mheslep said:
I've seen this take on Trenberth's email before, and don't want to let it pass again, so I'm jumping in here -
This is not my reading of Trenbert's email or paper. Your use of the terms 'instrument' and 'measure' implying the problem is a lack of a mechanical adroitness. No doubt Trenberth would like better instrumentation, as does every physical scientist, but he is allowing for a more a fundamental problem. The query "do we have an adequate system?" in the paper is not just a call for better sea gauges. It also allows there may be some gap in the understanding of the climate system. Some part of it may be unknown or misunderstood.
It's not "mechanical adroitness"; just a lack of an adequate system for tracking energy flows.
If you are going to read the emails, don't just stop at the one email only. There's a lot of selection going on in the press and blogs right now which is actively contributing to distortions of what the scientists were actually saying; and singling out this one email is a case in point. In fact this email is part of a longish exchange of emails in a quite heated discussion, where Trenberth is challenged to explain himself, and where he does just that.
Better than the emails is the paper, where it is all spelled out in much more detail and in a form that is intended for wider readers, without making assumptions about colleagues Trenberth knows well.
The paper is explicitly a call for better tracking systems; not a set of questions about theory. He points out gaps in knowledge, of course; but they are not new gaps. They are questions of detail that have never been known, and which require adequate data on energy flows before answers can be given.
The travesty is the lack of adequate systems to obtain that data -- especially given its evident importance. There are always questions, of course. The questions Trenberth wants to address are the questions of detail in energy flow, and the great imperative to address those questions is adequate data. Without that, they can't get the detail of short term and regional change.
It's worth bearing in mind that if you are at all a skeptic about anthropogenic global warming, then you will be reading opinions you do not share. Trenberth is no doubt whatsoever about warming. In his own words from his paper: "global warming is unequivocally happening".
Look at the title of his paper. It is "An imperative for climate change planning: tracking Earth’s global energy". That is, in order to plan for climate change, it is imperative to track Earth's global energy. He really is focusing on the importance of measurements, and obtaining data.
Look at the abstract. (My bolding.)
Planned adaptation to climate change requires information about what is happening and why. While a long-term trend is for global warming, short-term periods of cooling can occur and have physical causes associated with natural variability. However, such natural variability means that energy is rearranged or changed within the climate system, and should be traceable. An assessment is given of our ability to track changes in reservoirs and flows of energy within the climate system. Arguments are given that developing the ability to do this is important, as it affects interpretations of global and especially regional climate change, and prospects for the future.[/color]
His focus is
our ability to track changes. This information, this data, this measurement, is NEEDED in order to plan for adapting to climate change.
If you read any of this as needing data to be sure climate change is real, or to be sure that the planet really is warming, or to be sure that this is caused by anthropogenic effects, then you've not understood him at all. These are underlying basics that are thoroughly established to Trenberth's satisfaction; and indeed to the satisfaction of the vast majority of working climate scientists.
We can look at the alternative views of skeptics of AGW, of course, and we do it quite often. But that isn't the question here at all, when looking at Trenberth's concerns. It is entirely to do with tracking and measuring where Earth's energy goes, in detail, over short term variations and local regional changes.
Look at the top of page 20, right hand column. He starts out with the basic groundwork of what we do know.
The present-day climate is changing mainly in response to human-induced changes in the composition of the atmosphere as increases in greenhouse gases promote warming, while changes in aerosols can increase or diminish this warming regionally depending on the nature of the aerosols and their interactions with clouds. The current radiative imbalance at the TOA has increased from a very small imbalance only 40 years ago when carbon dioxide increases and radiative forcing were less than half of those today. The excess in heat does several things. ...[/color]
The warming, and the main cause of warming, is taken for granted. Sure, in principle, everything in science is open to question. But for working climate scientists, and Trenberth in particular, these are no longer the important unknowns. The unknowns are the modulating effects of aerosols and cloud -- which are smaller than the greenhouse warming but still significant and much less well known and hence a proper focus for investigation. He goes on to describe four effects of the known excess heat: only one of which is the increasing surface temperature.
But to get the detail of those effects, they must be measured, and on page 23 he comes back to his recurring complaint:
We cannot track energy in absolute terms because the accuracy of several measurements is simply not good enough.[/color]
sylas said:
Trenberth is, of course, in no doubt that the short term drop in temperature in 2008 is a local short term effect.
This contradicts statements in the paper. Yes if heat was somehow absorbed an ocean sink or melting ice, examples he gives, then the recent lack of temperature rise would be temporary. However he also allows:
(Trenberth 2009)
Was it compensated for temporarily by changes in clouds or aerosols, or other changes in atmospheric circulation that allowed more radiation to escape to space?
[highlights mine]
If the (excess) heat can escape to space now via some misunderstood mechanism it may (or may not) continue to do so.
This is not a contradiction at all; you've misunderstood him completely. Immediately prior to this he said:
The stock answer is that natural variability plays a key role [1] and there was a major La Nina event early in 2008 that led to the month of January having the lowest anomaly in global temperature since 2000. While this is true, it is an incomplete explanation. In particular, what are the physical processes?[/color]
He GIVES you the stock explanation. It really is short term natural variability for a cooler 2008. This is not in any credible doubt; and what is lacking is detail. We know the La Nina was involved; the question is... how does it do it, physically? Where does the energy go?
We KNOW the energy is there. The greenhouse forcing didn't suddenly stop, and there was no less sunlight. So all that energy was still coming in. HOW did that La Nina event lead to lowered temperatures? There are several credible possibilities.
The inference you have made is as follows: "If the (excess) heat can escape to space now via some misunderstood mechanism it may (or may not) continue to do so." That's not Trenberth's inference, or mine either. Trenberth is quite sure about the La Nina association, and recognizes that it definitely will not all just keep going on. It will go away at the next El Nino (which is now, as it turns out, and so we are hotting up again of course, just like we always do with El Nino).
The question Trenberth is asking is simply this: during these La Nina events, what is the actual energy flow that gives this short term cooling? It's not about some strange "misunderstood" mechanism. It's rather that we don't have the tracking systems in place to tell which mechanisms are the ones involved.
I've missed it if anyone in this thread attempted to say global warming stopped over the long term. The OP BBC piece phrase was
"For the last 11 years we have not observed any increase", Andre used the term
"stagnate", and Trenberth leaves it as an open question:
(Trenberth 2009) last paragraph:
A climate information system that firstly determines what
is taking place and then establishes why is better able to
provide a sound basis for predictions and which can
answer important questions such as ‘Has global warming
really slowed or not?’
[highlights mine]
Trenberth is right. Andre, and Hudson, are wrong; or at least misleading.
We simply do not have the statistical data to say that global warming has "stagnated" or "slowed". As I showed in a previous post, this is a straight statistical question. We know the process involves both long term trend plus short term variations. And the trend may not be constant. So how can we tell whether it has really slowed or not? Most people seem to think you tell by just looking at trends with the data.
They are wrong. Statistically, the natural variation is too great to let you determine what the trend is doing from a short period of measurement, like eleven years. Heck, in all seriousness, the data is actually consistent with the global warming trend having accelerated!
That's what Trenberth is saying. Statistically you cannot tell what warming is doing by looking at eleven years of global anomalies. The skeptics take it for granted that global warming has "slowed" or "stagnated" or something else; which is incorrect. A short trend line does not let you infer that.
Trenberth notes that the only way you can possibly tell this is by actually understanding the natural variation, rather than simply treating it as a random process of some kind... which is what you do to estimate confidence limits on the trend calculations. So Trenberth is saying that it is imperative to get the tracking systems in place that actually let us measure where the energy is going. That's the key to understanding what is going on, because the trend is masked over the short term by natural variations.
Cheers -- sylas
Actually, this might be a good thread topic sometime.) You can get a trend with regression. Estimating the confidence limits on trend is a bit tricky as there is a significant amount of autocorrelation in the time series, but that's a statistical detail that can be addressed. The upshot is, you CAN falsify warming; but not with eleven years of data. That works both ways, you can't prove warming with eleven years of data either.
