Temperature Doesn't Follow CO2
As Alarmists Claim
by Benjamin Deniston
Aug. 3, 2015—Those supporting the narrative of an impending man-made climate change catastrophe base this on an assertion that the Earth's climate is extremely sensitive to increases in CO2 emissions and that CO2 ranks high among the most important factors determining climate across many timescales. When you hear about rising human CO2 emissions causing everything from devastating droughts to worsening storms, from sea level rise to mass extinctions, realize that these are all based on computer models built on the assertion that changes in CO2 will have a strong effect on global climate. However, there is one minor problem with their arguments: reality does not support that assertion.
The climate is always changing, with many factors involved (as discussed in the accompanying article, “What Causes Climate Change? The Sun, the Solar System, and the Galaxy”), and the historical and geological evidence tells us that CO2 is a relatively minor factor (if much of a factor at all).
Case 1: 20th Century
Start by comparing CO2 levels and temperature over the past century. From 1900 to the present the relation between the claimed human greenhouse gas emissions and the yearly average global temperature is far from self-evident. Figure 1 compares global average temperature with increases in greenhouse gas and CO2 emissions (above a baseline of 300 parts per million).
The data shows global temperature increase from 1910 to 1945, during a period when human greenhouse emissions were relatively low. As the rate of CO2 increase began to accelerate over the following 30 years, global temperatures did not increase along with them; the temperatures went flat from 1945 to 1975. The only period where these processes correspond is the recent warming phase, from 1975 to 1998. However, since 1998 global temperatures have again gone flat, breaking from the upward trend in CO2 emissions.
Before going on, it should be emphasized that this disagreement is evident in the most recent historical data provided by NOAA and other government agencies. As will be discussed in the accompanying article, “The ‘Methods’ of Climate Alarmists,” we have strong reasons to question the accuracy of the historical data provided by government agencies with a vested interest in the man-made climate change catastrophe narrative, as they have been seen to repeatedly cherry-pick the data that supports their assertions, or even “adjust” historical data to fit their claims. That stated, even with these biases in the data selection and adjustment processes, we still see this disagreement between CO2 and temperature.
Case 2: The Pause
Focusing on this more recent period (1998 to the present), two different assessments of global temperature based on satellite measurements both show that global temperatures have shown no increasing trend since 1998 – despite the relatively large increase in CO2 levels. These satellite measurements represent an important, independent temperature record, free from the manipulations discussed in the accompanying article, “The ‘Methods’ of Climate Alarmists.”
This recent flat-line in global temperature has been popularized as the global warming “pause” or “hiatus.” Even with CO2 and other greenhouse emissions continuing to accelerate over the past two decades, the Earth hasn’t warmed in response. While there are literally dozens of purported explanations for why this pause shouldn’t question the narrative that the climate is extremely sensitive to CO2 levels and continued human CO2 emissions will cause catastrophic climate change, the simple fact of the matter is that these are all post hoc excuses. None of the climate models predicted this pause before it occurred, and now you’re being told to trust those same climate models for future predictions of how CO2 increases will devastate the Earth’s climate.
The spectacular failure of computer models to accurately predict how the Earth’s climate will respond to changes in CO2 levels can be further illustrated by comparing the predictions made by dozens of computer models with the actual results that occurred. As can be seen in Figure 3, actual temperature has remained below the vast majority of all climate model predictions, and well below the average of all predictions.
These results indicate that the Earth’s climate is not responding to CO2 emissions as claimed by those supporting the man-made climate change crisis narrative. Surprised? You shouldn’t be. This is completely consistent with the picture we get from historical and geological records – a climate that is not highly responsive to CO2 levels. On certain timescales we see the opposite of what we’re generally told by alarmists, CO2 levels being determined by climate (rather than CO2 determining climate).
Case 3: CO2 Lags Behind Temperature
One of the more infamous illustrations of this comes from the evidence popularized by none other than Al Gore in his science fiction film, An Inconvenient Truth. Gore presented a close correlation between CO2 levels and temperature records going back a half million years (recorded in ice core samples from Antarctica). This was presented as conclusive evidence that CO2 changes drive changes in global temperature, with Gore stating “there is one relationship that is far more powerful than all the others, and it is this: when there is more carbon dioxide the temperature gets warmer, because it traps more heat from the Sun inside.”
However, what Gore didn’t mention was that it was already known that the changes in CO2 levels came after changes in temperature, indicating that CO2 was not causing the climate to change, but only responding to temperature change. This is no surprise. The oceans absorb, store, and release large amounts of CO2, and because the ocean temperature determines how much CO2 can be stored, changes in climate (and ocean temperature) can increase or decrease the CO2 in the atmosphere. For example, warming causes more CO2 to be released into the atmosphere, so a CO2 increase would be expected to come after (lag behind) a temperature rise.
Records of CO2 changes following temperatures have repeatedly been shown in multiple studies. A 1999 study showed that CO2 changes followed behind temperature changes by 600 years during the last three transitions from ice ages to interglacial periods.A 2000 study found that CO2 lagged temperature changes by 1,200 years in Antarctic ice cores between 60,000 and 20,000 years ago (see Figure 4). A 2001 study demonstrated an 800 year CO2 lag in the beginning of the most recent interglacial. And a 2005 study showed CO2 lagging temperature changes in temperature by 1,900 years in Antarctic data.
Case 4: The Phanerozoic
The lack of climate sensitivity to CO2 is further supported when we look at longer timescales, covering hundreds of millions of years. For records covering the entire time of advanced animal life on Earth (the Phanerozoic Eon, from 540 million years ago to the present) we see no evidence that CO2 changes drive global climate. We see periods where CO2 levels were much higher than today, with lower global temperatures (as in the Ordovician and Jurassic periods). And we see long term trends of CO2 increase associated with temperature decrease, following by CO2 decrease being associated with temperature increase (from the late Permian, through the Triassic, Jurassic, and Cretaceous). Again, this shows the absurdity of the assertion that the Earth’s climate is highly responsive to atmospheric CO2 levels, and the criminality of the alarmists demands that human CO2 emissions be drastically cut back.
Whether we look at the recent changes of the Earth’s climate over the past decades and centuries, or longer term records covering the past hundreds of thousands or hundreds of millions of years, we see clear evidence demonstrating that CO2 is not a major factor determining the Earth’s climate. As discussed in the accompanying article, “What Causes Climate Change? The Sun, the Solar System, and the Galaxy.”
Bottom line: is CO2 a greenhouse gas? Yes. Could an increase in CO2 levels affect the climate? Sure, that is possible, but the evidence indicates it wouldn’t be much of an effect (if any). Is there any reason to believe that human CO2 emissions are going to bring the world climate system to the verge of some catastrophic change? Absolutely not.
[fn_1]. Many supporters of the man-made climate change crisis narrative don’t dispute that CO2 changes follow behind temperature changes, but they argue that different causes (other than CO2) initiate the temperature change, which then releases more CO2, and then CO2 acts to amplify these temperature changes. However, this is just reasserting their thesis, and providing no proof. According to this scenario these geological records don’t provide any evidence to support the claim that the climate is highly sensitive to CO2 change (as Gore claimed). [back to text for fn_1]