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Comments 120701 to 120750:

120701. Berényi Péter at 16:28 PM on 22 April 2010
        Tracking the energy from global warming
        #61 kdkd at 12:48 PM on 22 April, 2010 Is this possible, or is that data not available? CERES FLASHFlux only goes back to 2000. If I take all ten years and apply the same procedure it looks like this: The fit is awful because of the huge step-like change of OHC in early 2003 and also the high noise level before. I guess these features are measurement errors due to changing coverage & instrumentation.
120702. Acushla at 16:13 PM on 22 April 2010
        Greenland's ice mass loss has spread to the northwest
        It has happened to Greenland in the past when ALL the ice melted. The people had a prosperous time for many years and they enjoyed it.
        Response: There is no recorded history of the last time ALL the Greenland ice melted - the Greenland ice sheet is at least 400,000 to 800,000 years old.
120703. cloneof at 15:53 PM on 22 April 2010
        Models are unreliable
        Riccardo As I have just a few minutes let me first just apologize for not giving the refrence. It was almost ill responsible to brag about a paper that I didn't even give the refrence to. I will give you an response later today.
120704. Berényi Péter at 15:41 PM on 22 April 2010
        Where is global warming going?
        #39 chris at 00:18 AM on 22 April, 2010 so what Peter? Have a look and compare coverage.
120705. barry1487 at 14:22 PM on 22 April 2010
        The significance of past climate change
        So if someone asked about CO2 being much higher in the past (noone did bring that up at the talk), I would say that the sun has been getting steadily brighter over Earth's history. I go a bit further - but as I'm a layman I would like to check with you. I put it that the configuration of the biosphere was also very different, notably a big difference in where land masses are situated. Albedo has a strong influence, so if there is more or less land on our near the poles, this can strongly impact the radiation budget. Directly comparing the biosphere now with that of millions and millions of years ago, in terms of CO2 influence, is a bit of an apples to oranges thing. Is this a fair comment or have I been getting it wrong? Also, would different ocean/atmosphere heat transport dynamics in the distant past have an impact on the total radiation budget, or does it even out for the global total? (Hope that made sense)
120706. kdkd at 12:48 PM on 22 April 2010
        Tracking the energy from global warming
        BP #60 That's interesting. But I want to see it on a more appropriate time scale. 30 years is a good minimum for looking at climatic effects (rather than weather effects). Is this possible, or is that data not available?
120707. gallopingcamel at 12:43 PM on 22 April 2010
        Are we too stupid?
        Jacob Bock Axelsen (#106) "Now, enough of what I know. What are your solutions to mitigate climate change?" Two things I could support: 1. Reducing Carbon Emissions As long as this is done via a rapid build up of innovative nuclear power plants (Generation IV) until the cost of electricity is low enough to convince “Joe Six-pack” to trade in his 4X4 for an electric vehicle. No government mandates; just let intelligent self interest persuade the masses. I love my electric car because it is fun to drive rather than its ability to reduce my “Carbon Footprint”! 2. Major Carbon Sequestration Programs Carbon should be sequestered along the lines pioneered by Hammurabi (Babylonian empire). Farmers should be encouraged to overproduce non-perishable foods and timber. The EEC was on the right track with its “Butter Mountains” and “Wine Lakes” although these products were too perishable. Have you ever wondered what would happen to our wonderful high tech civilisation if the recent Icelandic volcano had been a Mount Tambora? How well would we handle another 1816, the “Year without a summer”?
120708. Glenn Tamblyn at 12:39 PM on 22 April 2010
        The significance of past climate change
        #30 unrecovered "Another aspect, I have found difficult for engineers and many other scientists to grasp is: How a system where all feedbacks sum up to a net "positive" does not constitute a run-away system. This is not and easy thing to explain and typically requires too much time in a short talk. But may constitute a stumbling block for engineers in particular. " Perhaps the key point to get across is that the feedbacks are positive, but they also finite or decline with the increase. Methane runs out when the sources are drained, CO2's impact is logarithmic with concentration, when the ice sheets are melting away the albedo change tapers off. And some feedbacks such as Milankovitch Cycles actually cycle between positive & negative.
120709. Andy Skuce at 11:49 AM on 22 April 2010
        The significance of past climate change
        Petroleum reservoir engineers construct numerical models to forecast the production from an oil or gas field. They calibrate their models against recorded production rates in a process they refer to as a "history match". See, for example, this abstract which would, I guess, look familiar in many methodological aspects to climate modellers. So, if you were presenting to a bunch of petroleum engineers, you wouldn't have much problem explaining why palaeoclimate was important in calibrating forecast models. I think a major problem with people's misinterpreting the significance of palaeoclimate is the naturalistic fallacy: what's natural is good for us, or the Nietzschean corollary (recently popularized by the Koch brothers in the Smithsonian exhibit)that what doesn't kill us makes us stronger. What the general public doesn't usually understand is the extremely rapid rate of current changes compared to past changes, as well as the fact that the most extreme palaeoclimates would not permit the survival of our current civilization. There's also the logical fallacy that bverheggen noted (about past and present causes) that seems so elementary (to me) I'm amazed that people keep making it. Nevertheless, I've lost count of the number of times that I've used the forest fires/arson metaphor.
120710. Bern at 11:25 AM on 22 April 2010
        The significance of past climate change
        John, this mechanical engineer had no problem understanding either your previous explanation, or the new simplified one. As you've mentioned, though, perhaps the issue is that you got bogged down in the details. A different order of presentation may be required, where you present a simplified overview, then explore a few areas in more depth, perhaps having some of those detailed explanations in reserve to answer questions. Also, from personal experience - if you were presenting to a bunch of students, then the 'blank looks' & shortage of questions aren't that uncommon while people are digesting the information just presented. Explaining AGW in terms of radiative heat transfer, though, is something any fourth-year engineering students should understand (heat transfer was 3rd year subject when I studied at UQ, but that was nearly 20 years ago...)
120711. MattJ at 11:17 AM on 22 April 2010
        The significance of past climate change
        Oh, and about understanding thermodynamics: I had a VERY long argument in Topix with somebody who clearly had an engineering background, yet believed that EVERY climate scientist claiming AGW was relying on violations of the First Law of Thermodynamics (occasionally he claimed 2nd too) in their understanding of the energy balance. He even claimed to find this flaw in Trenberth's famous diagram. But when I turned to the diagram (and Trenberth's original paper, whose title I forget), what I saw was something very different: I could not find evidence of any such violation (of course), but I DID find evidence of some very disappointing mistakes in presentation that made it difficult to verify that the First Law is satisfied by his numbers. So what is the implication of all this for this article? I would say two things 1) do NOT assume a deep understanding of Thermodynamics, not even from engineers 2) make sure that quantities, variables, scales etc. are CLEARLY marked in the diagrams, and that simple questions like which way how much heat/energy flux flows are easily visible on the diagram. Diagrams like the one in post#27 in this thread are damn near useless.
120712. GFW at 11:11 AM on 22 April 2010
        Where is global warming going?
        Thanks HR. Looks like a good review.
120713. MattJ at 11:08 AM on 22 April 2010
        The significance of past climate change
        Everything in the "dumbed down" talk sounds good and true, but it seems to miss the point. The skeptics, for example, could immediately make it all SOUND meaningless by pointint out that in the past (was it Late Triassic? I forget), we had MUCH higher CO2 levels, but rather small climate change due to it. This would APPEAR to overrule the presentation's observations that 1) climate changes took place in the past due to forcings and 2) CO2 is a forcing. What is the right approach to this? My understanding (I would certainly welcome Cook's corrections) is that the degree to which the climate is sensitive to forcings has itself also been highly variable. Specifically, that with the Late Triassic configuration of continents and corresponding ocean currents, even a rather large CO2 forcing had a surprisingly small effect; but with modern ocean currents, it is well-expected to have a MUCH larger effect. So if that understanding is correct, then it certainly should be included in the presentation for engineers.
        Response: Funnily enough, this was one of the questions I was asked at the presentation - "are you saying climate sensitivity was lower in the past?"
        
        On the contrary, climate sensitivity has been surprisingly consistent in the past, even going back millions of years. So if someone asked about CO2 being much higher in the past (noone did bring that up at the talk), I would say that the sun has been getting steadily brighter over Earth's history. Millions of years ago when CO2 was much higher, solar output was lower. The combined effect of sun and CO2 show good correlation with climate. For more details, see CO2 was higher in the past.
        
        In fact, it's because the sun was cooler in the past that CO2 was so much higher. CO2 acts as a natural thermostat for our climate, regulated by rock weather which is the process of removing CO2 from the atmosphere by chemical reactions. When it's cooler, rock weathering activity slows so there's less removal of CO2 from the air. This means CO2 builds up, warms up the planet. Then as it gets warmer, rock weathering activity increases which removes CO2 out of the atmosphere.
        
        This process is a natural way of keeping our climate within a certain temperature range. It means that if the sun was cooler, temperatures get cooler so rock weathering slows down, increasing CO2 levels. This is a fascinating process but of course, I didn't go into that much detail at the talk - I just mentioned that climate sensitivity has been consistent in the past.
        
120714. scaddenp at 11:06 AM on 22 April 2010
        The significance of past climate change
        CO2 science has something of history in misrepresentation of science papers by selective quoting. I think you can get a list of other examples by putting "CO2science misrepresent" into google and follow links sounding like annoyed authors.
120715. Berényi Péter at 10:48 AM on 22 April 2010
        Tracking the energy from global warming
        Well, I think I have found the solution. OHC reconstructions before mid 2003 are simply wrong. Otherwise satellite TOA energy imbalance measurements have low accuracy but reasonable precision while ARGO OHC measurements are just the opposite. Therefore I have calculated the integral of CERES FLASHFlux net TOA radiation imbalance between the fourth quarter of 2003 and third quarter of 2009. The linear component of this integral is arbitrary due to low precision. So I have calculated a least square fit linear approximation to the difference of the integral above and the NODC OHC reconstruction for the same period. It gives the correct offset for TOA net radiation imbalance. With this correction we get the graph below: The match is pretty good. I think the fluctuations of OHC around the TOA energy accumulation curve are not real, it's just measurement noise. Thermal energy content of the climate system has decreased in this 6 years long period at a 0.19 × 10²² J/year rate. It corresponds to a -118 mW m^-2 radiative imbalance at TOA.
120716. yocta at 10:21 AM on 22 April 2010
        The significance of past climate change
        RE#36 garythompson, #37 Riccardo Two things: From eyeballing the adapted "CO2 science" graph (with my ruler on the monitor I get 0.27 deg warmer in the MWP than today based on matching the red peak to the blue peak so I don't know how they got that. But when I quickly read over the journal paper as far as I can tell it was incorrect method anyway to interpret figure 2b or at least to compare it to modern times as they author's state a few things: ...reconstruction suggests that at least during the Medieval Warm Period, and possibly the preceding 1,000 years, Indonesian SSTs were similar to modern SSTs....Contrary to the Indonesia SST reconstruction, however, the Northern Hemisphere temperature reconstruction does not estimate temperatures as warm as modern at any time during the past two millennia. The author's then continues to say: We note that the high-amplitude variations resulting fromthese hypothesized changes in G. ruber seasonality also preclude accurate estimates of the rates of SST change in the past and a meaningful comparison to the rate of SST increase during the past decade. Reading this, makes me instantly skeptical of the claim at "CO2 Science" that the Medieval Warm Period was warmer than the Current Warm Period. I infer that they intentional (not just that they can't read graphs) with their lack of transparency over how they interpret the science.
120717. HumanityRules at 09:53 AM on 22 April 2010
        Where is global warming going?
        40.GFW This is a review paper on sea level rise. I'd draw your attention to table 1 on page 7. Most of the relevant references to the original data are in here.
120718. HumanityRules at 09:43 AM on 22 April 2010
        The significance of past climate change
        Few comments. It seems fairly straightforward to me but I supposed I've been following the science for a year or so. As you say it depends on audience and what you can assume about them. One thing that jumped out is that you switch between energy/heat/temperature alot. You could think about just talking about one of them. I think the clearest is talking about energy building up in the system. I don't know whether by sticking to one term it makes the ideas flow better. With one line to at the start or end to say that energy build up = rising temperatures.
120719. Josie at 09:39 AM on 22 April 2010
        The significance of past climate change
        Keenon350: I would be very wary of David Wasdell. He is an odd example of someone who uses denialist logic and tactics on the opposite side - to claim that climate scientists are all underestimating the scale of the problem and we are all going to die tomorrow. He has repeated classic denialist rubbish in the past while putting the opposite spin on it - like that climate models don't include the role of water vapour (utter nonsense). He also frequently says misleading things about his CV to suggest that he is a climate scientist when in fact he is a psychotherapist. After he accused the IPCC of political corruption in the New Scientist (or rather Fred Pearce did on his behalf, quoting him) a letter "From the co-ordinating lead authors of Working Group 1 of the IPCC Fourth Assessment Report" signed by 20 major climate organisations was posted in protest, pointing out major falsehoods in Wasdell's claims. It can be viewed here: http://www.newscientist.com/article/mg19325960.900-climate-with-care.html
120720. Momerath at 08:41 AM on 22 April 2010
        The significance of past climate change
        scaddenp, Thanks for the help on that!
120721. johnd at 08:40 AM on 22 April 2010
        Flowers blooming earlier now than any time in last 250 years
        michael sweet at 04:54 AM, firstly your Australian report link doesn't work. Secondly, for Spring to occur the soil needs both warmth and moisture. The warmth is primarily driven by lengthening hours of daylight which AGW or no AGW, are not changing. The moisture, in situations not subject to irrigation as many flowers may well be, is a function of rainfall which is highly variable both over short terms, but more importantly over longer terms as well as identified by the PDO, IPO, AMO, IOD etc. etc. which cycle over terms of perhaps six or seven decades, certainly longer than the length of time some reports use to establish and extrapolate AGW trends. Even with the graph First Flowering Index used for this topic, data from 250 years ago show the flowering was close to present day timing from which it went backwards for a considerable length of time. Just using the graph it is impossible to determine what is "normal" and what is not. As was mentioned in an earlier reply, the difference may will be due to variations in rainfall. As I also mentioned earlier, little can be drawn from the graph unless the main variable, rainfall, is incorporated or plotted against it and until that is done nothing has been proved. With regards to the 20% reduction in rainfall for Australia, 20% against what benchmark. 20% against the period of the late 1900's, or the late 1800's? What period of time represents "normal" rainfall for Australia? What information is available tends to suggest that "normal" is generally drier than what was experienced in the second half of the 1900's, hence calculations for irrigation schemes, water supply storages, etc were based on unusual rather than normal rainfall patterns. Time will tell, but from the limited information available and reconstructions of some of the longer term cycles mentioned, there are indications that the trend is positive. The big guess is whether any supposed changes forced by additional CO2 are sufficient to overwhelm those natural cycles, and at the end of the day, that is what they are, guesses and theories.
120722. pdt at 08:03 AM on 22 April 2010
        The significance of past climate change
        "On the contrary, the past tells us that climate is highly sensitive to the CO2 warming we're now causing." I would suggest not using words like "highly". That word has little scientific value.
120723. Riccardo at 07:39 AM on 22 April 2010
        Models are unreliable
        cloneof, i'd like to add that, as a rule of thumb, when a paper is ignored by the other scientists you can safely assume that it is considered of no value, not even worth of a reply or a quote.
120724. Riccardo at 07:33 AM on 22 April 2010
        Models are unreliable
        cloneof, well, it's hard to make any comment on a paper if you do not give a reference. Assuming it's J. Clim. 2008, 21, 5624, it has nothing to do with models. It's on the empirical (mainly from satellite data) determination of feedback operation.
120725. scaddenp at 07:29 AM on 22 April 2010
        The significance of past climate change
        "One more question. I did not know that ice cores could reveal solar activity. What in the frozen ice gives us that information? " C14 and Be10 production are proxies for solar activity. I believe Be10 is used in ice core.
120726. Momerath at 07:21 AM on 22 April 2010
        The significance of past climate change
        Being engineers I’m sure at least one asked to see a graph of atmospheric CO2 concentration verses temperature for our planet. Since such a graph does not exist how were you able to explain that to your audience? You could point out that over a very short period of time mankind has removed and burned an enormous quantity of fossil fuels that had been comfortably buried for, roughly, the past 500 million years of earth history. I think if you can graphically show an estimate of how much fossil fuel by weight has been burned since the industrial revolution and compare that with the rise in atmospheric CO2 concentration over the same period, it might convince some. Past climate change is used to help us understand what changes we will likely see for the future. When climate has changed in the past scientists have struggled to understand the cause. This time the cause is obvious. One more question. I did not know that ice cores could reveal solar activity. What in the frozen ice gives us that information?
120727. scaddenp at 07:16 AM on 22 April 2010
        The significance of past climate change
        garythompson - Mann et al 2009 for more on the latest data and analysis of MCA, including causes. All data and programs available in supplementary materials so you can reproduce their results. thingadonta- rates. The "Heinrich" events as we moved out of last ice age look to have dramatic temperature swings in the scale of decades. However, we have no reason to believe that such swings are feasible in an interglacial from natural causes.
120728. rydell at 06:23 AM on 22 April 2010
        Ocean acidification: Global warming's evil twin
        I don't disagree with any of the statements in this paper but I do take issue with the graph. I've just read some very detailed arguemtnts refuting the inaccuracies in Ian Plimer's book. One of the major concerns wah his improper use of graphs. I think it behooves us to also take care with the graphs presented. If you look at the graph presented herein, supposedly showing acidification of the ocean and increasing CO2 (present level is I believe 380 ppm) this graph does no such thing. The graph should reflect the text and vice versa. A small point perhaps but but we should be consistent.
        Response: The purpose of Figure 1 is to show that in the past, when CO2 changed, pH levels changed accordingly. I think that's fairly clearly explained in the preceding paragraph.
        
120729. cloneof at 06:13 AM on 22 April 2010
        Models are unreliable
        Riccardo I was talking about paper released in 2008 by Spencer and Braswell that discussed a potential positive feedback bias caused by cloud variability. The paper makes a strong claim how this bias basicly makes the models show too much positive feedback. The link you gave me talks about one of hi's un-peer reviewed blog posts how PDO would affect climate. See that posts comment number 171. To this day I have not seen a debunking article nor any response from the modelling community about this paper. Considering this paper was released in the pretigius Journal of Climate and even Piers Forsters couldn't but give him a green light, I must wonder.
120730. Riccardo at 06:00 AM on 22 April 2010
        Models are unreliable
        cloneof, not sure about which paper you're refering at, but take a look at this RealClimate post.
120731. Riccardo at 05:06 AM on 22 April 2010
        The significance of past climate change
        garythompson, in the original fig.2b the line labeled "1997-2007 mean annual SST" is higher than any other line for the whole period shown. So, when co2science says that following the paper it was 0.4 degree warmer, it is blatantly false. You may be right that this is not a lie, they possibly can't read a graph.
120732. cloneof at 04:56 AM on 22 April 2010
        Models are unreliable
        Just asking around the people. Does Spencer & Braswell 2008 affect the credibility of the models how? I have been asking numerous people around and some of my more skeptical friends seem to wave this around and it appears to make some solid points. Anyone know how to answer to this one?
120733. michael sweet at 04:54 AM on 22 April 2010
        Flowers blooming earlier now than any time in last 250 years
        Johnd, It is good to see that we agree that soil moisture is tracked. Scientists have certainly considered what the effect of AGW is on soil moisture. I have not seen that data, perhaps it is contained in this Australian report. This report is not so sanguine as you about the future rain prospects for Australia. They suggest 20% less rain for southern Australia, (rain is predicted to increase in north Australia). Can you provide a reference for your claim that "the longer term trend for Australian rainfall [is] positive"? It seems to me that predictions of 20% decrease in rain is negative. To repeat: the point of this thread was to establish that AGW has caused spring to come earlier. Data has shown that spring has advanced worldwide. You have suggested that the advance of spring should be measured differently, and that it will not cause problems anyway. I think that the data is clear and convincing on the advance of spring. Data has not been presented in this thread on the problems that will cause. The debate over how much trouble AGW will cause is for another thread where data is presented about damages and cost. For here, I believe the data shows that the damage will be more costly than mitagation. You seem to feel that the damage will not be bad. We will have to see what data is produced when a thread discusses the damage that AGW will cause.
120734. garythompson at 04:51 AM on 22 April 2010
        The significance of past climate change
        thanks Philippe (#34). i enjoyed reading the comments on the skepticalscience thread from gallopingcamel and i did print out the paper you referenced and i'll take a look at that for a description as to why we aren't due for another glacial period now. #32 Riccardo, that figure on CO2 science appears to match the figure 2b in the paper. the graph in 2b does show temperatures during the MWP that are above modern temperatures. here is the graph from the Nature website. what rise are you talking about and why would you call the graph on the CO2 Science website a lie? i didn't read the article on the Nature website but instead just went to the graph that you referenced. thanks all (barry at #33 too) for the quick feedback - just another reason why this is the place to come when I have questions.
120735. ubrew12 at 04:42 AM on 22 April 2010
        The significance of past climate change
        Most engineers would understand the concept of 'signal conditioning'. If you put a signal of a certain amplitude into the box, what amplitude do you get out of the box? Likewise, if you put external forcings of certain amplitudes into the earth-box, what temperature amplitude do you get out of the box? If the amplitude out of the box is larger than you'd expect just on the basis of the input forcings, then the box is a amplifier: it contains internal reinforcings that are more positive than negative. What they are, exactly, is unimportant and maybe even confusing to discuss initially. After the point has been driven home, that earth is an amplifier, you can go into the details about what those mechanisms are that climatologists have discovered: albedo, methane, water vapor, etc, that make it so.
120736. GFW at 03:55 AM on 22 April 2010
        Where is global warming going?
        @35 HR. Do you have a cite for lack of thermal expansion in the current period. My recollection without going back to check is that sea level rise is currently at least 50% thermal, with most of the rest from "reglar" glaciers and ice caps, and the small remaining bit from the two big ice sheets. However, very recent results show non-trivial acceleration from the two big ice sheets.
120737. Philippe Chantreau at 02:59 AM on 22 April 2010
        The significance of past climate change
        Gary Thompson, it has, by GallopingCamel. The next glacial would settle over the next 20000 years or so, which is way more than enough for humans to devise solutions or exterminate themselves. See this thread or this paper
120738. hu? at 02:56 AM on 22 April 2010
        Trenberth can't account for the lack of warming
        'If an official inquiry demands the information stored on public computers then yes of course you would have to disclose the contents but only then.' But didn't that happen?
120739. barry1487 at 02:56 AM on 22 April 2010
        The significance of past climate change
        i'm surprised i've never seen comments related to the fact that maybe we humans are counteracting that normal temperature decline wiht our GHG production I have, and not just from the skeptical optimists. ;-) The next ice age isn't due for tens of thousands of years. The earth has cooled by about half a degree C since the end of the climb out of the last glaciation 10k years ago. We've countered that and more within a century. Our immediate concern is the next hundred years or so. Here is the issue I suggested earlier regarding rate of change. We can adapt to long-term slow changes much more comfortably than relatively fast changes in the near-term (relatively speaking). Perhaps in 10 000 years, if we haven't warred ourselves to extinction or succumbed to a devastating plague, we may be knowledgeable enough to fashion some kind of thermostat for the planet that doesn't interfere adversely with long-term, possibly necessary climate changes. We're not yet wise enough to deploy any form of geo-engineering. i've heard the MWP debunked as a localized event The language is too strong. We think the Earth was generally warm, but datasets all over the world show 'medieval' warmth at different times, as much as 500 years apart. And most of the data we have is from the Northern Hemisphere. The MWP may or may not have been a global event, but it would seem there is some evidence for that. Whether or not the warmth for some sequent decades in the past was comparable to the last few decades is the qualified assessment most discussed (probably not). Here's a map of data sets often deployed by skeptics. Check the warm dates for each of the time series. Ironically, skeptics don't realize that they're buttressing the 'not global' argument when they reference this - they don't investigate much further than the message. http://pages.science-skeptical.de/MWP/MedievalWarmPeriod.html The map, by the way, documents a small number of paleo data sets (47). There are now hundreds. No doubt these have been selected to buttress the message. Ironic then...
120740. Riccardo at 02:55 AM on 22 April 2010
        The significance of past climate change
        garythompson, you should always refer to the original scientific papers. The link you provide on the MWP has been "adapted" to hide the rise and erroneously draw to the conclusion that "Medieval Warm Period was about 0.4°C warmer than the Current Warm Period.". Nothing similar can be found in the original fig. 2b. On the contrary, it explicitly shows that the average 1997-2007 SST is higher than any other period in the last 2000+ years.
120741. KeenOn350 at 02:45 AM on 22 April 2010
        The significance of past climate change
        Hi John, You may already be familiar with this presentation in June 2008 to the Tällberg Forum by David Wasdell: Planet Earth - We Have a Problem In case not, you might want to review it - he does an excellent job on feedbacks, and you may find some ideas therein. I find this an excellent presentation, not only for it's content, but also for the passion with which it is delivered. Thanks for all your excellent work!
120742. Unrecovered at 02:44 AM on 22 April 2010
        The significance of past climate change
        I think one important aspect missed in your discussion is the distinction between internal and forced variability. I think engineers, in particular do get that. You make it sound like all climate change is "forced" by some external mechanism. But it is not. There is internal natural variability that causes ups and downs and those are much more difficult to understand. The challenge in climate science is to separate those two and examine whether the "forced" variability is much greater the expected internal variability over the time or spatial scales one is interested in. Daansgard-Oeschger might stand as an example for internal variability that is indeed larger than than recent variability, but the mechanisms involved are tied to glaciated periods and the spatial scale is not global. Another aspect, I have found difficult for engineers and many other scientists to grasp is: How a system where all feedbacks sum up to a net "positive" does not constitute a run-away system. This is not and easy thing to explain and typically requires too much time in a short talk. But may constitute a stumbling block for engineers in particular.
120743. johnd at 02:29 AM on 22 April 2010
        Flowers blooming earlier now than any time in last 250 years
        michael sweet at 09:39 AM, you appear to be missing the point that soil moisture levels, which might surprise you, are tracked and well documented, are more dependant on total rainfall and it's distribution throughout the year than any slight changes in temperature. Whilst maximum and minimum temperatures may in some locations show slight changes, the other contributing factor, hours of daylight, and hours of darkness, also do not change from year to year despite the idea of many that daylight saving does give more daylight hours. As for long term trends in rainfall, for Australia generally, the last half of the 1900's were wetter than the first half, with the wettest period on record being during the mid 1970's, that possibly being the wettest period since first settlement. Despite the absence of weather data from the official BOM records, what records do exist indicate the 1800's being drier and more drought prone than the 1900's. So despite the most recent drought, and in spite of it, the indications are that the longer term trend for Australian rainfall are positive, and this will be the determining factor as to whether seasons advance or extend more so than any very minor changes in temperature. Global warming does not stop the natural cycles driven by other yet to be fully understood forces, and the next few decades of predicted and expected generally wetter conditions for much of Australia should provide much greater insight as scientists are now better prepared to poke, prod and measure than any time previous such a cycle occurred.
120744. garythompson at 02:08 AM on 22 April 2010
        The significance of past climate change
        john, as usual, a great post that is thought provoking and a joy to read. what was the reason for the MWP? there seems to be a new paper on this topic that points to this happening in the Indo-Pacific so it appears this event wasn't localized to Greenland. were we in a solar optimum at that point? i've heard the MWP debunked as a localized event but there are other papers such as this that show it happened other places on the Earth at the same time. I've also seen graphs of vostok ice cores showing we are due for another glacial period and i'm surprised i've never seen comments related to the fact that maybe we humans are counteracting that normal temperature decline wiht our GHG production. the up shot being, even if you subsribe to the AGW theory, it might not be a bad thing for the next 1000 years or so since plus 1 to 2 degrees C is easier to adapt to than negative 8 to 10 degrees C. forgive me if this has been already discussed ad nauseaum.
120745. angliss at 01:40 AM on 22 April 2010
        The significance of past climate change
        If you don't mind my asking, do you know what kind of engineers you were presenting to? In general, different engineering disciplines have different levels of understanding of advanced math, statistics, physics, chemistry, and so on. So what works for a room full of electrical engineers won't necessarily work for a room full of software engineers, mechanical engineers, nuclear engineers, or chemical engineers. Unfortunately, that means you'll need a few different presentations instead of just one, and you should ask the group that's sponsoring your presentation what the audience is likely to be before (and maybe ask the audience too and tailor your presentation accordingly).
        Response: They were mechanical engineers but let me be clear that I'm not commenting on their ability to understand past climate change but on my ability to explain it. The blank stares I receive are fairly universal. A university group once borrowed my info to write a short debunking flyer and I noticed they went with a completely different answer to the 'climate's changed before' argument - presumably they either didn't like or didn't understand my explanation (or thought they could do a better job). Hence I'm going back to the drawing board.
        
120746. theendisfar at 01:09 AM on 22 April 2010
        The significance of past climate change
        "See, this is the thing. In my presentation to the engineers, I did up this gorgeous little schematic of positive feedbacks, showing increased evaporation, more water vapor causing an increased greenhouse effect, more clouds, etc. Very colourful, I was very proud of it :-)" Do you have a link to this schematic? I am an engineer and would be pleased review it as well. I find your answer lacking since it has been dumbed down. It is, with all due respect, meaningless in 'simplified' form. What I am especially interested in is the detail of the positive feedbacks and whether you have satisfied the negative feedbacks sufficiently. Regards
        Response: Here's the slide I showed at the talk. Note - its purpose was just to introduce the concept of positive and negative feedbacks - that warming initiates a series of climate responses. It was not about accounting for every individual feedback (sea ice feedback is noticeably absent) - the general gist was to communicate that there are a myriad of different feedbacks which makes it difficult to work out the net feedback. But the way to cut through all that and calculate the net feedback without having to worry about the individual components was to look at past climate change.
        
        
        
120747. rawsnacks at 00:45 AM on 22 April 2010
        The significance of past climate change
        Seems like the question "why hasn't the climate changed over the millennia ought to garner some interest as well. It's been stable enough to grow stuff for a long time. Don't need esoteric statistics to see that.
120748. barry1487 at 00:45 AM on 22 April 2010
        The significance of past climate change
        My first thought was - do positive feedbacks kick in as strongly when the energy balance shifts towards cooling? My initial guess is "not so strongly", or, "negative feedbacks come into play more", judging by the slow cooling period compared to warming in the late quaternary ice ages. I don't know if covering this would dilute the message, but I think it would help give a more balanced assessment - skeptics scorn commentary that only talks about warming, for example. And I don't know if this goes beyond your intent, but it might be worth mentioning the rate of change now compared to past warming events. What you already have, though, is pretty clear I think. I'm not a scientist or an engineer, but it makes sense to me. (I am a fairly well-read layman, though)
120749. Alexandre at 00:25 AM on 22 April 2010
        The significance of past climate change
        nautilus_mr #10 I agree with you. Paleoclimatology is just one of the many lines of evidence to climate sensitivity. And if you pick one specific period -like the Medieval Warm Period- it's just one tiny fraction of this. So even if there had been a strong MWM... not much would change in the science.
120750. Alexandre at 00:19 AM on 22 April 2010
        The significance of past climate change
        chris #21 I would add in your response to Péter that this interglacial is remarkably stable when compared to the previous ones. So his assertion "temperature diminishes with temperature" has little supporting evidence. Besides, some events like PETM support a self-reinforced warming hypothesis.

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