“A fact is a simple statement that everyone believes. It is innocent, unless found guilty. A hypothesis is a novel suggestion that no one wants to believe. It is guilty, until found effective.”
—Edward Teller
There are many skeptics and deniers of global warming out there. And they have different points along a spectrum of denial where they reside. Some are stick-their-heads-in-the-sand deniers that don’t believe global warming is even taking place, despite overwhelming evidence to the contrary. Others believe in the changing climate our planet is experiencing but don’t believe the conclusion that it’s due in large part to our greenhouse gas emissions. Some of these people are even very well versed in scientific knowledge and choose to hold onto “facts” put forth from the two percent of fringe scientists who don’t believe what the mainstream scientists and every national academy of science around the world believes: that it’s our fault.
One of the arguments often quoted from this educated group is that in eons past, when there have been increases in carbon dioxide and increases in global temperatures, the carbon dioxide levels lagged behind the temperature rise and not the other way around. This theory was supported by an article published in Science magazine, so a reputable scientific journal was helping advance this concept, not just some fringe journal that nobody has ever heard of.
In fact, science would support that increasing temperatures around the planet should lead to a secondary increase in carbon dioxide levels, at least in part. Most of our planet’s history over the last 500,000 years has been one of long ice ages with brief periods of warming known as interglacials. These interglacials come along about every 100,000 years and are largely due to Milankovitch cycles, those subtle changes in Earth’s orbit around the sun.
One result of increasing global temperatures is that carbon dioxide becomes less soluble in the deepest part of the oceans where it is usually found as carbonic acid. As a result, it is more likely to escape back into the atmosphere as carbon dioxide gas, although the mechanism behind this phenomenon is not well understood. And since carbon dioxide is a greenhouse gas and therefore helps to trap heat, it will help to amplify the initial temperature rise.
Interestingly, a new study just reported in Science Daily suggests that the longest interglacial reported within the last half million years seems to have been driven mostly by carbon dioxide levels, rather than this reported lag phenomenon. This particular interglacial that was studied has the rather unexciting name of MIS 11 (for marine isotope stage 11) and occurred about 400,000 years ago.
Paleoclimatologists, those scientists who try to study the climate of the past, prefer to study MIS 11 because that particular era closely matches what our planet has been experiencing over the last 5,000 years with respect to greenhouse gas levels, orbital configurations of our planet, and climate in general.
Das Dharma and his team looked at fifteen different parameters of marine and terrestrial climate during MIS 11 and used new statistical and mathematical techniques to try to quantify the particular interactions among them, trying to determine which parameters were the driving forces behind the climate change observed at the time.
Their conclusions are that atmospheric carbon dioxide was the primary driver for climate change both on land and in the oceans. Their observations indicate that sea surface temperatures and the isotope makeup of carbon in both land and sea reservoirs responded “instantaneously,” which is to say within 1,000 years on this type of time scale.
One interesting observation they made is that during the colder phases of MIS 11, sea surface and air temperatures responded very quickly to any increase in atmospheric carbon dioxide levels, more so than when MIS 11 was going through warmer phases and the factors appeared more independent of each other.
A final conclusion of the authors is that it is likely going to be very difficult to accurately predict air and sea surface temperature changes over the next century, given the complexity of these various interactions. That will be welcome news to the skeptics and deniers who like to point out how poorly some prediction models have been so far, indicating that concerns about rising greenhouse gas concentrations are unfounded as a result.
As far as I’m concerned, I think any criticisms of this type are misplaced. First of all, it’s extremely difficult to derive completely accurate records of our planet’s climate from hundreds of thousands of years ago to a point where there’s no room for argument. Secondly, this present time in our planet’s history is completely without precedent. In the past, any changes in carbon dioxide levels and global temperature were completely due to natural cycles. Now, however, we have changed that. By adding over a trillion tonnes of carbon dioxide to the atmosphere in the last fifty years, now at a rate of greater than 31 billion tonnes a year and continuing to climb, we have altered one significant parameter in a very unnatural way. This makes it doubly difficult to use the past to tell us how the present and future will be with respect to climate change.
Regardless of how skeptics and deniers will attack these data, it’s certainly interesting to see more evidence that even in the past, atmospheric carbon dioxide was at some points the primary driver of global warming during interglacial periods. It only makes sense that it would be again.
