Degenerating Climatology 1: IPCC Statements on Human Caused Warming

This is the first in an occasional series of illustrating the degeneration of climatology away from an empirical science. In my view, for climatology to be progressing it needs to be making ever clearer empirical statements that support the Catastrophic Anthropogenic Global Warming (CAGW) hypothesis and moving away from the bland statements that can just as easily support a weaker form of the hypothesis, or support random fluctuations. In figure 1 this progression is illustrated by the red arrow, with increasing depth of colour. The example given below is an illustration of the opposite tendency.

Obscuring the slowdown in warming in AR5

Every major temperature data set shows that the warming rate this century has been lower than that towards the end of the end of the twentieth century. This is becoming a severe issue for those who believe that the main driver of warming is increasing atmospheric greenhouse gas levels. This gave a severe problem for the IPCC in trying to find evidence for the theory when they published in late 2013.

In the IPCC Fifth Assessment Report Working Group 1 (The Physical Science Basis) Summary for Policy Makers, the headline summary on the atmosphere is:-

Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years (medium confidence).

There are three parts to this.

  • The last three decades have been successively warmer according to the major surface temperature data sets. The 1980s were warmer than the 1970s; the 1990s warmer than the 1980s; and the 2000s warmer than the 1990s.
  • The 1980s was warmer than any preceding decade from the 1850s.
  • In the collective opinion of the climate experts there is greater than a 66% chance that the 1980s was the warmest decade in 1400 years.

What the does not include are the following.

  1. That global average temperature rises have slowed down in the last decade compared with the 1990s. From 2003 in the HADCRUT4 temperature series warming had stopped.
  2. That global average temperature also rose significantly in the mid-nineteenth and early twentieth centuries.
  3. That global average temperature fell in 4 or 5 of the 13 decades from 1880 to 2010.
  4. That in the last 1400 years there was a warm period about 1000 years ago and a significantly cold period that could have reached bottomed out around 1820. That is a Medieval Warm Period and the Little Ice Age.
  5. That there is strong evidence of Roman Warm Period that about 2000 years ago and a Bronze Age warm period about 3000 years ago.

Point (i) to (iii) can be confirmed by figure 2. Both the two major data surface temperature anomalies show warming trends in each of the last three decades, implying successive warming. A similar statement could have been made in 1943 if the data had been available.

In so far as the CAGW hypothesis is broadly defined as a non-trivial human-caused rise in temperatures (the narrower more precise definition being that the temperature change has catastrophic consequences) there is no empirical support found from the actual temperature records or from the longer data reconstructions from proxy data.

The major statement above is amplified by the major statement from the press release of 27/09/2013.

It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. The evidence for this has grown, thanks to more and better observations, an improved understanding of the climate system response and improved climate models.

This statement does exclude other types of temperature change, let alone other causes of the temperature change. The cooling in the 1960s is not included. The observed temperature change is only the net impact of all influences, known or unknown. Further, the likelihood is based upon expert opinion. If the experts have always given prominence to human influences on warming (as opposed to natural and random influences) then their opinion will be biased. Over time if this opinion is not objectively adjusted in the light of evidence that does not conform to the theory the basis of Bayesian statistic is undermined.

Does the above mean that climatology is degenerating away from a rigorous scientific discipline? I have chosen the latest expert statements, but not compared them with previous statements. A comparable highlighted statement to the human influence statement from the fourth assessment report WG1 SPM (Page 3) is

The understanding of anthropogenic warming and cooling influences on climate has improved since the TAR, leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m–2

The differences are

  • The greenhouse gas effect is no longer emphasised. It is now the broader “human influence”.
  • The previous statement was prepared to associate the influence with a much longer period. Probably the collapse of hockey stick studies, with their portrayal of unprecedented warming, has something to do with this.
  • Conversely, the earlier statement is only prepared to say that since 1750 the net effect of human influences has been one of warming. The more recent statement claims a dominant cause of warming has been human caused.

This leads my final point indicating degeneration of climatology away from science. When comparing the WG1 SPMs for TAR, AR4 and AR5 there are shifting statements. In each report the authors have chosen the best statements to fit their case at that point in time. The result is a lack of continuity that might demonstrate and increasing correspondence between theory and data.

Kevin Marshall

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