A blast from the past (if we knew now what we knew then)

Peter Sinclair’s recent Climate Denial Crock of the Week is fascinating viewing. He has unearthed a video of a talk given by climate scientist Mike McCracken thirty years ago and asks him in a recent interview what he would say differently today.

Very little has changed. The younger McCracken:

“CO2 probably has been very high in past geologic terms but certainly not in past historic times, and so we’re really doing a giant experiment and the question is what is the outcome going to be?”

The lecture was some years prior to the detailed work of Michael Mann and others on the reconstruction of past temperatures, but the reconstruction used by McCracken, taken from a 1975 report from the US National Academy of Sciences, was not far off our current understanding of recent temperature rises to a level higher than humanity has experienced in at least the last 2000 years.

On fingerprinting the comparative effects of greenhouse gases and other possible factors such as the sun or volcanoes the lecture was very much in line with current understanding. Unlike the effects of solar radiation, the CO2 fingerprint is seen in the cooling of the stratosphere at the same time as the warming of the Earth’s surface. Polar amplification is the other fingerprint the younger McCracken discusses, explaining that the polar regions were warming more rapidly than those around the equator.

On climate sensitivity the lecture spoke of an estimated temperature rise of three, plus or minus one and a half, degrees for a doubling of CO2. This compares very well with the estimate of the 2007 IPCC report as “…likely to be in the range of 2oC to 4.5 oC with a best estimate of about 3 oC…”

Such an increase McCracken pointed out would be an unprecedented event in terms of human history.

Amplifying feedbacks were well understood. The lecture explained that increased water in the atmosphere as a result of warming will lead to more capture of solar radiation and more trapping of infrared radiation because water, like CO2, traps the outgoing radiation.  And this process will feed back on itself. McCracken also spoke of the effect of the reduction of sea ice in increasing the amount of radiation absorbed by the ocean.

Thirty years on the material presented by the younger McCracken is recognisably basic to our current understanding of climate change. And it’s not that he was advancing some individual insight. Quite the opposite. The older McCracken explains to Peter Sinclair: “I was trying to represent the view of the broad scientific community.”

In other words the basic scientific evidence for human-caused climate change was clear thirty years ago.  And it was capable of being communicated to government agencies and lay audiences.

Sinclair to McCracken:

“So now it’s thirty years later. We haven’t done a whole lot to address this. Are you surprised?”

McCracken’s reply:

“I’m disappointed. I’m becoming very worried about how fast it’s occurring. What’s been evident in the impact of the changes is that they are occurring faster than we projected they would.  We’re seeing the sea ice disappearing in the Arctic faster than the models are projecting.”

Sinclair’s video illustrates in an arresting way that the science of climate change has been coherent and readily communicable for some decades, and that in the passing of time as research continues there is only confirmation of its basic understandings. The conservatism of its conclusions is underlined by the fact that some of the predicted impacts are occurring much more quickly than was expected. It’s a sad commentary on human society that we remain unable to fully take on board the science and its implications.

The gratification of those such as Lord Lawson who set themselves up in opposition to the science is all the more sickening when one considers how well-founded the scientific picture now is. He was self-congratulatory recently in hailing the success of his Global Warming Policy Foundation (GWPF):

“Before we came into existence there was virtually no debate about global warming policy in the UK. There is now increasingly lively debate and, within the media, only the BBC continues to regard the matter as being definitively settled and not a proper subject for debate. The GWPF has played an important part in achieving this change.”

Good on the BBC, I say, though I would have thought the Guardian would also merit his displeasure.

What to do?  Sinclair’s video ends with McCracken speaking of a colleague who went home very discouraged to his daughter, a fifteen-year-old. She listened to his discouragement and protested. “You can’t take away my hope.”

McCracken concludes: “I think we have an obligation to try and see if we can’t find a path…”


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