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Yes; the climate has always changed, man-made climate change is just a new precedent. Looking at 'precedents' or past forcings helps us with what might come next. |
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19. I tend to find the non-scientific mind has a poor conception of order of magnitude and probability. For example they are quite happy to imply that climate change happening now is natural by referring to climate change during an epoch perhaps hundreds of thousands or millions of years ago. |
All indications are that climate hasn't changed significantly for the best part of 10,000 years, so for it to suddenly change in the last 150 years just at the same time as mans influence on the biosphere has become significant, strongly implies this is the most likely cause. This is without any knowledge of greenhouse gases or other causes, it is a pure statistical explanation. The other more direct experimental evidence such as radiation exchange simply increases this probability further. |
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20. It is a temperature reconstruction from a Greenland ice core (close to summit, at 72.6 N, 38.5 W, altitude 3200 m) for the last fifty thousand years. |
As you can clearly see, temperature is much more variable when it is cold. In other words: climate sensitivity diminishes with increasing temperatures. |
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21. Berenyi Peter, I suspect you say stuff that you know is wrong or illogic (but you say it anyway). |
(1) The Dansgaard-Oeschger events in your graphics are measurements of rapid temperature changes in Greenland cores. They are barely recognizable (and asynchronous) in Antarctic cores. Thus they are not representative of global warming/cooling events. |
(2) In fact these events are recognised likely to arise from major rapid shut down and restarting of the major ocean circulations (thermohaline circulation) that strongly participiates in bringing heat (or "thermal energy" if we're stil being pedantic about that!) from the equator to the high Northern latitudes. |
In other words they are indicative of major redistribution of Earth heat as opposed to global scale warming or cooling events. |
(3) Thus they have nothing to do with "climate sensitivity" which is the equilibrium response of the Earth's global temperature to changes in radative forcing. |
(4) The fact that D/O events (and similar large scale jumps/drops in high Northern latitude temperatures) aren't apparent in the Holocene part of the record you posted, is that these events only occur under conditions that major ice sheets occupy the high N. latitudes (that's part of the likely mechanism of the D/O events). Since we're in an interglacial period when these major ice sheets have melted away, we can't have D/O events. |
It's got nothing to do with temperature "being much more variable when it's cold" or "climate sensitivity diminishing with increasing temperature". |
One should really address these issue in terms of what we know! |
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22. I assume this is intended to replace the text on the “Climate’s changed before” page. It seems like a good explanation to me – but then I understood the explanation on the original page (at least I think I did). I also think it’s worth including all the climate sensitivity info that was in the old version. I recommend that you keep your more detailed explanation and link to it from the new version. |
Also, is it really possible to derive solar activity from ice cores? I’m sure there are other proxies (carbon-14 comes to mind), but ice cores? |
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Response: The more common method of working out past solar activity is using radiocarbon data from tree-rings. But Beryllium isotopes from ice cores are also a proxy for solar activity, going further back than tree-rings. |
23. 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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24. 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. |
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25. 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) |
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26. 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. |
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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. |
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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. |
28. 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). |
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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. |
29. 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. |
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30. 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. |
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31. 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! |
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32. 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. |
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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. |
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... |
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34. 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 |
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35. 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. |
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36. 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. |
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37. 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. |
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38. 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. |
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39. 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? |
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40. "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. |
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41. "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. |
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42. scaddenp, |
Thanks for the help on that! |
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43. 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: |
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