Consensus on Consensus

Consensus on Consensus

Originally published in Corporate Knights Magazine


In 1998 and 1999, American scientists Michael Mann, Raymond Bradley and Malcolm Hughes published two papers that reconstructed the average temperatures of the northern hemisphere back to the year 1000. The articles showed a temperature profile that gently declined from 1000 to 1850, fluctuating a little along the way, with a sudden increase in the late nineteenth and the twentieth centuries.  The graph was nick-named “the Hockey Stick”, with its long relatively straight handle showing the stable pre-industrial climate and the blade representing the sudden uptick in the last 150 years.

The diagram was a striking depiction of the abrupt warming that had occurred since the Industrial Revolution compared to what happened before. For those opposed to the scientific consensus on Anthropogenic Global Warming (AGW), the Hockey Stick posed a threat and had to be broken. Continue reading

No global warming since February 2016

No global warming since February 2016

Forgive the facetious, click-bait headline.

The NASA GISTEMP global temperature anomalies for March are now available. March 2016 had by far the largest temperature anomaly (1.28°C) for any March on record and the second highest anomaly for any month ever, beaten only by February 2016 (1.34°C), hence the snarky headline.

Here is the plot of month-by-month anomalies for recent warm years.


Clearly, my guesswork, what-if, forecast for the year is still running one-tenth of a degree cool. The NOAA forecast is for the El Niño to end in the next few months, with a rising probability of a La Niña forming in the latter half of the year. Continue reading

James Powell is wrong about the 99.99% AGW consensus

James Powell is wrong about the 99.99% AGW consensus

In a recent article in Skeptical Inquirer, geologist and writer James Lawrence Powell, claims that there is a 99.99% scientific consensus on Anthropogenic Global Warming (AGW). You might think that after all of the harsh criticism that the 2013 Cook et al. paper (C13) has received from climate contrarians that we would be pleased to embrace the results of a critique that claims we were far too conservative in assessing the consensus. While it certainly does make a nice change from the usual rants and overblown methodological nit-picks from the contrarians, Powell is wrong to claim such a very high degree of agreement.

He makes many of the same errors that contrarian critics make: ignoring the papers self-rated by the original authors; and making unwarranted assumptions about what the “no-position” abstracts and papers mean.

Powell’s methodology was to search the Web of Science to review abstracts from 2013 and 2014. He added the search term “climate change” to the terms “global climate change” and “global warming” that were used by C13.  He examined 24,210 papers co-authored by 69,406 scientists and found only five papers written by four authors that explicitly reject AGW. Assuming the rest of the abstracts endorsed AGW, this gives consensus figures of 99.98% (by abstract) and 99.99% (by author).

His definition of explicit rejection would align roughly with the seventh level of endorsement used in C13: “Explicitly states that humans are causing less than half of global warming” . In the abstracts from 1991-2011, C13 found 9 out of 11,914 that fit level 7, which using Powell’s consensus calculation assumptions, would yield 99.92%. So, there is probably not much difference between the two approaches when it comes to identifying an outright rejection paper. It’s what you assume the other abstracts say—or do not say—that is the problem.

C13 also counted as “reject AGW” abstracts that: “Implies humans have had a minimal impact on global warming without saying so explicitly, e.g., proposing a natural mechanism is the main cause of global warming”. These are more numerous than the explicit rejections and include papers by scientists who consider that natural causes are more important than human causes in recent warming, but who do not outright reject some small human contribution.


Competing Climate Consensus Pacmen. Cook on the left, Powell on the right.

Continue reading

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