Iain Stewart

Caught between a rock and a warm place: A geologist's perspective

3 March 2011

Dr Iain Stewart, earth scientist and TV presenter

Earth scientist and TV presenter Iain Stewart looks at how geologists view global warming.

"As a scientist, you should be ashamed of yourself," proffered one helpful email.

Another derided: "...thank-you for this scatological attack on honest scientists who are trying to really understand the data. It will only come back to haunt you."

Such scathing comments from ardent rejectionists of mainstream climate science wasn't entirely unexpected given that my BBC television series, Earth: The Climate Wars, had just endorsed the climate science behind global warming.

Geologists' antipathy

More surprising to me, however, was the antipathy that came from fellow geologists.

One lamented: "I am a single honours geology graduate... and I find myself quite shocked, that you, as an earth scientist yourself, will ignore a view of cyclicity - of cycles within cycles within cycles."

It is a fair point. Earth history is all about cycles. It is a story of the unceasing motion of landmasses that constantly scatter and reform, and of the perpetual change of a planet wobbling along an elliptical orbit around the Sun. The combination orchestrates a climate that switches episodically between greenhouse and icehouse states. Which is exactly why many geologists abhor the implied notion that climate change is somehow a modern aberration.

"Climate is, and will continue to be, created and controlled by immense and complex natural forces, not by political fact, " chides one geologist, Bob Carter. He goes on to argue,  in his book, Climate - The Counter Consensus, that: "Any practical way forward out of the present 'stop global warming' fiasco must acknowledge that reality."

It's a question of time

Acknowledging that reality, it seems, necessitates a different view of time.

It is argued that politicians, journalists and the public are gullible over climate change because they lack a long-term perspective on how the Earth's ambient conditions can, and do, vary. In contrast, geologists, by virtue of an intimate appreciation of 'deep time' (i.e. change over many billions of years), have a better handle on this.

In his work Heaven and Earth, Ian Plimer, an economic geologist thoroughly unconvinced by 'global warming speak', puts it succinctly: "Human forces are orders of magnitude lower than natural forces that drive climate. The global cooling and warming observed during the last 150 years is just a short episode in geologic history and current global warming is most likely a result of the combined effects of many natural drivers of climate, and cannot be attributed to human impact."

Higher carbon dioxide levels

So, do the rock-tinted spectacles of deep time give a different lens through which to examine global warming?

The likes of Plimer and Carter argue yes, because:

  • When viewed over the last billion years, we humans live in a CO2-deficient world. Back when complex life really started motoring, levels of this greenhouse gas were in the thousands of parts per millions, rather than the paltry 386 ppm or so that vexes us today.
  • At least two global ice age gripped that CO2-choked world, so temperatures and greenhouse gas levels need not be coupled; cosmic ray fluxes appear to give a clearer partnership.
  • In an echo of the view that global warming will be good for crop productivity, the balmy conditions in which early life evolved was a positive boom.

 "Global warming and high CO2 do not lead to extinction", contends Plimer. "Warming creates biodiversity, a thriving life, species migration and adaptation."

C02 and mass extinction of species graph

Fig 1. Plot of atmospheric CO2 levels from 550 million years ago to present and highlighting the timing of major and minor mass extinctions of life.

(Source: modified from Ward, P. 2007 Under A Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Their Future, Harper Collins, New York)

Geological consensus

On most of these aspects, however, Plimer and fellow geo-contrarians are out-of-step with the geological consensus.

Biological crisis

Leading palaeontologists now regard dramatic bouts of global warming as instigating the biggest biological crises in the fossil record. Among those geochemists tracking the chemical signatures of past atmospheres there is little patience for talk of cosmic rays. Instead a crude, but convincing, correlation between temperature and carbon dioxide prevails. Crude simply because of the demands of the rock record.

Details lost in time

While the recent history of carbon dioxide levels comes from modern instruments, or before that from annual coral or tree growth rings or snow layers, the distant geological history of CO2 marches back in steps of 10 million years. In other words, the further back you peer in time, the more the subtle intricacies of climate are smeared out.

In that sense, it is rather like watching an inter-city train speed through a minor station - distant carriages can be seen with some semblance of detail but close up all resolution is lost as passengers whiz by. The point is, for all its longevity, the geological record is a rather blurry instrument with which to challenge modern climate theories.

Geological record

Fig 2. Schematic plot of the scale and timescales of the climate system, highlighting how geologists focus on large-scale mechanisms operating over millions of years (white area).

The extent to which geological studies reveal the shorter-term semi-chaotic intricacies of the climate system (green area) is questionable.

(Source: modified from Maslin et al. (2003) "Evidence of Holocene climate variability from marine sediments" In Global Change in the Holocene (Ed: A. Mackay, et al.))

Pockets of resistance

It is the very opaqueness of the planet's past that allows 'maverick' geoscientists to root their scepticism in the rocks. I use the term 'maverick' deliberately, because it is clear that the bulk of geologists appear entirely satisfied with the prevailing scientific view.

All the major scientific bodies have a position statement confirming that contemporary changes to climate are out of kilter with past natural cycles and were very likely to reflect human activity. These include:

Only the American Association of Petroleum Geologists is equivocal on the issue, perhaps unsurprising given the findings of a 2009 survey of earth scientists . Although more than 90% of geoscientists consulted supported the theory of human-induced climate change (and in the case of active climate change researchers, more than 97%), economic geologists led the dissenting pack at 55% - interestingly, with meteorologists close behind at 64%.

Overall, it is clear that geology is no festering hotbed of anti-warmist revolutionary turmoil, but there are undoubtedly isolated pockets of resistance amid those that fear the economic repercussions.

What is perhaps more problematic to the majority is precisely what role, utility or value the past record of the rocks has in helping contemporary climate change. After all, as Plimer complains: "If we cannot understand the biggest climate changes of all times, then we have to be circumspect about claiming that we can understand modern climate."

To the chagrin of many of my geological colleagues, I think this is one sceptical statement with which I tend to agree.

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