A Review of the Documentary "Thin Ice" produced by Oxford University, United Kingdom, Victoria University of Wellington, New Zealand (VUW), and London-based DOX Productions.
Written by Charles McKenna
Editor's note: The trailer for the documentary can be viewed at the end of this article.
Scientists have just released the results of new work that broadens their database and provides more accurate estimates of expected temperature rise due to climate change. Their recent conclusion: Past estimates of global warming have severely underestimated the actual temperature rise we are likely to experience.
Instead of an estimated 2-4 degrees Fahrenheit temperature rise for each doubling of carbon dioxide in the atmosphere, it will be more like 7-9 degrees. Right now, the atmosphere contains about 400 parts per million CO2 - and rising. That's close to 43 percent of the way to doubling the 280 ppm that existed before the industrial revolution. Unless we begin immediately to drastically reduce our fossil fuel use, by 2100 we could have temperatures that would result in a sea level rise of 10 meters, or about 33 feet, and a temperature increase of 8 degrees F or more. What would that do to coastal communities, our farms, to wildlife and to us?
The following is my attempt to better understand and articulate how the Earth's systems are responding to our additions of CO2 to the atmosphere. It is also a description of the recent work of climate research scientists around the globe that has led to a far more accurate predictive model for the climate warming consequences of our past and current use of fossil fuels.
"Past estimates of global warming have severely underestimated the actual temperature rise we are likely to experience."
CO2 in the atmosphere is the planet's primary system for regulating its surface temperature. It allows energy to radiate out of the atmosphere into space in limited amounts to balance what's needed from the sun to maintain a life-supporting range of temperatures. It's essentially an insulating blanket. And as we add CO2 to the atmosphere, we increase the thickness of the Earth's CO2 blanket and our temperatures increase. That's what's happening.
And as the planet warms, so, too, do the oceans. But due their size and depth they warm much more slowly and lag behind the atmosphere. The oceans, at their current temperatures, absorb about a third of the CO2 we add to the atmosphere. But as the oceans warm, they become less able to absorb CO2, which means that more of the CO2 we add to the atmosphere stays in it, thereby thickening our global blanket and creating more warming.
"So even if our carbon emissions were to stop immediately, we'd be in for significant additional warming."
This warming, in turn, further increases ocean temperatures, further decreasing the oceans' carbon dioxide absorption ability, leading to more warming, and so on. This feedback loop continues for years until the oceans' temperature distribution reaches a stable level relative to the temperature of the atmosphere. So even if our carbon emissions were to stop immediately, we'd be in for significant additional warming.
Recently, climate models have incorporated temperature and CO2 data from conditions that occurred millions of years ago when crocodiles and sub-tropical plants and animals were living in the arctic and there was no ice existing year-round on the planet. Using these data to calibrate their climate change models has shown that the Earth's warming sensitivity to CO2 is much higher than previously assumed, and that the predicted warming shown by these previous models was far too low.
"...the planet's climate was far more sensitive to CO2 [in deep geologic time when the earth was ice-free]"
Until now, models were calibrated based on reproducing the historical temperature change recorded over the past 100 years as it related to measured increases in CO2 in the atmosphere during that time. When these trends were extended into the future, it predicted a temperature rise that is now seen as far too low. To find CO2 sensitivity that would allow the computer models to take us from days when the planet was significantly warmer and accurately predict today's climate, they took sediment cores down 1,284 meters below the ocean floor under Antarctica's ice shelf and analyzed them to determine the amount of CO2 in the atmosphere millions of years ago. Using these figures and their corresponding temperatures, they found that the planet's climate was far more sensitive to CO2 then previously thought. This led to their revised predictions.
"One reason [for previous underestimation] involves the lag in the earth's CO2 warming response..."
One reason for this change, and the reason that only looking at the temperature rise over the last 100 years was insufficient, involves the lag in the earth's CO2 warming response - a warming response currently in its early stages. Much of that lag lies in the slow response of the ocean to warming by the atmosphere, and for its reduced CO2 absorption rates to eventually show their impact. It will take a long time for ocean temperature distribution to reach equilibrium. So without realizing it, by burning billions of tons of carbon-based fuels over a relatively few years, we have unknowingly committed ourselves to significant climate change whose growth will continue for many years.
The "Thin Ice" trailer can be viewed below.
Visit the thiniceclimate.org website for more information about the film and the people involved.