One of the conclusions on Climate Science is that there is no predictive skill in multi-decadal regional climate predictions (see #6). Evidence for such a conclusion, for example, have been summarized in a number of weblogs (e.g. see, and see).
There is an interesting candid new quote from Mike Mann on February 14, 2007 on this issue. It reads
“…..Until we are sure how climate change impacts El Nino, regional climate change forecasts over most regions of the world are likely to remain of somewhat limited utility. Its important to keep all of this in perspective.”
This statement needs to be related to news articles which purport to claim that there is regional predictive skill on decadal climate scales (e.g. see). Such news articles are clearly not supported by current capabilities in modeling the climate system.
Indeed, since significant human climate forcings (e.g. land use/cover change, aerosols) also occur on regional scales, are of a similar magnitude of heating and cooling in the troposphere with respect to an El Nino, and last for long periods of time (e.g. see the discussion in
Pielke Sr., R.A., 2001: Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Rev. Geophys., 39, 151-177),
Mike Mann’s conclusion therefore also applies to our current inability to skillfully predict the multi-decadal regional climate in response to these forcings (or using Mike Mann’s wording “remain of somewhat limited utility”), and through teleconnections, the global climate response.
As written in the 2001 Pielke paper,
” The effect of well above average ocean temperatures in the eastern and central Pacific Ocean, which is referred to as ‘El Nino,’ has been shown to have a major effect on weather thousands of kilometers from this region [Shabbar et al., 1997]. The presence of the warm ocean surface conditions permits thunderstorms to occur there that would not happen with the average colder ocean surface. These thunderstorms export vast amounts of heat, moisture, and kinetic energy to the middle and higher latitudes, particularly in the winter hemisphere. This transfer alters the ridge and trough pattern associated with the polar jet stream [Hou, 1998]. This transfer of heat, moisture, and kinetic energy is referred to as âteleconnectionsâ? [Namias, 1978; Wallace and Gutzler, 1981; Glantz et al., 1991]. Almost two thirds of the global precipitation occurs associated with mesoscale cumulonimbus and stratiform cloud systems located equatorward of 30 degrees [Keenan et al., 1994]. In addition, much of the worldâs lightning occurs over tropical landmasses, with maximums also over the midlatitude land masses in the warm seasons [Lyons, 1999; Rosenfeld, 2000]. These tropical regions are also undergoing rapid landscape change [OâBrien, 2000].
As shown in the pioneering study by Riehl and Malkus  and by Riehl and Simpson , 1500â5000 thunderstorms (which they refer to as âhot towersâ?) are the conduit to transport this heat, moisture, and wind energy to higher latitudes. Since thunderstorms occur only in a relatively small percentage of the area of the tropics, a change in their spatial patterns would be expected to have global consequences.
Wu and Newell  concluded that sea surface temperature variations in the tropical eastern Pacific Ocean have three unique properties that allow this region to influence the atmosphere effectively: large magnitude, long persistence, and spatial coherence. Since land use change has the same three attributes, a similar teleconnection would be expected with respect to landscape patterns in the tropics.”
The same three attributes of large magnitude, long persistence, and spatial coherence apply to aerosol forcings (e.g. see
Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974).
Thus the message that should be taken from Mike Mann’s comment on Real Climate is that there is “somewhat limited utility” in the prediction of multi-decadal regional climate variability and change. Statements and claims to the contrary in the media (and in scientific journals) are not mainstream views in climate science.