Let’s talk about atmospheric carbon

Since a fellow science blogger has closed her post “Why can’t we talk about atmospheric carbon?” to comments, and has not accepted my most recent critical comment to her previous blog entry “Ancient carbon dioxide: Surprisingly Irrelevant?”, I have decided to continue the discussion here. She is welcome to argue her case without concern that I will screen or change her comments.

My issue with her earlier entry was journalistic, not scientific. I like the idea that she has decided to feature the work of early-career scientists. In fact, I do something similar every Friday at my Facebook SciFact Central page. I feature scientists whose work I think should be better known to my young readers either for the science or for an interesting biography.

What bothered me most about her first entry was the title which implied that CO2 in the atmosphere was not relevant to global temperatures in the late miocene period. In fact, the research she cites was not disputing the importance of the greenhouse effect due to CO2 at that time. Rather, the researcher noted that the temperature at that time was warmer than at present even though the CO2 levels were comparable to the concentrations in the pre-industrial period (lower than today by about 100 parts per million). Given what we know about greenhouse gases, the temperature should have been lower, everything else being equal.

Of course, the answer turned out to be that all else was not equal. The most significant was a difference in geography. The researcher described it to me this way in an email message:

Geochemical and fossil-based paleo-reconstructions indicate that the late Miocene was warmer-than-modern and that pCO2 was relatively low (near pre-industrial levels). We suggested that the ocean circulation and associated atmospheric feedbacks that existed in the late Miocene could have helped to maintain these warm conditions. We also suggested that ultimately this configuration of feedbacks was possible in the late Miocene because the ocean basins were shaped differently then they are today (the Central American Seaway was open, Indonesian throughflow was less constricted, the Bering Strait was closed). In other words, the late Miocene conditions are not an analogue for modern climate because the boundary conditions at that time were much different than those of today.

Compounding the misleading title was this in her blog entry itself: “Today, we are still exploring how CO2 has affected the climate of the distant past. However, our interpretation is becoming more nuanced. What if our assumptions on the role of CO2 in climate change are wrong?”

That was not the researcher’s question at all, but it conveys the distinct misimpression that it was.

In this time when blogs by politically motivated climate-change deniers are muddying the scientific conversation, we need to be careful not to feed their message machine. It is very important that we discuss the science of climate change and the impact of CO2 accurately and with care.

I have no quibbles with the science and nothing but respect for my fellow Science Blogger’s intent. But I assert that her careless language implied that her featured scientist had discovered something new that contradicted the consensus on human contributions to climate change.

So my answer to her question, “Why can’t we talk about atmospheric carbon?” is simple. We can and we should. But when we do, we need to be careful not to toss around misleading questions like “Surpringly irrelevant?” and “What if our assumptions on the role of CO2 in climate change are wrong?” when (a) the research we are describing did not address those questions and (b) the research does not suggest that the answer to either question is yes.