gmoran

When talking about AGW, there are two components: the greenhouse effect (GHE), the effect of infra-red active gases on atmospheric radiative transfer, and; climate sensitivity, the feedbacks that amplify and dampen climate forcings, which are believed to be high (2.5'C or greater for a doubling of CO2). The GHE is uncontroversial and well understood, as such it is climate sensitivity that lies at the core of disagreements around global warming. The majority (if not all) of the evidence that support high climate sensitivity are based on the inability of climate models to project the 20th century climate without high sensitivity - however there is also an assumption of low internal variability, as such the argument is somewhat "boot-strapped". In this viewpoint the cooling in the 50's, 60's and 70's is due to aerosols and the high rate of warming in the 80's and 90's is almost all due to anthropogenic forcing - leaving little room for other explanations for the pattern of warming in the 20th century (e.g. a long term warming trend plus high internal variability. Such arguments are termed detection and attribution. The modern British climate of BBQ summers and mild winters was also presented as evidence supporting the detection and attribution arguments of AGW. It is therefore plainly problematic to the AGW hypothesis of high climate sensitivity if we are entering a post modern climate of severe winters and late summer monsoons; particularly if there are wider synoptic changes that are consistent with high internal variability (e.g. the southward migration of the jet stream). SF's posts assumed that the modern British climate would make severe winter weather events a rarity and less extreme. The progressing pattern of the last three years therefore must have come as an unpleasant surprise. The MetO must find themselves in a similar predicament, as in the summer in their contribution to the transport winter resilience report they stated that they did not believe the previous two summers indicated a trend, and that the chances of another severe winter would still only be 5% (once every twenty years ). I find the Potsdam institute paper that TWS mentioned unconvincing as it is plainly revisionist in nature - preferring the climate regime shift work of Swanson and Tsonis as some sort of explanation of current patterns.

Firstly, what we are talking about are skilful predictions; if I predict that the sun will still be functioning next year, then I'd probably be right, but it isn't particularly skilful. From a pure commonsense perspective, and a scientific one as well, it is obvious that future climate states cannot be skilfully predicted: climate system is non-linear; climate patterns (PDO, AMO, ENSO, AO) are poorly understood; future solar irradiance cannot be predicted; future volcanic stratospheric eruptions cannot be predicted - hence future climate cannot be predicted. Climate modellers are not attempting to predict future climate, but future boundary conditions given changes in forcing. Therefore yes, it is impossible to predict future climate, including GMST, using our knowledge of the climate system. It is however possible to make naive predictions, e.g. the long term warming trend is .7'C per century, and it would be a reasonable bet that this would continue (however it is far from certain). As an example, if at the start of the 21C you were to predict the rate of change for the next decade using the naive method (.07'/D), you would have done far better than the GCM method (.2'/D), the actual change (Hadcrut3 dataset for the 120 months to Nov 2009) was .04'/D. Don't you think this is an interesting point? If you take the synoptic definition of climate, then any prediction of future climate must involve skilful predictions of regional climate. Yet you think this is impossible to predict (a concept that this paper agrees with Koutsoyiannis et al 2008)? Why do you think predicting future global climate, using a synoptic model or a GCM, should be any easier?

I'll refer you to climate scientist and modeller Gavin Schmidt of NASA GISS: "there is so much unforced variability in the system which we can’t predict — the chaotic component of the climate system — which is not predictable beyond two weeks, even theoretically.", interview available here: Gavin Schmidt Interview. This is what I mean when I say it is physically impossible to predict future climate; and is subtly different to whether GCM's can skilfully project future boundary conditions in response to a forcing - though so far they do not appear to be skilfull in even this regard.

What ticks a lot of people off, me included, is that the MetOffice have been putting out these annual and seasonal forecasts for some ten years now, and they really seem nothing more than a propaganda exercise to prove: AGW is occurring, and; climate predictions have some value. I think for a good proportion of this time the Meto have been helped by a warming trend, so they were (most of the time) backing the form horse. However since the mid noughties (globally) and from 2007 in the UK, things have changed, forecasting warmth has no longer provided such good dividends and the Meto have been caught out. GOOD. It is physically impossible to predict skilfully beyond what the current synoptics and teleconnections allow. As far as these forecasts: they should stop with annual projects of GMST - GMST is highly correlated data, so naive forecasts are not particularly difficult, and proclaiming that GMST will be X above the anomaly is not skilful, or significant (a situation the Meto constantly misuse) and is merely propaganda; secondly seasonal forecasts are fine but should concentrate on what the synoptics show when the forecast is made, and should only extend as far forward as they allow - something akin to GPs forecasts would be useful. Finally the Meto should stop with the propaganda. They constantly make announcements that this year will be in the top 10 warmest years as if this is proof of AGW; they did it at Copenhagen Meto Copenhagen Announcement - but this is not as significant as they imply, because GMST is highly correlated, if climate is plateauing, or dipping GMST would still be high. Their director untruthfully stated on a BBC news show that they had predicted the levelling off of temperatures in the noughties Meto Director On BBC news. How many times have you heard that medium term predictions are difficult, but long range predictions of climate are accurate. Sorry this is rubbish, it is impossible to predict the future state of the climate beyond the current synoptics - what GCM's do is to try to determine the differing boundary conditions when different forcings are applied, but they have not yet proven to be particularly skilful in this endeavour (hindcasting demonstrates basic competency but not skill). I think the Meto would benefit if they split out their climate group. In summary I think the Meto are the author of their own misfortune, and I have no sympathy for them.

While there might be future "tipping points" waiting for us if global temperatures start rising again; there certainly have not been any "tipping points" associated with the current warming phase(1977 - ) or the long term warming trend (17?? - ). What is very likely however is that there has been a change in synoptics affecting the UK. Likely causes are ocean circulation cycles (any opinions on this?). If so the synoptics could (are likely to?) flip back.

In my reply to Reef I mentioned that averages hide details. What you are posting here is somewhat related: what should we expect the CET to do under GW; what is the significance of global mean averages? I understand that one of the areas climate modelers are keen to improve is the regional performance of GCM's! How meaningful are GCM projections of GMST, if regional projections are known to be weaker? At any rate, the point raised is a good one, CET can go up or down, and have no significance to GW whatsoever; the UK must be a poor marker for GW being an island in the north east of the Atlantic ocean.

The graph is very interesting: the trend looks slight, and given the large amount of variability I'd guess not particularly significant. What is the trend, what's the standard deviation, and do any of the data points breach the 95% confidence intervals? It is obvious that British weather patterns have changed significantly since the 1960s, but annual mean averages and rolling 12 month averages will probably hide some of the information.

It's a case of cherry picking: looking for a pattern in data and then attaching undue significance ( http://en.wikipedia.org/wiki/Cherry_picking ). A calendar month is a sample period uncorrelated to the data you are attempting to attach significance to, it is not biased.

One of the problems with looking for statistical trends is cherry picking, finding data that suits your model and then attaching significance to it in retrospect. Using calendar months prevents that, such that a calendar month of sub 3'C has more statistical significance than finding 31 consecutive days that are sub 3'C. Since 1860 we have been able to observe a long term global mean surface warming trend of .08'C per decade; since approx 1975 the warming trend is .16'C per decade. The interesting question at this time is whether the shorter term warming trend since the 1970's has now come to an end, and we can expect some cooling or at least some stasis. In the UK it may mean that synoptics since the early 1990's that have tended to preclude cold and snowy winters are now changing. Answers to these questions may take some years to become apparent.

I'm not sure where you are getting your data here? HADCRUT3 clearly shows that 2008 GMST continues the cooling trend (.321'C to Nov) since 2005, each year being subsequently cooler than the previous and now on the edge of the 95% confidence intervals (2*SD of residuals 1975-2007). If this continues in 2009 it will be unarguable that the GCMs are missing something. Anyone pointing to a linear regression of the data, or failing to account for the high correlation between adjacent years in GMST, is either unaware of the subtleties or is willfully misrepresenting. It will be interesting to see what the final HADCRUT3 figure is for the year but it won't significantly change from what it is currently, both RSS and UAH anomalies are in and are down on November and demonstrate that December was not warm in comparison to recent trends.

looks like a slight warming

Well it's a play on words, as AGW advocates often label opponents as denialists. And the hockey stick produced in MBH98 is beyond being defended, Mann's statistical methodology was proven to be wrong, and it was only Mann's reconstruction that I was criticizing. Mann's reconstruction was discredited. Before then the accepted data did not show that trend. Some Reconstructions post Mann have HS attributes, those based on bore holes (regarded by some as being a better source of data) don't. The evidence for past climate variability is good, and furthermore is what would be expected. Fair cop

Not at all; there is a warming at the end of the 20th/beginning of the 21st that is distinct in the last millennium. But I don't like seeing the last 1000 years revised for idealogical purposes. AGW? evidence looks reasonable. Alarmist AG and I'd have to say I'm naturally skeptical of such an anthropocentric and catastrophic perspective, especially given the number of elephants standing in the room.

It isn't the global temps that is important in this regard. It's that there was concern about datasets and methodologies, access to which were requested and denied, and it was then found that there was a significant error. Does the error show AGW isn't happening? no; does it show US temps aren't showing a warming trend since the 90's? no; but the change is still interesting and significant. The "blade" still "stands", the flattening of the stick does not; and only some sort of denialist would claim that MBh98's statistical methods, use of bristle-cone data and HS graphic are anything other than dis-credited. Storch web site