History may see the interview of CRU’s Professor Phil Jones by the BBC’s Roger Harrabin on 12 February 2010 as the opening of the end-phase of the long-running “alarmists versus sceptics” debate.
The gap between these two schools has never yawned as widely as media reports often suggest. Both agree that climate is always changing, that we have recently been in a warming period (with tiny temperature changes), that “greenhouse theory” has some validity, and that human activities are capable of impacting climate. The core dispute lies in the detection and attribution of ‘anthropogenic global warming’ (AGW), and is brought out in the following exchange:
Harrabin – How confident are you that warming has taken place and that humans are mainly responsible?
Jones – I’m 100% confident that the climate has warmed. As to the second question, I would go along with IPCC Chapter 9 – there’s evidence that most of the warming since the 1950s is due to human activity.
Sceptics say any human causation was trivial. This dispute was addressed directly:
Harrabin – what factors convince you that recent warming has been largely man-made?
Jones – The fact that we can’t explain the warming from the 1950s by solar and volcanic forcing.
“The warming from the 1950s” didn’t actually commence until 1975, and the 1975-2009 warming is identified by Professor Jones as a trend-rate of temperature increase of 0.161C per decade.
This decadal figure is significant, but only just. In the second interview question, Jones says a trend of “0.12C per decade is not significant at the 95% significance level”.
The world has been experiencing a long-term gentle warming since the end of the Little Ice Age. Professor Jones has said elsewhere[i] that this natural variability has averaged 0.11C per decade. So, the “extraordinary” recent warming that calls for explanation is the balance of 0.051C per decade.
This is the smoking gun. It is the sole evidence that a measurable but unexplained increase in global temperatures has coincided with the post-1950 increase in human-induced greenhouse gas emissions. Jones says that this correlation is evidence of causation, because the IPCC has no other explanation.
The first rejoinder by sceptics is that this is an argument from ignorance. Humanity cops the blame solely because IPCC researchers know so little about all the vast natural forces and cycles influencing global temperatures that they can’t pin it firmly on any one suspect. Cast in this way, the strength of the IPPC’s case is inversely proportional to the depth of their climatic understanding. But why should homo sapiens be the default option?
Secondly, doubters say it is not surprising that IPCC models can’t explain an infinitesimal heat anomaly of five-hundredths of a degree over a 10-year period. They have a track record of being wrong about much larger matters, including their prediction of 0.2C warming over the past decade. Phil Jones says there has been no significant warming since 1995.
Thirdly, a very important question arises as to the precision of the instrumental record, as well as all the statistical processing, that produces this key trend figure of 0.161C per decade. This seems an impossibly precise figure for all the world’s temperatures, over lengthy periods, in all seasons, using diverse and changing instruments. What are the margins of error for the thermometers? What are the statistical confidence intervals for the homogenization of records? What of the spatial and temporal gaps?
Error bars narrow over time, but the IPCC accepts that even the most modern gridded readings contain errors of +/- 0.17. When this level is applied to Professor Jones’ trend for 1975-2009 it overwhelms it. The anomaly which “we can’t explain” is so small as to be swamped by the margins of error.
Doubts about the accuracy of data processing are heightened by the ongoing unavailability of worldwide raw data and metadata. CRU evaded Freedom of Information obligations and then confessed that computer data was lost. This pattern was mirrored by the actions of NIWA in New Zealand, and perhaps others. What of the ‘Climategate’ accusations of manipulation, also mirrored in New Zealand? There are a great many known unknowns, and perhaps just as many unknown unknowns.
The fourth objection is that a trend of 0.161C per decade is NOT outside the boundaries of internal natural variability. This is where the BBC testimony of Professor Jones becomes invaluable in settling the argument:
Harrabin – Do you agree that according to the global temperature record used by the IPCC, the rates of global warming from 1860-1880, 1910-1940 and 1975-1998 were identical?
Jones – The 1860-1880 period is only 21 years in length. As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different.
It is common ground that the warmings commencing in 1860 and 1910 were not human-caused, so they must have resulted from oscillations or other cyclical or chaotic aspects of internal variability. An unexplained warming trend of 0.16C/decade, which has occurred three times in the last 150 years is, by definition, within the natural variability of the global climate system.
The first two IPCC reports accepted that the medieval warm period (MWP) was the warmest period of the millennium, but this was challenged in 2001 by the ‘hockey sticks’ produced by Mann, Briffa, and others. These projects, which focused on tree rings in North America and Siberia, were illuminated by the BBC interview:
Harrabin– There is a debate over whether the Medieval Warm Period (MWP) was global.
Jones – For it to be global in extent the MWP would need to be seen clearly in more records from the tropical regions and the Southern Hemisphere. There are very few paleoclimatic records for these latter two regions.
So the ‘hockey team’ go under a bus, along with the IPCC’s dogmatic claim that current temperatures are the warmest experienced for a thousand years. The MWP which was established by history records still stands – as yet unchallenged by proxy temperature records.
The fifth argument accepts that all three warmings since 1860 (and the MWP) could have exceeded the bounds of natural variability, if all were forced by the same external influence. Possibilities are legion and include solar flares, cosmic rays, orbital anomalies, undocumented cycles, aerosols, ocean currents and magnetic realignments. Nobody actually blames these warmings on volcanoes or solar irradiance, which are the only two influences considered by Phil Jones.
The sixth problem is that the correlation between the respective increases of GHGs and temperatures, which has always been poor, has become non-existent in the past 15years. Whilst CO2 emissions have rocketed since 1995, Phil Jones confirms there has been no detectable increase in global warming.
The real value of the Harrabin/Jones interview is the fact that straight questions received straight answers, for the first time in recent memory.