Two degrees C in 100 years...or not

As promised, I have made a very simple climate model. I used the HADCRUT4 temperature record, although BEST and GISSTEMP are indistinguishable over the time period I consider. Use any.

As I said before, the air-T record has two 60-year dips that may result from more heat being sunk into the oceans. So I compared the 2, 50-year periods where air T has risen, using 1908-1957 and 1963-2012. If you look at HADCRUT4, you will see why I chose those intervals. Those are the ‘ups’.

This is a very simple model related only to CO2. CO2 came from Scripps for 1963 (319 ppm) and 2012 (395 ppm), and I back interpolated for 1957 (314 ppm) and 1908 (307 ppm). Using slightly different ‘earlier’ values would not have changed the results. Using much different ‘earlier’ values would require some justification.

This model is extremely simple. A change in CO2 expressed as ratios that co-occurred with a change in air T. From that correlation, I predict air T 50 years and 100 years later. It is based on physical certainty that CO2 absorbs infrared energy, and that increasing air T increases water vapor in the atmosphere, also absorbing infrared energy. Thanks to Mojo for pushing me that literature. You make me better.

But the point is that the model is simple. A small increase in CO2 correlated with a small increase in T, and larger with larger. Next, use that same correlation for anticipated CO2 increases in 50 years (to 600 ppm) and 100 years (to 900 ppm). I get those future CO2 expectations from IPCC. Now solve the model.

In 50 years air T would increase by 1 oC, and in 100 years by 2 oC. In no way do I doubt that the ultimate effect of doubling CO2 will ultimately increase air T by 3 oC, but based on the last century, that increase will not happen soon.

Because I intentionally excluded the air-T dips, this could be an overestimate. During the next century, the ocean could sink more added heat. I have also excluded any positive feedbacks, and the most prominent among them appear to be carbon outgassing from peat/frozen soils and marine methane hydrates. We lack parameters to include such things! But that knowledge would cost money. Who wants to pay for that knowledge?

So I could be wrong low or wrong high. But it is a simple model and you know where to get all the data I used and you could run it a different way. I am sure that if you used times of the air-T dips instead, you could predict no air-T increase during all in the century. Don't care.

My simple model predicts much less than 3 degrees per CO2 doubling. That factor is well established by the paleo research, but they can not tell us how fast it arrives. I guess it will be later.

I set aside the fancy CIMP5 models here, in favor of much simpler. But simple may not be good enough. We need to know how added heat affects soil and marine C not yet in the atmosphere. We need to know how the ocean handles added heat over multi-decadal times. Not knowing those things, ours eyes are covered and I hate that.

 

For those who have viewed this, and not commented on its appalling oversimplicity, Thanks.

I will bring two your attention a couple of other approaches that have recently been published.

http://folk.uio.no/gunnarmy/paper/aldrin_env_2012.pdf

Second one seems not convenient to link to but if you open google scholar and search
"
Causes of the Global Warming Observed Since the 19th Century

it will pop up first.

You will see that both of these are much more comprehensive models. Yet they are not radiative-transfer models. They are driven by century (or few-) scale observed changes in the earth system. Both of them predict doubled CO2 temperatures of 2 oC or a bit under. I am not qualified to explain them in detail, but I believe that they deserve some consideration.

What does it mean? is the doubling number we should be thinking about for this century is 3, 2 , or a bit less degrees? This is not for me to decide. I will say that I have no doubt of the 3 degrees as revealed by 'paleo', but I an not sure that such studies tell us how fast it can happen. There have been previous 'attribution' studies that have considered aerosols, volcanoes, and ocean-heat periodicities that favor the 3. I have linked to them here before.

I'd be much happier if all such efforts (and omitting my too-simple approach above) fell within a narrower band. But they do not. If one of the endpoints is characterized by fatal errors, I can't find that for you. I would suppose that both the Aldrin and the Ring will get discussed in upcoming literature and we ought to watch for that.

But, if the ocean (in its mysterious ways) hangs on to a lot of heat, I'd bet air T will trend closer to the smaller increases. If on the other hand, high-latitude soils (or marine hydrates) transfer a lot of methane to the atmosphere, the high side is still unpredictable. None of the models have methane stability nailed down.

So I offer you no certainty for Christmas, but the possibility (at least) that the wheels won't fall off for the next few decades. This would be quite helpful, because the most likely path during that time is continued global release of fossil-fuel CO2. I think we all agree about that last part.

A water planet is essential for life, and that's what we've got. Be of good cheer. But such planets are whacking hard to understand!

 

Austin I don't understand the last point. Do you suggest that fossil-C emissions are overestimated?