Christopher Monckton:
I have now had the opportunity to study SteveF’s remarkable essay at Lucia’s Blackboard, to which Anthony kindly draws attention in his footnote to my earlier posting on theabsence of statistically-significant global warming for 17 years 4 months.
SteveF’s conclusion is that once allowance has been made for three naturally-occurring influences – volcanic aerosols, the ~11-year solar cycle and the el Niño/la Niña cycles – the HadCRUt4 warming rate from 1979-1996 was six times faster than from 1997-2012. In the abstract, to allow for uncertainties, he cautiously reduces this to three times faster.
Even if one were to take the unadjusted HadCRUt4 data, the rate of warming from 1979-1996 was more than twice as fast as the rate from 1997-2012.
I decided to look not only at HadCRUt4, as SteveF did, but also at the two satellite datasets, RSS and UAH. RSS showed warming at 0.7 Cº/century from 1979-1996 and cooling at almost 0.1 Cº/century from 1997-2012.
UAH, however, in contrast to both HadCRUt4 and RSS, showed warming in the later period, 1997-2012, that was thrice as fast as the warming of the earlier period, 1979-1996.
SteveF’s essay takes no account of the most substantial medium-term natural cycle that seems to influence global temperatures: the Pacific Decadal Oscillation. The cycles of that great Oscillation tend to exercise a warming influence for about 30 years followed by a cooling influence for about 30 years. This cyclical influence is visible throughout the HadCRUt4 global temperature record since 1850.
There was a remarkably sharp transition from the “cooling” to the “warming” phase of the PDO at the beginning of 1976 and a transition back to “cooling” late in 2001.
The HadCRUt4 warming rate from 1976-2001 was equivalent to almost 1.8 Cº/century (compared with warming at just 1.1 Cº/century from 1979-1996), but from 2002 to the present HadCRUt4 shows cooling at a rate equivalent to almost 0.5 Cº/century (compared with warming at almost 0.5 Cº/century from 1997-2012).
Much of the fall in the warming rate identified by SteveF, therefore, appears to be attributable to the PDO. It would be interesting to adjust the global instrumental temperature anomaly record not only for volcanic aerosols, solar cycles and el Niños but also for the cycles of the PDO, but that is above my present pay-grade.
What is far from clear is the influence, if any, from CO2. Its influence must be very small, for it seems easily overwhelmed by natural influences such as the PDO and the three phenomena studied by SteveF.
During the three “warming” phases of the PDO that are visible in the HadCRUt4 instrumental record since 1850, the warming rates were as follows: 1860-1880 less than 1.0 Cº/century; 1910-1940 1.4 Cº/century; and 1976-2001 1.8 Cº/century.
Superficially, there appears to be an inexorable and strikingly near-linear increase in the warming rates during successive “warming” phases of the PDO. Might this increase be attributable to the monotonic increase in CO2 over recent decades?
If the increase in warming rates were to continue, perhaps as a result of the growing warming influence from CO2, the warming from about 2040-2070 might be equivalent to 2.2 Cº/century; and from 2100-2130 2.6 Cº/century.
It would not be until around 2160-2190 that the warming rate would reach the IPCC’s currently-projected central estimate of 3.0 Cº/century. And, even then, the mean centennial rate after allowing for the “cooling” phases of the PDO would be considerably less.
However, the apparently tidy 1.0 to 1.4 to 1.8 Cº/century-equivalent increase in the rates of global warming during the “warming” phases of the PDO may not be attributable to CO2 at all. The true cause may be another and more sinister man-made phenomenon: Orwellian data revisionism.
