Thoughts On The AR6 Summary for Policymakers

Guest Essay by Ian Cunningham

 

 


Some observations on statements made in the Summary for Policymakers IPCC AR6 WGI

(red text)

 

 

A. The Current State of the Climate

A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.

This statement adds nothing to our understanding. Nobody disputes that humans have increased the quantity of carbon dioxide in the atmosphere and that given that carbon dioxide is a greenhouse gas it should cause some warming. There is also broad agreement that there has been warming but how much of this is natural and how much is human induced? The second sentence would apply to both natural and human induced changes. The use of ‘rapid’ is questionable; a 1.07°C rise (see A.1.3) over about 150 years can hardly be described as such.

A.1.3 The likely range of total human-caused global surface temperature increase from 1850–1900 to 2010–2019 is 0.8°C to 1.3°C, with a best estimate of 1.07°C.

A recent peer reviewed paper points out that there are problems in determining global surface temperatures (eg rural stations show less warming than urban stations). Indeed a global average temperature is a seriously flawed concept. Also in concluding that the sun has had no influence on surface temperatures it appears that the IPCC used only a selection of the available data sets which estimate the solar contribution. Depending on which data sets are used all of the recent warming could be due to changes in solar activity or all of it could be due to human activities. The statement at A.1.3 therefore cannot be relied upon.

A.2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.

To support this there is a ‘hockey stick’ graph at page SPM7. Such a graph was also included in earlier IPCC reports but was completely discredited because it was apparently constructed by omitting tree ring data which did not fit the desired shape. It was not included in the last report. An analysis by the same mathematician who discovered the flaws in the earlier version has also revealed similar flaws in this new ‘hockey stick’. "Rather than hiding the decline in the final product, they did so for individual trees: they excluded the “divergent portions” of individual trees that had decreasing growth in recent years."

A.2 therefore cannot be relied upon.

A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since AR5.

Given that the degree of human influence is not clear (vide supra) this statement would be better started without the words ‘Human-induced’.

But has the warming since 1850-1900 produced more climate extremes as claimed? In a warming world higher temperature extremes might be expected and minimum temperatures might also be higher.

In paragraphs A.3.1 to A.3.5 statements are made where it is claimed that human induced climate change is the main driver of many events. Helpfully it is explained in a footnote that ‘main driver’ means responsible for more than 50% of the change. This seems somewhat at odds with A.1.3 which claims changes in temperatures are almost all due to humans but here it might just be 51%.

A number of diagrams are provide at SPM12. The second picture is entitled

b) Synthesis of assessment of observed change in heavy precipitation and
confidence in human contribution to the observed changes in the world’s regions.

From this 19 regions out of 47 are said to have experienced an increase in heavy precipitation events since 1950 but in 45 out of 47 there is only low confidence of a human contribution. Note the base line is now 1950 and not 1850-1900.

Similarly in the next picture entitled:-

c) Synthesis of assessment of observed change in agricultural and ecological drought
and confidence in human contribution to the observed changes in the world’s regions.

it is said that in 12 out of 47 regions there has been an increase but in 45 out of 47 there is no evidence of a human contribution. Note also that some of this is based on simulated changes in total column soil moisture,

For both examples (b) and (c) it is not stated what the level of increase was and whether it was beneficial or not.

It is interesting to compare these pictures and the data with the text at A.3.2 where it states

The frequency and intensity of heavy precipitation events have increased since the 1950s over most land area for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver.

Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to increased land evapotranspiration (medium confidence).

At best these statements are grossly misleading when set against the data above and therefore are not to be relied upon.

At A.3.4 it is stated

There is low confidence in long-term (multi-decadal to centennial) trends in the
frequency of all-category tropical cyclones. Event attribution studies and physical understanding indicate that human-induced climate change increases heavy precipitation associated with tropical cyclones (high confidence) but data limitations inhibit clear detection of past trends on the global scale.

Simplified this means that globally it has not become stormier and it is not possible to know whether current storms produce more intense rainfall than happened in the past.


Throughout the Summary mention is made of attribution studies.

Another peer reviewed publication has just pointed out that nearly all such studies depend on methodology developed in 1999. This methodology is now said to be flawed and hence any claims of weather events being attributed to human-induced climate change cannot be relied upon.

Elsewhere no explanation is provided for the apparent overall stability of the Antarctic Ice sheet (parts losing and parts gaining ice). Statements are made about Arctic sea ice and glaciers which appear to be at odds with well-recorded historical events.

The rest of the summary about the future is speculation based on flawed assumptions made in section A set out above.

There is no mention of the beneficial effects of increased levels of carbon dioxide and warmer temperatures.

This is not science; it is a selected set of data, manipulated in a selective manner and based on flawed methodology. It attempts to re-write history but fails.

via NOT A LOT OF PEOPLE KNOW THAT

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August 27, 2021 at 04:06AM

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