Doug L. Hoffman's 2009 blog post on his website www.thereslientearth.com concerns the Early Anthropogenic Hypothesis (EAH). Ignoring the pejorative language, the first six paragraphs provide a reasonable if simplified summary of EAH. He then proceeds to seek papers that refute it; I thought it would be informative follow his trail...
The first (uncited) reference is to Schmidt's 2004 commentary which does not address EAH directly but does, usefully, highlight the possible effect of methane clathrates without directly relating them to anomalous Holocene warming. Next, we are directed to (Zimov et al, 2006) who explore how permafrost stores and releases carbon dioxide and methane and explain how radiocarbon (14C) can be used to differentiate between carbon released into the atmosphere at different times; they conclude by stating that a warming climate will melt permafrost and so cause more carbon to be released. The implication is, I think, that the EAH has not accounted for this effect but (i) such a release would happen during the warming period of every interglacial and (ii) if anthropogenic activity is causing a warmer climate then the efffect would be to increase that release, adding to and compounding the effect of anthropogenic warming caused by early farming. The referenced paper concerning the seasonal fluxing of methane releases (Mastepanov et al, 2008) is very interesting but does not suggest any specific connection with anthropogenic warming and neither do the quotes attributed to Christensen, which are from a separate 2008 Reuters interview.
A supplementary 2009 comment refers to a paper (Elsig et al, 2009) which considers the changes in δ13C in Holocene Antarctic ice cores to determine the origins of atmospheric carbon dioxide. This effectively rejects the EAH and attributes the rise to an "increase in land biosphere and to changes in the marine carbonate cycle" (p.509). This paper does not address methane changes and does not extend the methodology to pre-Holocene time periods to verify the model.
Finally, in a supplementary 2011 comment, Hoffman invokes a paper (Singarayer et al, 2011) which, using climate models, projects and compares the Holocene and Eemian methane releases based on vegetation cover and insolation. This found that the predicted methane concentrations were consistent with the ice core records, suggesting that the EAH is wrong; it is however noticeable that the effect of CO2 on CH4 concentrations was modelled but the resulting CO2 concentrations were not, and that the response of boreal warming (as discussed by Zimov et al above) was specifically excluded from the model.
What did I learn from being sceptical about Hoffman? His sources and arguments are selective and incomplete, and his personalised criticism, language and writing are unacceptable for someone who claims an academic background. But he has pointed me in the direction of some interesting alternatives to EAH. And I am questioning my earlier assertion that refuting EAH must deal with both CO2 and CH4 in the same counter-hypothesis.
24.12.2014: As an addendum to this post I was amused to find this criticism of Hoffman and Simmons' book "The Resilient Earth" at Amazon:
"However, the reader should be strongly cautioned that the source document is likely to be saying something completely opposite to the point being made in this book. Probably it would be best to just check out the source documents, and then optionally read this book afterward. As an example, very few of the N.A.S.A., NOAA or NAS references support the conclusions about climate science presented in the book when taken in their entirety."
No comments:
Post a Comment