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Post by socold on Aug 16, 2009 23:55:15 GMT
However I disagree almost entirely that such things as D-O events " have little significance to the longer scale temperature changes". Au contraire, with D-O events averaging 1,500 years within a natural range of 1,000 to 4,000 years, and seemingly paced by the 1,500 year average isotopically known solar variation, these abrupt shifts are indeed relevant. As far as explaining the magnitude of temperature changes over interglacial/glacial transitions they have no significance. Ie whether or not DO events occured there would still be far too much temperature change from glacial to interglacial than the orbital forcing can explain. Either there was some currently unknown far more significant forcing, or more likely climate sensitivity was high - something which is backed up by climate models which find the climate was and still is subject to high sensitivity to any forcing. When both the models and the paleo data suggest a high climate sensitivity, this increases the risk of doubling co2 within the space of a few hundred years. When the paleo data also shows abrupt and rapid climate changes can occur, the risk of nudging climate is compounded. And when uncertainty suggests climate sensitivity could be even higher than models predict, eg: Then the risk increases even more. In this case the uncertainty increases the risk rather than decreasing it.
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Post by jimcripwell on Aug 17, 2009 0:36:45 GMT
glc writes "But in 2007 it moved it a bit too easily. "
Again absolute garbage. The wind blew extremely unusally strongly. The wind conditions which were present in 2007 were considered to be very highly unusual. Of course such a pattern could set up again, but it is highly unlikely. Do I have a reference for this? No I dont. I read all sorts of stuff, and dont keep track of everything. But if challenged, when I get back to Ottawa, I am sure I could find a reference. But then again, even if I do you wont read it anyway, so why should I bother.
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Post by sigurdur on Aug 17, 2009 1:00:54 GMT
However I disagree almost entirely that such things as D-O events " have little significance to the longer scale temperature changes". Au contraire, with D-O events averaging 1,500 years within a natural range of 1,000 to 4,000 years, and seemingly paced by the 1,500 year average isotopically known solar variation, these abrupt shifts are indeed relevant. As far as explaining the magnitude of temperature changes over interglacial/glacial transitions they have no significance. Ie whether or not DO events occured there would still be far too much temperature change from glacial to interglacial than the orbital forcing can explain. Either there was some currently unknown far more significant forcing, or more likely climate sensitivity was high - something which is backed up by climate models which find the climate was and still is subject to high sensitivity to any forcing. When both the models and the paleo data suggest a high climate sensitivity, this increases the risk of doubling co2 within the space of a few hundred years. When the paleo data also shows abrupt and rapid climate changes can occur, the risk of nudging climate is compounded. And when uncertainty suggests climate sensitivity could be even higher than models predict, eg: Then the risk increases even more. In this case the uncertainty increases the risk rather than decreasing it. Socold: What you have writtten unllines how much haste should be put into finding out WHAT the drivers of those changes were. IT is very obvious it wasn't co2 so we can rule that out with near certainty. IT is time to get off the co2 kick, and actually search for that "missing link" in climate don't you think? That sir is off the utmost importance, and all this discussion aimlessly about what co2 "might/could/maybe" do is aimless and distracting from the true path that climatologists should be taking.
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Post by socold on Aug 17, 2009 1:42:36 GMT
Socold: What you have writtten unllines how much haste should be put into finding out WHAT the drivers of those changes were. IT is very obvious it wasn't co2 so we can rule that out with near certainty. IT is time to get off the co2 kick, and actually search for that "missing link" in climate don't you think? Climatologists have never just looked at co2 on it's own. co2 is just one of many contributors to temperature changes in the past.
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Post by sigurdur on Aug 17, 2009 1:52:43 GMT
Socold: What you have writtten unllines how much haste should be put into finding out WHAT the drivers of those changes were. IT is very obvious it wasn't co2 so we can rule that out with near certainty. IT is time to get off the co2 kick, and actually search for that "missing link" in climate don't you think? Climatologists have never just looked at co2 on it's own. co2 is just one of many contributors to temperature changes in the past. Yes, a contributor potentially. I have looked at graphs of co2 and temp from proxi data and the co2 will keep climbing even as the temps drop like a big rock in the ocean. From that simple observation it would appear co2 is not what would or could be called a primary driver of temps. Some other force is a huge driver of rapid changes, and I am most curious as to what it is.
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Post by chrisc on Aug 17, 2009 7:34:59 GMT
socold, thanks for the link to my posting (chriscolose.wordpress) on "more on Abrupt Climate Change." I offer a bit of insight into the ongoing discussion here. Hopefully I remember to check back in the future. Despite the many uncertainties that exist in understanding past climate change and in projections of future natural and anthropogenic influence, there is virtually no doubt that CO2 is and will be a significant influence in climate change. This follows from the fundamental physics of radiative transfer, namely 1) All objects emit radiation according to the Planck law 2) At equilibrium, the absorbed solar radiation (i.e., the incoming solar energy weighted by the geometry and albedo of the planet) must be balanced by the outgoing thermal energy at the top of the atmosphere. This is a principle of energy balance which defines the basic boundary conditions that constrain the global climate of all Earth-like planets. 3) Adding CO2 to the atmosphere changes the "effective height" at which radiation can escape to space, forcing the planet to become a weaker radiator at a given temperature, and thus mandating that the planet warms. 4) The radiative forcing of CO2 can be calculated to high accuracy and is proportional to the logarithm of the CO2 content change in the atmosphere. It follows that CO2 has contributed about 1.7 Watts per square meter of radiative forcing relative to pre-industrial times, which is a very strong impact on decadal timescales, and we know that impact can only get stronger as concentration continue to rise. 5) There's really no way around this except to violate basic physical principles like conservation of energy. This physics is outlined quantitatively at the level of advanced textbooks such as Dennis Hartmann's "Global Physical Climatology" or Ray Pierrehumbert's online work "Principles of Planetary Climate." The fact is that CO2 sets a good starting stage for understanding most cases of deep-time climate and the geologic scale evolution of climates on other planets (e.g., Faint Young Sun, Cretaceous, Eocene, Venus, Mars, etc) and thus the predictive and explanatory power of CO2's strong influence on climate has been borne out with high confidence. 6) Many skeptical arguments do not come to face with these basic physics, but are rooted in logical fallacies or other half-truths which do not appropriately represent how climate works or how humans are or may influence the radiation balance of the planet. This is unfortunate since the first predictions of CO2 causing warming go back to the late 1800's and this basic picture has not changed, but rather the real discussion/debate in the scientific literature and at academic conferences is on much more detailed things like how changes in SSTs and wind shear will influence hurricane activity, how fast it takes Greenland to lose its ice, how ecosystems will respond in a warmer world, etc. Understanding past climate change obviously depends on the time period, time interval, etc you are talking about. The strong role of CO2 is most clearly seen on very long timescales where the atmospheric chemistry and climate were sufficiently different and at equilibrium. Unfortunately, there are few cases where CO2 provides a very rapid driver of climate change, for the simple reason that you don't expect a very rapid out-gassing of CO2 to be a common event. The PETM is a good event for paleoclimatologists to look at since it provides a relatively rapid climb of CO2 and then temperature, but the analog to modern day change is limited. Humans have taken millions-of-year old carbon stored underground and are releasing it on very rapid timescales, and so the anthropocene has to be looked at as a somewhat interesting and special case in geologic time. That said, understanding the causes of climate change is like a detective case in that a) there are a lot of physically plausible ways by which climate could change b) There are a lot of different ways climate has changed in the past c) Understanding past climate changes helps to lend confidence we can grasp the basic workings of the climate system but it cannot tell us, by itself, what is causing the change today nor does it allow us to predict future change in the presence of new forcing mechanisms. This is the purpose of full-fledged attribution studies which are discussed for instance in e-reports-ext.llnl.gov/pdf/315840.pdf , in the IPCC TAR and AR4 documents, and in physically based reports such as USCCP (2006) on temperature trends in the lower atmosphere. Formal attribution makes use of spatio-temporal patterns associated with a given set of forcings (e.g., Knutti 2008) and thus can be performed even when subtracting global mean trends. It's important to note that CO2 gets attention only because it's the largest industrial forcing mechanism and is expected to rise in the 21st century in sync with human activities, although methane, CFC's/HFC's, aerosols, and natural influences like solar and volcanic also play a role, which highlights that climate change (in the past or present) is not a simple black and white picture. Thus broad statements at dinner-table concentrations like "it's a cycle" or "we're doing it" need to be elaborated upon and qualified. Since discussion has developed about glacial-interglacial cycles and within them, abrupt climate changes, note that the larger global climate changes are predominately forced by Milankovitch orbital changes. As eccentricity increases, you get a small increase in solar insulation (it's very small though) and the much larger effects from the changing tilt of the Earth and increased Northern Hemispheric insulation, especially in the summertime. As noted throughout the literature though, (e.g. Monnin et al 2001; Caillon et al 2003) CO2 clearly plays a large role in a feedback mechanism whereby a changing baseline climate alters the atmospheric chemistry (via changes in ocean solubility, deep ocean upwelling, see for instance chriscolose.wordpress.com/2009/03/14/a-new-hypothesis-for-deglacial-co2-rise/ ) which then contributes to a radiative forcing of over 2 Watts per square meter and explains a good chunk of the magnitude of glacial-interglacial variations, and this influence is more globally-mixed then Milankovitch. This occurs over timescales far longer than the current warming or CO2 rise. The much more rapid climate changes within the ice core record are different in that the warmings and coolings were not in sync globally (the so-called "bipolar see-saw") aside from relatively small global radiative forcings like CO2/CH4 and albedo changes that can communicate latitudinal climate shifts over the planet. You can't really get these events in the Holocene, since only glacial boundary conditions promote such events (convection is in the Nordic Seas in the Holocene). For those interested in the topic of climate sensitivity (i.e., the global temperature increase per unit radiative forcing), there's a lot of good literature detailing or summarizing evidence which places sensitivity around a central value of 3 C per doubling of CO2, but with a large uncertainty band of about 50% on either side. See a good overview of this topic at www.iac.ethz.ch/people/knuttir/papers/knutti08natgeo.pdf . Higher values are more difficult to rule out since the mathematics of feedbacks is such that the climate reaction asymptotes as the gain factor (from feedbacks) approaches unity (discussed in Roe and Baker 2007). That said, the paleoclimate record is pretty robust in offering the insight that sensitivity is not very low nor is it too high. Cloud feedbacks are the largest obstacle in significantly narrowing the range of climate sensitivity. Cheers, chris
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Post by glc on Aug 17, 2009 8:54:54 GMT
Dear ChrisC
Although I'm not convinced about 3 deg C warming per CO2 doubling, I do nevertheless agree with most of your points - particularly (1) to (4). In fact, I've spent hours on this blog arguing these very points. One particular poster simply refuses to accept that the 'primary' effect of CO2 (i.e. without feedbacks) can be determined with a reasonable degree of confidence. This relates your point (4), i.e.
4) The radiative forcing of CO2 can be calculated to high accuracy and is proportional to the logarithm of the CO2 content change in the atmosphere. It follows that CO2 has contributed about 1.7 Watts per square meter of radiative forcing relative to pre-industrial times, which is a very strong impact on decadal timescales, and we know that impact can only get stronger as concentration continue to rise.
I have discussed radiative transfer equations, lab experiments, emission spectra etc ad infinitum but to no avail. Have you anything to add which may be more convincing than my efforts.
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Post by jimcripwell on Aug 17, 2009 12:08:05 GMT
chrisc writes "The radiative forcing of CO2 can be calculated to high accuracy and is proportional to the logarithm of the CO2 content change in the atmosphere."
We seem to have acquired someone new who believes in fairy tales. First, I object strongly to the use of the term "calculated". Calculate should only be used where one has an exact formula. Like each year I can calculate how much income tax I owe, or one can calculate the value of pi to as many significant digfits as one likes. The correct word is estimate.
No methodology is given, so I suppose the usual mistake has been made. That is the use of non-validated computer programs which assume the problem can be solved by considering only what happens to radiation in the atmosphere, neglecting the effects of conduction, convection, and the latent heat of water.
You cannot do the experiment of adding CO2 to the atmsophere, and measuring how much global temperatures rise. Therefore, any estimate may be subject to the Kelvin Fallacy, and so is unreliable.
I know, I know, I have said this all before on heaven knows how many occasions. But I still think it needs to be said again when one sees this sort of message being posted.
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Post by nautonnier on Aug 17, 2009 12:10:19 GMT
You keep saying "it is not possible to explain.....", yet are provided several references in the literature that say otherwise, not to mention your examples are invariably derived from climate models. I haven't been provided with any such references. I am sure you have at some time or other referenced something, but I am sure it didn't say what you think it said. I'll repeat what I said again for clarity: Without the climate system itself amplifying the forcing in some way, and ghg changes are one such way, it is not possible to explain the magnitude of temperature change (from glacial to interglacial) That isn't an attempt to explain the warming and is thus off topic. I don't wish to get divided into multiple subtopics, I know that's the common "tactic" to derail my points rather than addressing them, but on this occasion I will not comply. This is the Kelvin Fallacy - we know everything there is to know therefore : "Without the climate system itself amplifying the forcing in some way, and ghg changes are one such way, it is not possible to explain the magnitude of temperature change (from glacial to interglacial)"The Kelvin Fallacy is a kind of hubris So as AGW proponents cannot conceive of another reason for Earth to warm, it must be CO 2. This despite the warming and cooling in the past out of synchronization with the level of CO 2, so obviously something else can heat and warm the planet.
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Post by sigurdur on Aug 17, 2009 12:10:19 GMT
We know how eco systems will respond to a warmer world as we have been warmer in the recent past. They have flourished.
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Post by nautonnier on Aug 17, 2009 12:51:31 GMT
socold, thanks for the link to my posting (chriscolose.wordpress) on "more on Abrupt Climate Change." I offer a bit of insight into the ongoing discussion here. Hopefully I remember to check back in the future. Despite the many uncertainties that exist in understanding past climate change and in projections of future natural and anthropogenic influence, there is virtually no doubt that CO2 is and will be a significant influence in climate change. This follows from the fundamental physics of radiative transfer, namely 1) All objects emit radiation according to the Planck law 2) At equilibrium, the absorbed solar radiation (i.e., the incoming solar energy weighted by the geometry and albedo of the planet) must be balanced by the outgoing thermal energy at the top of the atmosphere. This is a principle of energy balance which defines the basic boundary conditions that constrain the global climate of all Earth-like planets. 3) Adding CO2 to the atmosphere changes the "effective height" at which radiation can escape to space, forcing the planet to become a weaker radiator at a given temperature, and thus mandating that the planet warms. 4) The radiative forcing of CO2 can be calculated to high accuracy and is proportional to the logarithm of the CO2 content change in the atmosphere. It follows that CO2 has contributed about 1.7 Watts per square meter of radiative forcing relative to pre-industrial times, which is a very strong impact on decadal timescales, and we know that impact can only get stronger as concentration continue to rise. 5) There's really no way around this except to violate basic physical principles like conservation of energy. This physics is outlined quantitatively at the level of advanced textbooks such as Dennis Hartmann's "Global Physical Climatology" or Ray Pierrehumbert's online work "Principles of Planetary Climate." The fact is that CO2 sets a good starting stage for understanding most cases of deep-time climate and the geologic scale evolution of climates on other planets (e.g., Faint Young Sun, Cretaceous, Eocene, Venus, Mars, etc) and thus the predictive and explanatory power of CO2's strong influence on climate has been borne out with high confidence. 6) Many skeptical arguments do not come to face with these basic physics, but are rooted in logical fallacies or other half-truths which do not appropriately represent how climate works or how humans are or may influence the radiation balance of the planet. This is unfortunate since the first predictions of CO2 causing warming go back to the late 1800's and this basic picture has not changed, but rather the real discussion/debate in the scientific literature and at academic conferences is on much more detailed things like how changes in SSTs and wind shear will influence hurricane activity, how fast it takes Greenland to lose its ice, how ecosystems will respond in a warmer world, etc. Understanding past climate change obviously depends on the time period, time interval, etc you are talking about. The strong role of CO2 is most clearly seen on very long timescales where the atmospheric chemistry and climate were sufficiently different and at equilibrium. Unfortunately, there are few cases where CO2 provides a very rapid driver of climate change, for the simple reason that you don't expect a very rapid out-gassing of CO2 to be a common event. The PETM is a good event for paleoclimatologists to look at since it provides a relatively rapid climb of CO2 and then temperature, but the analog to modern day change is limited. Humans have taken millions-of-year old carbon stored underground and are releasing it on very rapid timescales, and so the anthropocene has to be looked at as a somewhat interesting and special case in geologic time. That said, understanding the causes of climate change is like a detective case in that a) there are a lot of physically plausible ways by which climate could change b) There are a lot of different ways climate has changed in the past c) Understanding past climate changes helps to lend confidence we can grasp the basic workings of the climate system but it cannot tell us, by itself, what is causing the change today nor does it allow us to predict future change in the presence of new forcing mechanisms. This is the purpose of full-fledged attribution studies which are discussed for instance in e-reports-ext.llnl.gov/pdf/315840.pdf , in the IPCC TAR and AR4 documents, and in physically based reports such as USCCP (2006) on temperature trends in the lower atmosphere. Formal attribution makes use of spatio-temporal patterns associated with a given set of forcings (e.g., Knutti 2008) and thus can be performed even when subtracting global mean trends. It's important to note that CO2 gets attention only because it's the largest industrial forcing mechanism and is expected to rise in the 21st century in sync with human activities, although methane, CFC's/HFC's, aerosols, and natural influences like solar and volcanic also play a role, which highlights that climate change (in the past or present) is not a simple black and white picture. Thus broad statements at dinner-table concentrations like "it's a cycle" or "we're doing it" need to be elaborated upon and qualified. Since discussion has developed about glacial-interglacial cycles and within them, abrupt climate changes, note that the larger global climate changes are predominately forced by Milankovitch orbital changes. As eccentricity increases, you get a small increase in solar insulation (it's very small though) and the much larger effects from the changing tilt of the Earth and increased Northern Hemispheric insulation, especially in the summertime. As noted throughout the literature though, (e.g. Monnin et al 2001; Caillon et al 2003) CO2 clearly plays a large role in a feedback mechanism whereby a changing baseline climate alters the atmospheric chemistry (via changes in ocean solubility, deep ocean upwelling, see for instance chriscolose.wordpress.com/2009/03/14/a-new-hypothesis-for-deglacial-co2-rise/ ) which then contributes to a radiative forcing of over 2 Watts per square meter and explains a good chunk of the magnitude of glacial-interglacial variations, and this influence is more globally-mixed then Milankovitch. This occurs over timescales far longer than the current warming or CO2 rise. The much more rapid climate changes within the ice core record are different in that the warmings and coolings were not in sync globally (the so-called "bipolar see-saw") aside from relatively small global radiative forcings like CO2/CH4 and albedo changes that can communicate latitudinal climate shifts over the planet. You can't really get these events in the Holocene, since only glacial boundary conditions promote such events (convection is in the Nordic Seas in the Holocene). For those interested in the topic of climate sensitivity (i.e., the global temperature increase per unit radiative forcing), there's a lot of good literature detailing or summarizing evidence which places sensitivity around a central value of 3 C per doubling of CO2, but with a large uncertainty band of about 50% on either side. See a good overview of this topic at www.iac.ethz.ch/people/knuttir/papers/knutti08natgeo.pdf . Higher values are more difficult to rule out since the mathematics of feedbacks is such that the climate reaction asymptotes as the gain factor (from feedbacks) approaches unity (discussed in Roe and Baker 2007). That said, the paleoclimate record is pretty robust in offering the insight that sensitivity is not very low nor is it too high. Cloud feedbacks are the largest obstacle in significantly narrowing the range of climate sensitivity. Cheers, chris I think that some small assumptions need to be clarified "1) All objects emit radiation according to the Planck law"Radiation is accepted to be the only way thermal energy can leave the earth however, is radiation the ONLY way that energy can leave an 'object' such as the surface of the Earth or the Surface of the Ocean or a plant? "2) At equilibrium, the absorbed solar radiation (i.e., the incoming solar energy weighted by the geometry and albedo of the planet) must be balanced by the outgoing thermal energy at the top of the atmosphere. This is a principle of energy balance which defines the basic boundary conditions that constrain the global climate of all Earth-like planets." Is the ONLY way that energy can reach the Earth radiation? What is the accurately quantified effect of albedo in reflecting away incoming short wave radiation caused by tropical convective clouds, cirrus and other clouds? What is the accurately quantified albedo variance with humidity, surface temperatures and convection? If the atmosphere shrinks (as apparently it has done) what is the accurately quantified effect on insolation and the amount of input and output energy? Heat carried to the tropopause by the hydrologic cycle as latent heat or just as hot updrafts, bypassing most of the dense atmosphere, what is the accurately quantified reduction in the 'forcing' of GHG at the tropopause (where forcing is measured) due to this non-radiative heat transport? "Accurately quantified" for the purposes of this post is the same accuracy that your post uses i.e. 0.1WM -2 - however, you should define the surface that you are measuring in meters -2, the WGS84 ellipsoid, the Tropopause or the TOA. If you use either of the latter then explain how your calculations are modified by the expansion and contraction of these atmospheric layers. You should of course provide the answers to the above questions from actual metrics and measures physically carried out rather than other assumptions, calculations or models.
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Post by socold on Aug 17, 2009 12:58:16 GMT
Thanks for your input Chris, unfortunately as you can see it will only be met with obfuscation and word games.
"We must dismiss it by any means"
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Post by socold on Aug 17, 2009 13:00:58 GMT
I haven't been provided with any such references. I am sure you have at some time or other referenced something, but I am sure it didn't say what you think it said. I'll repeat what I said again for clarity: Without the climate system itself amplifying the forcing in some way, and ghg changes are one such way, it is not possible to explain the magnitude of temperature change (from glacial to interglacial) That isn't an attempt to explain the warming and is thus off topic. I don't wish to get divided into multiple subtopics, I know that's the common "tactic" to derail my points rather than addressing them, but on this occasion I will not comply. This is the Kelvin Fallacy - we know everything there is to know therefore : "Without the climate system itself amplifying the forcing in some way, and ghg changes are one such way, it is not possible to explain the magnitude of temperature change (from glacial to interglacial)"The Kelvin Fallacy is a kind of hubris So as AGW proponents cannot conceive of another reason for Earth to warm, it must be CO 2. This despite the warming and cooling in the past out of synchronization with the level of CO 2, so obviously something else can heat and warm the planet. This is the Strawman Fallacy. Misinterpreting what someone wrote, attacking that misinterpretation and then claiming to have addressed what they wrote. The Stawman Fallacy is a kind of Hubris.
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Post by icefisher on Aug 17, 2009 13:22:53 GMT
Why dont you get the references and find out for yourself. That is what references are for. And I still have no reference for Arctic ice being fragile.We don't need references for arctic ise. It's obviously fragile or it wouldn't have lost so much in 2007 due to "wind". Point me to the Eddy/Maunder Minimum stuff. It's you who so convinced by this stuff. What is it that's convinced you? I see where this is going. . . .an increase in fragile multiyear ice. The invention of a new oxymoron.
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Post by woodstove on Aug 17, 2009 15:14:06 GMT
The Little Ice Age, including and especially the Maunder Minimum, was real. This just a statement based on what exactly? What you have yet to do, glc, is propose a driver that began getting us out of the Little Ice Age two hundred years ago. So far, you're stuck with time-traveling co2 molecules.What you have to do is provide solid evidence that the LIA existed and the precise timeframe of it's duration. I'm going to adopt the Jim Cripwell strategy from now on. I don't believe the LIA is based on anything more than a few anecdotes and some iffy proxies. As for the MWP - forget it . You have no reliable temperature data to support the existence of the LIA or MWP. NASA (including Gavin Schmidt) thinks the Maunder Minimum took place: earthobservatory.nasa.gov/Features/Paleoclimatology_Understanding/They are unambiguous about the decrease in temperature and solar causation: "Reduced solar output led to lower temperatures in much of the Northern Hemisphere during the Maunder Minimum, in the late 1600s." NASA also acknowledges the wider phenomenon of the Little Ice Age, as anyone with an 8th grade education can deduce from this article about ice core data: "The near-surface ice temperature, like the atmosphere today, is warm, and then the temperature drops in the layers formed roughly between AD 1450 and 1850, a period known as the Little Ice Age, one of several cold snaps that briefly interrupted the overall warming trend ongoing since the end of the Ice Age." more here: earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/Glancing at the graph of temperature compiled from a worldwide series of ice cores, one can plainly see the Roman Optimum, Medieval Warm Period, and Little Ice Age. One can also plainly see that the current temperature trend is unremarkable. To sum up, the Little Ice Age took place, it was caused by solar minima, the warming since the end of the 100,000-year ice age that preceded the Little Ice Age re-commenced at the conclusion of the LIA. That's according to NASA, though, glc, and we all know how wary you are of their take on things.
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