A new study published yesterday by climate activist Michael Mann is coming under scrutiny from other climate experts because it claims any warming since 1950 is 100 percent man-made and that since 2000, 13 of those years had record-breaking temps. But Mann’s study does not adequately account for natural variability such as ocean oscillations, which have been shown to dramatically affect the climate. Published in Nature Scientific Reports and co-authored by an environmental group, it shows there have been a string of record-breaking ‘hot years since 2000’ that Mann says is ‘almost certainly a sign of man-made global warming.’
The so-called hottest years also fall within the global warming hiatus, a time frame lasting nearly 19 years before a strong El Niño in 2015 raised temps worldwide. Both the UN’s Intergovernmental Panel on Climate Change (IPCC) and leading climate scientists have acknowledged this hiatus. That’s because the satellite record dataset shows no statistical increase in warming as predicted by global warming theory. Even land- and sea-based temperature stations show much less warming than predicted by climate models.
The study, which relied primarily on computer simulations and dubbed itself “semi-empirical,” indicated it “estimated the chance of the record run – with up to 13 of the 15 warmest years all from 2000 to 2014 – was between one in 770 and one in 10,000 if the series were random with no human influence.” Mann, a professor of meteorology at Pennsylvania State University, told Reuters that “climate change is real, human caused and no longer subtle.” He set out to prove what he believes to be fact.
One of the study’s co-authors, Stefan Rahmstorf of the Potsdam Institute of Climate Impact, said in a statement, “Natural climate variations just can’t explain the observed recent global heat records, but man-made global warming can.” The scientists tried to account for factors including “heat from one year spilling into the next.” Except “temperatures in many years are almost identical, making it hard to rank their heat with confidence.”
Mann, who is an advocate of catastrophic man-made global warming, has done paid speaking engagements, environmental activist videos, lectures, written books (Dire Predictions, The Hockey Stick and the Climate Wars), numerous articles, and more. He has called anyone that doesn’t believe in the catastrophic man-made global warming narrative ‘anti-science.’ He also said in legal court documents (page 2, paragraph 2) that he had been “awarded the Nobel Peace Prize.” He wasn’t.
Nic Lewis, a leading climate scientist in the UK, writes in an email that Mann’s latest study is a “scientifically valueless paper even if it is 100 percent correct.” That’s because there is “nothing in this study that considers the probability of the high, recently recorded temperatures having arisen in the case where there is an anthropogenic [man-made] component, but it is less strong than simulated by the CMIP5 models, e.g. because they are too sensitive.” He also says the “analyses” they cite in the study’s intro is an “editorial comment” by Michael Mann.
First, Mann et al had to devise a simulation using computer models to create the following scenario: what observed temperature records would have been with and without human influence. That may explain why Mann recently tried to discredit the satellite dataset in an environmental group’s video, as it shows no statistical global warming for the past 18 years 8 months. And 2015, which wasn’t included in this study, was as warm as 1998 due to a naturally occurring El Niño event and the Pacific blob.
“The analysis of Mann et al. glosses over three major disputes in climate research, ” Judith Curry, a climate scientist and Georgia Tech professor, writes in an email. “These disputes are errors and uncertainty in the temperature record” and “reconciling the surface temperature record (which shows some warming in the recent decades) against the global satellite record (which shows essentially no warming for the past 18 years).”
Curry says that for the past decade, “global average surface temperatures have been at the bottom of the envelope of climate model simulations.” To separate out what is natural and what is man-made, Mann et al use the “method of Steinmann et al to infer the forced variability (e.g. CO2, solar, volcanoes), calculating the internal variability (e.g. from ocean circulations) as a residual.”
She says the multi-model ensemble used by Steinmann et al assumes that all the recent warming is caused by carbon dioxide (CO2). Curry et al, led by Sergey Kravtsov, recently published a paper in Science arguing that the Steinman et al method is flawed, “resulting in substantial underestimates of the internal variability from large-scale, multi-decadal ocean oscillations.”
Curry, who also runs the popular website Climate Etc, also notes that global temperatures have been increasing for more than 200 years and that man-made CO2 emissions can’t explain the “significant amount of this warming prior to 1950.” She says that figuring out how to attribute the recent variations in global temperatures are still an issue associated with “substantial uncertainty.”
And while Curry subscribes to the basic tenets of man-made global warming, Mann and some climate scientists consider her moderate views “anti-science.” They believe the sun, volcanic activity, and ocean oscillations play little to no role in Earth’s warming. This is despite any statistical warming since 2000.
“The latest IPCC assessment reports conclude ‘more than half’ of the warming since 1950 is caused by humans, with more than half implying greater than 50 percent,” Curry points out. “This assessment acknowledges uncertainties in climate models, which finds that some of the warming since 1950 is caused by humans.”
The Mann et al paper is assuming that “all of the warming has been caused by humans,” which “given our current state of knowledge is an unwarranted assumption,” Curry says.