Decadal prediction part 3

The first one isn't really a decadal prediction, but having finally got round to downloading the HadCRUT4 data and plotting it out, it seemed an obvious comparison to make. The pic is the famous IPCC AR4 (CMIP3) model hindcast and projections from the AR4 (it's Fig 5 in the SPM), with real data plotted on top (appropriately anomalised). I've blown up the relevant portion on the left:

As you can see, it looks pretty good up to about 2000. In fact, it looks ok up to about 2007, but since then has perhaps started to go a little bit pear-shaped. The yellow line should be ignored, of course - it's from the "constant composition" integrations, which hold the atmospheric composition fixed at year 2000 values. The other colours refer to three main projections, all of which give basically indistinguishable results over this time scale. The shaded region only covers ±1σ of the ensemble, and more importantly, I must point out quite clearly that the IPCC explicitly state that this analysis is not intended as a probabilistic prediction, so the fact that reality lies quite clearly outside this shaded areas for the last couple of years does not invalidate or falsify any particular prediction. On the other hand, it does suggest that the models are generally warming up a bit too fast. I make that statement here without prejudice as to whether this is due to errors in physics, or forcing, or just blind luck. Of course, I'm sure most of you will have also seen the equivalent with the CMIP5 models on Ed Hawkins' blog, but in that case it is more of an open question as to how much they might have been tuned to recent data. In the case of CMIP3, the "historical" scenario ended in 2000, so even if this was used to some extent (and there are strong arguments that it was), data subsequent to that is much less likely to have been used.

As Ed shows, the CMIP5 models are running a little hot too. More amusing, is to do a similar evaluation on the latest forecast from Stott et al (inc Hawkins), as published in ERL just recently. These authors did another D&A-type of analysis and concluded that "The upper end of climate model temperature projections is inconsistent with past warming". They also generated their own probabilistic predictions, based on data up to 2010. Since (in contrast to Allen et al's decadal means) their forecasts were explicitly provided for annual temp, we can already evaluate against the two years of 2011 and 2012. As Paul S pointed out in the comments, the prediction is again for decadally averaged temperatures, so we can't yet evaluate a true forecast, but we can still see how it is looking based on another 2 years of data:

Blue is HadCRUT4, showing the latest 2 years, and red is the decadal average (up to the latest available 2003-2012 interval, therefore plotted at year 2007.5). Even though they downscaled the model projections, both years since 2010 already lie outside the 5-95% range of the decadal mean prediction (though not by a huge margin). The decadal average is bumping along near the bottom of their forecast range and looks quite like likely to lie outside the CMIP5 spread, even though this is already normalised to 1986-2005.

 It's not really that surprising in hindsight, since the last year they used (2010) was an El Nino year, and yet they still managed to forecast more warming immediately following. Furthermore, their lower 5th percentile line seems to have a slope of about 0.2C per decade, implying high confidence in at least a maintenance of the recent warming rate

Incidentally, there is no sign of any El Nino on the horizon, so 2013 isn't likely to be particularly warm either (quite possibly below 2003, meaning the new decadal mean would drop). The current 2-month anomaly has it running a bit above 2012's result but still probably just outside the 5th percentile line in the above pic, though that could easily change. Anyone want to take bets on when (if?) we'll see a year inside the forecast range?