A Test for the AGW Hypothesis

On the 16th July last year, Roger Pielke Sr made the following post on his blog:

Comments On The Current Record Global Average Lower TroposphereTemperatures

In the last couple of weeks, the onset of the El Niño, that was discussed on in my weblog on July 11 2009 would appear to be a possible explanation for the sudden increase in lower tropospheric temperatures to a record level (e.g. see the latest tropospheric temperature data at Daily Earth Temperatures from Satellite). This sudden warming is also discussed on other websites (see and see).

The current and recent anomalies at 500 mb (as representative of the tropospheric temperatures) are provided by the excellent NOAA analyses at

http://www.cpc.noaa.gov/products/intraseasonal/z500_nh_anim.shtml

http://www.cpc.noaa.gov/products/intraseasonal/z500_sh_anim.shtml

The location for the sudden warming (in the global average tropospheric temperatures as reported from the AMSU data) at 500 mb in the Northern Hemisphere is not obvious, however, except perhaps for a large area with weak positive anomalies in the lower latitudes. There is some warming in the El Niño area, but it is relatively small. In the lower latitude eastern hemisphere In the southern hemisphere, there is a strong warm anomaly near Antarctica. Maybe that is part of the reason for major region for the large positive AMSU temperature value.

This record event is an effective test of two hypotheses.

Hypothesis #1: Roy Spencer’s hypothesis on the role of circulation patterns in global warming (e.g. see) might explain most or all of the current anomaly since it clearly is spatially very variable, and its onset was so sudden. If the lower atmosphere cools again to its long term average or lower, this would support Roy’s viewpoint.

Hypothesis #2: Alternatively, if the large anomaly persists, it will support the claims by the IPCC and others (e.g. see Cool Spells Normal in Warming World) that well-mixed greenhouse gas warming is the dominate climate forcing in the coming decades and is again causing global warming after the interruption of the last few years.

Only time will tell which is correct, however, we now have short term information to test the two hypotheses. The results of this real world test will certainly influence my viewpoint on climate science.

Roger has updated this on the 9th June this year with the following observation:

Since the warm anomalies persist (e.g. see and see; Fig 7), the coming months are key to determining which of the two hypotheses with respect to global warming and cooling can be rejected. If we move into a La Niña without a corresponding cooling of the lower troposphere, it would support the rejection of hypothesis #1. However, if the lower troposphere cools, in terms of anomalies, to at or below the long-term average, this would support the rejection of hypothesis #2.

Of course, the two hypotheses do not cover all of the possibilities. If the warm anomalies persist, this could be due primarily to other human climate forcings besides carbon dioxide, such as black carbon. However, this would still indicate hypothesis #1 should be rejected.

I will again revisit this topic in a few months.

I agree we have here a very good testable situation which may help determine which hypothesis is more likely to be correct. I'll be following Roger's subsequent observations with interest and will update this entry accordingly.