Saturday, April 26, 2008

Are Skeptics Right? Is the World Cooling?

This is one of those moments when one must suck it up and take a hard look at one's convictions. The data have been showing right along that greenhouse gases have been driving climate change during the last half-century or so. Nothing else could explain why the global-average temperature was rising while solar activity declined after 1990.

But then the climate gremlins struck. Skeptics believed themselves fully vindicated when temperature data showed the global-average temperature to have declined during the last five years, with a very sharp drop in the last year. Here are two plots that show the striking effect.

Since we are determined to follow the science where it goes, not where we want it to go, this startling development demanded a cold-blooded analysis, not defensive handwaving.

The puzzle gains difficulty when we look at the data for the northern and southern hemispheres separately, as shown here. The northern hemisphere is continuing to warm up while the southern hemisphere has cooled a surprising amount. Before we can proceed, we have to understand why the two hemispheres would be so dissimilar. In particular, the skeptics can't claim to be right unless they can explain why the northern hemisphere is warming.

As we look at the data for the two, we see that they agree only in broad strokes. When we look at them in detail, we see that there are notable differences. For example, the southern hemisphere was warming in the 1960s while the northern hemisphere was cooling.

That doesn't help us much to understand what's going on, though. What does help us is the explanation of la Niña events, as given here together with some surface-temperature data, given here. The data show the effects of la Niña events, in which stronger winds over the South Pacific cause ocean water to turn over, bringing cold water to the surface. That explains the cooler average surface temperature over the southern hemisphere. The average temperature seems to be headed down; what actually is happening is that the last el Niño event (a period of relative calm over the South Pacific) was fairly strong and the current la Niña event is especially strong, putting a kink in the curve. It is not the case that the world is cooling off; rather, warm water is being driven down to lower depths and colder water is being raised to the surface.

So that's where we stand. La Niña events explain why the southern hemisphere is showing a cooler average surface temperature. Only global warming due to greenhouse gases explains why the northern hemisphere is warming.

It seems reasonable that global warming could be causing the stronger and more-frequent la Niña events, but that's a question for experts.

Monday, April 21, 2008

A Skeptic with a Degree

This article is a review of the book, Climate Confusion: How Global Warming Hysteria Leads to Bad Science, Pandering Politicians and Misguided Policies that Hurt the Poor, by Roy W. Spencer.

According to the dust jacket, Dr. Spencer holds a PhD in Meteorology and is a Principal Research Scientist in Climate Science at the University of Alabama. His expressed skepticism about human-caused climate change would, therefore, seem to be the clearest possible vindication of the skeptics' view on that topic.

Since Dr. Spencer is a professional scientist writing about his own specialty, one would expect any book he writes to be jammed with scientific information about this complex subject. But one would be disappointed. In fact, his scientific coverage extends over two pages, from page 80 to 82. In this short passage, he sums up the knowledge about climate change thus:

"First, we know that mankind is producing carbon dioxide as a result of our use of a wide variety of fuels, from coal and petroleum to natural gas and wood."

"A second observation we are certain of is that the carbon dioxide content of the global atmosphere has been slowly increasing. We are now about 40 percent of the way to a doubling of the pre-industrial concentrations of atmospheric carbon dioxide."

"Thirdly, we know that carbon dioxide is a greenhouse gas, which means that it traps infrared radiation and so tries to warm the lower troposphere to a higher temperature than if the gas was not there."

"Finally, we are pretty sure that the globally averaged surface temperature of the Earth is at least 1° Fahrenheit warmer now than it was about a century ago."

This is as clear a proof of climate change as could be imagined. Yet, Dr. Spencer demurs from stating the natural and obvious conclusion. Why, you may wonder. He says that he's withholding his conclusion because temperature rise and CO2 concentration rise might occur together only by coincidence. That is, global warming might be due to natural variability.

Natural variability is outside our experience with thermodynamic systems. We know why car engines warm up; it's because of fuel being burned. We know why houses warm up; it's either because the sun is beating on them or because of their furnaces. Our bodies warm up because we're exercising muscles or because the temperature control mechanisms are impaired by illness. But Dr. Spencer thinks it is realistically possible that Earth could just naturally change temperature without any cause. And that possibility prevents him from accepting the prevailing scientific view.

After seeing the subtitle of the book, though, one might wonder if that really is the reason. The other 180 pages could have been transcripted straight from hate-talk shows on AM radio. Environmentalists put the needs of wildlife above those of humans. Governments and philanthropic foundations reward and punish scientists according to their positions on climate change. Europeans prospered 1000 years ago because of unusually-warm conditions. People overreact when cities are wiped out by hurricanes. Scientists don't know as much as they think they do. Global warming is a religion. Politicians are using it as a trick for taking money away from working people. Scientists are milking it like a cow. Reducing emissions will harm the economy. The Precautionary Principle is wrong. Global warming is good for poor people. Left wingers killed millions of people by banning DDT. The United Nations works to make everybody poor.

Why is all this right-wing propaganda in a book written by a scientist? Since it takes up the largest part of the book by far, we can in all fairness ask if Dr. Spencer's skepticism is really due to scientific rigor or if his political views have overcome his objectivity.