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Anthropogenic-CO2-Induced Global Warming: Proven or Unproven?

Reference
Solomon, S., Daniel, J.S., Neely III, R.R., Vernier, J.-P., Dutton, E.G. and Thomason, L.W. 2011. The persistently variable "background" stratospheric aerosol layer and global climate change. Science 333: 10.1126/science.1206027.
The fact that there has been little to no net warming of the Earth over the past dozen or so years, in almost all of the global temperature databases that are maintained by the various research groups that study this important subject, has led many people to suggest that anthropogenic CO2 emissions are not having the large global warming effect the world's climate alarmists assign to it. And this fact has led many climate alarmists to devise complex explanations for this dilemma.

On 12 August 2011, for example, Science published Solomon et al.'s contribution to this effort, which begins with the statement that "understanding climate changes on time scales of years, decades, centuries, or more requires determining the effects of all external drivers of radiative forcing of Earth's climate, including anthropogenic greenhouse gases and aerosols, natural aerosols, and solar forcing, as well as natural internal variability." The result of their effort in this undertaking was the finding that "near-global satellite aerosol data imply a negative radiative forcing due to stratospheric aerosol changes over this period [since AD 2000] of about -0.1 watt per square meter, reducing the recent global warming that would otherwise have occurred," although they emphasize that additional contributions to global climate variations of the past and future decades such as from solar variations, natural variability, or other processes "are not ruled out by this study," which pretty much means that the study does not mean very much, and that it can thus be forgotten within the context within which it was conducted.

Subsequently, on 18 November 2011, the Journal of Geophysical Research published Santer et al.'s contribution to the climate alarmists' cause; and they too begin by noting that "the warming signal arising from slow, human-caused changes in atmospheric concentrations of greenhouse gases is embedded in the background 'noise' of natural climate variability." And after many mathematical machinations designed to ferret out the impact of anthropogenic greenhouse gas emissions, the group of seventeen scientists conclude that "minimal warming over a single decade does not disprove the existence of a slowly-evolving anthropogenic warming signal."

However, it should be equally noted that their work must also imply that it does not disprove the existence of a slowly-evolving non-anthropogenic warming signal, such as whatever it is that drives the well-established millennial-scale cycling of Earth's climate that has alternately brought the planet into and out of the Roman Warm Period, the Dark Ages Cold Period, the Medieval Warm Period, the Little Ice Age and the initial phase of the Current Warm Period, which phenomenon appears to have operated over the eons, throughout glacial and interglacial periods alike (Oppo et al., 1998; McManus et al., 1999).

Clearly, the weight of real-world evidence continues to suggest that it is the recurrent millennial-scale cycling of Earth's mean global air temperature that has been responsible for the bulk of the warming of the 20th century, which could yet continue its upward course, level out, or begin a slow decline; for this phenomenon has created such warmings and subsequent coolings time and time again without any help from mankind. And if it's done so before - innumerable times, in fact - it can do it again. In fact, it has actually got to be expected that it would do so, and at about this point in Earth's history.

Additional References
McManus, J.F., Oppo, D.W. and Cullen, J.L. 1999. A 0.5-million-year record of millennial-scale climate variability in the North Atlantic. Science 283: 971-974.

Oppo, D.W., McManus, J.F. and Cullen, J.L. 1998. Abrupt climate events 500,000 to 340,000 years ago: Evidence from subpolar North Atlantic sediments. Science 279: 1335-1338.

Santer, B.D., Mears, C., Doutriaux, C., Caldwell, P., Gleckler, P.J., Wigley, T.M.L., Solomon, S., Gillett, N.P., Ivanova, D., Karl, T.R., Lanzante, J.R., Meehl, G.A., Stott, P.A., Taylor, K.E., Thorne, P.W., Wehner, M.F. and Wentz, F.J. 2011. Separating signal and noise in atmospheric temperature changes: The importance of timescale. Journal of Geophysical Research 116: 10.1029/2011JD016263.

Archived 13 March 2012