by Judith Curry
A changing climate means that weather-related disasters like droughts, wildfires, storms [and] floods are potentially going to be costlier and they’re going to be harsher. – President Obama
Justin Gillis of the NYTimes responded to the statements made by President Obama in his February 14 visit to California to discuss the drought, in a post entitled Science linking drought to global warming in dispute. Excerpt:
In delivering aid to drought-stricken California last week,President Obama and his aides cited the state as an example of what could be in store for much of the rest of the country as human-caused climate change intensifies.
But in doing so, they were pushing at the boundaries of scientific knowledge about the relationship between climate change and drought. While a trend of increasing drought that may be linked to global warming has been documented in some regions, including parts of the Mediterranean and in the Southwestern United States, there is no scientific consensus yet that it is a worldwide phenomenon. Nor is there definitive evidence that it is causing California’s problems.
Holdren and Romm
The main arguments being put forward regarding AGW making the drought worse seem to be put forward by John Holdren and Joe Romm. John Holdren has prepared a document entitled Drought and Climate Change: A Critique of Statements Made by Roger Pielke Jr. The existence of this document is astonishing in itself (Holdren is Director of the White House Office of Science and Technology Policy) – it was written in response to tweets and blog posts by Pielke. Joe Romm has a follow on post Climatologist who predicted drought 10 years ago says it may become even more dire. He lays out the arguments in support of global warming influencing the drought. The arguments aren’t strong, an excerpt:
In my recent comments about observed and projected increases in drought in the American West, I mentioned four relatively well understood mechanisms by which climate change can play a role in drought. (I have always been careful to note that, scientifically, we cannot say that climate change caused a particular drought, but only that it is expected to increase the frequency, intensity, and duration of drought in some regions―and that such changes are being observed.)
The four mechanisms are:
- In a warming world, a larger fraction of total precipitation falls in downpours, which means a larger fraction is lost to storm runoff (as opposed to being absorbed in soil).
- In mountain regions that are warming, as most are, a larger fraction of precipitation falls as rain rather than as snow, which means lower stream flows in spring and summer.
- What snowpack there is melts earlier in a warming world, further reducing flows later in the year.
- Where temperatures are higher, losses of water from soil and reservoirs due to evaporation are likewise higher than they would otherwise be.
Romm’s article also cites Mann:
Michael Mann, one of the country’s leading climatologists, told me:
There is credible peer-reviewed scientific work by leading climate scientists, published more than a decade ago, that hypothesized that precisely this sort of blocking pattern would become more frequent with disappearing Arctic sea ice. Moreover, Arctic sea ice has declined precipitously in the intervening decade. So it seems quite clear that there is a potential connection, in a statistical sense, between human-caused global warming, declining Arctic sea ice, and the anomalous blocking pattern this winter that has added to other factors we know are tied to human-caused climate change (warmer temperatures and increased soil evaporation, and decreased winter snowpack and freshwater runoff) to produce the unprecedented drought this year in California.
To claim that it is “quite clear” there is no connection at all turns the burden of scientific evidence completely on its head. Such a statement defies logic.
Past California droughts
MSN news has an article Past California droughts have lasted 200 years. Subtitle: Researchers have documented multiple droughts in California that lasted 10 or 20 years in a row during the past 1,000 years. Excerpts:
“We continue to run California as if the longest drought we are ever going to encounter is about seven years,” said Scott Stine, a professor of geography and environmental studies at Cal State East Bay. “We’re living in a dream world.”
Stine, who has spent decades studying tree stumps in Mono Lake, Tenaya Lake, the Walker River and other parts of the Sierra Nevada, said that the past century has been among the wettest of the last 7,000 years.
Looking back, the long-term record also shows some staggeringly wet periods. The decades between the two medieval megadroughts, for example, delivered years of above-normal rainfall — the kind that would cause devastating floods today.
The longest droughts of the 20th century, what Californians think of as severe, occurred from 1987 to 1992 and from 1928 to 1934. Both, Stine said, are minor compared to the ancient droughts of 850 to 1090 and 1140 to 1320.
Already, the 2013-14 rainfall season is shaping up to be the driest in 434 years, based on tree ring data, according to Lynn Ingram, a paleoclimatologist at UC Berkeley.
“It’s important to be aware of what the climate is capable of,” she said, “so that we can prepare for it.”
Martin Hoerling
Andy Revkin has a post entitled A climate analyst clarifies the science behind California’s extreme drought. Of particular interest to me is a note that Revkin received from Marty Hoerling of NOAA, excerpts:
Andy, I’ve been engaged in understanding this drought event, having just returned from Sacramento where I briefed a group of water managers and emergency responders on the drought. [The event: “California Drought Outlook Forum: What’s Ahead and What We Can Do.”]
This drought has many of the attributes of past historical droughts over the region — widespread lack of storms and rainfall that would normally enter the region from the Pacific with considerable frequency. It resembles the 1975-76 and 1976-77 California droughts, when two consecutive years were at least as dry as the last two years have been for the state as a whole.
The bottom line is that this type of drought has been observed before. And, to state the obvious, this drought has occurred principally due to a lack of rains, not principally due to warmer temperatures.
This may seem pretty obvious (and trivial) from simple inspection of historical observations, and indeed this drought is quite familiar to anyone who lived in California during the mid-1970s, as I did.
But the obligations for water have greatly increased in the state, and it may very well be that the stress created by the current failed rains is more severe than for similar rainfall deficits 40 years earlier. Without making a strong claim, it is at least intuitive that sociological and economic changes in California could be reducing resiliency to natural hazards, like drought.
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. 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.
Peter Gleick
Peter Gleick has an article Clarifying the discussion about California drought and climate change. I am not a fan of Gleick, but this article is a useful contribution to the debate. His punch line:
The research and the debate over climate change and California droughts will continue. But before commenting, let’s make sure we understand what question is actually being asked, what question should be asked, and what question is actually being answered.
National Geographic
The National Geographic has an article Could the California drought last 200 years? Excerpt:
Ingram and other paleoclimatologists have correlated several historic megadroughts with a shift in the surface temperature of the Pacific Ocean that occurs every 20 to 30 years—something called the Pacific Decadal Oscillation (PDO). The PDO is similar to an El Nino event except it lasts for decades—as its name implies—whereas an El Nino event lasts 6 to 18 months. Cool phases of the PDO result in less precipitation because cooler sea temperatures bump the jet stream north, which in turn pushes off storms that would otherwise provide rain and snow to California. Ingram says entire lakes dried up in California following a cool phase of the PDO several thousand years ago. Warm phases have been linked to numerous storms along the California coast.
“We have been in a fairly cold phase of PDO since the early 2000s,” says Brian Fuchs, a climatologist at the National Drought Mitigation Center, “so the drought we are seeing now makes sense.”
The Dust Bowl Returns
An op-ed in the NYTimes entitled The Dust Bown Returns, asks the question: How long can we continue to grow a third of the nation’s fruit and vegetables? Excerpts:
Yet for all the doom around us, here in Fresno itself it is hard to find evidence that the drought is changing the behavior of city dwellers.
And while religious communities around the valley organized a day of prayer and fasting, entreating God to send rain, concrete efforts to solve the water problem are less apparent. Gov. Jerry Brown has called on all Californians to reduce their water use by 20 percent, but residential lawns, seeded each year with winter ryegrass, continue to glow in brilliant, bright-green hues, kept alive by sprinkler systems that are activated in the dark of night.
Fresnans have long resisted water-saving measures, clinging tenaciously to a flat rate, all-you-can-use system. Nudged by state and federal officials, Fresno began outfitting new homes with water meters in the early 1990s, but voters passed a ballot initiative prohibiting the city from actually reading them. It took two decades for all area homes to acquire meters and for the city to start monitoring the units. To its credit, Fresno has a watering schedule, limiting when residents can water their lawns. But enforcement, to put it charitably, is lax.
Our behavior here in the valley feels untenable and self-destructive, and for much of it we are to blame. But we also find support among an enthusiastic group of enablers: tens of millions of American shoppers who devour the lettuce and raisins, carrots and tomatoes, almonds and pistachios grown in our fields.
California’s drought is due to politics
Investors Business Daily has an article California’s Drought Isn’t Due to Global Warming, But Politics. Excerpts:
Instead of blaming the man-made political causes of California’s worst water shortage, [Obama]’s come with $2 billion in “relief” that’s nothing but a tired effort to divert attention from fellow Democrats’ dereliction of duty in using the state’s water infrastructure.
The one thing that will mitigate droughts in California — a permanent feature of the state — is to restore the water flow from California’s water-heavy north to farmers in the central and south. That’s just what House Bill 3964, which passed by a 229-191 vote last week, does.
But Obama’s plan is not to get that worthy bill through the Senate (where Democrats are holding it up) but to shovel pork to environmental activists and their victims, insultingly offering out-of-work farmers a “summer meal plan” in his package.
“They want to blame the drought for the lack of water, but they wasted water for the past five years,” said Nunes.
The two explain that California’s system of aqueducts and storage tanks was designed long ago to take advantage of rain and mountain runoff from wet years and store it for use in dry years. But it’s now inactive — by design. “California’s forefathers built a system (of aqueducts and storage facilities) designed to withstand five years of drought,” said Nunes.
Environmental special interests managed to dismantle the system by diverting water meant for farms to pet projects, such as saving delta smelt, a baitfish. That move forced the flushing of 3 million acre-feet of water originally slated for the Central Valley into the ocean over the past five years.
An article in Forbes entitled Drought Stokes California’s Class War. Excerpts:
There are two prevailing views about how to deal with the drought. Farming interests in the Central Valley want the state to fund construction of additional water storage capacity so that the 700,000 acres of some of world’s richest farmland now fallowed bysteep water cutbacks can be put back into production.
The predominant view embraced by the media and ruling political class identifies the drought as yetanother manifestation of relentless global warming, which means the focus should be on reducing greenhouse gas emissions. Greens balk at the idea of massive new spending on water storage for the agriculture sector, the state’s biggest water user, advocating instead for more conservation. New dams and reservoirs would have high environmental impacts, they argue, and their benefits may not justify the costs.
JC reflections
It seems that only Holdren, Romm and Mann (well Obama also) are pushing the link between the current drought and AGW. Holdren is a political appointee, Romm works for a political appointee, and Mann is a self declared advocate. Hard to know whether Obama is the dog or the tail on this one.
The California drought raises some interesting questions regarding detection and attribution related to AGW. If the drought is not the biggest in 100 years, or 1000 years, we can’t say it was caused by AGW. If you want to say that it was worsened by AGW, you need to have a convincing mechanism or evidence from climate models (climate models indicate more rainfall in CA under anthropogenic forcing).
The water resource issue in CA is looming very large; the demands continue to increase and agriculture seems the obvious loser under a water shortage scenario. The CA enviros seem to be an enemy of sane water policies. The final statement in Justin Gillis’ article sums it up:
“It all adds up across the Southwest to an increasingly stressed water system. That’s what they might as well get ready for.”