Yes, “human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events” over much of the NH

Do climate scientists have to caveat every attribution? Not until reporters do.

Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas.

This statement is, according to NYT opinion blogger Andy Revkin, so unacceptably definitive as to warrant a whole blog post:  “In scientific literature you rarely see statements so streamlined and definitive. For climate science, this is the equivalent of a smoking gun.”

Actually, the statement isn’t a terribly strong one for the scientific literature, particularly given the use of the phrase “have contributed,” and most especially for a study about the trend in increased heavy precipitation, which is a trend many other studies have identified and is a very basic prediction of climate science.

A key reason Revkin’s piece (which cites a blog post by Roger Pielke, Jr.)  — and one by Time‘s Bryan Walsh (which cites Pielke and a blog post by Judith Curry) — are picking the wrong fight is that this particular climate impact is very basic physics.

Dr. Kevin Trenberth, head of NCAR’s Climate Analysis Section, has explained the connection between human-caused global warming and extreme deluges:  “There is a systematic influence on all of these weather events now-a-days because of the fact that there is this extra water vapor lurking around in the atmosphere than there used to be say 30 years ago. It’s about a 4% extra amount, it invigorates the storms, it provides plenty of moisture for these storms and it’s unfortunate that the public is not associating these with the fact that this is one manifestation of climate change. And the prospects are that these kinds of things will only get bigger and worse in the future.”

Trenberth has further said, “It’s not the right question to ask if this storm or that storm is due to global warming, or is it natural variability. Nowadays, there’s always an element of both.”

I asked Trenberth for this opinion on these critiques.  His reply gets to the heart of the matter:

To me the arguments are all wrong.  Rather than proving that there is a human influence we should be trying to prove there isn’t.  Given that there is a human influence on climate and the oceans have warmed, etc.,  how can there not be an influence on water vapor and precipitation?  The physical relationship is so strong that it has to be,  and one should then have to prove otherwise. To do that one has to use the same flawed models, and so one can not prove the reverse.  That should be the challenge to Pielke Jr and Curry.

So my criticism is first that the scientists even try to do this and pretend (or have a null hypothesis) that there is no human influence when the whole system is crying out that there is. The fact that these studies show a convincing relationship in spite of the inadequate tools shows how robust it is,  and indeed it relates to basic physics.  But the details are certainly questionable in several respects.

The robust features relate to the warming,  the increased water holding capacity, the observed increased atmospheric moisture,  and thus the supply of moisture for all storms.  The changes in storms themselves, where they go,  how long they last, and the overall precipitation amount are more uncertain,  but the increases in intensity of events are surely robust.


Revkin goes on and on about how the Nature piece “Human contribution to more-intense precipitation extremes” (subs. req’d) supposedly failed to put in enough caveats to suit his taste.  But in fact it ends with the sentence, “There are, however, uncertainties related to observational limitations missing or uncertain external forcings and model performance.”

And its key Figure 3 — “the results of four optimal detection analyses using the time evolution of extreme precipitation indices averaged over the Northern Hemisphere, over northern mid-latitudes and northern tropics individually” — has the requisite error bars:

Results from optimal detection analyses of extreme precipitation indices.

I won’t explain these figures in detail except to point out that they chart  “Best estimates (data points) and 5-95% uncertainty ranges (error bars).”  These are pretty straightforward caveats.

Scientists do not have to caveat every single sentence or paragraph in a scientific paper.

Revkin actually queries coauthor “Gabriele C. Hegerl of the University of Edinburgh, someone whose expertise I’ve drawn on many times over the years” about this.  She replies:

The paper is restricted in length, and that is particularly the case for the abstract (there are tough length guidelines). Therefore, it is not always possible to discuss findings in the detail that would be desirable IN THE ABSTRACT. As Myles [Myles Allen, an author of the other precipitation/climate paper] pointed out, ‘detection and attribution’ is code for a hypothesis test, meaning that we are checking this hypothesis at some confidence level. Every specialist in the area will understand this, and every scientist who looks at abstract AND figures will as well (common practice), and the remaining text is very explicit about methods and the accounted for uncertainties.

Figure 3 shows the results with 5-95% confidence ranges, showing that there is uncertainty in the findings.

The data uncertainties affect all results including the enhancement in observations relative to models.

So, of course there are uncertainties in the findings, as in any attribution and detection result, there is a remaining chance that the observed change is due to internal climate variability (5-ish %) particularly if the models would underestimate that variability. Natural forcings are expected to cause weak changes over that period.

The Nature paper is written for other scientists.

Revkin not only buries the lede, he never bothers to explain precisely what Hegerl’s statement means in lay terms.  Since he doesn’t correct her in the text, I’m going to take her statements at face value.  A couple of commenters, notably dhogaza, who often comments on CP, too, notes, “95% significance is “pretty definitive”.”  We can go a farther than that.

The language that the IPCC uses for statements that are not 100% certain is spelled out here.  For things that are 95% probability, the phrase is “Extremely likely.”  You can see here how the IPCC uses that here in the Fourth Assessment:

The observed warming is highly significant relative to estimates of internal climate variability which, while obtained from models, are consistent with estimates obtained from both instrumental data and palaeoclimate reconstructions. It is extremely unlikely (<5%) that recent global warming is due to internal variability alone such as might arise from El Ni±o (Section 9.4.1). The widespread nature of the warming (Figures 3.9 and 9.6) reduces the possibility that the warming could have resulted from internal variability. No known mode of internal variability leads to such widespread, near universal warming as has been observed in the past few decades.

So the much ado in Revkin’s post is all because the authors say don’t say “it is extremely likely that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events.”

Misleaders!  Cue the Spanish Inquisition.

Yet for all of the complaining about the lack of sufficient caveats in the attribution, it would be nice if, for once, Revkin would caveat attributions to Pielke’s blog posts by noting that those posts and other writings have been extensively debunked by leading climate scientists (see various links in Foreign Policy’s “Guide to Climate Skeptics” includes Roger Pielke, Jr. and Trenberth’s review of Pielke’s book in Science).  The same goes for Walsh quoting Curry, who has arguably surpassed even Pielke in the breadth and depth of debunking by scientists (see a partial list here, and Skeptical Science here.).

I’m not talking about the occasional critique that everyone who blogs is subject to — I’m talking about detailed scientific or technical take downs of many different posts by many different scientists over an extended period of time.  Surely that warrants at least a brief caveat if one is going to cite either Pielke or Curry in order to critique the work of climate scientists in a major study in Nature, no?

And getting back to Revkin, he bizarrely double downs on the most unscientific statement he has ever written:

As I wrote recently, there seems to be an inverse relationship between the definitiveness of an assertion and its credibility. This doesn’t mean that everything definitive is wrong (only Joe Romm could find a way to interpret it thus). It means that a reporter, or citizen, confronted with a flat statement on a tough issue would do well to dig a bit deeper.

No.  Not even close.

There does NOT seem to be an inverse relationship between the definitiveness of an assertion and its credibility in climate science.  It remains a generally laughable statement for a science journalist — one that is utterly false as a rule in science and especially in climate science.  It is the whole point of science to allow us to make credible assertions as definitively as possible.

Try reading the IPCC reports, especially the summary for policy makers — they are filled with highly caveated statements where definitiveness and credibility are as closely aligned as is possible, as in the quote above.

It is particularly remarkable that Revkin would repeat the statement in this blog post because, as he himself seems to have shown, the attribution finding was “extremely likely” — hardly an inverse relationship between the supposedly definitive nature of the finding, which, again, was merely that “human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events.”  As Trenberth says, that conclusion is obvious and entirely expected.  The burden of proof should be on those trying to disprove that statement.

It is time for Revkin to retract the statement.

I would note that the Nature study does not extend beyond the year 1999, so it misses the hottest decade on record and the wettest year on record.  How much do you want to bet that when the analysis is done in a few years that includes 2000 to 2010 it yields an even more confident conclusion?

This kerfuffle actually misses the most important conclusion of the study:

Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.

Apr¨s nous le d©luge!

Related Posts:

A new study by a Duke University-led team of climate scientists suggests that global warming is the main cause of a significant intensification in the North Atlantic Subtropical High (NASH) that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the southeastern United States“¦.

The models – known as  Coupled Model Intercomparison Project Phase 3 (CMIP3) models – predict the NASH will continue to intensify and expand as concentrations of carbon dioxide and other greenhouse gases increase in Earth’s atmosphere in coming decades.”This intensification will further increase the likelihood of extreme summer precipitation variability – periods of drought or deluge – in southeastern states in coming decades,” Li says.


26 Responses to Yes, “human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events” over much of the NH

  1. paulm says:

    The guy is such a waste of time.

  2. Dana says:

    It’s worth noting that Hegerl has done some really good work in the climate science field (particularly on climate sensitivity), and has much more expertise in the field than Revkin, Pielke Jr., Curry, etc.

    These guys love to create manufactured controversies rather than put in the time to understand what climate scientists are really saying. Curry most notably in her recent rehashing of “hide the decline”.

    Curry is also a noted uncertainty inflator, so it’s not surprising that she takes offense to any wording communicating any level of certainty. She has said we can’t narrow down climate sensitivity any more than 0–10°C for 2xCO2 at a 90% confidence level, which is absolutely absurd.

  3. Richard Brenne says:

    One needs to keep in mind that scientists feel that virtually nothing is 100 per cent certain, for instance all existence could be a dream, a bad episode of Dallas or both.

    Thus it is only “extremely likely” (or maybe “extremely extremely likely”) that when you jump up on a trampoline on Earth, gravity will bring you back down.

    And so avoiding Dick Caveats (and vice-versa) for human-speak: “Humans are warming the climate. Period.”

  4. Joan Savage says:

    Trenberth’s “Rather than proving that there is a human influence, we should be trying to prove there isn’t,” definitely would benefit from some explanation to the public about a scientific hypothesis, which is expressed in the negative. It would also help to show how a scientific proof is established differently from a legal proof.

    With that in mind, I wholeheartedly endorse the intent of his suggestion!

    The non-human influence factors are part of the matrix of variability. Are they enough to explain the pattern of events? Not.

    Let’s not have a narrow list of changes, either. Include meteorology and ocean heat retention of course, but everything is fair game: permafrost melt, biotic migration, insect infestations, drought depth, the works.

  5. Steve Bloom says:

    What’s even more depressing is the number of important new results that Revkin ignored in order to devote space to this ridiculous confabulation. I’m thinking in particular of the NSIDC permafrost paper, but there are others. Revkin really is getting deeper and deeper into his genteel form of denial (i.e. admit the science but deny that anything very bad can happen very soon).

  6. Mark Shapiro says:

    Revkin said:

    “It means that a reporter, or citizen, confronted with a flat statement on a tough issue would do well to dig a bit deeper.”

    Yeah. F’rinstance, rather than stop after the opening paragraph, he could finish reading the article, and maybe even look at the pretty graphs. Now that would be some real investigative reporting!

  7. Leif says:

    It would be interesting to poll Doctors on the probability of dying if you fell out of a five story window. My guess it would not be 100%.

  8. Also surprised Andy decided to critique a press release when the real issue in both studies was solid attribution of impacts from pre 2000 warming of only .4-.6 C. Those temps are less than where are today and a hell of lot less than where we’re headed. That is the real story and the one I wrote for IPS

    In the same article I also reported on some of the recent extreme weather costs and on a solution : 95 percent of all energy can be renewable by 2050… plus a five- to six-trillion-dollar “windfall” for humanity by 2050.

  9. Barry says:

    Sure seems like folks like Revkin and Curry really “need” climate science to be far more uncertain than it is. Once you stake out that position publicly, as they both have, it is very hard to save face as climate impacts get worse.

    Reminds me of that study just out that showed GOP folks were much more likely to agree that “climate change” was happening than that “global warming” was happening. It seems it has to do with them not wanting “global warming” to be true because they see it as coming with changes to their lives they don’t like.

    It is not about the science. It is about their personal narrative.

    For Revkin it seems what really bugs him is a sense of “confidence” by climate scientists. He just doesn’t like them to be sure of what is happening. The threat is in the certainty for him.

    Maybe he would be happier being a technical editor for science papers.

  10. George Ennis says:

    “As I wrote recently, there seems to be an inverse relationship between the definitiveness of an assertion and its credibility.”

    That seems credible some of us may have heard about this scientist who has definitively asserted “that every massive particle in the universe attracts every other massive particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.”

    Perhaps Revkin should be looking at this bald assertion, by Isaac Newton.

  11. Dappledwater says:

    Steve Bloom @ 5 – Revkin really is getting deeper and deeper into his genteel form of denial

    Yeah, they even have a name for that – concern troll

    “In an argument (usually a political debate), a concern troll is someone who is on one side of the discussion, but pretends to be a supporter of the other side with “concerns”. The idea behind this is that your opponents will take your arguments more seriously if they think you’re an ally.”

  12. David B. Benson says:

    Warmer air holds more moisture.

    It isn’t that hard, y’know.

  13. Dappledwater quotes from Urban Dictionary:

    The idea behind this is that your opponents will take your arguments more seriously if they think you’re an ally.

    I never paid Revkin any attention (OK there was that first day until about ten minutes into looking at his blog) since it was pretty obvious that he was into the “objectivity as balance” school of thought. However, regarding “concern trolls,” even if people do not take the arguments seriously many of them are bound to find it somewhat demoralizing that someone “on their side” is expressing paralyzing doubts so divorced from reality. The greater the justification for their views and the lack of justification on the part of the concerned troll the more demoralizing — that is until you figure out his game.

  14. Aaron Lewis says:

    There are so many lines of evidence, that falsifying the theory of anthropogenic global warming would shake modern science to its core and falsify most of its tenets. The odds of that happening are trivial.

    At this point, we are far enough along the path of AGW that the excess heat affects every aspect of our climate and weather. If the science was uncertain, we would need caveats. If the effects were uncertain we would need caveats. However, the science is certain, and the effects are as predicted. When we see the predicted effects, we should stand up and tell the whole truth. We saw it! We did not see 95%, we saw the whole thing.

    I figure anybody that puts in extra weasel words, is getting paid by the word.

  15. Mossy says:

    Simply put, Andy doesn’t get it. At a forum, after my husband asked a question, Andy queried, “First of all, what is “IT?”

    Later, in response to another question, Andy pointed at my husband and said, “That man’s grandchildren will be fine.”

    The grandchildren are 3 and 7. They should be alive for most of this century. We fear greatly for them.

  16. David Graves says:

    Then there is the Andy Revkin argument that the email hack at East Anglia Uni. somehow was not a crime. Tortured logic indeed.

  17. Colorado Bob says:

    Observed events will run over these debates, like a cross town bus. They already have, the data looking backwards will take all or breath away.

    There is 1 form of life that no one has looked at viruses. Nothing on earth rolls generations as fast as viruses. Nothing on earth can share information like they do. How will 5C warmer affect them ?

  18. Mike says:

    The common flu, the influenza virus, might become less of a problem, but the West Nile virus may become more of a concern. Medical researchers who study climate change have looked into this, but I am sure there are a lot of unknowns.

  19. Mike says:

    The thugs are coming. In rare moment of openness A Watts reveals his true face:

    Update: James Taylor’s post on Forbes supports our position. A number of alarmists have been organized to team up on the comment section to defend the undefensible. Please add your voice of support to shout them down in the comments section.

    No pretense that this is a debate about science.

    You can find James Taylor’s Op-Ed piece here: Global Warming Alarmists Flip-Flop On Snowfall. If you disagree with him, be respectful and explain your reasons. Ignore the goons.

  20. Lewis C says:

    Leif – you’re quite right, some would survive.

    We’ve just had a climber fall off a mountain in the north of the UK, with his body careening off scree and crags and boulders till it came to rest over 1,000 feet below the rest of his group.

    They phoned for the air-ambulance chopper.

    When it arrived it went first to the group, who pointed over the edge. It descended and eventually found a man standing looking at his map. He waved and they put a man down to him, and found that he was bleeding, battered and shaking, and had been wondering how to climb back up !

    I guess the moral of the story is the antidote to defeatism – you never know your luck and, regardless of the odds, you should never ever give up trying.



  21. MarkB says:

    The Earth is not flat. I say that definitively. By Revkin’s logic, my assertion isn’t credible.

  22. Prokaryotes says:

    “The common flu, the influenza virus, might become less of a problem, but the West Nile virus may become more of a concern. Medical researchers …”

    CC is a threat multiplier and because CC weakens the health (plus more stress), makes the influenza not a less a problem. The question is if humans are better off with the natural training of the immune system or with current approach to engineer virus defends.

  23. Steve UK says:

    Dr Romm,
    Trenberth’s quote in the above piece seems to have sprouted a crop of commas where they are not needed. A minor point, but it would be more readable with a bit of editing.

    [JR: Fixed!]

  24. Anne van der Bom says:

    It seems as if everybody is caught in the latest denier fad, called ‘uncertainty’. Even reporters like Andy Revkin, that I consedered to be serious, mindlessly jump on the uncertainty bandwagon.

    With the ‘Global warming has stopped’ incantation rendered powerless by Nature, the denier cult shifted to a new one. And unfirm journalists get taken in.


  25. with the doves says:

    Revkin has a niche – explainer of mysteries of science to the bourgeois but not scientifically literate who follow him. If actual scientists are clear and straightforward enough, Revkin’s niche disappears.

    So he bites back with this concern trolling to defend his turf.

    I heard him on the radio once. He came off as self-referential and not very informative.

    Thanks as always for your work here.

  26. climate undergrad says:

    What’s ironic is that revkins inverse-relationship assertion, I think, can hold weight in certain cases.

    Think, “climate change is a hoax” or the NIPCC conclusions, etc…. Most denier points are accompanied by exactly ZERO mention of the uncertainty of their claims.

    In the peer-reviewed science, however, this relationship clearly does not apply.