Dr. Ricky Rood's Climate Change Blog

Simply Uncertain

Posted by: Dr. Ricky Rood, 7:10 AM GMT en Febrero 21, 2012

+11

Simply Uncertain

This past week I had a short letter published in Scientific American. The letter concerned a statement made in an article that climate models do not include clouds. This is an incorrect statement that has been around for many years, and it shows up, in my experience, in more science-focused publications. I remember an exchange of letters in Physics Today in 2005. As best as I can tell, the statement is traced to a historical document that stated the first climate models written in the late 1960s contained specified clouds – meaning that they did not change as the climate changed. By the end of the 1970s, cloud parameterizations were becoming standard in climate models, and the interplay between clouds and solar radiation emerged in the 1980s as one of the most important metrics of model performance.

My letter goes on to state that the uncertainty in climate projections associated with the physical climate model is smaller than the uncertainty associated with the models of emission scenarios that are used to project carbon dioxide emissions. This statement is worthy of more discussion. Let me start with a couple of reminders. In all of these endeavors looking to the future we use models. Models are constructed based on observed behavior and are tools for projecting future outcomes. By “physical climate model” I mean a mathematical representation based on the laws of physics. Most simply, in this case, how is solar energy absorbed by the Earth, redistributed, and then emitted back to space? More generally, laws that govern physics, chemistry and biology are incorporated into climate models.

Another important ingredient in making climate projections is what is our future emission of carbon dioxide and other greenhouse gases? “Emission scenario” models are based on assumptions of population growth, economic development and sources of energy to drive the economy. Historically, one type of scenario is called “business as usual” and simply extrapolates curves of past energy use into the future. If we take emission curves that, for example, stop in 2005 and project them forward, we see that in the last couple of years we are ahead of those emissions. Generally, business as usual is assumed to be the worst case. We have several emission models based on various assumptions about development and deployment of technology. Current efforts in climate science are striving to make emission models and physical climate models talk to each other – to interact.

Physical climate models are based on the laws of physics and that does provide strategies for determining cause and effect. If cause and effect can be determined to a high degree of certainty, then we can be quite certain about predictions. The economic models, that I know, are based on observations of economic systems that are then represented through a set of mathematical relationships. These relationships are often represented by statistical methods, strive to represent human behavior, and include measures of value that rely on how much humans value something. In atmospheric science, for example, there are a set of “primitive equations” which all agree describe the motion of the atmosphere. Such a set of physically derived equations do not sit at the basis of economic projections. I hope I have stayed out of trouble here. As in a number of previous entries, I draw your attention to Daniel Farber’s Climate Models: A User’s Guide. Farber is neither climate scientist or economist, a fact that I always view as providing a measure of objective evaluation. He evaluates model robustness.

I want to discuss this uncertainty issue a little bit more, and will rely on an old standard figure from the 2001 IPCC Report. This figure has a lot of information about uncertainty.

Figure 1: From 2001 IPCC Third Assessment Report Variations of the Earth’s surface temperature: year 1000 to year 2100

The figure shows the temperature since the year 1000 forward to year 2100. The temperatures from the past are from observations of different types. The temperatures in the future are from model projections. There are a set of different physical climate models all using a standard set of emission scenarios. I have marked three types of uncertainty on the figure.

In light blue I point to a measure of observational uncertainty. This is the gray spread around the bold red temperature line. This gets smaller as more and more observations become available over time. Going into the future there are the individual colored lines of different models and on the right of the figure are the ranges associated with those models for the set of emission scenarios. The envelope of all of the models with all of the emission scenarios is pointed out by the green arrows. A simple estimate of uncertainty is the spread of the models. This uncertainty grows with time, and the spread when all of the scenarios are included is larger than the spread of any individual model. If one were to look at the individual models, you would see much the same thing. In the absence of different scenarios the models would have a significantly more narrow spread.

There are a number of important points in this simple approach to thinking about uncertainty. Looking at the spread of all models with all scenarios, the spread at, say, 30 years in the future is quite well defined by the lines of the individual models. It takes 30 or 40 years before the difference in the scenarios makes a difference. As a rule of thumb a simple description of uncertainty is that in the next couple of decades “internal variability,” that is, the spread is mostly due to things like El Nino and La Nina is most important. Then there is a length of time where the spread is due mostly to model differences. And as time approaches a century or longer, the spread due to emission scenarios begins to dominate. I note that model differences are always important, and that this difference is strongly related to details of the treatment of clouds. This uncertainty is expressed in how fast does it warm?

The physical climate model is like a telescope into the future; it provides actionable knowledge the Earth will warm, ice will melt, sea level will rise, and the weather will change. As the models improve, that future comes into more and more focus. There are physical relationships that allow a high degree of confidence to be attributed to some aspects of climate projections. For example, the surface of the globe will warm, in any carbon dioxide emission scenario. On this global scale, both model uncertainty and emission scenario uncertainty address the issue of how fast the surface will warm. Neither suggest any plausible scenario where the Earth does not warm. And simply to make the point, this plot does not suggest that the warming stops at 2100; that's just as far as the information is plotted. At local spatial scales, scales for which the models were not designed, the uncertainty analysis follows a much different logic than presented here.

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Old Entry on Uncertainty and Definition of Model Types

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451. Neapolitan 1:02 AM GMT en Marzo 09, 2012
Quoting NeapolitanFan: James Hansen doesn't like the temperature so he simply changes the data: Link James Hansen tells it like it is: Member Since: Noviembre 8, 2009 Posts: 4 Comments: 11139

452. Ossqss 1:56 AM GMT en Marzo 09, 2012
Quoting Neapolitan: James Hansen tells it like it is: LOL, really ? Hottest October on record … was really a September posted at 9:42 am on November 16, 2008 "GISS’s computerised temperature maps seemed to show readings across a large part of Russia had been up to 10 degrees higher than normal. But when expert readers of the two leading warming-sceptic blogs, Watts Up With That and Climate Audit, began detailed analysis of the GISS data they made an astonishing discovery. The reason for the freak figures was that scores of temperature records from Russia and elsewhere were not based on October readings at all. Figures from the previous month had simply been carried over and repeated two months running." No worries though. Those records from the 1800's and early 1900 are all digitally calibrated to hundredths of a degree, right, so we can claim they are the 4th, 5th, or whatever, warmest since then right? There were also thousands of those stations available, just like today right? Masters regurgitates that it is the 4th warmest Winter on record. I say it is the 778th warmest in the last 1,000 years. Who is right? :) I believe in Climate Science Change! Wait for it >>>>>>>>>> its coming to a thought near you........ Member Since: Junio 12, 2005 Posts: 6 Comments: 8154

453. nymore 2:42 AM GMT en Marzo 09, 2012
Quoting Ossqss: LOL, really ? Hottest October on record … was really a September posted at 9:42 am on November 16, 2008 "GISS’s computerised temperature maps seemed to show readings across a large part of Russia had been up to 10 degrees higher than normal. But when expert readers of the two leading warming-sceptic blogs, Watts Up With That and Climate Audit, began detailed analysis of the GISS data they made an astonishing discovery. The reason for the freak figures was that scores of temperature records from Russia and elsewhere were not based on October readings at all. Figures from the previous month had simply been carried over and repeated two months running." No worries though. Those records from the 1800's and early 1900 are all digitally calibrated to hundredths of a degree, right, so we can claim they are the 4th, 5th, or whatever, warmest since then right? There were also thousands of those stations available, just like today right? Masters regurgitates that it is the 4th warmest Winter on record. I say it is the 778th warmest in the last 1,000 years. Who is right? :) I believe in Climate Science Change! Wait for it >>>>>>>>>> its coming to a thought near you........ Does this surprise you. I showed a few blogs ago how NOAA/NCDC moved their global baseline from 1961-1990 to 1901-2000 to make the anomaly appear almost 0.1C higher. What do you expect from U.S. gov't agencies. There is never any accountability. Just garbage agendas on both sides of the aisle. I personally would not believe them if they told me water was wet. Member Since: Julio 6, 2011 Posts: 0 Comments: 2047

454. Ossqss 3:00 AM GMT en Marzo 09, 2012
Quoting nymore: Does this surprise you. I showed a few blogs ago how NOAA/NCDC moved their global baseline from 1961-1990 to 1901-2000 to make the anomaly appear almost 0.1C higher. What do you expect from U.S. gov't agencies. There is never any accountability. Just garbage agendas on both sides of the aisle. I personally would not believe them if they told me water was wet. I hear ya. I am not opposed to much of anything aside from someone feeding me their ideological rhetoric, when it comes to weather and climate, for political gain. Not right, period..... If ya want to have some fun, just look at the IPCC output. How credible should they be globally setting policy as they are currently doing ? Whole different set of rules when you are not skeptical of the theory of AGW, no? Conflict of interest guidelines for the IPCC Edit: oops the vid was lost in the shuffle ª¿► Member Since: Junio 12, 2005 Posts: 6 Comments: 8154

455. Ossqss 3:23 AM GMT en Marzo 09, 2012
Here, a distraction for you all. And you thought the climate was a difficult thing to quantify! Gnight>> Member Since: Junio 12, 2005 Posts: 6 Comments: 8154

457. Birthmark 4:08 AM GMT en Marzo 09, 2012
Quoting Ossqss: LOL, really ? Hottest October on record … was really a September posted at 9:42 am on November 16, 2008 "GISS’s computerised temperature maps seemed to show readings across a large part of Russia had been up to 10 degrees higher than normal. But when expert readers of the two leading warming-sceptic blogs, Watts Up With That and Climate Audit, began detailed analysis of the GISS data they made an astonishing discovery. 1. Did they admit their error when it was pointed out to them? 2. Did the correct the error? 3. Did it make any real difference in the long run? Question: Do you think that Hansen manually enters global temperature data into the GISS computers? lol Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

458. Birthmark 4:10 AM GMT en Marzo 09, 2012
Quoting NeapolitanFan: James Hansen doesn't like the temperature so he simply changes the data: Link Steve Goddard is not a reliable source. In short, he lies. Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

459. Birthmark 4:11 AM GMT en Marzo 09, 2012
Quoting nymore: Does this surprise you. I showed a few blogs ago how NOAA/NCDC moved their global baseline from 1961-1990 to 1901-2000 to make the anomaly appear almost 0.1C higher. You do realize, don't you, that that's only possible if there was warming? D'oh! Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

460. Birthmark 4:12 AM GMT en Marzo 09, 2012
Quoting Ossqss: I hear ya. I am not opposed to much of anything aside from someone feeding me their ideological rhetoric, when it comes to weather and climate, for political gain. Not right, period..... If ya want to have some fun, just look at the IPCC output. How credible should they be globally setting policy as they are currently doing ? Whole different set of rules when you are not skeptical of the theory of AGW, no? Conflict of interest guidelines for the IPCC Edit: oops the vid was lost in the shuffle ª¿► Yet somehow it continues to warm. Astonishing, isn't it? lol Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

461. Birthmark 4:15 AM GMT en Marzo 09, 2012
Quoting nymore: You can not use adjusted data when you do not even know how to adjust the data or as they say in the paper all KNOWN data. The temp where I am at right now is 14F if I adjust for wind chill it is -2F. The temp is the temp So what, specifically, in the paper is wrong? What is it that you think is unknown that should have been included? Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

462. Neapolitan 4:28 AM GMT en Marzo 09, 2012
Quoting nymore: Does this surprise you. I showed a few blogs ago how NOAA/NCDC moved their global baseline from 1961-1990 to 1901-2000 to make the anomaly appear almost 0.1C higher. What do you expect from U.S. gov't agencies. There is never any accountability. Just garbage agendas on both sides of the aisle. I personally would not believe them if they told me water was wet. Do you still not understand how baselines and anomalies work? When a temperature baseline is raised, departures from average become smaller on the warm side, and larger on the cool side. IOW, raising the baseline temperature has the effect of making warm anomalies less noticeable, and cool anomalies more noticeable. The baselines were raised because the planet is warming, period. Member Since: Noviembre 8, 2009 Posts: 4 Comments: 11139

463. nymore 4:30 AM GMT en Marzo 09, 2012
Quoting Birthmark: You do realize, don't you, that that's only possible if there was warming? D'oh! Can you give me one good reason why they would move the baseline backward? Member Since: Julio 6, 2011 Posts: 0 Comments: 2047

464. nymore 4:34 AM GMT en Marzo 09, 2012
Quoting Birthmark: So what, specifically, in the paper is wrong? What is it that you think is unknown that should have been included? Well can you or they tell me with absolute truth exactly what each of these contribute to cooling. Member Since: Julio 6, 2011 Posts: 0 Comments: 2047

465. nymore 4:38 AM GMT en Marzo 09, 2012
Quoting Neapolitan: Do you still not understand how baselines and anomalies work? When a temperature baseline is raised, departures from average become smaller on the warm side, and larger on the cool side. IOW, raising the baseline temperature has the effect of making warm anomalies less noticeable, and cool anomalies more noticeable. The baselines were raised because the planet is warming, period. The baseline in 1997 was 1961-1990, sometime after that they moved it back to 1901-2000. Which lowered the baseline for global temps and raised the warming anomaly. Period end of story. I know you never do but can you back up your claim they raised the global baseline? They must have raised it from 1801-1900 LOL Member Since: Julio 6, 2011 Posts: 0 Comments: 2047

466. Birthmark 5:27 AM GMT en Marzo 09, 2012
Quoting nymore: Can you give me one good reason why they would move the baseline backward? Because they wanted a longer baseline and moving it forward really wasn't an option, was it? :) In point of fact, they did move the end of the baseline forward by 10 years to the year 2000, no? By doing so they include the big El Niño year of 1998. It also means that the entire 20th century in now the baseline. If you're really concerned, perhaps you should look for the explanation on their website. If it's not there, then ask them in an e-mail. Find out what they say the reason is, then form a conspiracy theory. Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

467. Birthmark 5:31 AM GMT en Marzo 09, 2012
Quoting nymore: Well can you or they tell me with absolute truth exactly what each of these contribute to cooling. Absolute truth is the province of philosophy, not science. Science, at its best, is a learning process. Absolute truth is impossible in science since absolute truth requires that we know everything about the thing that can ever be known. Obviously, we are in no position to make such a claim. Do you find a specific fault with the paper or have any valid reason to believe that there are non-trivial unknowns in play? Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

468. Birthmark 5:33 AM GMT en Marzo 09, 2012
Quoting nymore: The baseline in 1997 was 1961-1990, sometime after that they moved it back to 1901-2000. Which lowered the baseline for global temps and raised the warming anomaly. Period end of story. I know you never do but can you back up your claim they raised the global baseline? They must have raised it from 1801-1900 LOL It did not raise the anomaly in the slightest. The anomaly with respect to the 1961-1990 baseline is precisely the same. If the anomaly appears numerically larger using the new baseline it is due to the fact that the warming had already begun prior to the old baseline. Therefore, the new baseline is probably more realistic if one is trying to ascertain the amount of warming. Member Since: Octubre 30, 2005 Posts: 0 Comments: 1404

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