Tuesday, December 6, 2011

Rate of Global Temperature Increase

There's a very interesting new paper out from Grant Foster (who blogs at Open Mind) and Stefan Rahmstorf (who occasionally blogs at Real Climate).  What the paper does is take five global temperature series that look like this:

And then uses statistical techniques to remove the influence of three sources of natural variation: the El-Nino oscillation, volcanic eruptions, and solar variability.  After that, the adjusted series look like this:

Basically there is a clearly linear trend (the global warming signal) with a much smaller amount of noise left over that is a) fairly correlated between the different sources, and b) not very autocorrelated - ie it looks like the annual fluctuations in the weather.

I won't say too much about their analysis since it's well covered at Open Mind.  What I was curious about is the extrapolation, since the data seem to cluster so tightly about a linear trend.  I read off the average of the five adjusted series above and then did a simple linear least squares which gave the overall slope as 1.63 ± 0.09 C/century.  This statistical error of about 5% is much much smaller than the uncertainties from climate models.  Of course, the linear nature of the data is purely an empirical observation that could break down in the future (whereas the climate models attempt to capture the underlying physics of the global climate system).

In fahrenheit terms this is 2.94 ± 0.15 F/century.  It's important to note that this is a global average - the rate will be lowest over the oceans and at low latitudes and higher over land and in the Arctic.

To give a feel for a different stability analysis - here's a comparison of the linear and quadratic extrapolations over the rest of the century:

Over that timeframe the uncertainty in extrapolation is dominated by the small non-linear component present in the data.  Still - the uncertainty is not that large and will be rapidly reduced by another decade or two of data.  So this gives us an idea of how much global warming we - and the planet we love - will have to adapt to.

It's worth adding the caveats that 90 years is a long time - if indeed solar power becomes cheaper than coal in a couple of decades time, or we manage to invent Freeman Dyson's carbon-eating trees, then the situation could be much better.  On the other hand, since we are making fairly large changes in a system that we don't understand very well, there could well be thresholds in the climate system above which it starts to change much faster (eg a lot of the forests burning up and releasing their carbon into the atmosphere).  Any of those kinds of things could render a straightforward extrapolation of the last thirty years pretty pointless.


Dean said...

Another caveat is that this analysis doesn't go back into the last 'cold PDO regime'. I would have been very interested to see what was happening then.

But it seems that the analysis usually starts at the beginning of the big upswing in temps, ignoring the previous 30 years (which may be similar to the last 10, plus next 10-20).

Anonymous said...

Very interesting post.
There may be more factors contributing to the warming. The solar magnetic field may also be influencing cloudcover by reducing cosmic radiation (Svensmark theory).

We cannot predict what the El Nino-oscillation, the Earth's volcanoes and the Sun will do in the next century.
But we know pretty sure that fossil fuels will run out and manmade CO2-emissions will drop.

Lars-Eric Bjerke said...


I used your curve together with the CO2 increase in the atmosphere from Wikipedia to calculate the climate sensitivity, not taking into account any delaying effects. The result was 3.3 C for a doubling of CO2 content, pretty close to the IPCC best estimate of 3 C.

1leone said...

As you correctly say that we are making changes to a large system that we don't understand, I would also add that it is a complex system, governed by laws of caos. It seems inevitable unfortunately that if we carry on this way, at some stage, the increase will cease to be linear and change to an exponential growth

Mike Aucott said...

Interesting; thanks for posting. Lars and I are on the same page. Although the article doesn't discuss it, the data provide empirical evidence that the sensitivity of climate to carbon dioxide is just about where the geological record and climate models put it.

And this has been understood for 30years. CO2 was about 338 ppm in 1979, and it's about 385 ppm today. During this period, the nearly linear increase of CO2 has paralleled the increase in temperature that now totals about 0.5 degrees C. There's been some increase in other greenhouse gases during this period also. Adjusting the projection somewhat to account for the perhaps 10% contribution of these other gases, a doubling of CO2 should lead to an increase in global temperature of about 3 degrees C. This is smack in the middle of the range of 1.5 to 4.5 degrees C. first estimated by the National Academy of Sciences, chaired by Jule Charney of MIT, in 1979.

bordoe said...

"Russian Permafrost Melt - BBC"


Tenney Naumer said...

Perhaps Stefan and tamino were thinking of the over 90% of the energy imbalance that is going into the ocean that will soon come back to bite us in the butt -- in fact, it already is if temperatures during the so-called La Nina "cooling" years are anything to go by. Have a good look at this graph, which is one of the scariest I've ever seen.


Or have a look at Fig. 8 here"

Tenney Naumer said...
This comment has been removed by the author.
Unknown said...

Interesting. I have no idea how can this come about since the underling trend of the satellite record is different from the surface station record. The difference is especially marked between GISS and the satellites:



The Rational Pessimist said...

Stuart. As Lars says, your number comes close to the Charney sensitivity, which is the basis for the IPCC's best estimate of 3C. Changes in the carbon cycle feedbacks lead us toward the Earth System sensitivity, which is a somewhat different thing.

Media very confused about these two types of sensitivities in general as per the reaction to the Schmittner et al paper over the last couple of weeks. I talk about this confusion here:


buck smith said...

Humans have been adapting to climate change for tens of thousands of years. A few degrees of warming beats the heck out of an ice age, which, in the long run or possibly even the short run is coming. The idea that there is something sacred about the global temperature range of the last 100 years is kind of silly, especially if look at geologic time.

Tenney Naumer said...


Humans adapted to temperature changes that occurred over tens of thousands of years.

What we have here is a rate of change that is occurring over 100 years, a mere blick of the eye in geologic time.

Many species will be unable to adapt, including food crops.

A few degrees of warming means many meters of sea level rise -- billions will become refugees. Many will not survive.

buck smith said...


But we had a similar temperature rise during Medieval Warm Period and the global disasters you forecast did not occur. When there is climate change, where it is man-made or natural mankind will adapt. If crops are failing we will breed or genetically engineering new crops. Or more likely we will use some form of geo-engineering to keep the climate in a desirable range.

1leone said...

@buck smith, the medieval period you refer to has been largely refuted in so far it was localized warming whilst overall global temperature did not alter significantly. Similarly, the so called little ice age that subsequently followed was again a localized phenomena and not global in perspective.

The problem with geo-engineering climate is that, given that climate is a complex system, the inputs that we may fabricate will be 1) irreversible 2) trigger unforeseeable consequences further down the road. Think of the proverbial butterfly flapping it's wings in Brazil causes a storm in Europe....

As it was said a long time ago, "to command the weather, one has to obey it"

Tenney Naumer said...


There is evidence suggests that warming during the Middle Ages was not global in nature. Further, it was not as warm as now. And, we are going towards temperatures not seen for tens of thousands of years and CO2 levels not seen since well before humans existed.

And we are going to do this in the blink of an eye -- evolution to survive this is not possible.

Stephen B. said...

Okay, I'm a little late to comment on this blog post, but I have to chuckle at the idea that we can geo-engineer the global climate.

Assume that we even can partially understand the system that we are altering and can come up with a mechanism sufficiently significant enough to effect change, just who gets to decide what's warm enough or cold enough? Who decides what is a proper amount of precipitation and where to disperse it?

Civilization cannot come to consensus on much of anything, and yet we are to take active control of the climate too?

I just cannot imagine it.

Bernd Paysan said...

About the natural range of variability: The end of the last ice age took somewhere between 50 and 100 years. In which the global temperature increased faster and by more than this prediction. It was chaotic, it had a set-back when the great lakes spilled a huge amount of sweet water, temporarily shutting down the gulf stream.

One can argue, we shouldn't have started it. It is too late for that, we already started it. What is pretty obvious: We can't stop it. The conference of Durban showed: The two biggest sources of CO2 on this planet are unwilling to do anything about it. They are full of lame excuses and finger-pointing. An old Chinese saying says when pointing at someone else, three fingers point at yourself. Well, China, that's still true today.

We have also a longer running natural momentum, that is our solar system is leaving the dusty spiral arm, which means the 5 million year long ice age period is going to end. In geological terms, not within the next 100 years.

Nature can adapt. There have been times where Earth was 10 degrees warmer than today. We are still in the middle of an ice age, and the climate is still way below average. The way nature quickly adapts to changing situations is by having animals and plants moving around. Animals move quickly, it takes them years for 1000km, plants are a bit slower to move, it takes them decades for 1000km. But they all can move, can change their habitats. Many former European ice age plants nowadays are only to be found in the alps, and if there was another ice age, they would come back from this retreat quickly. Some ice age creatures vanished, though there had been arctic retreats for quite a while. Nature is not nice and cozy, nature is hard. Survival of the fittest, you know. Mutation and selection. Selection happens in waves, it is part of the game.

Concerning crops: Do you know how much crops changed over the last 100 years? It's incredible. Adjusting these crops to a mere 3°C/century temperature gradient is a total no-brainer, we can do that. And we can move the zones where we plant particular crops. Quickly, on a per-year basis. Unlike natural plants, which can only migrate by wind or on the feet of birds, industrial agriculture is not limited - whatever new or modified crop we have cultivated, it takes a few weeks to get it anywhere on the world. This is four or five orders of magnitudes faster than natural change. And natural change can keep up with the temperature slope we have today. So that is not something to be concerned about.

Despite the predictions have been made timely and were correct, we failed to convince society to do something about this problem. We must realize that it is too late to stop this trend. We must learn to live with it.