Global warming “skeptics” (also known as paid hacks or reality deniers) have pointed to studies of Antarctic ice cores that seem to indicate that a rise in temperature preceded the rise in atmospheric CO2. While the studies showed a strong relationship between temperature and CO2, it appeared that the rise in temperature came first.
A new study by Harvard researcher Jeremy D. Shakun and colleauges in Nature takes another look. Shakun describes the issue
People drilled down through the Antarctic ice sheets, and we actually have a record of [the link between CO2 and temperature] that goes back to almost a million years ago. … ..if you look at these two [CO2 and temperature] together, you see that they have this amazing correlation. It’s a better correlation than you almost ever get from nature – the two just go lockstep up and down together over the ice ages for the last 1 million years almost”
The curveball, as Shakun puts it, is that when scientists looked more closely at the ice-core records they had from Antartica, they found that the temperature in Antartica actually started changing a bit before the CO2 did ….This is something that [current] global warming skeptics have jumped on, to say ‘ah jeez, obviously CO2 must not cause warming because if we look in the past, in these ice cores, the CO2 comes after the warming.
The problem is that while CO2 levels from the ice core bubbles tell us the global concentration of CO2 in the atmosphere, the temperature is ONLY from one place. In order to gain an understanding of global temperature change, you need to take temperature measurements from a variety of sources. We see this today. While the data clearly shows an increase in global temperatures, you can find individual locations that have gotten cooler.
To get a better picture Shakun and colleagues from Harvard, Columbia, and other research institutions, searched for as many temperature readings from the end of the last ice age as possible.
“People have records of temperature from ice cores in Greenland, we have lots of ocean cores that people pull up from the sea floor, we have lake cores on land… people have used all these different kinds of ways to construct what temperature was in the past,” Shakun said. This data is especially rich from around the last ice age, as a point in the not-too-distant past of vast importance for past climate research. Samples can also be dated reliably using carbon-dating, ensuring an excellent picture of past climate conditions
“What you see when you put them all together is a pattern of global warming at the end of the ice age that really strongly mirrors the rise in CO2 at the end of the ice age. Even more interesting, you find that the global temperature started warming a bit after the CO2 rose.” This is very different from the view that many people currently hold that temperature changed first during the last glacial melt. “That is true for Antartica, but if you look globally, that’s not the case,” Shakun said. “Global temperatures are following CO2.”
And this should come as no surprise to anyone. The only questions we have to ask are what we can do to reduce CO2 levels, and whether it is too late to stave off the effects of global warming