Guest Post by Willis Eschenbach
As a result of a tweet by Steve McIntyre, I was made aware of an interesting dataset. This is a look by Vinther et al. at the last ~12,000 years of temperatures on the Greenland ice cap. The dataset is available here.
Figure 1 shows the full length of the data, along with the change in summer insolation at 75°N, the general location of the ice cores used to create the temperature dataset.
Figure 1. Temperature anomalies of the Greenland ice sheet (left scale, yellow/black line), and the summer insolation in watts per square metre at 75°N (right scale, blue/black line). The red horizontal dashed line shows the average ice sheet temperature 1960-1980.
I’ll only say a few things about each of the graphs in this post. Regarding Figure 1, the insolation swing shown above is about fifty watts per square metre. Over the period in question, the temperature dropped about two and a half degrees from the peak in about 5800 BCE. That would mean the change is on the order of 0.05°C for each watt per square metre change in insolation …
From about 8300 BCE to 800 BCE, the average temperature of the ice sheet, not the maximum temperature but the average temperature of the ice sheet, was greater than the 1960-1980 average temperature of the ice sheet. That’s 7,500 years of the Holocene when Greenland’s ice sheet was warmer than recent temperatures.
Next, Figure 2 shows the same temperature data as in Figure 1, but this time with the EPICA Dome C ice core CO2 data.
Figure 2. Temperature anomalies of the Greenland ice sheet (left scale, yellow/black line), and EPICA Dome C ice core CO2 data, 9000 BCE – 1515 AD (right scale, blue/black line)
Hmmm … for about 7,000 years, CO2 is going up … and Greenland temperature is going down … who knew?
Finally, here’s the recent Vinther data:
Figure 3. Recent temperature anomalies of the Greenland ice sheet.
Not a whole lot to say about that except that the Greenland ice sheet has been as warm or warmer than the 1960-1980 average a number of times during the last 2000 years.
Finally, I took a look to see if there were any solar-related or other strong cycles in the Vinther data. Neither a Fourier periodogram nor a CEEMD analysis revealed any significant cycles.
And that’s the story of the Vinther reconstruction … here, we’ve had lovely rain for a couple of days now. Our cat wanders the house looking for the door into summer. He goes out time after time hoping for a different outcome … and he is back in ten minutes, wanting to be let in again.
My best to all, rain or shine,
PS—When you comment please quote the exact words you are referring to so we can all understand exactly what you are discussing.