Real Climate - 2 Prominent 2007/8 Papers Predicted Decade Of Global Cooling; They Weren't Even Close
Remember the forecast of a temporary global cooling which made headlines around the world in 2008? We didn’t think it was reliable and offered a bet. The forecast period is now over: we were right, the forecast was not skillful.
Back around 2007/8, two high-profile papers claimed to produce, for the first time, skilful predictions of decadal climate change, based on new techniques of ocean state initialization in climate models. Both papers made forecasts of the future evolution of global mean and regional temperatures. The first paper, Smith et al. (2007), predicted “that internal variability will partially offset the anthropogenic global warming signal for the next few years. However, climate will continue to warm, with at least half of the years after 2009 predicted to exceed the warmest year currently on record.” The second, Keenlyside et al., (2008), forecast in contrast that “global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.”
This month marks the end of the forecast period for Keenlyside et al and so their forecasts can now be cleanly compared to what actually happened. This is particularly interesting to RealClimate, since we offered a bet to the authors on whether the results would be accurate based on our assessment of their methodology. They ignored our offer but now the time period of the bet has passed, it’s worth checking how it would have gone.
Keenlyside and colleagues specifically forecast temperatures for the overlapping decadal periods of Nov 2000-Oct 2010, and Nov 2004-Oct 2015. At the end of the first period, we checked in on the forecast and noted that the predicted global cooling had not occurred. We can now update this for the second period as well.
Blue dots and curve show global temperature data (NASA GISTEMP), red dots with confidence intervals the model forecasts and hindcast, for the same 10-year intervals chosen by Keenlyside et al in their paper. (The observed 12-month running average is also shown.) Temperature anomalies are shown relative to the period November 1994 – October 2004 as in the Keenlyside paper. The forecasts for a cooling (relative to the previous 10-year interval) were clearly wrong: decadal average temperatures have kept increasing, despite the ever-present shorter-term variability shown in the grey curve.
EDIT
http://www.realclimate.org/index.php/archives/2015/11/and-the-winner-is/#more-18851
