January 26, 2005

Yesteryear’s Climate Catastrophe

Filed under: Climate History

We’ve been waiting for this one. Back when acid rain was all the rage, it was acid rain that was blamed for the greatest extinction in earth’s history. A few years later, along came concern about the ozone hole and it, purportedly, caused a different huge extinction. Now, it’s Global Warming: Mass Murderer.

Before you get too worked up about recent headlines linking global warming and mass extinctions we want to, in the not-quite inimitable words of Richard Nixon, make one thing perfectly clear (well two, actually). First, earth was a very different place 250 million years ago when the last mass extinction took place. Second, global warming then is not comparable to global warming now. Nonetheless, Reuters was eager to shout, “Global Warming May Have Caused Extinction — Study” in its recent headline. CBS — a paragon of source vetting — dubbed it an “Ancient Global Warming Disaster.” Meanwhile, TheWashington Post in something just short of panic used a headline to opine: “Extinction Tied to Global Warming: Greenhouse Effect Cited in Mass Decline 250 Million Years Ago.”

All this media hubbub draws attention to a pair of papers recently published in Science magazine’s on-line pre-publication section Sciencexpress. The editorial philosophy behind Sciencexpress appears to be, “We’ve got a paper to publish that’s just too hot for Science to sit on while it works its way through the normal print publication process.”

Both papers concern paleological research aimed at shedding greater light on the cause of an apparent worldwide mass extinction about 250 million years ago referred to as the “Great Dying.” That even marks the boundary between the Permian and Triassic periods. Scientists believe during the Great Dying about sixty percent of all land species and ninety percent of all ocean species abruptly died out. In the formulation used in those Lemony Snickett’s books, “abrupt” in this context means “over the course of tens to hundreds of thousands of years.”

A popular theory is that a meteor impact, similar to the one believed to have caused the mass extinction at the Cretaceous/Tertiary boundary about 65 million years ago, might be the cause of the Great Dying. But two research teams (one working with fossil data collected in South Africa and the other with data collected from sites in Western Australia and in South China) find no evidence of a large meteor’s impact. One set of researchers find evidence suggesting that the die-off was more protracted and less sudden than likely would be the case after a devastating meteor strike. The other group believes they discovered what might have been the cause.

That team, headed by the University of Washington’s Peter Ward, spent seven years collecting fossil skulls from the Karoo Basin in South Africa. They examined the distribution pattern in the fossils throughout geologic strata and were able to assess the sequence and timing of the observed extinctions. They interpret their findings to be “consistent with a period of environmental stress…punctuated by a short interval of even greater perturbation.” They suggest “a single proximal cause might explain the extinction patterns, such as a long-term environmental degradation having reached a critical threshold that triggered a short term extinction event through ecosystem collapse.”

As to what form this environmental degradation took, Ward and his colleagues open their paper with a list of hypothetical causes advanced by other researchers. Their list includes “climate change due to increased atmospheric CO2 and/or CH4 [methane], the effects of extraterrestrial impact, the effect of the eruption of the Siberian Traps, and some synergistic combination of these, among others.” But, nowhere in their paper do they advance a theory as to the cause of the deteriorated environmental conditions other than to say signs of extraterrestrial impact are not well manifest in their results.

The second paper is by a team led by Kliti Grice of the Curtin University of Technology in Perth, Australia. Grice’s team analyzes the chemical make-up of various strata extracted from two sediment cores. One was drilled in western Australia and the other in southern China. They looked for evidence they could use to test a theory that the oxygen content of the atmosphere and oceans had been drawn down to levels sufficiently low to cause mass extinctions. They found evidence that not only did oxygen levels appear to have been very low, but that levels of poisonous sulfur were greatly elevated. This combination, they suggest, proved deadly. “We propose that sulfide toxicity in the ocean and emissions of hydrogen sulfide to the atmosphere was an important driver of the largest mass extinction in the past 500 million years and may also have been a factor in the protracted recovery.” Guess what? Nowhere in this paper is there any mention of “global warming.”

So on what do the headlines hang linking the mass extinctions to global warming? Apparently, representative authors of the papers were willing to tell reporters they feel an enhanced greenhouse effect from large-scale volcanic outgassing is behind the climate changes that triggered to the extinctions. Ward is quoted by Reuters as saying, “Animals and plants both on land and in the sea were dying at the same time, and apparently from the same causes — too much heat and too little oxygen.” The chain of events in Ward’s theory actually is a lot more complicated than global-warming-heated-things-up-and-everything-died.

The so-called global warming in this particular instance involved large-scale volcanism in Siberia accompanied by an increased atmospheric concentration of greenhouse gases (among them carbon dioxide and methane), a large drop in sea level, big declines in the atmospheric concentration of oxygen and in the oceans, a big rise in atmospheric and oceanic concentrations of poisonous sulfur compounds, and other things. Even if this alternative theory can ever proven to be the right, saying global warming caused the Great Dying is far easier in the popular press than when making a case for it than in peer-reviewed scientific literature.

It appears our friends in the press corps and a cadre of scientists and politicians eager to link whatever catastrophe they can to the phrase “global warming” (even if it was 250 million years ago) in order to advance their social, political, and/or financial agendas seek, in novelist Michael Crichton’s phraseology, to foster and maintain a State of Fear.

Despite recent headlines, the global warming we know today isn’t the same as contributed to mass extinctions 250 million years ago . Saying global warming caused the Great Dying is a far easier in the popular press than making a case for it than in peer-reviewed scientific literature.

Consider this. You’re trolling for research dollars to explain The Great Dying. Whatcha gonna use, today’s hot topic or yesterday’s? Just last year, Visscher et al. in the Proceedings of the National Academy of Sciences concluded the Great Dying was caused by a huge ozone hole. Back in 1988, Rampino and Volk grabbed a lot of press when they blamed acid rain for the mass extinction that killed the dinosaurs. In a state of funding fear, when Uncle Sam is willing throw money at environmental scientists, you’re well-advised to use the issue du jour so that your research proposal appears to address what just happens to be the most important player in our planet’s past, present, and future.

References:

Brice, K., et al., 2005. Photic Zone Euxinia During the Permian-Triassic Superanoxic Event. Sciencexpress, January 20, 2005.

Crichton, M., 2004. State of Fear. New York: Harper Collins Publishers, 603pp.

Rampino, M. R. and Volk, T., 1988. Mass extinctions, atmospheric sulphur and climactic warming at the K/T boundary. Nature, 332, 63-65.

Visscher, H., et al., 2004. Environmental mutagenesis during the end-Permian ecological crisis. Proceedings of the National Academy of Sciences, 101, 12952-12956.

Ward, P.D., et al. 2005. Abrupt and Gradual Extinction Among Late Permian Land Vertebrates in the Karoo Basin, South Africa. Sciencexpress, January 20, 2005.




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