As I noted last week, there is a new article in Nature that tries very hard to prove that CO2 increased prior to the warming at the onset of the current interglacial which is known as the Holocene. I read the article and was stunned by the conclusion and the charts which clearly showed that the warming took place after the CO2 rose. Since I have extensively studied much of the available data from the period 10-20k years ago, I knew right away that this paper did not give the same conclusion as any of the other data.
Last week I was also busy with work and didn’t have sufficient time to delve into the data, but I had time to consider how such a result could be achieved using real data. I considered this with the idea of how the Earth’s climate really behaves. The Holocene began because the orbital parameters changed so that the Northern Hemisphere started to receive increased energy from the Sun starting 22,000 years ago. Any warming that took place would have been evident first in the NH. As the warming pushed back the ice caps and glaciers in the NH, the dynamics of the Earth change and a full interglacial period develops which is what causes the warming in the rest of the world. The key is the NH.
When I looked closely at the charts that were in the press release, I noticed the first curious item.
The critical point used in the Nature paper is 17,400 Years before Present (YBP). That is when the CO2 level starts to show the discussed rise. The Antarctic temperature is rising prior to that, but the global temperature only rises after CO2 increased.
While I didn’t have time to review all the data I have on this, I was able to consider how to create the above charts. The key part would be to focus on the locations that would see the warming last, which would be the Tropics, especially the Tropical oceans. Those locations see the smallest change in temperature, but it really takes a big change globally to change the temperature in the tropics. So if I wanted to re-create the above charts, I would weight everything towards the tropics and use as little data as possible from the Northern Hemisphere.
The temperature reconstruction they performed was what I expected and more. They included only two ice cores from the Northern Hemisphere and used 4 pollen reconstructions from Alaska. The only place a pollen reconstruction included in their study are the ones in the upper NH, which in turn makes them the majority of the studies from the NH. A vast majority of the overall data sources used were ocean reconstructions between +/- 30° latitude. Any combined temperature reconstruction from this source of data will show very little global temperature change and it will take place much later.
That is precisely what the reconstructed global temperature chart shows. It shows that the Earth was only 3.6 °C cooler at the depths of the last ice age. The only way to achieve that result is to weight the study in such a way that the tropics dominate the overall temperature. This will also show a delay in the onset of warming.
I also found the following chart in the supplementary information with the Nature study.
The breakfit is a practical method of determining when noisy data changes trends. Climate data is always very noisy so this is a useful way to show changes. Of course if I do the same thing for the data from the Northern Hemisphere, the results are slightly different.
The earliest detected rise in the atmospheric CO2 level was 17,400 YBP. The ice cores in the NH show that warming started to take place ~19,800 YBP. Which is ~2,400 years before the global CO2 levels started to rise. That point ~17,000 YBP when the temperature dropped in the NH coincides with a meltwater pulse. Those take place when massive freshwater lakes that have formed on ice caps flow into the ocean and disrupt the ocean currents. That is the point where the rest of the Earth starts to catch up with the warming that was already well under way in the Northern Hemisphere.
The paper in Nature is a very deceitful attempt to portray the Earth’s temperature as dependent on the level of CO2 in the atmosphere. The weighting of locations to the places to warm up last and the overload of pollen reconstructions in the Northern Hemisphere all ensure that the final result showed that warming took place much later. This article is one of the most intentionally misleading ones I have ever come across.