Australian physicist John Cook, in a Skeptical Science cross-post
Of all the people that doubt the science of climate change, geologists seem to be the most vocal. But they, of all people, should be the most concerned.
I was headed to the Sydney ABC studio to talk about my new book on climate change denial. What was unique about this interview was my coauthor Haydn Washington and I would have the opportunity to answer questions from callers. Considering the topic at hand, we expected some demanding questions from those who doubt the climate science. On the way, I declared to Haydn I’d put money on someone bringing up past climate change. In every interview over the weeks following the launch of our book Climate Change Denial, the same question always arose: “Climate has changed naturally in the past so how do we know current climate change is caused by humans?”
Haydn wisely didn’t accept the wager. And sure enough, the first caller (listen) introduced himself as a geologist and proceeded to discuss past climate change. Afterwards, I reflected on geologists and the perception that they tend to be sceptical about human-caused global warming. Australia’s most well known skeptic, Ian Plimer, is a geologist, as is another well known sceptic Bob Carter. But is the characterisation that geologists are mostly sceptics accurate?
One survey of earth scientists found that while 97 per cent of actively publishing climate scientists agree humans are changing global temperatures, only 47 per cent of economic geologists (those who study geology with a view to its commerical exploitation) concur (pdf). In fact, among all earth scientists, economic geologists are the most sceptical.
Similarly, in response to the consensus on global warming, the American Association of Petroleum Geologists “respects these scientific opinions but wants to add that the current climate warming projections could fall within well-documented natural variations in past climate and observed temperature data”. You’d call that type of endorsement damning with faint praise.
However, the broader community of geologists seems convinced by the evidence that humans are causing global warming. The European Federation of Geologists says climate change is predominantly caused by anthropogenic emissions of CO2 and poses significant risks to human civilisation. The Geological Society of America concurs that “greenhouse gases have been an increasingly important contributor [to global warming] since the mid-1800s and the major factor since the mid-1900s”. The Geological Society of London states that “evidence from the geological record is consistent with the physics that shows that adding large amounts of carbon dioxide to the atmosphere warms the world and may lead to: higher sea levels and flooding of low-lying coasts; greatly changed patterns of rainfall; increased acidity of the oceans; and decreased oxygen levels in seawater”.
So climate scepticism seems strongest among geologists closely linked to the mining and fossil fuel industries. Perhaps the words of Upton Sinclair shine some understanding on the forces at play here: “It is difficult to get a man to understand something, when his salary depends upon his not understanding it.”
Regardless of motive, the question of past climate change is certainly an important one that provides much insight into how our climate behaves. Plimer’s conceit is that as a geologist, he has taken into account Earth’s past while climate scientists have ignored it. This is a curious position considering there is an entire field of climate science, paleoclimatology, that examines past climate change. What do they find?
Climate has changed in the past. Sometimes it changes quite dramatically. Why? When something causes a change in global temperature, such as varying solar activity or changes in the Earth’s orbit, feedbacks amplify these changes. The atmosphere grows more humid and as water vapour is a greenhouse gas, this traps more heat. Arctic sea ice melts, causing the exposed ocean to absorb more heat. The feedbacks aren’t so large that they lead to runaway warming but they are enough to amplify one degree of greenhouse warming to three degrees of total warming. Many different periods throughout Earth’s history, from the last few millennia to millions of years ago, yield remarkably consistent results establishing this amount of climate feedback.
When geologists bring up past climate change, they’re actually citing evidence for climate feedback. Dramatic swings in global temperature, dragging the planet in and out of ice ages, are possible because of these feedbacks. Renowned paleoclimatologist Wally Broecker sums it up beautifully: “The paleoclimate record shouts out to us that, far from being self-stabilising, the Earth’s climate system is an ornery beast which overreacts to even small nudges.”
We have already given our climate a big nudge. How do we know it’s us causing the warming and not natural causes? Because we’ve directly measured it. Satellites measure reductions in heat escaping to space – direct empirical evidence that carbon emissions are trapping heat. Surface measurements measure more heat returning to Earth, confirming the increased greenhouse effect. We see many signatures of greenhouse warming such as winters warming faster than summers, cooling upper atmosphere with warming lower atmosphere and nights warming faster than days. The case for human-caused warming is based on many independent lines of evidence.
The feedbacks that amplified past climate change are now amplifying the warming caused by our carbon emissions. We’re measuring more water vapour in the atmosphere, a strong feedback. Arctic sea ice is disappearing and satellites measure less sunlight reflected back to space – another significant feedback. The Earth’s past and modern measurements all paint a consistent picture – our climate is already overreacting to our “nudge”.
The peer-reviewed literature on past climate change sends a strong message, in stark contrast to what we hear from petroleum geologists. Past climate change is not a source of comfort. It’s a cause for concern.
– John Cook