Bob Tisdale goes AMO-ing to a big chill - not!

Update: The University of Southampton has issued a clarification. It doesn't address the substantive issues raised here. There's also no mention of 0.5C.

Also see Gerard McCarthy's replies to my query to him via Twitter - here and here and here.

Sou 2 June 2015

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There was a new paper that came out this week in Nature, which had a bit of coverage around the traps. Deniers rather liked it not so much because of what was in the paper itself, but because of what was in the press release.

The paper was by a team from the University of Southampton, led by Dr. Gerard D. McCarthy. The paper was about the Atlantic Multidecadal Oscillation or AMO and ocean heat transport, and related.

The AMO is used to indicate changes in sea surface temperature in the North Atlantic. It is of such long duration that there aren't instrumental records going back far enough to show multiple repeating patterns. It's probably not a regular cycle with a fixed period. Estimates seem to place the latest period at around 70 years (from the beginning of a warm phase in the 1920s to the end of a cool phase in the 1990s - see here). The latest IPCC report had this to say about it (page TS-25):

A number of studies have investigated the effects of the Atlantic Multidecadal Oscillation (AMO) on global mean surface temperature. While some studies find a significant role for the AMO in driving multi-decadal variability in GMST, the AMO exhibited little trend over the period 1951-2010 on which these assessments are based, and the AMO is assessed with high confidence to have made little contribution to the GMST trend between 1951 and 2010 (considerably less than 0.1°C). {2.4, 9.8.1, 10.3; FAQ 9.1}.

From the above paragraph I take it that the nature of the AMO is not all that well agreed upon - by some at least.

Bits and pieces from the IPCC WG1 - methane, AMO and anthropogenic forcing

While I'm working my way through the IPCC reports, here are some more snippets of interest from the AR5 Technical Summary.

On methane emissions (page TS-23)

Models and ecosystem warming experiments show high agreement that wetland CH4 emissions will increase per unit area in a warmer climate, but wetland areal extent may increase or decrease depending on regional changes in temperature and precipitation affecting wetland hydrology, so that there is low confidence in quantitative projections of wetland CH4 emissions. Reservoirs of carbon in hydrates and permafrost are very large, and thus could potentially act as very powerful feedbacks. Although poorly constrained, the 21st century global release of CH4 from hydrates to the atmosphere is likely to be low due to the under-saturated state of the ocean, long-ventilation time of the ocean, and slow propagation of warming through the seafloor. Release of carbon from thawing permafrost is very likely to provide a positive feedback, but there is limited confidence in quantitative projections of its strength. {6.4}

Atlantic Multidecadal Oscillation made little contribution to GMST* (page TS-25)

A number of studies have investigated the effects of the Atlantic Multidecadal Oscillation (AMO) on global mean surface temperature. While some studies find a significant role for the AMO in driving multi-decadal variability in GMST, the AMO exhibited little trend over the period 1951-2010 on which these assessments are based, and the AMO is assessed with high confidence to have made little contribution to the GMST trend between 1951 and 2010 (considerably less than 0.1°C). {2.4, 9.8.1, 10.3; FAQ 9.1}.

*GMST = global mean surface temperature.

Human activities had by far the greatest impact on global surface temperature (page TS-26)

Greenhouse gases contributed a global mean surface warming likely to be between 0.5°C and 1.3°C over the period between 1951 and 2010, with the contributions from other anthropogenic forcings likely to be between –0.6°C and 0.1°C and from natural forcings likely to be between –0.1°C and 0.1°C. Together these assessed contributions are consistent with the observed warming of approximately 0.6°C over this period (Figure TS.10). {10.3}...

...Observed warming over the past sixty years is far outside the range of internal climate variability estimated from pre-instrumental data, and it is also far outside the range of internal variability simulated in climate models. Model-based simulations of internal variability are assessed to be adequate to make this assessment. Further, the spatial pattern of observed warming differs from those associated with internal variability. Based on this evidence, the contribution of internal variability to the 1951–2010 global mean surface temperature trend was assessed to be likely between –0.1°C and 0.1°C, and it is virtually certain that warming since 1951 cannot be explained by internal variability alone. {9.5, 10.3, 10.7}

The instrumental record shows a pronounced warming during the first half of the 20th century. Consistent with AR4, it is assessed that the early 20th century warming is very unlikely to be due to internal variability alone. It remains difficult to quantify the contributions to this early century warming from internal variability, natural forcing and anthropogenic forcing, due to forcing and response uncertainties and incomplete observational coverage. {10.3}