It’s been more than a decade since An Inconvenient Truth debuted, so you are all well aware that over the past 800,000 years, periodic changes in Earth’s temperature have generally followed those in greenhouse gases like carbon dioxide (CO2). We know this primarily from the study of ice cores, which simultaneously provide the following bits of information:
- Multiple proxies for the average air temperature during snowfall (i.e. when each layer of ice was formed), and…
- Trapped bubbles of local atmosphere, from which we can infer the concentration of CO2, CH4, and other gases.
Now, this is not a post about whether CO2 increases temperature or temperature increases CO2 (both statements are true), or even about Answers in Genesis’s own rantings against climate science, which are so badly misinformed that they refute themselves. Instead, I want to posit a more fundamental question to those like Ken Ham, who believe that both the Greenland and Antarctic ice sheets are younger than Noah’s Flood:
Why, in our layer-by-layer analysis of glacial ice, do we find any correlation between CO2 and proxies for air temperature?
Think about this question for a moment. Young-Earth Creationists insist that glaciologists have overestimated the age of continental ice sheets by a factor of up to 200, concealing their true age of ~4,000 years. Given that ice sheets exhibit annual cycles in their chemistry and appearance well beyond 20–45,000 years (depending on the location), this is a bold claim indeed. But let’s grant—for the sake of discussion—that critiques by Michael Oard and others are correct, and that more than 26.5 million km3 of glacial ice accumulated in Antarctica alone within a few centuries following Noah’s flood.
The young-Earth timeline would imply that large fluctuations in stable-isotope ratios of oxygen (δ18O) could not actually reflect air temperature (which slowly adjusted to changes in Earth’s orbit, etc.), but rather some chaotic and complicated weather processes during the post-Flood ice age. Of course, this position is untenable, due to the covariation between ice core data from one pole to the other, and between ice cores and cave/marine archives (figure right), but again, we’re giving YEC’s the best possible benefit of the doubt. If oxygen-isotope variations within Antarctic ice cores do not reflect global air temperature, however, then why do they track variations in carbon dioxide and methane?
Scientists have long understood that Earth’s atmosphere is warmed by gases such as CO2, which absorb infrared radiation. Even the most skeptical of global warming contrarians acknowledge that these variables had an intimate connection for much of Earth history. Therefore, it makes complete sense that we should find a positive correlation between them in high-resolution datasets like ice cores. The impact of greenhouse gases on air temperature, for example, is called radiative forcing. When the sum radiative forcing of those gases (as reconstructed from Antarctic ice cores) is compared against global temperature (as inferred from δ18O in Antarctic ice cores), here is the result:
Note that variations in greenhouse gases track not only air temperature over the ice sheet, but water temperature in the deep ocean. In other words, greenhouse gas concentrations are closely linked to global climate, according to the analysis of Antarctic ice sheets. Makes sense, right?
Sure, unless you’re a Young-Earth Creationist.
One cannot seriously contend that Earth’s temperature oscillated wildly every 10-20 years following Noah’s Flood and that these fluctuations were caused by changes in greenhouse gases. Since the atmosphere and oceans are such large reservoirs, there is too much thermal inertia for temperature changes to occur so rapidly and too large a mass of carbon for greenhouse gases to fluctuate so rapidly. Where did the heat come from and where did it go? The same can be asked with respect to trace gases.
Put succinctly, the only way to reject chronologies derived from the Greenland and Antarctic ice sheets—which collectively document global climate change over the past 800 millennia—is to reinterpret their stable-isotope data arbitrarily to reflect some phenomenon besides global air temperature. However, this leaves one in an even more uncomfortable position, having to explain the covariance of these data with greenhouse gas concentrations. From a young-Earth perspective, the relationship must have been accidental. Arguing from the absurdity of its consequences, therefore, we can safely reject Ken Ham’s position that the Greenland and Antarctic ice sheets resulted from a global flood.
Featured image: Awesome Antarctica!