http://landshape.org/enm/surfa.....he-trends/

By my calculations using more robust statistics, it would take 20 years or more than twice as many years to produce a 95% confidence interval of 0.2C per decade or 2C per century.

Cheers

If this were a lab experiment, you just wait a long enough time between data samples to ensure each is uncorrelated with the previous sample. The problem is, with the earth’s climate, you need to wait about 3 years to space samples in a way that ensure they are independent.

In a lab experiment studying pipe flow, you might work .1 second.

So, you can see the problem.

Anyway, let’s assume Gavin is right and aggregate global weather is noisy/chaotic and we do have sampling problems, then it would appear to be a simple problem (simple theoretically, not necessarily logistically). Take truly random samples of temperature over the earth’s surface.

My knowledge of statistics is fairly basic, but I don’t believe it would take a large number of random temperature measurements to get a measure of global temperature with a high statistical confidence. This would at least answer the question – How noisy is global aggregate weather?

Or am I missing something here?

BTW, I agree with you. The only significant source of (aggregate) weather noise I.e. not external forcings) I can think of is variations in ocean/atmosphere heat exchange (and perhaps water exchange).

if the IPCC current predictions for mid rate of temp growth were applied to the last5, 8 and 10 years for which data have been available. Would the IPCC forecast have been falsified?

No, no and no.

With respect to the 5 years– there is just too short an amount of time.

The maths here is way out of my league, but my question is, if the IPCC current predictions for mid rate of temp growth were applied to the last5, 8 and 10 years for which data have been available. Would the IPCC forecast have been falsified?

Interesting to know what would be inconsistent with the most dire predictions, but I should add that a positive ten year trend wouldn’t necessarily prove the catastrophic point. Pat Michaels tends to argue that warming will probably be exactly on the long term linear trend line, which wouldn’t be much at all.

we are talking about the aggregate weather across the entire planet. How noisy is that?

How noisy?… it depends what you call “noise”. Weather is variable, or “fluctuates” or what have you. Gavin likes the word weather noise to describe variability. I’m not sure I’d use that precise word, since the weather is the weather. Still, when posting on a blog and trying to describe the difference between climate and weather noise is as good a word as any.

How big is the noise in GMST? Counting measurement and weather “noise” together, the residuals to straight line fit to annual average GMST appear to be ±0.1C. That’s my estimate of noise!

Weather– as measured by temperature, is a bit noisy, even averaged over the surface of the planet and over a year. After all, there is heat in the ocean etc. Given the equations that govern weather, it should be noisy– the only question is how noisy, and on what time and spatial scales.

Fluctuations in surface temperatures don’t falsify the IPCC. We expect temperature to fluctuation around a “mean” value even when constant forcing is applied. We see the same things in engineered systems involving transport of mass, momentum and energy. It just happens.

Of course, at any given location weather is noisy, but we are talking about the aggregate weather across the entire planet. How noisy is that?

Given that weather is just heat and moisture moving across the Earth’s surface. I don’t see how there can be much noise in it (over the entire planet).

Most of the ‘noise’ will result from measurement issues, i.e. we can’t accurately measure the temperature across the entire planet.

And I’d add, that if the noise isn’t due to measurement issues then the Earth’s atmospheric heat content is fluctuating up and down (ignoring seasonality), which would seem to invalidate the IPCC’s Forcings model, or perhaps show there are significant forcings not recognized by the IPCC.

The 2.0 is in the guide for policy makers. So, that’s why I picked it. Otherwise, I would also have picked 2.6 C/century.

The range of 2100 projections is based on scenarios with different changes in emissions through the century. All scenarios have similar projected emissions and therefore the midrange projected rise up to 2030 is about 2.6C/century. Therefore it would be valid to take the 0.6C/century target over the next 10 years rather than the zero warming target.

In contrast, if they’d said solar variations did still matter, and the sun got ’stuck’ in a maunder, they could attribute a flat spot to the sun.

Still, it appears that bloggers doing things as a hobby can at least talk about HOW it could be done.

I do, indeed, work for ANL. But part time, which gives me lots of time for hobby blogging.

A last comment and then we’ll just agree to disagree. There are an infinite number of wrong temperature maps that will produce a given trend but there’s only one map that matches the physical climate. I think that maps would quickly sort out which, if any, of the models are correct. My bet is none of them.

I looked up Lisle, IL. Do you work at Argonne or FermiLab? I spent time at both in the long ago.

With respect, I don’t think that this is so. The IPCC “prediction” in question is based on simulations which make use of the projections of future emissions specified in the Panel’s Special Report on Emissions Scenarios (SRES). This Report was approved and published by the IPCC in 2000. As the Panel decided at its Plenary Meeting at Vienna in November 2003 that ‘the SRES scenarios provide a credible and sound set of projections, appropriate for use in the AR4’, NO post-2000 data have been incorporated into the ‘prediction’ that you are seeking to test. It is therefore valid to use post-2000 data to test the ‘prediction’ for 2000-2010 in AR4.

As there has been a good deal of misunderstanding of the matter at issue, I’ll key in here the text of a letter sent to the Chair of the IPCC, Dr. Pachauri, by Dr. John Mitchell on 30 October 2002. Dr. Mitchell was writing in his capacity as Chair of a Group which included representatives from all of the major modelling groups, and his letter was tabled at the 28th Session of the IPCC Bureau in Geneva in December 2002.

“The World Meteorological Organisation JSC/CLIVAR Working Group on Coupled Models (WGCM), which includes representatives from almost all the major climate modelling centres contributing to the Third Assessment Report, recently considered what work needed to be done to ensure that the best modelling advice will be available for the next IPCC Assessment, due to report in 2007. For each emission scenario, it is necessary to run an ensemble of simulations to define the uncertainty due to natural variability, and to do this with as many models as possible to define the range of uncertainty in modelling the earth system. These uncertainties mean that there is little scientific justification in running new scenarios since the resulting climate change outcome is unlikely to be indistinguishable (sic) from existing scenarios with similar radiative forcing. Hence the WGCM unanimously urge IPCC to retain the current SRES scenarios without change, to make sure a sufficient number of model runs are available for the next assessment;

- to define the uncertainty range associated with current scenarios; and,
- to ensure that these simulations are available in time in a wide range of impact studies in the 4AR.

“We appreciate that small changes in the emission scenarios may require large economic and social changes, and that the effect of the social and economic changes could be assessed in time for the next report. However, unless the accompanying changes in radiative forcing are likely to produce detectable changes in climate, we believe that [it] is better not to try and run new model experiments, but to stick to the scenarios used in the TAR. This will allow a better definition of the range of uncertainty in projected changes due to model uncertainty and natural variability, which are likely to dwarf any difference due to tweaking the existing emissions scenarios. This we believe will provide the best scientific basis for the next IPCC Assessment. Please feel free to contact me if you need clarification or further information.”

Thus the evidence suggests that the IPCC retained the SRES scenarios without change in order to allow “a better definition of the range of uncertainty in projected changes due to model uncertainty and natural variability” – i.e., in order to facilitate the type of analysis you are undertaking. The fact that the IPCC authors “knew” of changes in estimated observed temperatures after 2000 is irrelevant, because these data were not incorporated in the projections. I think that your comments 826 and 827 reflect some misunderstanding of the way in which the temperature ‘predictions’ in AR4 were produced.

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