SkepticLance

For example "http://www.ipcc.ch/pdf/assessment-re...1-chapter2.pdf The combined anthropogenic RF is estimated to be +1.6 [–1.0, +0.8]2 W m–2, indicating that, since 1750, it is extremely likely that humans have exerted a substantial warming influence on climate. This RF estimate is likely to be at least five times greater than that due to solar irradiance changes. For the period 1950 to 2005, it is exceptionally unlikely that the combined natural RF (solar irradiance plus volcanic aerosol) has had a warming influence comparable to that of the combined anthropogenic RF. Since the start of the industrial era (about 1750), the overall effect of human activities on climate has been a warming influence. The human impact on climate during this era greatly exceeds that due to known changes in natural processes, such as solar changes and volcanic eruptions. " The bit in bold is pure opinion. At least, if it refers to total solar effect, including sunspots. One of the problems we have is that the energy output of the sun, as measured in the last few decades by satellites, has been increasing only to a very small degree, and cannot be a significant contributor to global warming. I get the impression that some people extend this backwards in time to before we had direct measurements and assume that changes in solar activity cannot be a significant contributor to global warming/cooling. You also posted a number of references which referred only to the time after 1950. Since you are totally aware of the fact that I have NEVER claimed sunspots had any significant effect on global warming after 1950, I can only assume this was a mischievous and dishonest attempt to mislead. Incidentally, after your last post, go and wash out your mouth with soap and water!

To iNow Your rain/umbrella analogy is number 2 on my list. Rain causes people to carry umbrellas. Causation. Reversing what is cause and what is effect is simply a silly and meaningless trick on your part. I am sure you knew that and were just trying to throw a red herring. On the business of opinions. There are literally dozens of web sites run by scientists which are sceptical to global warming. If I were to quote such a web site and present one of their opinions, iNow and Lockheed would quite rightly jump on me and pour scorn over that opinion. It also works the other way. If iNow presents the opinion of a scientist who supports the catastrophist's view, then I do not even have to reply. It is an opinion and hence worthless. If you read the points that iNow presented, most are pure opinion. I need the data, not someone's interpretation. The following statement : "It has been extremely well documented now that solar changes since about 1950 have a very minimal forcing, and maybe even negative." is not even pertinent to the discussion. I have not suggested that solar forcings after 1950 had much effect. If you insist on pushing the idea that recent solar forcings are weak, when I have not argued otherwise, then you are simply posting a red herring. The examples I gave for sunspot activity change causing warming or cooling were : Medieval Climate Optimum - 900 AD to 1200 AD Warm due to high sunspot activity. Cooling from 1200 to 1500 AD due to reducing sunspot activity. Little Ice Age from 1500 AD to 1800 AD - very low sunspot activity. Warming from 1800 AD to 1940 due to increasing sunspot activity. (allowing for a bit of up and down during that time) After 1950, sunspot activity was quite constant, except for the standard 11 and 22 year cycles, which produced a warming/cooling effect of maximum 0.2 C. Thus explains some of the fluctuations in temperature change over that time, but is not any significant part of overall warming. If you have good data to show that sunspots were not much of a driver of warming/cooling in the period of 900 AD to 1940, then post it. Please don't refer to the last 50 years, which is simply putting words in my mouth.

To the Cap'n. While it is true that correlation does not necessarily equal causation, it is a necessity for causation. That which does not correlate is not a cause. Where clear correlation exists, there are a few possibilities only. 1. The data is false. Not true in this case, since the correlation has been shown by numerous studies and for numerous historical warmings and coolings. As I said, even the IPCC agree. 2. Causation. 3. Both the phenomena that correlate to each other are caused by a third factor. If you can think of a third factor that can cause both sunspot activity and global temperature change, please let us know. A further clue to this is timing. Where factor A causes Factor B, we see A preceding B. If both are caused by factor C, then they tend to occur together. In the sunspot activity vs warming/cooling phenomenon, we see the change in sunspot activity preceding the change in global temperature. Pretty good evidence. One of the more serious factual flaws in Al Gores ridiculous movie related to the relationship between warming and CO2 increase in the interglacial warmings prior to the present stage, over the last million years of the current Ice Age. He claimed that this correlation demonstrated that CO2 increase caused warming back then. When you look at those warmings, you see the Earth's temperature increasing without CO2 increase initially, and CO2 starting to increase about 800 years later. Clearly, the warming was instigated by something other than CO2. While it is possible that CO2 was part of the mechanism that extended the warming period, it was not the cause, as claimed by Al Gore. In that case, correlation definitely was not causation. To iNow Your post 61 was a collection of people's opinions. It does not even need replying to. If you want to argue, use science.

To Swansont It can be a problem, can't it? You go off for a day and get back with so many extra posts on the thread that it is hard even to do justice to reading them, much less replying. Incidentally, and I know this is irrelevent. I was just reading an article on exercising the brain. While this was directed more at elderly people who need to fend off geriatric cerebral sclerosis, it does apply to some extent to all ages. We all need to exercise the old grey matter to keep it in good working condition. The article actually stated that our kind of forum discussion is one of the best brain exercises. Not just the debate, but also the chasing up of references via google, and educating ourselves on the subject being debated, in order to be better debaters. You mention the business of noise. I agree with you. I have always been a bit bemused by the signal to noise ratio problem in building up good data on long term climate changes. Take temperature. We have an average warming of 0.018 C per year (plus or minus a titch). This is the signal. The noise is overwhelming. If you take annual temperature difference, from the hottest place and time to the coldest, we have a range of well over 100 C. To extract a meaningful signal from all this noise is not easy. In mentioning this, I am not disputing the data. Just bemused by the difficulty. Swansont said : "If "scientists do not yet understand how sunspot activity changes global temperature" (a statement with which I do not agree), how can you state that the 0.4 ºC increase from 1910 to 1940 was due to sunspots?" This is the difference between theory and empirical data. I am saying that theory lags behind data. It is very clear that major historic temperature changes are correlated with sunspot activity change. This is not even in dispute. Even the IPCC agrees. When sunspot activity increases, and this is followed by temperature increase, at a time when other factors such as greenhouse gases and aerosols etc cannot explain the warming, the conclusion is not hard to draw. As far as the 0.4 C warming between 1910 and 1940 is concerned, this is associated with a trivial greenhouse gas increase (less than 1 ppm per decade of CO2). But it followed a major increase in sunspot activity. In addition, the 30 years prior also saw the same greenhouse gas increase associated with a cooling. That cooling was preceded by a drop in sunspot activity. One of the reasons I concentrate on the last 30 years in discussing global warming is that earlier warmings may have been a 'return to normal' following the Little Ice Age. This means that those warmings are not anthropogenic global warming at all. The Medieval Climate Optimum of 900 AD to 1200 AD was correlated with high sunspot activity. The cooling that followed, leading into the Little Ice Age was correlated with a drop in sunspot activity. And the warming leading up to 1940 was correlated with an increase in sunspot activity. The action of sunspots and their association with warming and cooling is not really in dispute. Even during the last 30 years there are temperature fluctuations which 'coincide' with highs and lows in the sunspot cycle. It is really only the last 50 years that the broad pattern has been disrupted, and the first 20 years of that period was a net cooling, and thus cannot be described as anthropogenic global warming. Only the last 30 years is clear cut AGW.

I have been away for 24 hours, and the number of posts seems to have accelerated. No way can I reply to all of them. There does seem to be an incredible amount of opinion cited. I look for good science, and see the opinions of scientists quoted as if that were good science. Something to be aware of.

To Swansont Yes, I agreed that the net cooling of 1940 to 1976 actually happened by 1950. That is off my point, though. The point I was making is that there was a temperature change (net cooling) which did not fit the forcings in the graph. The overall pattern of 1940 to 1976 is that of several coolings and warmings, which do NOT follow that predicted by greenhouse gases. Neither did it follow that predicted by sulphate aerosol. Nor that predicted by aerosol and greenhouse gases together. To explain the pattern, it is necessary to include a powerful sunspot effect also. And the calculated solar forcings do not do this. As I have argued before, scientists do not yet understand how sunspot activity changes global temperature, in spite of several theories. Until we understand the process, how the hell can we calculate it? If you do not believe me, take another look at the graph of solar forcings. The biggest increase in sunspot activity, which drove a 0.4 C warming at a time when greenhouse gas increase was trivial, occurred from 1910 to 1940. Does the red line of solar forcings show this? No. It shows a trivial and short lived increase only. Why? Because the whole thing is not understood well enough to permit accurate calculations. And to come to a final conclusion, if we do not understand something as powerful as sunspot forcings, and cannot calculate them, how can we make accurate predictions for the future? iNow said "Show me a half lung." iNow, I really cannot take your postings seriously. If you want to reply, please reply seriously and rationally.

To foursixandtwo Correct me if I am wrong, but does not the Mormon church have very strong social proscriptions against any of its members that stray, even a little? Humans are gregarious animals, and the most important thing in most of our lives are other humans. To be treated as an outsider, and treated with contempt, is one of the most powerful drivers of depression of them all. Maybe the Mormon church drives members or ex members to suicide by social ostracision and criticism??

To iNow Take a look at your graph of calculated forcings. Note how the net cooling of 1940 to 1976 is not explained by that graph. Note how the warming of 1910 to 1940 is not explained by that graph. Note how the line showing solar forcings is almost a straight line (ignoring minor fluctuations) for much of the time, in spite of our knowledge of relatively massive changes in sunspot activity. Note how there is no line representing the effect of variations in cloud formation. Conclusion : Predictions based on these figures will be poor.

Planets around other stars that have so far been discovered, are overwhelmingly different to our solar system. Giant planets close to the star. Strongly elliptical orbits. Few large planets out towards Jupiter orbit. These things mean there is a real possibility that our solar system represents a rare type. We need a Jupiter in its current orbit to sweep up asteroidal detritus and stop it reaching the Earth. We need circular orbits to prevent extremes in local temperature that would prevent life developing. Solar systems with a difference may never have a chance to develop life. Another point. We often talk about conditions for life. Few people talk about conditions for the genesis of life. They are quite different. Life on Earth came into being at a time when there was no oxygen in the atmosphere,and both physical and chemical conditions were very different to that we now see. It may even be that the conditions needed for first genesis of life may only have existed in a very small place (like a puddle of very hot water) for a very short time on Earth. For a planet to have life, it must not only have conditions for supporting life (like liquid water) but must also, at some stage, have had the right conditions for life to have come into being. We do not know what those conditions are, but it is very possible, they were very special, and rare conditions. Whatever they may be, the probability of having both the conditions for life to survive, and the conditions for life to come into being, is a lot less. I predict that we will find life on Mars, even if it is only a tiny amount of bacteria. However, I predict that when we study the genomes of such bacteria, we will find they are of Earth origin. Life can exist on Mars, but is unlikely to have originated there. I say this because of the life we have found in ultra cold conditions in Antarctica. Bacteria can survive, and even reproduce, in the microscopically thin film of liquid water surrounding dark specks of dust. Bacterial spores have also been exposed to the vacuum of space in vertain experiments. Most can survive for long periods. Meteors from Mars have been found on Earth, after asteroidal collisions hitting Mars have flicked debris into space. It is seriously probable that debris from Earth has made it to Mars also. If so, that debris will have carried bacterial spores. Carl Sagan and Dr. Drake used the Drake Equation to calculate the number of civilisations in the Milky Way Galaxy. Their estimate was one million. The SETI project has turned that estimate into a lie. Whatever the shortcomings of SETI, it is beyond the realms of credibility that there could be one million civilisations, and not one give out a radio signal SETI can detect.

To Chris C Your figure of 0.8 C warming. Can you tell me what time period it refers to? I assume it is average global temperature change?

You need to remember that the 0.5 C warming over the past 30 years is a global average. In the Arctic, the warming is 3 times that, or +1.5 C. This has little effect in the Arctic winter, when temperatures are well below minus 1.5. However, in summer, a lot of the sea temperature is slightly positive. An extra 1.5 C is enough to cause melting of sea ice. It even melts some ice on the fringes of the land, but not ice any distance from the sea. Of course, this means that in other parts of the world, warming has been a lot less than 0.5 C. The United States saw 0.4 C warming. In the tropics, it was much less than that.

Lockheed said " aging will still happen, simply because of sheer erosion of our bodies." Yeah, but with 100 + years of medical advances, it ain't necessarily so! Remember that our bodies are 'eroding' all the time, and being repaired all the time. The net 'erosion' effect is simply because, with enough ageing, deterioration exceeds repair. This is an accelerating process. Older people deteriorate quicker than young people, because their repair mechanisms are less effective. I know of no reason in theory, why treatments could not exist which boost the repair mechanisms while the patient is young, and thus keep them young. Why would anyone build space habitats? It is not going to be a case of some government or megacorporation suddenly saying: "Let's build a space habitat." These things evolve into being. I would imagine that the space elevator will be built long before the first big habitat. Once there is enough traffic up and down the elevator, and all the successive elevators, building space vehicles large enough to carry a community able almost to be self sustaining then becomes an economic advantage. Things will evolve from there. Remember we are talking about the distant future. Lots of time for new structures and new societies to evolve.

lucaspa said : "When we do genetic engineering, we are arbitrarily stating some traits are "good" and others "bad", without natural selection's ability to consider the entire organism re the environment." That goes without saying. However, did you not consider that the results of genetic engineering also are subject to selection - both natural and by humans? In other words, the mistakes will be eliminated (by deleting the genes that prove to be poor adaptors) from the population. Genetic engineering will accelerate what might otherwise happen with natural selection, and will introduce genes that would never otherwise exist. Sure there will be mistakes, which will need correcting. There will also be a degree of genetic innovation that natural processes could not achieve in less than hundreds of millions of years. "Why? How do you calculate "likely"?" Here we are talking about changes in human attitudes. When we look at recent human history, we can see how these change, and especially in response to the changes brought by technology. Not long ago, birth control was considered immoral by millions of people. Today, even amongst catholics, it is almost universally used. A few decades back, the idea of human artificial insemination was considered anathema by most people. Today, it is in such wide use, that it is almost unremarked. Numerous such examples exist. Today, the idea of human cloning is considered anathema, also. In another hundred years???? Ditto to attitudes towards human genetic engineering. Today, no way. Tomorrow it will probably be all go. Cultures change. Attitudes change. The only sure prediction is change. Genetic engineering will begin as the small, clearly obvious changes, such as preventing genetic disease. Then we will move on to small improvements - making people healthier, stronger, better eye sight etc. Later, we will introduce more powerful intelligence (when we work out what intelligence is, anyway). Further on, when we have people living in hostile environments, it will make sense to introduce genes that better adapt them to that environment. etc. "You think aging is only due to some genes." I have read a number of different theories of ageing. It seems probable that there are a number of causes. However, genes will be a major factor, and longevity will be achieved to some extent by gene alterations. How much is something we could debate without resolution for many posts. I doubt that the other, non gene, causes of ageing will be unamenable to treatment, when that treatment is backed by another 100+years of medical research. "That's the problem with this thread: people are being way too simplistic in looking at the situation. It's basically a cartoon of what the problems are. Simplify them down and then wish the problems away." This is probably correct, but so what! We are bouncing ideas around, and looking at possible futures. The one thing that we can be sure of regarding predictions, is that most will be wrong. In the mean time, we have fun, and both our spirits and imaginations are stirred. Society will develop in the way that society develops. All the complexity that is required for that future society will evolve. That situation will likely include a number of the concepts we are presently sharing, much modified to adapt to the situation. If we get only bits of it right, that is also fine. "In order to operate the habitats, you must have effective birth control. BUT, if the society has effective birth control, there is no reason to build the habitats to begin with!" Lucaspa, you appear to be a great believer in natural selection. Apply your brain to this. Given birth control, with women very successfully deciding how many children to have, and assuming that a part of that love of children is genetic, what will happen to the spread of the gene(s) for loving children over many generations? What will that do to population control in the long term? Also, add in the strong possibility of very long life to population size. The need for new human habitats could become critical. "But where does the reaction mass come from to accelerate and decelerate the habitats?" It comes from the muddy snowballs that are mined for resources. Even a small comet contains more mass in the form of volatiles than any space city is likely to need as reaction mass. The other thing is that the reaction mass effect is dependent on exhaust speed. We can assume that a highly advanced technology will be able to accelerate the reaction mass to close to the speed of light (after all, we can already do that in particle accelerators). The exhaust velocity effect is logarithmic. A small amount of mass at very high velocity gives strong acceleration.

To Lockheed Re harvesting matter in interstellar space. I meant this as a possibility only. We do not actually know how much matter is between stars. There is a strong body of thought that the Kuiper Belt, which extends way out into extrasolar space, contains a number of planets, moons and trillions of cometary bodies. These may well be available for harvesting in immense numbers throughout the galaxy, including half way between stars. When I was much younger, I worked as an indistrial chemist for a company that made a wide variety of products. One was a rock fibre for insulation. Basalt rock was melted in an arc furnace and blasted with air to blow it into fibres. A byproduct of the process was pig iron that was sold. I say this simply to point out that minerals can be obtained from what seems to be useless rock, even with our technology. A few thousand years from now, who knows what humans will be able to extract from cometary bodies. However, it may be that there is too little matter between stars. Our descendents will find out.

To lucaspa Your belief that we are not as smart as natural selection is probably right. The problem is that natural selection, when applied to humans, is exceedingly slow. A computer can run through a thousand generations in the time it takes you to blink. However, a thousand generations of humans takes 25,000 years. Thus, it is more likely that we will use genetic engineering to make whatever changes are needed. I doubt that our current reluctance to modify humans will last. Human cultures change. By the time we have millions of people living off Earth, our attitude to genetically modifying people is likely to be massively different to our current superstitions. Perhaps, when our computer and genetic science is sufficiently advanced, we can use computer based natural selection to model the human genome and simulate its evolution under differing environmental changes. Then we could synthesize the best genes and insert them into humans. The other thing that will happen, if we are looking at human society long term, is a massive extension of human life span. Once we learn to silence all the genes that cause ageing, humans will live for hundreds, if not thousands of years. This will probably not happen for at least another 100 years, but is rather likely eventually. What are the implications for social change? Lockheed does not like my idea of fusion power on board habitats. However, there are major benefits in terms of mobility - being self sufficient. It also creates independence from an external energy source that might be fought over by different competing human communities. It permits slow travel between star systems, which might take generations. And the energy availability is enormous. Small amounts of deuterium, in theory, could be enough to supply millions of people with all the energy they will need. A question related to Dyson Spheres. Where does the gravity come from? or is this a situation where we expect the future generations to be adapted to, and live in zero gravity? A Ringworld gets gravity from spin. A Dyson sphere?

We only know of one planet habitable by humans - Earth. And that was not habitable when it all began. It has taken literally billions of years by the right kind of organisms to re-form our planet into one that we can live on. Even after the first photosynthetic bacteria evolved, it took over 1000,000,000 years before there was enough oxygen in the air to support humans. So when you ask about a habitable planet, you are asking about a planet on which life appeared, which evolved into the right kind of life, including oxygen emitting life, with a long enough time period for the proper atmosphere to form. Odds against it for any specific planet. Astronomical!

To Lockheed Your post is interesting and intellectually stimulating. Thank you. Dyson sphere. The fact that the Dyson sphere will be moving, relative to the galaxy, at more or less the same speed and direction as its star will only slow down the problem. Without an active positioning system, sooner or later any minor differences will lead to the star approaching closer to one side than the opposite. That, inevitably will, in time, lead to disaster. Your point about an advanced civilisation not needing gravity is a good one. You convinced me. After thinking about it, I realised that the future human society could apply genetic engineering and create a human that does not suffer health problems in zero G. My point about not needing a sun was serious. Any human society will need an abundant source of energy. However, that might be internally generated inside the space habitat. A deuterium based fusion power plant would need water as feed-stock. If we take into account what we think we know about the Kuiper Belt, it seems likely that there is abundant mass at enormous distances from suns - possibly even in interstellar space. I could imagine a habitat moving from muddy snowball to muddy snowball way out there, mining the water and minerals, and never needing to approach any sun.

To Lockheed Lots of nice ideas in your post, and I tnd to agree with most of them. A couple of quibbles, though. 1. If you are discussing a Dyson Sphere, or even a Ringworld, there is a major technological problem. Larry Niven published his book 'Ringworld' without even realising this occurred, and had to be told by some of his readers. That is, a Dyson Sphere or Ringword is not an orbital structure. Thus it has no orbital stability. It will move through space independently of the star it surrounds. This means that it will require a separate mechanism for maintaining its position relative to its parent star. Otherwise, it is only a matter of time for a sphere before the star simply moves right through the sphere and on into outer space. Or for a ring, the star would probably move away, and leave the ring spinning in the deep cold of space. If you bear in mind that the ring or star would weigh as much or more than our entire solar system put together, the mind boggles at the mechanism that would continually adjust its position relative to the star. 2. Why should a civilisation want to concentrate itself on moons? The gravity would probably be too low to maintain good health, and it is limiting in terms of travel. Full gravity can be achieved by a spinning habitat in space, which would be able to move freely about the entire solar system and beyond. Raw materials can be harvested from anywhere. Bearing this in mind, my own picture of the distant future human civilisation is not a sphere or ring, but a cluster. A trillion habitats in orbit about a star. No problem adjusting position. Full gravity. And mobility. In fact, assuming advanced nuclear fusion power generation, why would they need a sun at all? Any time the peoples of a habitat, which might be a space city of many millions, want to move, they fire up the ion drive and slowly accelerate away. Such a civilisation would be infinitely mobile throughout the galaxy, only limited by their technology and the speed of light.

To swansont I have no argument with your statement about the 1941 to 1976 period. Sure, the cooling all happened between 1941 and 1950. However, it did not start warming again until 1976. Since we are talking about warming, why include a period of neither warming or cooling? To try to get a picture of current warming, we need a sufficiently long period to average out the year to year fluctuations, and we also need a clear pattern. The 30 year period does it. Yes, there will be other factors besides CO2 affecting temperature. For example : there are several sunspot cycles within that period, which have an impact of about 0.2 C from maximum to minimum activity. However, as far as I know, there are no factors that have a significant overall effect potent enough to change the pattern. If you look at the warming over 30 years, you will see annual fluctuations, but a smoothing out of those fluctuations approximates a straight line. This gives us something to work with. Adding in the net cooling of 1941 to 1976 (even if 1950 to 1976 showed overall net zero change) is simply a complication we can do without. The other thing that is worth bearing in mind is that only the last 50 odd years had sufficient CO2 increase annually to be a major factor in temperature change, with only the last 30 years showing actual warming. So, how can we use temperature change at a time when CO2 increase was trivial to try to ascertain the pattern today, when CO2 increase is substantial?

Another wonderful coincidence with our moon. Does anyone know what the odds are that, assuming one moon, that moon would have exactly the apparent diameter to exactly cover the sun during eclipses - to the extent that astronomers can see the sun's corona flaring all around the outside of the moon? With the exception of Charon, our moon is the largest with respect to its parent planet for our entire solar system. And Pluto and Charon are supposed to be twinned planets - and not a case of a moon that came from its parent.

To Swansont I do not have an internet citation for the CO2/temperature relationship. I first read it in Patrick Michaels book "Meltdown", which shows how an exponential increase in CO2 leads to a linear increase in temperature (Figure 2.4 on page 16). I have seen in on an internet source, but I did not keep the reference. Perhaps another person can post such a reference? This relationship is accepted climate science and is not controversial. Of course, it depends on how much the CO2 increase is. If there is a very strong curve on the CO2 graph, the temperature increase will also be a curve. However, the past 30 years in the real world saw an exponential growth in CO2 and an approximate linear growth in temperature, as fits this relationship. I would really prefer not to keep arguing the point of using the last 30 years as a reference. A glance at a temperature graph for the last century will give you the answer. Before 1976 the warming or cooling has too many variables. Only after 1976 do we have a simple situation with CO2 increase causing warming, without the complication of other very powerful factors. For example: 1941 to 1976 saw a net cooling. This makes that time period inappropriate as a reference in discussing global warming. The big difference between 1941 to 1976, and 1976 to 2007, is that the earlier time period was very strongly affected by several other factors - mainly sunspot activity change, and possible aerosol pollution change - while 1976 to present shows a simpler picture, with such extraneous factors being only of relatively minor concern. Do you not understand this?

To iNow Lockheed started this thread with the stated objective of keeping politics out of it. I presume he also meant to keep emotional garbage out also. Did not take long to degenerate. Please. If you want to continue the debate. Please, give good scientific ideas, or ask good questions.

To iNow Long term? Lousy question. I know this is a totally unsatisfactory answer, but it is : "It all depends." In geology, long term means hundreds of millions of years. In human paleoanthropology, it is hundreds of thousands. In human history, it is thousands. In politics, it has been said that a week is a long time. In other words, it is all relative. However, in terms of our debate, that is pure semantics, and a diversion from anything meaningful. I have used the figure of 30 years, for very good reason. Perhaps you may care to relate to that.

Swansont Please read the following, since you do not appear to have read my earlier postings. I have said before so many times. I am not claiming a linear extrapolation. Just that, the past 30 years have approximated linear, which makes it less likely that a major departure will occur in the near future. And yes. Long term trends can be and have been tested scientifically. It is simple. You make a prediction from a long term trend and see if it happens. Often, it does. At least a lot more often than predictions from other methods. Historically, projecting long term trends is a more reliable method of making predictions than almost any other. Of course, any prediction is very likely to fail, including those from long term trends, and from computer models. And no. 30 years is NOT arbitrary, as I have explained to you many times. It is the ONLY part of recent history in which global temperature change has occurred clearly as a result of greenhouse gas increase without some other factor dominating. For 30 years we had steady warming to a total of 0.5 C in line with the steady CO2 growth. For the 35 years before that we had a net cooling of 0.2 C, which makes it hard to talk about global warming for THAT period. For the 30 years before that, we had warming of 0.4C, but with only trivial CO2 growth, making a cause and effect conclusion rather shaky. And for the 30 years before THAT, we had cooling, associated with almost exactly the same trivial CO2 growth associated with the 0.4 C warming. ONLY the last 30 years shows a clear cut relationship between CO2 and warming. Do you get it now? Choosing 30 years is far from arbitrary. It is the ONLY time period with a clear relationship between CO2 and warming.

To Dak Thank you for that reply. It was intelliegent and researched. A very good example of how such a debate should be continued. I agree that warming will most probably continue for some time to come, and will be significant. I come to that from a slightly different angle, in that the warming in response to greenhouse gas increase over the past 30 years has been steady. This means a long term trend, and long term trends have been shown by history to have a tendency to continue. Does anyone think that my suspicion of the long term accuracy of global climate models is without foundation?