Comments 1 to 16:

1. bill4344 at 16:12 PM on 29 July, 2012
   Another great vid from Potholer. So, who's been fiddling with the charts, then? Between this and Muller's 'call me a Converted Skeptic' NYT OpEd this is turning into quite the memorable day!
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2. JohnMashey at 17:44 PM on 29 July, 2012
   Great video, only one real not and one minor one. 1) Wegman Report. Everybody agreed non-centered PCA was not right, but it was also shown (by Wahl&Amman) that it made no significant difference. There was no new good statistics in the Wegman Report, which reran McIntyre's code, and the only way to get his effects was: a) Use unrealistically high persistence parameters b) Do a 1:100 cherry-pick of the most positive hockey-stick looking charts. See Deep Climate's Replication and due diligence, Wegman style. After (falsely) criticizing Mann for never providing code, Wegman then told untruths to Rep Henry Waxman, promising to release the code (never done), as soon as it got through US Navy release procedures. The Navy had nothing to do with it. Anyway, the Wegman Report shows little evidence of statistical expertise. 2) As a minor nit, this shows CO2 over last 2000 years, from Law Dome. While I would never ascribe all the temperature jiggles to CO2, one might notice where the low and high points are compared to the temperature reconstructions. In Plows, Plagues and Petroleum (and earlier papers), Bill Ruddiman proposed several hypotheses: a) Even pre-industrial era, human land-use changes (cutting down trees, rice farming~methane, etc) kept Earth warmer than one would expect from past interglacials. I.e., without humans, CO2 in 1000AD would have been lower. b) CO2 jiggles over last 2000 years have at least in part been caused by human plagues, which caused reforestration, which drew down CO2. The biggest, sharpest dip (1535-1600) seems to have been caused by the single biggest plague in history, the 50M person die-off in the Americas, post-Columbus. c) While controversial ~2005, more scientists have gotten involved and evidence has been piling up in support of these hypotheses. In effect, it means that since agriculture started, humans mostly nullified the start of the long, slow descent to ~180ppm CO2 one would normally expect. Hence, we actually did contribute to the MWP, perhaps and the LIA. The latter is ironic: Europeans gave America smallpox, etc, but got the LIA in return.
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3. mercpl at 23:07 PM on 29 July, 2012
   Bill, With reference to your comment about Muller's op-Ed piece, i wonder if that is the major announcement that has caused the WUWT site to as suspended publication. Maybe Anthony Watts has changed his mind too.
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4. shoyemore at 00:29 AM on 30 July, 2012
   Another small "nit" that might have been mentioned, but possibly was too complicated to explain If the earth heated up very quickly in the MWP (not due to CO2) then that says something about the earth's climate sensitivity to the forcing agent, whatever it was. If it was the sun, it suggests that as the sun becomes more active, coupled with the anthropogenic CO2, then the earth's climate will heat up even faster than it is doing now. Not a propsect Lord Monckton and his minions want to deal with, it seems. PS Well played, Peter Hadfield. Thank God someone has the patience to hunt down those "adjusted" charts. I know I would not.
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5. Pete Dunkelberg at 00:48 AM on 30 July, 2012
   This video shows so many deniers it makes me wonder if there is a list of significant public deniers anywhere. How many are there, between 20 and 30?
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6. Lanfear at 01:21 AM on 30 July, 2012
   Pete@5 You mean something like this? There seems to be one separately for politicians too (US only).
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7. Pete Dunkelberg at 02:27 AM on 30 July, 2012
   Thanks, Lanfear.
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8. Daniel J. Andrews at 03:19 AM on 30 July, 2012
   One of the "frustrating" things about this site is that it highlights how quickly my knowledge falls out of date despite my efforts to stay semi-current. Sigh. I can see why denialists harp on a 14 year old hockey stick--it is a lot of work trying to stay current. So once again, thank you to SS and Peter. Time to hit the journals again. Any chance you can do a post or two on some of those ideas highlighted by John in the comments? Intriguing ideas.
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9. Daniel J. Andrews at 03:21 AM on 30 July, 2012
   Oops. I can check Bill Ruddiman's sources on that last item.
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10. JohnMashey at 06:18 AM on 30 July, 2012
    Daniel: See Ruddiman. But also, go to Real Climate and search for Ruddiman, as there are a few guest posts and commentaries. All this is a dandy example of real science in action, as hypotheses are proposed, challenged, modified, are disproved or (in this case) gain interest and evidence. I'd summarize all this as: 1) Bill has proposed that the CO2 and CH4 behaviors of this interglacial have departed fairly far from those seen in past interglacials, synchronized with the start of agriculture (CO2) and rice (+cows, etc) (CH4). Some of the arguments get complex in analyzing and properly aligning interglacials. Also, there has been a long set of arguments about land-use, i.e., during different eras, how much land had to be cleared per capita? Evidence is accumulating that early farmers needed more land, increasing their CO2 impact. If so, the numbers work pretty well. 2) Bill has proposed that some of the big CO2 jiggles over last 2,000 years came from human plagues, with the 1600AD even being the most obvious. See abstract of the 2008 paper by Nevele, Bird. ' Published reconstructions of Pre-Columbian demography indicate that during European conquest, pandemics killed ~90% of the indigenous American population (~60 million), estimated to represent ~20% of the 16th century global population. Our predictive calculations suggest that fire reduction in the tropical Americas is associated with massive forest regeneration on ~5 x 105 km2 of land and sequestration of 5-10 Gt C into the terrestrial biosphere, which can account for 13- 50% of the ~2% global reduction in atmospheric CO2 levels and the 0.1‰ increase in δ13C of atmospheric CO2 from 1500 to 1700 CE recorded in Antarctic ice cores and tropical sponges. New archeological discoveries revealing extensive networks of geoglyphs and urban polities in Pre-Columbian Amazonia suggest that our estimates of reforestation, and consequent effects on atmospheric CO2, may be conservative.' Or see the News release from Stanfrod. (Basically, in last few decades, researchers have found evidence of a much larger pre-Columbus population, most of whom died, and most were in areas that could regenerate especially large biomass, i.e., like Central America, Brazil.) See also the August 2011 issue of THe Holocene, whose abstracts you can read, including newer one by Nevle, Bird, Ruddiman, Dull. All this is highly interdisciplinary, combining multiple lines of evidence, with researchers and references spread all over the place, like Chinese archaelogists studying the spread of rice farming. Of course, the anti-science crowd, if they understand this, will utterly hate Bill's conclusions, even more than the hockey stick, perhaps, since they mean that humans inadvertently created a thermostat that kept Holocene temperatures within a fairly narrow range ... about to be departed on the high side via the Industrial Revolution.
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11. Sceptical Wombat at 13:32 PM on 30 July, 2012
    Bill @ 1 Muller now accepts that global warming has been happening, is continuing and is almost entirely CO2 induced. He appears to be saying that there is no evidence that it is a particularly big problem.
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12. skywatcher at 14:12 PM on 30 July, 2012
    #11: Muller's plying catch-up with the science. According to Mann, he's reached about the 1990s in his understanding of the science:

    "Some additional thoughts about Muller and 'BEST': Muller's announcement last year that the Earth is indeed warming brought him up to date w/ where the scientific community was in the the 1980s. His announcement this week that the warming can only be explained by human influences, brings him up to date with where the science was in the mid 1990s. At this rate, Muller should be caught up to the current state of climate science within a matter of a few years!" (source)

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13. Sceptical Wombat at 16:08 PM on 30 July, 2012
    Mercpl @3 I admire your optimism
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14. chriskoz at 21:00 PM on 30 July, 2012
    JohnMashey@10, I'm not interested in MWP hypothesis by Ruddiman. I'm interested in another one Ruddiman's famous for: Tibet and Himalayan uplift speeding up igneous rock weathering and creating the late Cenozoic cooling. I canot find the original article (perhaps still hidden behind paywall), nor the comprehensive review of the state of the art here. Do you have a ready pointer or a suggestion where to search?
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15. cynicus at 21:11 PM on 30 July, 2012
    @14 See first hit in Google Scholar after searching for "cenozoic himalaya ruddiman".
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16. eksommer at 13:22 PM on 1 August, 2012
    Thank you Mr. Hadfield for an excellent presentation. I have completely believed in anthropogenic climate change for decades. However, as I have returned late in life to a graduate program, I am out of necessity for my thesis reading a great deal written by climate change deniers and skeptics. As my background is journalism and not science, occasionally, I am drawn into what seems like a plausible argument, such as MWP. Your video snapped that thought right out of my head. Attention to detail and good investigation--something that competent scientists and journalists share. Most skeptics I;m reading, though, seem to come up short on facts, provide few references, and resort to attacking opponents. Reminds me more of sleight of hand when I read their books and papers.
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