After 8 years of total inaction on climate change it appears that the people in Washington might finally take some kind of steps to start changing the amount of CO2 we release in to the atmosphere. As this possibility gets closer to happening the forces that are opposed have started to ramp up their efforts to muddy the waters. The strategy seems to be to make things just confusing enough for us laymen to push some of us from supporters of doing something to either opposed or not sure. From outrageous accusations of fraud based on nothing more than innuendo, like the stolen and quote mined CRU emails, to a resurgence of much debunked claims flooding the UK press the heat is on, so to speak.
Since I’ve been reading about the subject recently I wanted to write something about it. I wasn’t really sure what I could add though. There are already some very excellent sites out there and I don’t think I could really do a better job than them. I finally decided I would just collect together some information from a couple different sources, if for no other reason that to have it all in one place for myself. Also, I have been personally surprised at just how clear and simple the evidence for The Big Picture® actually is. For all the arguing coming from the critics you would think it was all pretty complicated. While the details may be complicated, the overall picture is pretty clear.
All credit is due to the sites I am using. Primarily Skeptical Science but also Real Climate for research purposes. All the nifty graphs come from Skeptical Science though it is ultimately getting them from the original scientific literature and/or the IPCC Reports.
The Big Picture
Taking the broadest view of climate change the argument is basically this. There are gases in the atmosphere that absorb and trap long wave radiation keeping it close to the earth. CO2 is one of these gases. The concentrations of CO2 in the atmosphere are increasing. The increase is due to human activity. Observation shows the amount of radiation escaping the planet is in fact going down. Observation shows the amount of radiation re-emitted toward the earth from the greenhouse gases are in fact going up. Observation shows the earth’s land, atmosphere and oceans are in fact accumulating energy (heat).
Anyone who took a intro chemistry course in college, or maybe even high school, might remember doing a lab where you saw something like this:
What you were seeing was the emission spectrum of a specific element (hydrogen and iron in the examples above). Each element has a unique pattern of wavelengths where it absorbs or emits electromagnetic radiation (a.k.a. light). Above we are looking at the visible spectrum but the electromagnetic spectrum also extends to shorter wavelengths like ultraviolet and X-ray and to longer wavelengths like infrared, microwave and radio wave. Chemical compounds of more than one atom also have these same types of patterns.
When sunlight comes to the Earth it is in the visible and ultraviolet part of the spectrum. After the radiation is reflected or absorbed and re-emitted from the surface it is in the infrared part of the spectrum. CO2 is known to absorb wavelengths in this part of the spectrum. This is known both just from our knowledge of theoretical physics and chemistry, and from direct observation in the lab. This research goes back long before climate change research was even a concern.
It stands to reason that if there is more of a radiation absorbing gas in the atmosphere then more radiation will be absorbed. When that happens the molecules become more energetic, sometimes transferring their energy to other molecules thus increasing the kinetic energy (energy from motion) in the system. Temperature is simply a measure of average kinetic energy in a system, so this means the temperature will go up. Another possibility is the molecule will just reemit the radiation in all directions, including back to the surface of the Earth.
CO2 In The Atmosphere Is Increasing
This one is pretty simple. CO2 has been measured for several decades at over a hundred different stations. This video shows the change in parts per million over time.
Radiation Escape At CO2 Wavelengths
This is just a matter of direct observation. Since 1970, the radiation escaping the Earth at CO2 wavelengths has gone down. At least 3 different studies have shown this result using data from a few different satellites. This graph shows the change that occurred between 1970 and 1996. More recent studies have shown the trend has continued.
Re-emitted Radiation At Earth’s Surface
I mentioned above that once CO2 absorbs radiation that it re-emits it. This can happen in any direction. Some will leave the atmosphere, some will be absorbed by other molecules, some will come back to the Earth’s surface. Recordings at the surface show that this is indeed happening precisely at the wavelengths of CO2. The graph shows the increase in radiation reaching the earth at various wavelengths since 1973.
Humans Are Responsible For The CO2 Increase
So how do we know the increase in CO2 is from humans? Our first indication should just be common sense. We know that we are using fuels that release CO2 when burned. We are burning a lot of the stuff. 29 gigatonnes per year to be exact. The stuff has to go somewhere and we are seeing an increase of it in the atmosphere. The amount we are releasing is greater than the amount of increase in the atmosphere, which is 12 gigatonnes per year.
It could be though that maybe something else is absorbing what we release. Clearly all 29 gigatonnes are not staying in the atmosphere. In fact the oceans and the Earth’s biomass (plants) are taking some of it up. The oceans are absorbing some of it at about a rate of 6 gigatonnes per year and the biomass at the rate of 11 gigatonnes per year. That leaves the 12 gigatonnes increase we see in the atmosphere.
There is more evidence than that though. There are 2 types of carbon atoms that differ only by the number of neutrons in the nucleus. One is called C12 the other C13. Fossil fuels have a higher concentration of C12 to C13 than the atmosphere does. (Side note: this is because the fuels are essentially fossilized plant matter and plants “prefer” C12 since it is lighter and takes less energy to use). If the CO2 increase is from our fossil fuel burning then we should expect the ratios of C12 to C13 to change.
The below graph shows the measured change in ratio. There are 2 things to note about this graph. First is that it is using the C13/C12 ratio which means as fossil fuel emissions go up(i.e. C12 goes up), the ratio goes down. Also the scale on the right side of the graph is inverted. Notice the scale gets more negative as you go up. This is to more easily see the relationship between emissions and the ratio.
Is It Getting Warmer?
The unequivocal answer here is yes. I think we have already seen that if it isn’t we have some serious explaining to do. Less radiation is measured escaping. More radiation is measured at the surface. If it is not getting hotter then where the heck is it going?
From all the bickering from critics you would think that this is a contentious issue. “It hasn’t warmed since ’98”. “The CRU temperatures are a fraud.” And on and on. It is actually a pretty open and shut case. The ocean is a much better absorber of heat that the land or the atmosphere. Those who question warming are simply forgetting to look at the oceans!
From the graph we can probably see why the rise in land temperatures can be so hard to spot. It is a small fraction of the total. But the oceans absorbing that much heat has consequences as well. It melts ice which normally would reflect incoming radiation better than land does. This can lead to a feedback where hotter oceans lead to more trapped heat which leads to hotter oceans, etc. Hotter oceans also mean more evaporation which of course leads to more precipitation (everyone enjoying the massive snow precipitation this winter? get used to it).
Just how much heat is that anyway? As John Cook at Skeptical Science puts it, “imagine 190,000 nuclear power plants pouring their energy output directly into our oceans”. Thats a lot of heat!
Cycles Within Cycles or What Climate Change Doesn’t Predict
If someone said to you that the fact it gets colder at night was some kind of proof against global warming you’d probably give them a funny look. You might do the same if they said that the fact that there are still winters and still summers meant climate change was a scam. Yet, those are precisely the kinds of arguments people, especially conservative commentators, make all the time.
Climate change theory does not claim CO2 is the only driver of climate. It does not claim we will stop having summers and winters. It does not claim that every year will be hotter than the last in a continuous upward spiral. There are other cycles going on. One cold winter does not invalidate a long term trend. And neither does one big snow fall. In fact , as mentioned above, larger precipitation events are a predicted consequence of climate change. More heat = more evaporation = bigger snowfalls. There may be less total snowfalls due to the temperatures dropping to 32 less of the year but the events we do have may be bigger. In fact this is exactly what we have seen this year. The Earth as a whole had the hottest January on record!
What climate change theory does say is that those other cycles do not account for the changes we see. For instance the sun has had slightly cooling trend over the last 30 years or so. Other than the sun there are exchanges of heat between the oceans and the land and atmosphere (El Nino, La Nina ). These other factors can easily lead to year to year fluctuations but the overall trend (over decades) is up.
If you want to know more, or have specific questions you’ve wondered about, please stop by Skeptical Science. It is a great site and he has indexed most of the claims climate change critics make and gives answers by explaining the relevant scientific studies. He even has discussions of the claims being made in the news by critics the last few months. If you really like it you might even want to click the donate button on his front page. It is so nice to have a place that uses the science instead of spin to discuss this important topic