The naughties are now over. We have already read that NASA has officially declared the year 2010 as the warmest in the observational record, but are these temperature measurements telling us something?
Probably, the other four institutions estimating global temperatures – GISS, HadCRU and the satellite UHA and RSS – have or soon will publish their temperature rankings. All these data dates use in one sense or another different methodologies or cover different areas of the globe and so it is not completely surprising that their results differ a bit. But leaving aside the question of whether or not this year set a record or whether the temperature trend is now positive or negative, I think the last decade has been remarkable. The temperature evolution does not seem to fit well within the 'experience' of the last 40 years. Let us have a look at the HadCRUT record. The recent trend, independently of where one starts counting, seems smaller than the long-term trend. Also, the variability at short time-scales looks somehow different. The decades up to year 2000 display long-wave oscillations lasting several years, some times almost a whole decade. However, the temperature in the naughties look flatter apart from the sudden dip and recovery in February 2008. I am a bit sceptical about of the concept of 'regime shift', as some studies have pointed out, but it is indeed tempting to believe that the strong ENSO event in 1998 represented a dividing line between two regimes. Maybe the decade that now starts will shed some light and it surely will disappoint one camp, but which one ?