Arguments
Peter Hadfield takes on the MWP
Posted on 30 July 2012 by Rob Honeycutt
Mann, Bradley, and Hughes (MBH) 1999 seems to be getting a lot of attention these recent weeks in various places on the Internet, so it's quite timely that Peter has decided to produce what is his longest single video yet, on the topic of the "putative Medieval Warm Period" (MWP).
Peter aptly points out the fact that gets missed by so many denialists: science always moves forward. While they are caught up arguing over the MWP as it appears in schematic (non-proxy) drawings from the IPCC's First Assessment Report, and over McIntyre and McKitrick's criticisms of of the statistical techniques used in MBH1999, there have been numerous other subsequent reconstructions that improve on that early research. All the more recent research has continued to support MBH's conclusions that globally averaged temperature is likely warmer today than at any time in the past 1000 years.
As I recently stated to someone, getting all wrapped up on critiquing MBH98/99 is a little like castigating Newton for not coming up with Relativity.
Also interesting is how Peter diligently ferrets out various examples of other "skeptics" doctoring research paper charts to remove the instrumental record or even shift the time scale to make it look like the MWP was warmer than today.
Keep up the great work, Peter! The world today needs more journalists like you.
Between this and Muller's 'call me a Converted Skeptic' NYT OpEd this is turning into quite the memorable day!
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.
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.
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.
You mean something like this?
There seems to be one separately for politicians too (US only).
Any chance you can do a post or two on some of those ideas highlighted by John in the comments? Intriguing ideas.
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.
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.
I admire your optimism
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?