Global warming, models and language - Climate Change: The Facts - page 31

Table 1: The amount of 'aerosol' cancellation needed to change results in Figure 4 to
those in Figure 5. The latter are consistent with observed net warming
Examples of this natural (non-greenhouse related) internal variability are the El
Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation and the Atlantic
Multi-decadal Oscillation.
The instrumental record is too short to indicate longer period phenomena though such
longer periods are evident in proxy records of temperature. The so-called hiatus in global
warming over the past seventeen years is incontrovertible evidence of the importance of
this variability, and as a 2013 study by Jiansong Zhou and Ka-Kit Tung has shown, such
internal variability is likely to have accounted for about half of the warming since the late
1970s. 4 Under the circumstances, getting models to replicate the much reduced directly
forced warming will require even more implausible cancellation by aerosols. It should be
notedthattheIPCCclaimsforattributiondependonassumingnaturalinternalvariabilityto
be small. This is clearly not the case. However, what is generally ignored is that even if the
attribution claim were correct, it would still be completely consistent with low sensitivity.
After all, the above analysis assumed that more than 100 per cent of the observed warming
was due to man (allowing for cancellation of some of the warming by volcanoes). The
IPCC only insisted on 51 per cent being due to man.
It seems to me that the most reasonable conclusion to reach under the circumstances
is that climate sensitivity is small. Moreover, mild warming is likely to be a net benefit.
However, I would not be surprised to see advocates of alarm soon arguing that it was the
previouslyignorednaturalinternalvariabilitythathadactuallydisguisedthelargewarming
that would otherwise have occurred, thus leaving the possibility of dangerous warming in
place.