Is CO2 a Greenhouse Driver?

I have recently exchanged several comments with a reader who claims to show that CO2 is not a driver of the greenhouse effect and that there is no correlation between temperature and CO2 levels. I assured this person that CO2 really is a greenhouse driver and there was an amazing correlation between CO2 levels and temperature and I directed him to some websites that supported this. As expected, he denied it and continued in his beliefs.

This is an example of why I don’t really care to get into a ‘debate’ with global warming deniers. No amount of scientific evidence can ever change their minds. It really is a waste of time to try. And, when you finally give up with the one there will be an endless line of deniers waiting in line. It is unfortunate that they have chosen to reject science and logic, but they have the right to do so.

But, at the same time, it reminds me of why I do things such as this blog, do public speaking, conduct research and why I am devoting so much time to writing my book. The fact is, this person is putting this claim out there and there are people that have not yet made up their minds. They can still be swayed. The deniers are lost minds, but I can help prevent additional lost minds.

So, in that spirit, I am going to address some of the claims of this reader. By the way, I also encouraged him to make a submission to my $1000 Global Warming Skeptic Challenge. If he has proof that global warming is not real, then he should publicize it.

I was, admittedly, pretty dismissive of him. Check out his blog at http://agwunveiled.blogspot.com/ and you can see why very quickly. The first paragraph of his posting Calculated Mean Global Temperatures 1610-2012 states, "It does, however, consider the issue of Global Warming and the mistaken perception that human activity has a significant influence on it." This claim is so preposterous that the only conclusion is that anyone that believes it has rejected science. Simple, the amount of evidence of anthropogenic climate change is so overwhelming that anyone can prove it is true, even non-scientists. More evidence is reported every literally every day. It is not possible to keep up with the flood of scientific evidence of the truth of manmade global warming. It is simply not possible to examine the science in a logical manner and reach any other conclusion. In fact, that is the premise of my latest book, Undeniable: Dialogues on Global Warming.

So, when I read that paragraph and his claim that CO2 is not a driver, I knew enough. However, as a scientist reaching out to the public, I feel a sense of obligation to show why this person is wrong.

First, look at these plots:



Source: GRID-Arendal

These two plots show the carbon dioxide level (top) and global temperature (bottom) for the last 400,000 years, based on gases trapped in ice cores taken at Vostok Station, Antarctica. This is just one example. Many other cores and different methods have obtained nearly identical results. Now, the data goes back 800,000 years.

 
 Source: National Academy of Sciences


All of the data shows an amazing correlation between CO2 concentration and global temperature. You do not need to take my word for it, just look at the two plots above. If you want more, there is plenty more available on the Internet. You can find it by doing a simple search on the key words 'carbon dioxide' and 'temperature'. Of note, obviously the majority of this is naturally caused. Only the far right in both plots corresponds to the time period following the start of the industrial revolution.

Take a look at the level of CO2 in the atmosphere today (marked in the second set of figures) and compare it to the historical record. The level is so much higher than anything in the last 800,000 years that any rational person would be alarmed. Hopefully, you can understand why I was immediately dismissive of his claim that CO2 is not a driver global warming.

Are there other drivers? Certainly! Two of the most potent are water vapor and methane. However, the level of both are greatly influenced by the level of CO2. The U.S. Department of Energy estimates that humans emitted 36 billion tons of carbon dioxide in 2013, which accounts for approximately 77% of greenhouse gas (GHG) emissions. In comparison, methane makes up about 14% of GHG emissions.







Source: Environmental Protection Agency

Mr. Pangburn illustrates the problem with his claims with this statement:

A co-plot of CO2 and average global temperature (AGT) actually corroborates that CO2 does not drive AGT. I have done it. If you just look at the period 1974-2005 the correlation is excellent, but if you look at a longer period, say 1850-2013, you see the temperature trend going up, down, up, down, up, too-soon-to-tell while the CO2 level steadily, progressively increases. After 2001 the separation increases steadily as shown at http://endofgw.blogspot.com/

CO2 increase from 1800 to 2001 was 89.5 ppmv (parts per million by volume). The atmospheric carbon dioxide level has now (through December, 2013) increased since 2001 by 27.18 ppmv (an amount equal to 30.37% of the increase that took place from 1800 to 2001) (1800, 281.6 ppmv; 2001, 371.13 ppmv; December, 2013, 398.31 ppmv).

How do you rationalize that the temperature increase to 2001 was caused by a CO2 increase of 89.5 ppmv but that 27.18 ppmv additional CO2 increase had no effect on the average global temperature trend after 2001?

What he does here  is known as cherry-picking and refers to hand-picking the data in order to reach the conclusion you want. Has global warming slowed down? Yes! Has it stopped? No. In fact, nine of the ten hottest years ever recorded have occurred since 2000, including the hottest of them all in 2010, during the period when people such as Mr. Pangburn will tell you that global warming has stopped.

Does the slow down mean there is no correlation between CO2 levels and temperature? After all, as Mr. Pangburn points out, the CO2 level has continued to rise in the 21st century, even though the rate of increase in global temperature has slowed down. Mr. Pangburn is correct in his observation, but wrong in his conclusion. What this data really shows is that weather, climate and climate change are complicated subjects and there is no one, single factor driving everything. CO2 is just one of them, but is the one important one that we are responsible for.

The reason for the slowdown in temperature rise has been getting a lot of attention in all circles, especially by both deniers and researchers. The difference is that the deniers have been very strident in their claims while the researchers have been diligent in their work. We now know the primary cause of the slowdown and it really isn't good news.

Basically, currents in the Pacific Ocean have brought cold water to the surface and this cold water is helping to reduce global warming by absorbing the heat. It takes a gigantic amount of heat to raise the temperature of water. In fact, about 97% of all energy trapped in the environment goes into the oceans. This cold water is absorbing the heat and then, due to currents, takes it down into the ocean depths. We can measure the rise of the ocean temperatures and it is going up. This is actually bad news for two reasons. First, a warm ocean expands and this will contribute to rising sea levels worldwide. But also, this current will stop eventually and then the ocean will stop cooling global temperatures and we will likely see a big jump in global temperatures.

Any way you look at, Mr. Pangburn is wrong. I wish he was right because he is predicting a dramatic drop in temperature between now and 2020. I live in Texas and summers that were a little cooler would be welcome.

But, the science does not support Mr. Pangburn and his claim that CO2 is not a driver of global warming is simply in error.