Ice Cores, Temperatures, And CO2

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From Watts Up With That?

Guest Post by Willis Eschenbach

I got to thinking about the ice cores. It’s pretty amazing to realize that the air trapped in the tiny bubbles in the ice is the very air that was trapped there way back when the ice formed. And that air can be hundreds of thousands of years old. Not only that, but we can analyze the trapped air to see the changes in CO2 over time.

How accurate are the results? Well, different ice cores drilled and analyzed by different groups of scientists give very similar results. Here are some recent ice core CO2 measurements, along with the Mauna Loa measurements in orange.

Figure 1. CO2 measurements from a variety of ice cores, along with Mauna Loa measurements in orange.

As you can see, there’s very good agreement between all of the various ice cores, ice core analysis groups, and ice core CO2 measurement methods. And the ice core measurements agree with the Mauna Loa CO2 observations quite well.

Another thing that can be calculated from the isotopes in the air trapped in the ice-core bubbles are the temperatures back in the day. The Vostok ice core data, one of the longest datasets, recorded four glaciated intervals and five “interglacials” including our current interglacial, the Holocene.

Figure 2. Vostok global temperature reconstruction, along with modern (1850-2022) HadCRUT temperature measurements.

Now, there are several very interesting things about this graphic. First, people keep saying that a slight global warming is an “existential crisis”. But in both of the previous interglacials, temperatures were up to 2°C warmer than today. That’s 3.6°C warmer than the “preindustrial temperature”, far above the impending terror temperature of 1.5°C warmer than preindustrial that they keep scaring us with.

There were modern humans around for both of those hot spells, along with most modern life forms. It wasn’t an “existential crisis”. It wasn’t a crisis at all. It was a warm time.

And humans also existed through the glacial periods. In total, humans have seen a swing of +2°C warmer than today’s temperature to -9°C cooler than modern times … a very wide swing.

Next, the orange/black line at the right is the post-1850 warming. As you can see, the Vostok data indicates that the world has been warmer than today, both earlier during this interglacial as well as in every one of the previous interglacials in the record.

Call me crazy, but I’m not seeing any reason to panic or to demolish the fossil fuel economy in any of that …

Moving on, how about the Vostok CO2 data? Here’s a graph comparing the Vostok CO2 (right scale) and temperature (left scale) data.

Figure 3. Vostok Ice Core CO2 and Temperature.

So … is CO2 related to temperature? Is CO2 the secret temperature control?

The two are definitely related. And given the length of the dataset, almost half a million years, we can see that there is a clear physical relationship over the entire time. Either CO2 causes temperature changes, or temperature causes CO2 changes, or they both affect the other. As you might imagine, in nature the latter situation is the most common.

But regardless of the causation, clearly Figure 3 shows the long-term equilibrium relationship of the two. So we can investigate the various conditions.

First, let’s assume that CO2 is controlling the temperature. Analysis of the data in Figure 3 yields:

Change in temperature (∆T) = 13.4°C per doubling of CO2 (“climate sensitivity”)

Hmmm, sez I … the accepted value for climate sensitivity is not 13.4°C / 2xCO2. It’s somewhere around 2°C to 4°C / 2xCO2, far lower.

So let’s look at the opposite possibility, that temperature is changing the CO2. Analysis reveals the following relationship:

Change in CO2 (ppmv) = 9 ppmv per °C

Hmmm, sez I … seems possible. As the oceans warm, they outgas. However, that’s not enough to explain the modern CO2 increase.

Finally, it’s certainly possible that they are each affecting the other. CO2 might be adding a bit of warming or cooling to the changes of whatever’s driving the variations seen in Figure 2. Unfortunately, there’s no way to calculate that.

What else can we learn from the Vostok data? Folks keep talking about the speed of the current warming. Their claim is that the world can’t evolve or acclimatize fast enough to encomass the current rate of warming.

However, the Vostok data shows other times in the Holocene that it’s warmed (or cooled) that fast.

Figure 4. Warming rates in the Holocene, from the Vostok ice core data.

Finally, here’s a look at the ice core data overlaid with the modern changes in both CO2 and temperature.

Figure 5. Temperatures and CO2 levels. As in Figure 3, but with both ice core and modern observational data shown.

Hmmm, sez I, once again …

So that’s what I learned from the Vostok data—that humans have been through warmer periods many times in the past without them being an “existential crisis”, that oceanic outgassing isn’t the cause of the modern CO2 increase, and the speed of modern warming is far from unprecedented.

A rare day of soothing May rain here in California. At the end of last year, all the climate models and climatologists were predicting another very dry year … instead, it’s been one of the wetter years in history. The world’s best prognosticators were not just a little wrong. They were 100%, top to bottom and side to side wrong.

And these are the same models and folks who claim they can tell us what the average global temperature will be in 2100AD … yeah, that’s totally legit.

My best to all,


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