Monday, November 04, 2013 ... /////

RSS AMSU: tiny cooling trend in last 17.0 years

In 2011, Ben Santer et al. beat the crap out of... no, I don't mean Pat Michaels, I mean the temperature data. The paper with 17 co-authors concluded (see the last sentence of the abstract) that

Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.
Seventeen years were needed to see the global warming. So did we see a warming in the last 17 years? I repeatedly pointed out that the interval with an insignificant cooling trend was approach 17 years.

Now, when RSS AMSU has published its October 2013 temperature anomaly, the period with a cooling has finally reached 17.0 years. Note that each month in late 2013, the period with a cooling trend was actually getting longer not just by 1 month but by 2 months or so because a new relatively cool month in 2013 allowed you to include another comparably cool month in 1996 or 1997 (at the beginning of the interval) without spoiling the negative sign.

I don't want to annoy you with another superlong table showing all the temperature trends for periods with an arbitrary number of months.

Instead, let me just give you the table of temperature trends for periods ending by October 2013 and lasting a whole number of years.

 No. of years Since (1st month) Trend in °C/century 34 Nov 1979 +1.27 33 Nov 1980 +1.35 32 Nov 1981 +1.42 31 Nov 1982 +1.40 30 Nov 1983 +1.50 29 Nov 1984 +1.44 28 Nov 1985 +1.27 27 Nov 1986 +1.17 26 Nov 1987 +1.20 25 Nov 1988 +1.33 24 Nov 1989 +1.18 23 Nov 1990 +1.17 22 Nov 1991 +1.30 21 Nov 1992 +1.00 20 Nov 1993 +0.61 19 Nov 1994 +0.35 18 Nov 1995 +0.30 17 Nov 1996 –0.01 16 Nov 1997 –0.45 15 Nov 1998 +0.30 14 Nov 1999 +0.06 13 Nov 2000 –0.42 12 Nov 2001 –0.75 11 Nov 2002 –0.54 10 Nov 2003 –0.37 9 Nov 2004 –0.42 8 Nov 2005 +0.25 7 Nov 2006 +0.46 6 Nov 2007 +1.91 5 Nov 2008 –2.05 4 Nov 2009 –6.21 3 Nov 2010 +3.78 2 Nov 2011 +8.65 1 Nov 2012 –0.08

Out of the 17 most recent trends of this kind, 10 (a majority) are negative. All trends in this table over 18-year or longer intervals are positive although the trends over periods up to 20 years in length are arguably insignificant by any reasonable measure.

The trend in 12 recent years, i.e. since November 2001, is –0.75 °C per century which is close to becoming "significant". Judith Curry said that "[a]ttention in the public debate seems to be moving away from the 15-17 year ‘pause’ to the cooling since 2002". Except for her, I haven't observed such a paradigm shift in the public debate but I surely see where she is coming from. If someone said that there was any warming in the last 20 years, he would be approximately equally justified in saying that there was a significant cooling in the last 12 years.

What will happen in the next 5, 10, 20, 50, or 100 years is yet to be seen.