Monday, November 04, 2013 ... Deutsch/Español/Related posts from blogosphere

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
34Nov 1979+1.27
33Nov 1980+1.35
32Nov 1981+1.42
31Nov 1982+1.40
30Nov 1983+1.50
29Nov 1984+1.44
28Nov 1985+1.27
27Nov 1986+1.17
26Nov 1987+1.20
25Nov 1988+1.33
24Nov 1989+1.18
23Nov 1990+1.17
22Nov 1991+1.30
21Nov 1992+1.00
20Nov 1993+0.61
19Nov 1994+0.35
18Nov 1995+0.30
17Nov 1996–0.01
16Nov 1997–0.45
15Nov 1998+0.30
14Nov 1999+0.06
13Nov 2000–0.42
12Nov 2001–0.75
11Nov 2002–0.54
10Nov 2003–0.37
9Nov 2004–0.42
8Nov 2005+0.25
7Nov 2006+0.46
6Nov 2007+1.91
5Nov 2008–2.05
4Nov 2009–6.21
3Nov 2010+3.78
2Nov 2011+8.65
1Nov 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.

Add to Digg this Add to reddit

snail feedback (0) :