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NickD at 22:25 PM on 4 August 2010Confidence in climate forecasts
Dan Olner at 17:42 PM on 4 August, 2010 says: "If someone asks 'how come you can predict climate in 100 years but not weather in three weeks?'" I think this is a good question and I have heard the argument made often. Besides the response laid out here, I have heard an analogy that I think works pretty well for the average person. I should note that I'm not big on analogies, as the listener who disagrees with your point will simply look at what is wrong with your analogy and the point can easily get lost. That aside, I like the comparison to the stock market. We could say the stock market is much like climate. We can (and usually do via 401Ks and the like) make fairly safe assumptions that over the long term there will be an upward trend. This is based partially on economic models and historical data. What we can't accurately predict is the day to day fluctucations of the market, individual stocks, etc. Even the long-term forecast will have its fair share of "unexpected" events. The current recession might be comparable to a large volcanic eruption. Perhaps a depression would be akin to the same volcanic eruption combined with a deep solar minimum. Something along those lines. I hope that helps, as it can sometimes be difficult to speak to your audience, as others have noted. Speaking in technical terms might lose them quickly. Start talking about their wallet and relating it to current events might be beneficial. -
chris at 22:14 PM on 4 August 2010Confidence in climate forecasts
RSVP at 21:02 PM on 4 August, 2010 Hope you made it to lesson two RSVP! Computational models are so valuable in pretty much all scientific endeavours now that it would be a shame if you were still stuck in your lesson one. Obviously the way to address your GIGO conundrum is to take care in the coding and parameterization, use the most powerful computational resource available (if your model is effectively scalable without limit) and keep careful sight of the relationships between your model and the particular element of the real world that your model is simulating. It obviously helps to have a good understanding of the limitations of your model,to carefully frame the scope of the model in terms of the questions about the real world that your model is addressing, to have a means of addressing the relationships between model outputs and the real world, to update the model as parameterizations of the model inputs improve, etc.. Pretty much everyone that uses computational modelling has a handle on these things... -
Mike2811 at 22:01 PM on 4 August 2010Has Global Warming Stopped?
Hi Alden Good post but you do need to take some advice from a statistican on some of the language you use. Specifically relating to what significance and the null hypothesis means in the classical statistical approach. It is not a measure of the confidence in the value of some parameter or result. So in your first example, it's not that there is a 92.4% confidence in the result. That sort of language would make a classical statistican squirm. It's saying what if the data I see, are really generated by an underlying process where there is no trend, but where you see apparent trends because of the underlying variability in the data. In this case, 7.6% (or 76 out of 1000) of the cases in the long run would be consistent with the underlying trend being zero. Traditionally the mantra of p=0.05 would mean you would fail to reject the null hypothesis, but of course as you note, it's more complex than that. It may seem a small point, but the idea of classical significance being a % confidence in something is not correct -
chparadise at 21:53 PM on 4 August 2010Communicating climate science in plain English
For the three levels, perhaps "Basic", "More in depth", and "Expert take". Or "Introductory", "Advanced", "Expert". Snarkier version: "High School", "College", "Graduate School". -
Mystyk at 21:53 PM on 4 August 2010Communicating climate science in plain English
I think terminology more like "Basic/Advanced/Technical" would be appropriate. It gets across the point better for what each level encompasses, making each sound more like a user is selecting their desired detail level rather than their intelligence level. -
Ned at 21:44 PM on 4 August 2010Communicating climate science in plain English
How would this work for the comments? It would seem to be very redundant to have three parallel sets of comments for each of the arguments. On the other hand, it would also seem hard to have a discussion in the comment threads among people who are viewing three different versions of the source material. I could also imagine in a lot of cases people asking questions about the easy and medium versions of an argument and being told to view the hard version. That said, John, I applaud your tireless efforts to make this site more and more useful in communicating and discussing science.Response: Hmm, haven't worked that bit out. Most likely option - have different comments for different levels. Bit messy but seems like the best solution. All current comments would apply to Medium level. -
Daved Green at 21:38 PM on 4 August 2010Confidence in climate forecasts
Hi , does anyone else run climatemodels ? you run it on your computer when its idle , this way they can run thousands of simulations . Iam just interested in others opinions of this . Sorry if link doesnt work . -
Cornelius Breadbasket at 21:34 PM on 4 August 2010Why I care about climate change
Why I care about climate change I am an environmentalist both by choice and career. My driver is similar to John's in that I have children who will have to live in a changing world. I also have 'faith' that humanity has the potential and the intelligence to live sustainably. If I didn't, I'd find it increasingly difficult to have a positive attitude about anything. -
Ned at 21:31 PM on 4 August 2010Temp record is unreliable
As a reminder, BP's figures (like the first one in his comment above) are not particularly useful as long as he continues to use simple averages of the GHCN data set. That choice of method implicitly assumes that either (a) there is no spatial dependency in the climate statistics being examined, or (b) in every year the spatial distribution of stations is uniform. Since we know that both of these assumptions are invalid, one can't really draw any conclusions from his figures. In addition, BP writes: Obviously there was a selection procedure involved in determining which stations should be dropped and it's unlikely it was a random one. "Random" has a very specific meaning. It is unlikely that the probability of a given station dropping out of the GHCN record in a given year is random. That is not a problem, however. Statisticians and scientists work with data produced by systems with elements of non-randomness all the time. A more useful question is whether the change in numbers of stations has any impact on the derived global temperature trends. As has been emphasized many times here, it clearly does not have any meaningful impact. -
Bern at 21:27 PM on 4 August 2010Communicating climate science in plain English
Dappledwater, I would think the basic version would start with the one-liner response, and then provide a few paragraphs expanding on that a little - possibly covering a few more bases, or explaining some of the caveats (carefully, to avoid confusion!). -
huntjanin at 21:27 PM on 4 August 2010Communicating climate science in plain English
At the risk of being expelled forever from this august list, which I read several times a day, let me submit a very heretical view: I'm against dumbing down this excellent website, in any way, shape, or form.Response: On the contrary, this system would actually free up more advanced content. I've often held back on publishing more detailed content in order to keep things simple. With this system, having a simpler presentation gives me more license to go into more detail on the higher levels without fear of "beginner" readers. -
robert way at 21:23 PM on 4 August 2010Communicating climate science in plain English
I will give it a shot but it is true that it is very hard to bring things down to the easy level... -
ProfMandia at 21:20 PM on 4 August 2010Communicating climate science in plain English
John, I am starting to think you are not human. Do you sleep? :) -
Cornelius Breadbasket at 21:17 PM on 4 August 2010Why I care about climate change
I don't have a faith, but it is people like you, John, that help me realise how valuable it can be to have one. -
RSVP at 21:02 PM on 4 August 2010Confidence in climate forecasts
My first lesson in computers was, "garbage in, garbage out". -
RSVP at 20:57 PM on 4 August 2010Waste heat vs greenhouse warming
KR 177, 178 I have read both 177 and 178 twice now. Didnt see waste heat mentioned once, which is the topic of this thread. You say I have not, "...understood thermal diffusion in a gas". I assume you are referring to that which GHGs impart to non-GHGs. I have no problem with that idea. However, if you inject heat directly into non-GHGs (i.e. introduce waste heat), I assume it will work the other way around, in which case, non-GHG heat will impart thermally to GHGs which will in turn radiate heat (up and down) as you say. That which is going up, is cooling, and yet you say, "And more GHG's mean more warming. Period, end of story. No cooling,.." This last sentence may be true for radiation generated from the surface, but does not seem to apply for heat injected into the atmosphere. You dont have to admit you are wrong. I may even be wrong in the long run, but I dont think the idea on face value has no merit as you would like to make this seem (given you tone and remarks). -
Rob Painting at 20:53 PM on 4 August 2010Communicating climate science in plain English
Phew, and I thought you guys were busy enough already. As far as classifications are concerned, basic/intermediate/advanced sounds good to me. Given that the current rebuttals might be characterized as intermediate. What amount of information might the basic version entail?Response: My 'Debunk of the Week' on the Irregular Climate podcasts are good examples of 'basic' versions of the 'intermediate' rebuttals. When I kick this off, I'll start by using the half dozen or so podcast debunks. -
RSVP at 20:16 PM on 4 August 2010Why I care about climate change
macoles #18 "I choose to be an Atheist, not because of my understanding of science, but because I believe God is unnecessary" Is there a reason you capitalize the word atheist? This question aside, for most people belief in a deity is tantamount to having a sense of purpose, one that transcends our survival instinct. Perhaps the inability of science to explain this is proof enough for most. -
RSVP at 19:52 PM on 4 August 2010Why I care about climate change
BP #83 Thanks for the picture. Obviously more than just CO2 is coming out of the tail pipe given the "cutting edge" fuel and emission standards back then, which goes back to my "flawed" view. Emission standards are only a problem when everyone and their grandmother owns a motor vehicle. This was not the case in Hungary in 1956. If "horses were actually slaughtered en masse " as you say, it was done precisely to centralize dependencies (a bad thing). So I dont think my comment was so off. HumanityRules #82 Judging from your comment, there is no common ground, so I wont even bother. -
Dick Veldkamp at 19:40 PM on 4 August 2010Confidence in climate forecasts
I agree with John Russell above, what matters is the audience. If IPCC says 'there is at least 90% probability of 2-5 deg temperature rise in the next 50-100 years', what this means in normal language is: 'there is no doubt' or 'we can be pretty darn sure'. Like it or not, we use expressions like 'there is no doubt' and 'it is certain that' all the time to describe (future) events that have a probability of occurring of less than 1. It is a bit like with DNA evidence. Lawyer to expert: 'Is there a probability that the DNA match putting my client at the scene of the crime occurred by chance?' Expert: 'Yes, about 1 in a million.' Lawyer: 'Ladies and gentlemen of the jury: based on DNA-evidence you see it is not at all certain that my client was at the scene of the crime.' Of course this is ludicrous, a probabibilty of P = 0.999999 (or even P > 0.99 for that matter), is what we tend to call 'absolutely, totally certain' in layman speak. On a related note: what is often overlooked is that uncertainty also means that there is a probability that things will turn out to be WORSE than expected. So uncertainty in IPCC projections makes it MORE important to take swift action, not less. -
Rob Painting at 19:25 PM on 4 August 2010Confidence in climate forecasts
Chriscanaris @9 - your De Havilland Comet analogy is back to front. Continuing with your analogy - the models demonstrate a 90% probability of the aircraft crashing, but because of the remaining uncertainty you want to board the plane and fly anyway. -
chris1204 at 19:09 PM on 4 August 2010Confidence in climate forecasts
If the general principles of climate models were wrong, scientists would have known long ago: microwave ovens wouldn't work, aircraft wouldn't fly, weather couldn't be forecast. Aircraft however do fall out of the sky, microwave ovens fail, an weather forecasters get it wrong. With regard to aircraft falling out of the sky, I'm reminded of the troubled history of the De Havilland Comet aircraft - two spectacular crashes led to extensive research eventually isolating metal fatigue arising out of pressurisation and depressurization as the culprit. The models never predicted this. Moreover, only four Comets crashed (one because of pilot error, one because of issues relating to wing design, and the last two because of metal fatigue leading to significant redesign of subsequent Comets). Now none of us would ever get inside a plane if we were told that there was a chance of 'less than percent' of the aircraft crashing. So I think thingadonta's not totally out of place in citing the IPCC's uncertainty margins. The uncertainties arise because some things don't quite fit the models perfectly. With all respect to ubrew12 whose technical expertise far exceeds anything i could aspire to, the earth is a touch moire complex than an artificial satellite. I'm not too comfortable with the notion that the broad concepts are so simple as to be trivial. Models by their very nature oversimplify and need modification to bring them in closer accord with reality (and I recall a fine description in Spencer Weart's book on the the development of climate models). None of this in any way detracts from arguments that we should reduce CO2 emissions and fossil fuel reliance substantially - these are very arguably good things in themselves. However, let's not impoverish our understanding of our world by trivialising the sources of uncertainty - we might even end up with better focussed responses for the future of our planet. -
Ann at 19:05 PM on 4 August 2010Grappling With Change: London and the River Thames
This reminds me of a science fiction story by Stanislav Lem (quite an old story, dating from communist Poland). The story is about Master Oh, a universal benefactor and philantropist (Oh being an uttering of admiration at his genius). Master Oh arrived at a planet that was completely inundated. By the way, climate change had nothing to do with it. It was just an irrigation project from the government gone terribly wrong. Rather than doing something against the cause, Master Oh advised people to adapt to the circumstances. More specifically he advised them to evolve into fish. So the people lived in the water, they developed the most terrible rheumatism, tried unsuccessfully to breathe underwater, hoping they would one day reach the sainted fish state. Moral of the story: you can better do something about the actual cause of the problem, especially if YOU are causing the problem, than to adapt. I am also wondering: what costs are necessary to protect the Netherlands (and other low-lying regions worldwide) against a sea level rise of 1-2 (up till 6 ?) meters. And this is just one of the many costs the society – e.g. the tax payers - will have to bear as a consequence of global warming. And how does this cost compare to the cost that is necessary to stop global warming ? Another way of dealing with this problem is of course: giving up these regions. But that actually means that the people with the bad fortune of living in low-lying regions will ‘pay the price’. They will lose their property as a result of this human-caused disaster, and probably receive no compensation whatsoever. -
John Russell at 18:57 PM on 4 August 2010Confidence in climate forecasts
Dan Olner at 17:42 PM on 4 August, 2010 : Unless you know Kevin Judd's audience you can't know whether what he writes is over-simplistic. Only he can know whether he's pitched it right. Given that this is a general radio audience, if Kevin started talking about 'boundary conditions' and 'external forcings' he'd lose his audience immediately; they'd switch off. This is one of the problems of explaining climate science; for the man in the street you really need to go simple. If you over-qualify a statement you sound complicated and turn many people off; if you leave out the qualifications you leave yourself open to being criticised for not understanding the science. There's a perfect example in Kevin's radio piece. He says "...there is no doubt on the basic story that the earth's average temperature is going to rise 2 to 3 degrees over the next 50 to 100 years." Then, above, thingadonta says "according to the IPCC, [there's] roughly a <=10% doubt" . So to prevent criticism perhaps Kevin should have said, "there is a strong chance...", or even (to satisfy Thinga...) "there's a 90% chance? But then the audience say, "see; they don't really know!" -- which is true... or perhaps not. To be both simple and accurate is possible. But in this world of unequivocal -- arguably outrageous -- statements by politicians, advertisers and every pundit under the sun, for the man in the street the voice of the scientist can sound woolly and unconvincing. -
Arkadiusz Semczyszak at 18:43 PM on 4 August 2010The Past and Future of the Greenland Ice Sheet
“Please reduce the lengths of quotes in your comments.” You are right. Sorry. However works - paper Capron et al., it is important (according to not only me - it gives strong arguments of both skeptics and supporters of AGW theory) that it was more difficult for me to shorten the quotation, not to miss the most important observations of this great - numerous team of researchers. I’m wonder discussion in the scientific world that this work may cause. -
jdaviescoates at 18:30 PM on 4 August 2010It's land use
From one perspective "land use" can be seen to include everything we do that generates CO2 (how we grow food on land, how we mine minerals from land, how we transport over land, how we live on land etc etc.) If "land use" is analogous to "how we live on planet Earth" of course its land use. -
HumanityRules at 18:18 PM on 4 August 2010Confidence in climate forecasts
Thanks Kevin, I think if you were to flesh things out with details I'm not sure a model for the earths climate is in anyway similar to the model for how a microwave oven works Secondly I don't think it's a simple process of plugging in "laws" to the model and setting it going. You have to be sure you have all the laws in the first place. My understanding is that the history of climate models says they get it wrong more than they get it right, that they have needed to be constantly changed because they have tended to drift from observed results. That when they are changed they are not necessarily changed in a way that is a closer match to the forces at work in the real world but are changed to mimic the new observed data which means down the line there is a real possibility that they'll drift from observed results again. I have no problem with models per se but we should be realistic in how well they are working, I think there is an over emphasis on the skill. Part of the problem is that the interpretation of results are often subjective an example might be. Intrinsic versus Forced Variation in Coupled Climate Model Simulations over the Arctic during the Twentieth Century In this paper they look at the output of models for temperature change in the arctic and compare it with observed results. The arctic temperature record has two periods of strong warming, 1979-present and 1920-1940. Models can mimic well the present period but there are issues with the important earlier period. The authors of the paper think that because models predict the present period well we understand whats forcing arctic temperatures now, of course its CO2. They also try to stretch the skill of the models by redefining an early 20th century warming period. So instead of 30years @ 0.7oC above normal they say that a model has some skill in reproducing arctic temperatures if it manages a decade @ o.36oC. This is purely subjective and the authors aknowledge this. With this criteria some (still a minority) are shown to have skill. On this basis they think models are accurate. I think in more simple terms: this paper does a good job in showing that models do not reproduce the early 20th century warming period well and so do not contain all the "laws" governing the arctic temperature. Therefore we can't say for certain what is forcing arctic climate change in the early 20th century and therefore now. As an amateur I should defer to the experts but knowing that this paper isn't just about looking at arctic climate but also is trying to generate the consensus around AGW it makes the subjective nature of the interpretation problematic. -
Dan Olner at 17:42 PM on 4 August 2010Confidence in climate forecasts
Apologies for being critical, but I think this was a little over-simplistic. The most effective 'skeptic' meme about climate modelling is the 'too complex' argument. If someone asks "how come you can predict climate in 100 years but not weather in three weeks?", how will you answer? Saying you're building the equivalent of model steam trains is not going to help with that. There's an intuitive answer: climate is more like the seasons than like weather. One is caused by the angle of the Earth to the sun, the other by heat trapped by carbon, but it's the same principle: the system has a boundary condition, given by an external forcing. Temperatures can go up in winter and down in summer: that won't alter the seasons. Related, what role do feedbacks have? Lovelock's Daisyworld is a nice little model example. An albedo negative feedback there can keep the system's temperature within bounds - but external forcing, boundary conditions, win out in the end in that particular toy model. How much is that like our world? In what ways is it not? On that last question, I'd love to know what others think. One might argue: a negative feedback can only delay the effect of an external forcing. As in Daisyworld, where temperatures are regulated temporarily, but eventually snap back to where they would have been without the feedback control. Alternatively, albedo effects *do* actually change the energy throughput of the system, so feedbacks are not just internal effects, moving energy around within given boundary conditions. Related to that, how much can CO2 be considered a boundary condition in the same way seasonal forcing can? Have I got that all wrong? To sum up, I think we really need simple, intuitive ways to get at the core of what models can and can't do, not to mention what different kinds of model are good for. (Daisyworld = to get across a point about what systems *can* do to regulate themselves, which is why the wikipedia critique of 'lack of realism' doesn't count. Realism wasn't the model's aim.) -
Doug Bostrom at 16:51 PM on 4 August 2010Grappling With Change: London and the River Thames
GC inspired me to go hunting for some numbers on adaptation costs. The short answer is "It's going to be a lot but we don't have much of a clue exactly how much." Chapter 2 of this book provides the most recent completely comprehensive approach to summarizing "we don't know." "We don't know" is not information useful for formulating plans. This really is a heck of a mess. -
ubrew12 at 16:04 PM on 4 August 2010Confidence in climate forecasts
For 20 years I've been a spacecraft thermal engineer. I maintain thermal models of satellites so that I can predict their temperature over their 15 year lifespan. This increases due to degradation of materials. Earth is a satellite, so the broad concepts required for predicting its temperature over time are trivial to me, to the point of boring (it helps I was once a PhD candidate in Atmospheric Science, but left to become what I am). I would like to say its been amusing to watch the general public wise up to the reality that physics is actually codified in computers to model physical behaviors like those of satellites, but I also have children. And it is definitely not amusing considering what such general ignorance coupled with arrogance has condemned them to. -
Doug Bostrom at 16:00 PM on 4 August 2010Confidence in climate forecasts
That #3 sounds rather desperate. -
Doug Bostrom at 15:52 PM on 4 August 2010Grappling With Change: London and the River Thames
Oops, pardon me, I exaggerated. Only about half the Dutch will need to be relocated, a mere 8,000,000 or so, they can be packed into the rest of the country. Nothing to worry about, leaving aside the possible bankruptcy problem.
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Doug Bostrom at 15:34 PM on 4 August 2010Grappling With Change: London and the River Thames
GC I was thinking of the Florida Keys residents as opposed to the Dutch. Speaking of the Dutch, I wonder what sort of pumps will be necessary to move the entire Rhine river up and into the ocean? Also, where do they apply for passports once all the money spent trying to save the country has been squandered on building a national snorkel and no more credit is extended? "Hi, we are the bankrupt Dutch, please take us in, all 16,500,000 of us! We can do your laundry!" Maybe it would be better to spend all the money on something else and minimize the hassles. Some people are gonna be -really- mad when they crack their history books and see we knew the fundamentals of this scenario in 1980 and essentially were bamboozled into creating the final, largest fossil fuel subsidy of all, rearranging vast swathes of human culture in the interest of shareholder value. "But we were not quite sure!" will sound very lame. -
thingadonta at 15:30 PM on 4 August 2010Confidence in climate forecasts
"there is no doubt on the basic story that the earth's average temperature is going to rise 2 to 3 degrees over the next 50 to 100 years." This isn't what the IPCC says. There is, according to the IPCC, roughly a <=10% doubt. So according to you, the IPCC 'doesn't undertand how the science works, or is being deliberately misleading'. To say there is "no doubt" shows you don't understand the science. -
John Brookes at 15:27 PM on 4 August 2010Grappling With Change: London and the River Thames
Perth Western Australia is also sinking, due to our reliance on the Gnangara mound aquifer for our water supply. -
gallopingcamel at 15:16 PM on 4 August 2010Grappling With Change: London and the River Thames
doug_bostrom, The Dutch approach does indeed seem "quite implausible" but they are strongly determined to continue living where they do, regardless of rising sea levels. In my view, such adaptation is admirable but at some point it will be necessary to move to higher ground, whether one lives in Galveston, New Orleans, London, the Florida keys, Holland or Bangladesh. There is archaeological evidence of human habitation where the Black Sea is today leading some to speculate that this may be related to the story of Noah in the Bible and the Koran. -
thingadonta at 15:04 PM on 4 August 2010Why I care about climate change
You don't need a religious foundation to motivate one to pursue social values. But what strikes a scientist like me, is that if one can't perceive the natural underpinnings of a faith/religion like Christianity, it's no wonder one can't tell the natural underpinnings in something like climate change. I like, Doug Bostrom above, go as far as the Cosmological Constant, but believe religion is entirely a social construction, which has evolved in the human condition, and which has both positives and negatives. I recommend the book by Daniel Dennet "Breaking the Spell, Relgion as a Natural Phenomenon", in which he examines religion's natural, rather, than supernatural underpinnings, and humankind's evolved predisposition to certain kinds of religious faith in general. -
huntjanin at 14:52 PM on 4 August 2010Confidence in climate forecasts
This may not be the right place to post this, but let me mention that three sections of my book-in-progress on sea level rise are now available in clean drafts. These are: (1) the Preface, which describes the IPCC; (2) the Introduction, which offers a beginner's primer on global warming; and (3) Chapter l, which explains why rising sea levels are important to us. Should you wish to read any or all of these, and to give me your most critical comments on what you read, please contact me off-line at huntjanin@aol.com. -
Doug Bostrom at 14:35 PM on 4 August 2010Grappling With Change: London and the River Thames
I've a feeling London flood management plans are not done, if this brand new information is any indication. -
Doug Bostrom at 14:30 PM on 4 August 2010The Past and Future of the Greenland Ice Sheet
Just in: This morning I interviewed James White, the director of the Institute of Arctic and Alpine Research here in Boulder, for KGNU radio’s “How on Earth” science show. White is a paleoclimatologist — he studies ancient climates to understand better how Earth’s climate system works. He has just journeyed back from the Greenland ice sheet, where he has been part of an international science team working on the North Greenland Eemian Ice Drilling project, or NEEM... In White’s view, it’s already too late to turn back the clock on climate change to save low-lying coastal cities like Miami. The ice cores that he and his colleagues drill from Greenland and Antarctica tell us that the last time greenhouse gas concentrations in the atmosphere were as high as they are today, the world was even warmer than it is now, Greenland was largely deglaciated, and sea level was 10 to 15 feet higher. Oops, we broke the planet. What did our parents say? "It's all a lot of fun until somebody gets their eye put out?" Full story w/link to interview audio: Message from the Eemian. -
Doug Bostrom at 13:47 PM on 4 August 2010Grappling With Change: London and the River Thames
GC, it's pretty much an open-and-shut case that geology, geographical problems and general environmental conditions particularly of the outer Florida Keys make the Dutch approach quite implausible. Take a look at maps and you'll see what I mean. I'm not saying that adaptation is not possible anywhere, mind you, just that some places can and should be written off forthwith; we can put certain locations on the very top of the "dump" list and should not bother further with them. The Florida Keys seem to be on the wrong end of that list. Encouraging residents into imagining their younger children will be enjoying their middle years where Ma and Pa lived would be something less than right. It's an old problem, really. There are places on the mainland here in the U.S. that have become increasingly indefensible due to coastal erosion yet the Fed responds to local boosters by assisting with insurance on parcels regularly inundated by storm surges. Cnute, but minus the humility, heh! -
Daniel Bailey at 13:45 PM on 4 August 2010Confidence in climate forecasts
Perhaps most importantly for the purposes of this post: if the physics of the models were wrong, the computer you're reading this on and the Internet over which the data is transmitted wouldn't exist. And that would be a tragedy. :) Thanks, Kevin! The Yooper -
apeescape at 13:40 PM on 4 August 2010Has Global Warming Stopped?
oops, that should read "Of course the R^2 is going to be higher as you increase the degree." -
apeescape at 13:39 PM on 4 August 2010Has Global Warming Stopped?
fydijkstra, I calculated the power for your 1st graph (Cohen's f^2 as effect size), and I got 0.400 for the linear fit, and 0.389 for the 4th order poly fit. Aside from power though, poly regressions are just Taylor expansions about the data. Of course the R^2 is going to be lower as you increase the degree. You can use poly fits if you think there is a physical mechanism that shows a curvilinear relationship, you can go ahead and use it (and any other transformation). But because you're using it for such a short series (with decently noisy data), the poly fit gets great fits for the short term fluctuations instead of the trend. The poly fit that you have here is more reminiscent of the 1998 burst, instead of the trend. As a simple sensitivity analysis, you can change the value of 1998, and see the change in R^2 for the linear fits and the poly fits. I would bet the latter will be affected more strongly. -
Has Global Warming Stopped?
ABG - you made an excellent post here. Over-fitting the data is entirely too easy, and will usually give you bad results. You can always penalize fits of unknown data heavily by their polynomial order, increasing the penalty according to data variance, in order to avoid overfitting. But if you have any information on the underlying physical processes, use the simplest fit that goes through the center of variance. Otherwise (as you clearly show with your last figure) you're overfitting into la-la land. -
Temp record is unreliable
BP - an excellent and very interesting posting you present here. Kurtosis of the GHCN data set may be due to any number of things - I would put "weather" at the top of those. I'm not terribly surprised to see the temp kurtosis varying considerably over time, albeit with a rather constrained distribution (your figure 7); simple changes in year-to-year variability (tight means and lacks thereof) might account for that. If it were driven by station number reduction I would expect to see a trend in it, which I don't from your graphs. As to the temperature shift - that appears independent of kurtosis in your figure 7. Your standard deviation graph is much smaller than the rest - only 1967 to present. I would love to see it over the entire course of the data. As it is I would hesitate to draw any interpretations from it. The skewness, on the other hand, is extremely interesting. Smaller station counts should increase the variability of skewness - I'm not seeing that in the post-1993 data, but we may not have enough data yet. An upwards trend, a shift towards positive skewness, on the other hand, indicates more high temperature events than cold temperature events, which is exactly what I would expect (Figure 2) from an increasing temperature trend, matching the temperature anomalies. The skewness seems to me to be more related to warming trends than station bias, considering other analyses of station dropout which apparently bias temperature estimates slightly lower, not higher. The station dropout would therefore operate counter to the trend you see in skewness - it has to be stronger than the station dropout. Again, thanks for the analysis, BP. I do believe it supports the increasing temperature trends (which you might not like) - but a heck of a lot of work. -
kdkd at 13:19 PM on 4 August 2010Temp record is unreliable
BP #96 You can save a lot of bother first by computing the same set of statistics on the other temperature records, and seeing if the summary distribution statistics that you're observing are different for each dataset. In fact this would improve the rigour of your analysis because you could then demonstrate that you're not jumping in with the preconceived notion that the temperature record is dud. Your use of words like "its gets worse" also detracts from the quality of your reporting. "Another interesting feature of this data" is a perfectly good phrase that helps to de-emphasise your preconceived notion of what's happening with the dataset. Also, are you correcting for the different sample size at each point in time with your measurement. If you haven't this casts strong doubt on the validity of your analysis to date. -
Stu at 13:10 PM on 4 August 2010Why I care about climate change
ChrisG @ 74 Oh, no matter, but I would take a different outlook at John's response at #22. Time and space don't require matter to exist, but matter does require time and space. I kind of got what John was saying @22, but I think you're both right to some extent. Time and space don't require matter to exist, since both of those things exist in a perfect vacuum. But then so does a teeming broth of virtual particles doing something or other with zero-point energy (I've read all about this but it's conceptually so wierd I don't understand it). Do these virtual particles count as matter? Anyway, what John said in its entirety was "As is my understanding, there is no time before the big bang and no space outside the universe - time and space require matter to exist" and the premise is correct in my book, even if the conclusion may not be. I am also a Christian, and this is why I understand God to be eternal and unchanging. He is not part of the universe, and hence is unbound by time, which is a property of the universe. But yes, sadly, some of my motivation for coming here is that there is always someone wrong on the internet. I would prefer us not to feck up the planet any more too. -
Alden Griffith at 13:09 PM on 4 August 2010Has Global Warming Stopped?
Sorry, I'm at a conference right now so I haven't been able to reply as much as I would like. fydijkstra, Simply comparing R2 values between models with different numbers of parameters doesn’t tell you much. Fitting a higher order polynomial always increases your R2 value, which does not mean that the model is correct. To demonstrate, let’s try to decide which is the correct model below:
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Waste heat vs greenhouse warming
Some more explanation about black-body and real-life object emissivity and absorptivity, greenhouse effect, etc.: Every material has an absorption spectra. The emission spectra is identical in distribution (peaks, valleys, etc.), but the emission spectra is scaled by the temperature of the material. This scaling is proportional to the 4th power of the temperature. A "black-body", a theoretic 100% emissive material, has well defined spectral curves at different temperatures. Actual materials have spectra that will always be <= the black body energy at any wavelength. "Gray-body" materials (liquid water is a good example) come close to black-body spectra, while others like C02 have spiky spectra (always less than the black-body spectra for equivalent temperatures). When a material is in radiative equilibrium (assuming no other inputs), it's at a temperature where the emission spectra is scaled identically by temperature to the absorption spectra, and hence the same amount of radiative energy is emitted as is received - no energy changes, no temperature changes. Materials with low absorptivity at thermal wavelengths (like N2, O2, as they are too small and have no dipole moments) are essentially transparent (gasses/liquids) or reflective (solids) to IR - they do not heat or cool well through thermal radiation. A silver plate, for example, won't heat up in daylight very well - low absorptivity in that spectra. CO2, CH4, and H20, on the other hand, readily absorb at IR wavelengths. When they radiate (at a rate dependent on their temperature) they do so in an incoherent, isotropic fashion - random photons in random (spherically distributed) directions. In the greenhouse effect, an atmosphere with GHG's present will have surface IR absorbed by the GHG's, heating them. The GHG's will radiate spherically, which means half the emissivity spectra goes back to the surface. From outside the atmosphere, half the photons at the emitted wavelengths don't come out of the atmosphere. This changes the emissivity spectra of the planet, giving a smaller integrated spectra (and energy) emitted at any particular temperature. If the emissivity spectra is changed (absorption remaining the same, as daylight is 99% not absorbed by GHG's), energy emission changes as well, and there is an energy imbalance. Energy will accumulate or disperse, temperatures will change, until the atmosphere radiates the same integrated energy as it receives.
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