In a paper published in the journal Climatic Change in March of 2012, Kevin Trenberth ambitiously sets out to redefine science. The paper’s title is a clue–“Framing the Way to Relate Climate Extremes”. The paper’s subject is not to publish the results of a new experiment or years of analysis of data. The paper is essentially PR advice on how to convince the public that weather is now influenced by the climate change we have experienced.
The question he attempts to answer is one asked of scientists frequently: “Is it (a particular weather event) caused by climate change?” He saves his answer for the final sentence in the paper: “In reality the wrong question is being asked: the question is poorly posed and has no satisfactory answer. The answer is that all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.”
This paper is essentially a follow-on from published work in 2011 where he attempted to invert the null hypothesis regarding global warming, something that I will take up in another post. For now let me just say that it is every bit as ambitious in its attempt to redefine the norms of science as this one.
Since Trenberth’s publication, many in the media, including this section of the blogosphere, have taken his dictum to heart. People had been blaming climate change for bad weather as far back as Hurricane Katrina, but it has taken off in the past year in a big way.
This is a dramatic change from what science presented to us prior to 2012. Dramatic storms, floods and droughts were offered to us as previews of coming attractions by scientists–things that might become more common as global warming continued later in this century.
Indeed, in a sign that not everybody agrees with Trenberth, two weeks after his publication the Intergovernmental Panel on Climate Change published a special report titled ‘Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation.’
The language in the report is clear:
“There is medium evidence and high agreement that long-term trends in normalized losses have not been attributed to natural or anthropogenic climate change,” writes the IPCC in its new Special Report on Extremes (SREX) published today.
“The statement about the absence of trends in impacts attributable to natural or anthropogenic climate change holds for tropical and extratropical storms and tornados,” the authors conclude, adding for good measure that “absence of an attributable climate change signal in losses also holds for flood losses”.
However, on this topic the IPCC, normally considered the authoritative source on such issues, was ignored in favor of Dr. Trenberth’s scarier conclusions.
It is hard to know how one could either prove or disprove Trenberth’s assertion. That, of course, is why it redefines science. But there are questions that I don’t think Dr. Trenberth has been asked, or at least hasn’t answered.
Is current weather extreme by historical standards? Are droughts drier, floods wetter, storms stronger or more frequent? If so, when did this start? (James Hansen has tried to answer this question with a paper published in PNAS titled ‘Perception of Climate Change,’ (and I will address it in another post), but I don’t think Trenberth has.
Let’s look at hurricanes, for example. The National Hurricane Center published an NOAA Technical Memorandum titled “The Deadliest, Costliest and Most Intense United States Tropical Cyclones from 1851 to 2010“.
- Only one of the deadliest storms (Katrina) happened after 2000 and only one after 1950 (Audrey in 1957)
- On the other hand, all of the costliest hurricanes are very recent. Sadly, this is because they did not adjust for inflation or people moving in greater numbers to affected areas. Pielke and Landsea 1998 found no trends in normalized losses, a ﬁnding subsequently replicated by Katz 2002 . Recent analyses of longitudinal geophysical data ﬁnd that there are no trends on hurricane frequency and intensity at U.S. landfall. Landsea 2005, 2007; Emanuel 2005 . (Update: On rereading the article I note that they did try and normalize costs in a later table. They found 3 hurricanes in the top 10 costliest since 1945)
- Only two of the strongest ten hurricanes since 1850 occurred during the period when global warming is considered to have accelerated (Katrina and Andrew)
So–what does history tell us about global warming and hurricanes? I don’t know and I’ll bet you don’t either. Because there is literally no evidence that could either prove or disprove Trenberth’s assertion, there is no way of knowing.
I will be taking this up in a series of posts similar to what I just finished doing with Matt Ridley’s essay for the GWPF. But the point I want to make now is that, if Trenberth is wrong–if he’s advising scientists to tell people that any bad storm, drought or flood is caused in part or in whole by global warming–then he is giving a terrible hostage to fortune.
If your strategy for communicating urgency about climate change depends on the weather then you are vulnerable to the oldest trick in the book–when the weather is nice people don’t think about it. And if the worst phenomena occurring today are in fact previews of coming attractions, we will need more than seasonal support to address it.
- When did Xtreme Weather begin?
- How do we distinguish between events influenced by climate change and events that are not?
- What is the degree of change we see in individual events?
- What is the level of confidence in your calculations?