By Steve Goddard
Earlier in the month I wrote an article showing the trend in Arctic ice since 2002.
I took a lot of criticism from people for not measuring “crest to crest or trough to trough.”
Any one schooled in analysis of cyclical data would know that one must go from crest-to-crest or trough-to-trough, to maintain some semblance of symmetry about the x-axis.
It is time now to see how serious people are about their belief systems. We have passed the 2010 El Niño peak, and can see what the “real” trend is since the cyclical El Niño peak of 1998.
http://www.woodfortrees.org/plot/rss/from:1998/last:2010/plot/rss/from:1998/last:2010/trend
“Global warming on decadal timescales is continuing without let-up … we conclude that there has been no reduction in the global warming trend of 0.15-0.2C/decade that began in the late 1970s.”
Talk about cherry-picking! Look at his start point. He chose the worst case trough to crest to measure his trend.
Question for readers. Is Hansen correct, or does he need some serious graphing lessons? Below are the trend graphs from 1998-present for all four sources. GISS is way out of line.
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Alexej,
The time period from 1998 to present fails statistical significance. This is not calculated by selecting start/end points on a perceived cycle – that is a complete misunderstanding of the notion, which sky describes fairly well (although the bit on anomalies is irrelevant).
We also had an el Nino in 2007. According to you, we could measure from that peak to the present peak and get a statistically valid trend. Even a layperson should be able to tell this is nonsense.
It’s worth noting that el Nino periods are not symmetrically cyclical as is the case with annual fluctuations of sea ice cover. El Nino cycles are 5 years on average, but peak to peak can be as short as 2 years and as long as 7 years. Sea ice cover increases and decreases on a monotonous 1-year cycle, winter and summer.
El Nino periods themselves are not symmetrical in their duration. They also can peak at any month in the year, although they tend to be centred on the beginning/end of the years.
In order to discern an underlying trend from noisy, near-chaotic data, you need to work with a long enough time period where the noise is canceled out. 12 years is not enough.
One of these days, a competent statistician may work the sums for us, and deliver the statistical confidence value for the period 1998 – to present (August 2010). There are skeptical contributors to this website with the skill to do that, but for reasons unexplained, they never do (AFAIK).