus. It only collected the research and described the consensus.

This year's IPCC report states that the world is definitely warming and that it is highly probable (>90%) that human activities are the cause.

Another volume of the report describes the likely consequences of that warming. When I read about those consequences, I sincerely hope that policy makers make CO2 reduction a top political and social priority. It is totally irrelevant that a single survey of a group of scientists might place the priority lower.

Furthermore, that survey certainly doesn't negate the scientific consensus. Only new research can do that. Unfortunately for those who hope to get away without changing their lifestyles, most research is strengthening the consensus, though a few reports raise useful questions.

Those questions ought to be pursued. But the stakes are too high to delay formulation of policies while we wait for additional results.

Fred Bortz
Science and technology books for young readers (www.fredbortz.com)
and Science book reviews (www.scienceshelf.com)