Ice core data shows CO2 levels changed less than 10 parts per million from 1600-1800 during the MWP.
From the Hockey Schtick: A new paper from Schurer et al (with Mann as co-author) finds that climate “models cannot explain the warm conditions around 1000 [years before the present, during the Medieval Warming Period] seen in some [temperature] reconstructions.”
According to Schurer et al, “We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900.” They also claim, “but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800.” This claim is highly unlikely given that ice cores show CO2 levels only changed by less than 10 ppm from 1600-1800, and the effect of 10 ppm CO2 on the climate today remains undetectable even with modern instrumentation.
Separating forced from chaotic climate variability over the past millennium
Andrew Schurer,1 Gabriele Hegerl,1 Michael E. Mann,2 Simon F. B. Tett,1 and Steven J. Phipps3
Journal of Climate 2013 doi: http://dx.doi.org/10.1175/JCLI-D-12-00826.1
Abstract
Reconstructions of past climate show notable temperature variability over the past millennium, with relatively warm conditions during the ‘Medieval Climate Anomaly’ (MCA) and a relatively cold ‘Little Ice Age’ (LIA). We use multi-model simulations of the past millennium together with a wide range of reconstructions of Northern Hemispheric mean annual temperature to separate climate variability from 850 to 1950CE into components attributable to external forcing and internal climate variability. We find that external forcing contributed significantly to long-term temperature variations irrespective of the proxy reconstruction, particularly from 1400 onwards. Over the MCA alone, however, the effect of forcing is only detectable in about half of the reconstructions considered, and the response to forcing in the models cannot explain the warm conditions around 1000 [years before the present] seen in some reconstructions. We use the residual from the detection analysis to estimate internal variability independent from climate modelling and find that the recent observed 50-year and 100-year hemispheric temperature trends are substantially larger than any of the internally-generated trends even using the large residuals over the MCA. We find variations in solar output and explosive volcanism to be the main drivers of climate change from 1400-1900, but for the first time we are also able to detect a significant contribution from greenhouse gas variations to the cold conditions during 1600-1800. The proxy reconstructions tend to show a smaller forced response than is simulated by the models. We show that this discrepancy is likely to be, at least partly, associated with the difference in the response to large volcanic eruptions between reconstructions and model simulations.
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Heck, the climate models can’t even explain the present, let alone the past, so this really isn’t a surprise:
Mark Bofill says:
April 12, 2013 at 7:06 am
Thanks.
beng says:
April 12, 2013 at 5:55 am
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“richard verney says:
April 12, 2013 at 3:23 am
Despite claims to the effect that CO2 is a well mixed gas, CO2 is not particularly well mixed and its concentration varies quite substantially between seasons, and even the time of day.
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Richard, the GHG effect of CO2 is only important at high altitudes (say, above 30000 ft). Ground CO2 has little GHG effect.”
So, the calculation of PPM is made at high altitude only? And the PPM reported does not include the CO2 that is lower than the high altitude?
D.J. Hawkins says:
April 11, 2013 at 6:40 pm
I am depending on my prior knowledge that Mosher believes that models can substitute for scientific theory. I should have stated as much. Having done so, I now repeat that anyone who believes that models can substitute for scientific theory understands neither of them.
Volcanoes seem to be the dark energy hole where model error can be assigned as needed, more in some cases and ignored in others. I will remind readers that there is no global index of volcano emissions, it is a model dumping ground instead.
What? Pls, for future use, the plural form (meaning or indicating two or more of something) of volcano is “volcanoes” (I double checked that too!)
If you were to refer to a volcano’s plume or ash cloud, in this case the singular possessive form “volcano’s” is appropriate (the plume essentially belongs to the volvaco!)
(Pls bear with me on this; it is the one of the few pet peeves grammatically that sets me off … as not all who post here are native-English speakers/writers, please pardon me if this interruption in the dialog seems unwarranted.)
Plural and Possessive – usage and syntax
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Intractable solution. That is, “problems that can be solved in theory (e.g., given infinite time), but which in practice take too long for their solutions to be useful, are known as intractable.”
Take the last seven days here in Texas, the first four days we had low-overcast over half the state (and on northward into Oklahoma) and clear skies for the remainder, resulting in 90 degree high temperatures over those areas that saw ‘sun’ … while the overcast portion saw only 70’s as the high temp; with the cloud deck resulting in near 100% albedo for insolation (save for that small portion absorbed since we had _low_ overcast) for that large area and four-day timeframe … and THAT’S a lot of Energy! … Now, how is that accounted for macro-scale-wise in a GCM (model) given Hadley Cell circulation and Rossby waves and all?
Are misc fudge factors utilized? Are arbitrary ‘confidence’ figures and various ‘odds’ values used to calculate the chance occurrence of a ‘system’ as I described above? How predictable, how often do meteorological conditions allow such a setup, followed by a cold front and upper-level low initiating a *wide* band of showers having just today moved off the eastern shore but still affecting New England states and Canada in the models? Two, three, half a dozen a season? The same goes for hurricanes and other large, synoptic scale * ‘events’.
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* Synoptic scale: In meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 km – 620 miles or more.
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Theo Goodwin says:
April 12, 2013 at 8:12 am
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Further to your post, Mauna Loa is about 13,500ft, so quite a bit under half the 30,000ft suggested by Beng.
What about the CO2 measurements obtained from ice? From what height was this CO2 sequestered? Once again, probably considerably less than 30,000 ft.
Could the 1,000,000 °C temperature a mile under the earth according Al the Gore have anything to do with global warming?
Hey Penn State, you fired the wrong guy…hello, Happy Valley…yes somebody please pick up…Hello Mcfly, you there???
A rather late comment to this thread, so I guess it is one for the archives.
Further evidence that the MWP was a global event, see: http://www.dailymail.co.uk/sciencetech/article-2308225/Mayans-wiped-drought-say-scientists-tests-temple-beam-confirm-accuracy-ancient-calendar.html
There is debate as to whether the Mayan civilisation collapsed sometime before 1100AD because of climate change, and in particular drought.
I have on a number of occasions mentioned the Incas of Peru, whose civilisation peaked in the 14th century, and the settlement at Machu Picchu. In and around this settlement, there are stepped plateaus which many archaeologists consider were made for farming/agriculture. These archaeologists consider that the Incas farmed at height. It is not possible today to farm at this height in these latitudes, and the inevitable conclusion is that at the peak of the Inca settlement, the climate must have been warmer than today. Again, it is mooted that the settlement collapsed when this warm period was over and when the climate began to cool so that farming and agriculture was no longer viable.
The Archaeological evidence of both the Mayan and Inca civilisation suggests that there was a warm period in the Southern Hemisphere, and it would appear that the climate must have been warmer than today.
And his conclusion is — the MWP must be an illusion, the models say so? >:P
richard;
Cooling ==> drought Another reason to hope for warming!