The California Drought and Climate Change: Revkin and Hoerling

I think Revkin and Hoerling deserve a shout-out for this piece in terms of explaining how the IPCC reached their conclusion. Revkin quoted from a note from Martin Hoerling, a NOAA scientist, so I guess Dr. Hoerling has a gift for explaining things at what I consider the right level of detail (I know this is in the eye of the beholder). Here’s a link to the Revkin blog post. Below is part of the quote from Hoerling’s note.

Concerning the “debate” highlighted by the above exchanges between Pielke and Holdren, the issue isn’t about analogues to past droughts (which, by the way, the California resource managers were more interested in), but about the scientific evidence that California droughts have become more severe due to climate change.

To the extent that precipitation is key, it can be said with high confidence that there is no trend toward either wetter or drier conditions for statewide average precipitation since 1895, so that has not likely been a player. But there are other indicators, and aspects of rainfall behavior that could be conducive to drought, even if the mean seasonal rainfall isn’t changing. What is the evidence there?

The argument hinges mostly on temperature and how it may be affecting water resources. (Never mind, by the way, that the farmers and water managers are praying to the heavens for rain, not for cooler temperatures, to bust their drought!).

A way of integrating the effects of temperature on drought is to examine soil moisture time series. These have been assessed (based on simulations with sophisticated land models), the results of which are summarized by the IPCC (2012) report on extreme events (for which this drought qualifies). The Palmer Drought index and simple counts of consecutive dry days have also been diagnosed. That latest 2012 report, (the so-called SREX report) in their Table 3-2 examines the evidence for regional changes since 1950, and makes the following assessment of these various indicators for western North America:

“No overall or slight decrease in dryness since 1950; large variability; large drought of the 1930s dominate.”

The team of 42 authors assigned a “Medium Confidence” to that assessment. The report’s team in Table 3-3 then goes on to assess the scientific evidence for how drought in this region will change in the 21st century. They write:

“Inconsistent signal in consecutive dry days and soil moisture changes,” to which they assign a low confidence.

It is quite clear that the scientific evidence does not support an argument that this current California drought is appreciably, if at all, linked to human-induced climate change.

This is not to say that a warmer climate can’t and won’t act to decrease soil moisture. It simply reminds us that the current drought event, like its historical ancestors, continues to be strongly driven by the vagaries of storm tracks and the manner in which rains are delivered to the narrow stripe of the U.S. West Coast.

13 thoughts on “The California Drought and Climate Change: Revkin and Hoerling”

  1. the dilemma with the term “vagaries of storm tracks” implies an almost eccentric wandering unconnected to climate drivers. The latest evidence, according to climate scientist Branwen Williams at the Keck Science Department of the Claremont Colleges, suggests that those tracks — notably the jet stream — appears to have shifted a half of a degree north, a relatively small northward movement that will have major impact on whether precipitation reaches, for example, southern CA. I captured some of her other concerns as raised at a water scarcity conference in Claremont last weekend:

    • It’s a good question as to how those relate.. while I am asking around.. here is something Roger Pielke, Jr. posted from Michael Tobis that is pretty nuanced on the climate signal in extreme events question and why they don’t agree.

      Here’s what Roger says:
      “Interesting comments from Michael Tobis. Unlike some of his fellow travelers, he is fair and also correct:”

      Here’s what Michael Tobis said:

      “While I don’t think [Pielke’s] recent congressional testimony was helpful, I can’t help but see his point that Holdren’s response to it was both inappropriate and unconvincing. I wish Holdren had found firmer ground for his response.

      It also seems that there is a genuine rift in the climatological community about how to discuss the relationship between severe events and anthropogenic climate change. As always, I would recommend that society base its actions on IPCC WG I. It is also the case that, like it or not, WG I’s position is closer to Pielke’s position than to Holdren’s.

      I don’t particularly think that those of us (I include myself) who think there is a climate change footprint in severe events already need to shut up about it. But neither do I think we should pretend that our position is scientific consensus.

      The epistemic issues here are subtle and this is hard to work out in public. I think that the Pielke/Hoerling position is statistically naive, and the upshot is probably wrong. Explaining this in plain language is an interesting challenge. It may not be especially easy winning the scientific debate, either.

      Meanwhile it is important not to base defense of a strong climate on the as-yet hard-to-prove emergence of a change in specific classes of severe events at specific locations. That’s hardly the only reason for concern.

      And on this point Roger has a point. Why select unfavorable ground for your battles? The answer, of course, is the press’s obsession with disasters, and the politician’s hunger for press. Perhaps we should do something other than capitulate to it.”

      Here’s a link to Tobis’s comment:
      Here’s a link to Roger’s cite of it.

    • Thank to Roger Pielke, Jr. for helping me out with this… I am assuming that “shifting” and “wavy” are more or less describing the same kinds of observations/projections about the jet stream… if not, can someone please clarify?

      Here’s a discussion of the wavy jet stream idea in Science by Wallace et al.. here (note: you can register with Science and not pay to access this article. You do have to pretend you want to buy scientific equipment).

      “In contrast to the above examples, the notion that the demise of Arctic sea ice during summer should lead to colder winter weather over the United States seems counterintuitive. But that is exactly what an influential study has suggested (2). The authors hypothesize that global warming could perturb the polar vortex in a manner that renders the flow around it more wavy, leading to an increased incidence of both extreme warmth and extreme cold in temperate latitudes. It’s an interesting idea, but alternative observational analyses and simulations with climate models have not confirmed the hypothesis, and we do not view the theoretical arguments underlying it as compelling [see (3–6)]. ”

      and one in climate central blog..

      The work of Dr. Jennifer Francis and Steven Vavrus shows that as the Arctic warms faster than the tropics, a lessening of the temperature gradient between the equator and the North Pole slows the jet stream. As the jet stream slows, it supports a “wavier,” more frequently amplifying jet that increases the probability of extreme weather events, known as Arctic amplification.
      “However, not all research supports Arctic amplification and its impacts on mid-latitude weather patterns. For example, Screen and Simmonds (2013) tried to link the two through planetary wave patterns and did not find any clear trend. And recently, Barnes (2013)found no significant increase in the frequency of blocking events over North America and the North Atlantic, indicating that severe mid-latitude storms cannot simply be understood through Arctic amplification alone. This research does not mean that Francis and Vavrus’ hypothesis is wrong, it simply means that the atmosphere is complex and more research is needed.”

      I thought the scientists on this blog might appreciate the idea that contrary evidence means that “the atmosphere is complex and more research is needed”.. which is, of course, true, but also the rationale for an infinite blank check. Which could arguably be better spent, as the Californians are pointing out, dealing with the real world challenges regardless of “the reason this is happening.”

      Finally I think I did one of the dumbest blogging things ever, which was to post my request for info in the “rejected comments” section of Roger’s blog. Nothing like shooting yourself in the proverbial foot ;)!

  2. A life time fisherman, and now commercial salmon troller, returning to what I did in the 1960s and 1970s, I have followed salmon abundance for more than 50 years. It seems to ME (one person with no research to quote) that the abundance of all five species of salmon is cyclical, and the cycles work at and on latitudes. Abundance in the north and scarcity in the southern ranges. And then it reverses. Wild or hatchery, all have to grow and succeed in the ocean after or when or even if they get there as smolts or fingerlings. Big years in Alaska, and no fishing in Oregon and Calif. And now we see half of “normal” (or is that preferred?) runs to the north, with ESA possibilities for Yukon and Kenai chinook. And then the run forecast for the Columbia River comes in at three to four times the recent average annual returns for fall chinook. 1,600,000 forecast fall run. I thought that to be mind boggling. And the Klamath River return of over 300,000 adults last fall, and the attempt by the Westlands Irrigation District in the CA Central Valley to block sending BurRec water down the Trinity to cool the lower Klamath to prevent a die off in a drought was astounding and so selfish as to be stupid. The outcome in Federal Court of that, was the injunction was lifted, the water released, and no die off. Thank a dam for that. The lower Trinity tribes shot across the bow of irrigators, quoting their treaty for the creation of the Trinity River dam and noting diversion could be up for a new look-see and cultural rights will be addressed. The Court decision awarding the Klamath Treaty Tribes the #1 water right for the Klamath River in Oregon was certainly on their minds. Nice to see the Tribes playing hard ball with the arrogant CA irrigators. Salmon are the Indian raison d’etre. The essence of their beings. And CA had a big, albeit hatchery origin, run of chinook last year, and great fishing for tribes, sports and commercial alike.

    And then I read two days ago that the Fraser River sockeye (red) run 2014 forecast was for 72,000,000 fish!!! Mind boggling number. There was this “anomaly” run of an estimated 35 million reds up the Fraser in 2010, ( reds are a 4 and 5 year return fish), a run which there was no preparation for, no seasons and management in place for. It was a rodeo, and most of the traditional net fisheries went wanting, as did the intercept troll fishery in Johnstone Strait and in Georgia Straits. The upriver “First Nations” people hammered them by any and all means. Didn’t make a dent, apparently. So now there is this pre-European settlement fish run predicted. My question, of course, is how do you explain the returns in light of climate change and global warming? Is the current weather no more than a return to a past norm? If you read Oregon history, we had a major malaria outbreak along the Columbia River in the era of 1830-34. Decimated the Native American population. How warm does it have to be to allow that particular mosquito to survive and breed?

    There is a mediocre forecast for Bristol Bay reds in the north of Alaska. It’s an “even” year, which is the off year for the two ocean pink or humpy runs that were phenomenal last year in SE Alaska( a total catch of over 100 million fish). The AK trollers are very limited to chinook by coast wide treaty clear to Mexico, and only get their allowed quotas. CA trollers caught more chinook in 2013 than AK trollers did. But the southern components of the chinook biomass is evidently doing quite well despite onshore drought. That, of course, will all change if there is not water again this year in the creeks and rivers. Or the forecast el Nino warms the ocean, and changes the food chain.

    And then there is the collapse of the sardine or pilchard seine fishery off the Columbia River and elsewhere. But the largest biomass of anchovy seen in decades was in Monterrey Bay in Oct and Nov 2013. Oregon pink shrimp fishers did most of their fishing off Brookings in 2013, far south of the usual fishing areas. The hake fishery was south of the Columbia and was just fine. Rock and other bottom fish seem to be recovering. Only halibut are in short numbers, and that is probably in concert with the lower biomass of salmon in the far north.

    In other words, for the most part the ocean is right now very productive, albeit predicted to go into el Nino mode next winter. My guess has to be the whole of all of this is just cyclical, and “normal” but our increased ability to detect and measure has us all a twitter over stuff that has been around forever. CA is a Mediterranean climate. I would guess lower latitudes and dry with more sun is to be expected. Add the coast range mountains to create rain shadows, and the dependence on high elevation snow for seasonal irrigation, it would follow that neither climate nor weather are going to produce a level supply/demand curve. Get over it. Stasis is not a part of climate or weather. Irrigators are still not up to speed on that concept. Yet, in SoCal, there is really no water shortage due to their decades of preparation and contingency planning, and water reserves and banking, and they are just fine. It is the Central Valley and Northern Sacramento River basin that is droughty. Mt. Shasta north is now close to average for snow and rainfall. Raining still, in wet western Oregon, where it was essentially dry from Oct 1 to Jan 10. All that changed.

    The Great Lakes are going to regain their water losses. When they are 98% iced over, ( for one of the few times in a century of records), you have no evaporation, the bane of California water supplies. Losing an inch or more a day off the top of any reservoir or lake adds up, fast. Actually, you lose less in a drought because you have lost so much water surface in the meantime. Added to the Great Lakes deal is the “lake effect” snow is now just not there, with below zero dry wind from the Arctic cold scorching the apple and peach trees on lee shores.

    So, along with huge and powerful weather anomalies in parts of the US, in other parts there is cause for celebration if predictions come true. Bad for some can be good for others. If this moisture keeps on falling in the northern Rockies, there will be big time spring freshets on the Columbia and Fraser Rivers, and not much on the Sacramento. And the whole of the US north of Oklahoma clear to the Atlantic is about to see some really destructive “break ups”, ice floe caused flooding, as spring begins its journey to the summer solstice. Deviation from the mean. It’s our life experience, really.

  3. Thanks for posting all this, Sharon. I suppose our next assignment will be to take it into the forests, but meanwhile… “I thought the scientists on this blog might appreciate the idea that contrary evidence means that “the atmosphere is complex and more research is needed”.. which is, of course, true, but also the rationale for an infinite blank check. Which could arguably be better spent, as the Californians are pointing out, dealing with the real world challenges regardless of “the reason this is happening.”

    Always the conundrum, isn’t it… too many short-term problems, too many long-term issues, too little resources. Both perspectives are “real world” in my opinion, but I would agree that a priority for California in particular is dealing with water shortages that are going to continue regardless of climate change or who/what’s responsible for it, and how to adapt a gluttonous lifestyle and economy to that reality. Thanks for all the info posted, it’s a lot to digest, and maybe a good reminder to stay well on the periphery of climate change research/politics. Interesting how very political both Holdren and Pielke are, though perhaps worth noting that Holdren really is a scientist with a background as such, and Pielke actually is not (well, he’s a political scientist, if I can be permitted that distinction). Here’s a perspective from another viewpoint, off to the left somewhere, probably the truth lies somewhere in between but concealed under the big egos involved…

  4. Couldn’t help but notice Roger Pielke Jr in the news recently….

    Here’s the full article titled, “First Climate Article On Nate Silver’s Data Website Uses ‘Deeply Misleading’ Data, Top Climatologists Say” and below are some snips:

    [Nate] Silver’s FiveThirtyEight published its first article about climate change on Wednesday, entitled “Disasters Cost More Than Ever — But Not Because of Climate Change.” But climate scientists are condemning the article and its author, Roger Pielke Jr., saying he ignored critical data to produce a “deeply misleading” result….

    “Pielke’s piece is deeply misleading, confirming some of my worst fears that Nate Silver’s new venture may become yet another outlet for misinformation when it comes to the issue of human-caused climate change,” said Michael Mann, director of the Earth System Science Center at Pennsylvania State University. “Pielke uses a very misleading normalization procedure that likely serves to remove the very climate change-related damage signal that he claims to not be able to find.”

    Pielke, a political scientist who has proven to be Silver’s most controversial hire to date, has actually been making his argument about increased disaster costs for years….

    But just as Pielke’s article has been written before, so too it has been criticized before. Dr. Kevin E. Trenberth, a distinguished senior climate scientist at the National Center for Atmospheric Research, has criticized Pielke’s data for its simplistic nature. Simply showing that an increase in damage has corresponded to an increase in wealth ignores the fact that communities are now more prepared than ever for extreme storms, Trenberth wrote at the time.

    Trenberth says data on increased disaster preparation measures should, to some degree, cancel out Pielke’s findings.

    “This is the same old wrong Roger,” Trenberth said by e-mail. “He is demonstrably wrong and misleads.”

    • Pielke relies upon the IPCC, which has this to say about disaster costs and climate change:

      Increasing exposure of people and economic assets has been the major cause of long-term increases in economic losses from weather- and climate-related disasters (high confidence). Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded (high agreement, medium evidence). These conclusions are subject to a number of limitations in studies to date. Vulnerability is a key factor in disaster losses, yet it is not well accounted for. Other limitations are: (i) data availability, as most data are available for standard economic sectors in developed countries; and (ii) type of hazards studied, as most studies focus on cyclones, where confidence in observed trends and attribution of changes to human influence is low. The second conclusion is subject to additional limitations: (iii) the processes used to adjust loss data over time, and (iv) record length.”

      As Pielke points out, “To identify changes in extreme weather, it’s best to look at the statistics of extreme weather.” Trying to infer changes in extreme weather from economic data on disaster costs is so obviously fraught with “limitations” that I wonder why scientists bother.

      As to “extreme weather” itself, the IPCC offers not much: “Extreme events are rare, which means there are few data available to make assessments regarding changes in their frequency or intensity. The more rare the event the more difficult it is to identify long-term changes. Global-scale trends in a specific extreme may be either more reliable (e.g., for temperature extremes) or less reliable (e.g., for droughts) than some regional-scale trends, depending on the geographical uniformity of the trends in the specific extreme.”

      When it comes to what the IPCC is confident of, it’s “very likely” that there has been an “overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights” at the global scale, which doesn’t sound like a “disaster” by any measure. Also it’s “likely” that more regions have an increasing versus decreasing frequency of heavy precipitation events, with lots of regional variability.

  5. Matthew… the climate change community makes the folks on this blog look like we’re sitting around holding hands and singing Kumbayah.

    Your argument seems to be that Roger’s work is suspect because Mann and Trenbarth say bad things about it. However, Mann and Trenbarth are not unbiased themselves. People in climate change blogdom spend a lot of time discussing things like this and are awash in ad hominem arguments.

    Anyway, that’s why I quoted Tobis, as he is more in the “middle” if, in fact, there is one.

    • Mann is the director of the Earth System Science Center at Pennsylvania State University, while Trenberth is a distinguished senior climate scientist at the National Center for Atmospheric Research. Those facts seem to put them a notch or two above just being “people in climate change blogdom.”

        • Sorry Matthew and Guy.. I wasn’t clear on what I was saying.. for Matthew to use what folks said about Roger’s work on something else, and use it to make a statement about his testimony (which as Andy S. points out, was based on the IPCC), I originally called an ad hominem…”on the basis of some irrelevant fact about the author of or the person presenting the claim or argument.”

          Since Matthew is the one who posted it, he seems to be saying “. Trenbarth disagrees with Roger in terms of some papers he’s published, so therefore we shouldn’t believe him when he cites the IPCC?” To me, that’s irrelevant for this post, and ergo, ad hominem. It is a kind of a scientific ad hominem, but ad hominem nonetheless.

          Then Matthew says “Trenbarth’s and Mann’s positions put them “above” “people in climate change blogdom”. Well, folks who follow this know that Mann is a colorful character and has his own issues (I couldn’t decide if putting some links here would be ad hominem, and decided just to make the statement).

          It shouldn’t be whether you have a big name or title in the field, but about whether you are right. Of course we don’t ,and won’t, know if any of these folks are “right” because it’s not that kind of science . The models depend on variables, assumptions and estimates that no one individual is responsible for, and also depends on what the world actually does with GHG’s. All we can do is make observations in the real world, but we don’t have a long enough time period to really estimate “climate” changes. So all we can do is try to match what we observe with the model projections . And there seem to be hundreds of ways to do that, with varying answers.

          Guy, I said “climate change blogdom” is awash in ad hominem arguments, not this specific article. Are you really questioning that?

  6. I’d like to see someone plug “God” or “Gaia” into these models, based on expected behaviors. Of course, some people belittle their claimed effects, or deny them, altogether. Opponents of the “God Models” deny that there is any evidence of such effects, and claim that “the science is settled”. However, there are still millions who hold fast to their faith, in both their Gods, and their models.

    Will The Real God Please Stand Up?


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