IPCC has never waited for 30-year trends, and they were right.

Guest essay by Barry Brill

Under pressure at a media conference following release of its Summary for Policymakers, AR5 WG1 Co-Chair Thomas Stocker is reported to have said that “climate trends should not be considered for periods less than 30 years”.

Some have seen this as the beginning of an IPCC ploy to continue ignoring the 16-year-old temperature standstill for many years into the future. But even the IPCC must know that any such red herring is dead in the water:

1. When James Hansen launched the global warming scare in 1988, there had been no statistically significant warming over the previous 30 years and the warming trend during 1977-87 was 0.0°C. The IPCC was also established that year.

Source: Woodfortrees plot

2. At the time of the first IPCC report in 1991 (FAR), the warming trend was barely 11 years old.

Source: Woodfortrees plot

3. Most significantly, the Rio Earth Summit in 1992 adopted the UNFCCC treaty on the basis of a 30-year cooling trend followed by only 12 years of warming. That treaty dogmatically redefined “climate change” as being anthropogenic and eventually committed over 190 countries to combat “dangerous” warming.

4. The latest WG1 report bases its assessment of sea level rise and ocean heat content on the trend in satellite readings which have been available for only 19 years, coupled with ARGO reports for a period less than a decade. There is no apology for the short periods.

5. In 2007, the AR4 made much of the fact that the warming trend over the previous 15 years exceeded 0.2°C/decade. In 2013, the AR5 plays down the fact that there is no significant warming at all during the previous 15 years. (But AR5 cites 0.05°C/decade without mentioning that this figure is ±0.14°C).

6. If the IPCC wants to focus on 30-year trends, why did it make no comment on the fact that the current 30-year trend has fallen to 0.174°C/decade from the 0.182°C/decade trend that was the (1992-2006) backdrop to the AR4? Particularly, as the intervening 6-year period has been characterised by record increases in CO2 emissions.

7. Dr Stocker’s criticism of short-term trends as being influenced by start and end dates, ignores that long-term trends are similar. He picked a 60-year period (1951-2010) to produce a 0.12°C/decade trend, when a 70-year or 80-year period would have shown a much-reduced trend of 0.07°C.

8. WG1 scientists found it appropriate to include a statement in the AR5 SPM that

“Models do not generally reproduce the observed reduction in surface warming trend over the last 10 –15 years.”

3 months later, this crucial sentence was disappeared by a secret conclave of politicians/bureaucrats – not by scientists.

9. Dr Jarraud, secretary-general of the World Meteorological Organisation (WMO), told journalist David Rose that his question about the standstill was “ill-posed”. The WMO issues manuals on best practice for climatology and regards itself as the premier authority on measuring temperature trends. Here is what its manual WMO GUIDE TO CLIMATOLOGICAL PRACTICES (3RD EDTN) has to say about 30-year periods:

Chapter 4.8.1 Period of calculation“A number of studies have found that 30 years is not generally the optimal averaging period for normals used for prediction. The optimal period for temperatures is often substantially shorter than 30 years, but the optimal period for precipitation is often subtantially greater than 30 years.”And (at page 102):“The optimal length of record for predictive use of normals varies with element, geography, and secular trend. In general, the most recent 5‑ to 10‑year period of record has as much predictive value as a 30‑year record.”

Prior to release of the SPM, Bloomberg reported that some countries (notably Germany) wanted to wholly ignore the temperature standstill and pretend that the 20-year-old paradigm was still intact.

Few expected that would happen, predicting a sharply-reduced best estimate of sensitivity and rueful acknowledgment that natural factors had been under-estimated. The fact that days of debate culminated in this absurd canard about 30-year trends is a powerful indicator of just how desperate the climate establishment has now become.

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