April 12, 2005

Where are the headlines?

Filed under: Climate Forcings

New research shows that there has been no significant long-term trend (since measurements began in 1979) of the atmospheric concentrations of “hydroxyl radicals,” an important chemical species that helps to cleanse the atmosphere. This should have been big news. Let’s turn back the clock and see why.

Three years ago, in May 2001, Science magazine published a paper by M.I.T. scientist Ronald Prinn and collaborators that reported on a huge decline in the these radicals, known chemically as OH. OH is highly reactive. It reduces atmospheric levels of industrial emissions of methane, carbon monoxide, and sulfur dioxide.

That tied the decline of OH to global warming, because methane is one of the most potent of the human greenhouse emissions. Interestingly, its behavior in recent years should have tipped Prinn of that something was fishy with the OH story.

Anyway, the decline of OH was postulated to be linked to anthropogenic activities, providing another example of how mankind was harming the climate of the earth by causing the reduction in levels of an atmospheric cleaning compound. The logic seemed a little stretchy. Here’s what the 2001 paper said:

The overall negative acceleration [since 1989] in the global OH trend is dominated by changes in the northern hemisphere and suggests an anthropogenic cause for the major OH variations.

In other words, if there is a chemical change in the atmosphere where there is a high concentration of people, it must be caused by people.

Despite a rather loopy piece of logic that the peer-reviewers should have shot out of the 2001 paper (to see why, see here and here), the press went ga-ga. Reuters: “Atmosphere’s Pollution-fighting Chemical Waning.” AP: “Decline in Natural Air Cleaner.” New York Times: Study Finds a Decline in Natural Air Cleaner,” with the quote “Uncertain measurements tied to global warming.”

Not only did Prinn’s 2001 paper indicate that atmospheric OH levels were declining, but that they were accelerating downward (Figure 1). Prinn et al. describe the downward curving pink line in Figure 1 as a “polynomial fit” to the annual OH concentrations, and that the “trend accelerations represented by these polynomials are significantly nonzero.”

Atmospheric OH levels

Figure 1. Annual global average OH concentration (and error bars). The downward curving pink line is a polynomial fit to the data. (Source: Prinn et al., 2001).

The behavior of atmospheric methane should have tempered Prinn, even at that time. It had risen steadily from the first measurements in the early 20th century through 1990. Then the increase slowed, and finally stopped. Something was abating the increase in methane, and OH is a pretty good candidate.

Last week, Prinn and his team updated the OH record in a paper in Geophysical Research Letters. OH levels stopped declining and have now risen back up to the same levels that they were in 1979 (Figure 2)! And surprise, surprise, there has not been one single newspaper article that we have found that reports on this new result.

Atmospheric OH levels

Figure 2. Average annual atmospheric concentration of OH. The solid line is a polynomial fit to the data (from Prinn et al., 2005).

As for Prinn himself, he appears to recognize that things were a bit overplayed three years ago. In his GRL abstract he writes:

Analysis of these observations shows that global average OH levels had a small maximum around 1989 and a larger minimum around 1998, with OH concentrations in 2003 being comparable to those in 1979. This post-1998 recovery of OH reported here contrasts with the situation 4 years ago when reported OH was decreasing. The 1997–1999 OH minimum coincides with, and is likely caused by, major global wildfires and an intense El Nino event at this time.

This turnaround, from a human-induced decrease (reported in 2001) to largely natural variation (including the recent increase), reminds us the recent writing of NASA’s James Hansen, the scientist who started the bonfire of the greenhouse vanities with his inflammatory 1988 congressional testimony. From the 2003 journal Natural Science:

Emphasis on extreme scenarios may have been appropriate at one time, when the public and decision-makers were relatively unaware of the global warming issue. Now, however, the need is for demonstrably objective scenarios, consistent with what is realistic under current conditions.

One lesson here is that a couple of years at the end of a record should not be interpreted as an anthropogenerated trend. The other lesson, of course, if that if you want a lot of press coverage, and publication in a prestigious journal, interpret a couple of years at the end of the record as a anthropgenerated trend, not matter how tenuous the logic or how sketchy the data. In today’s climate of hype-by-science, the peer-reviewers are guaranteed to look the other way.

References:

Hansen, J.E., 2003. The global warming time bomb? Natural Science, http://www.naturalscience.com/ns/articles/01-16/ns_jeh.html

Prinn, R.G., 2001. Evidence for substantial variations of atmospheric hydroxyl radicals in the past two decades. Science, 292, 1882-1888.

Prinn, R.G., et al., 2005. Evidence for variability of atmospheric hydroxyl radicals over the past quarter century. Geophysical Research Letters, 32, L07809, doi: 10.1029/2004GL022228.




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