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Global warming and drought are turning the Golden State brown

Posted on 30 March 2015 by dana1981

There’s a rapidly growing body of scientific research finding that California is in the midst of its worst drought in over a millennium, global warming has made the drought worse, and decades-long mega-droughts could become the norm in the state later this century. A new study published in the Proceedings of the National Academy of Science (PNAS) by scientists at Stanford University adds to this bleak picture for the Golden State.

There has been some confusion about the human contribution to California’s drought, now entering its fourth consecutive year, because some reports have said that humans have not influenced the amount of precipitation falling in the state thus far. This is a subject of debate – some studies have found evidence of a human ‘fingerprint’ in the high pressure ridge that’s diverted storms away from California over the past three years. But overall, while precipitation has been low, there have been a few years in the historical record where it was lower.

However, evidence indicates that California is in the midst of its worst drought in over 1,200 years. The new PNAS paper helps reconcile these two facts. As an accompanying commentary by Michael Mann and Peter Gleick notes,

Part of the challenge is that the term “drought” can be defined in different ways: for example, meteorological, hydrological, agricultural, and socioeconomic drought. Drought, most simply defined, is the mismatch between the amounts of water nature provides and the amounts of water that humans and the environment demand.

California’s worst droughts have historically happened in years that are both dry and hot. While humans may or may not be influencing the amount of rain falling in the state, we are indisputably making it hotter. If we could flip coins representing precipitation and temperature each year, the first could come up wet or dry, but humans are weighting the second such that it will increasingly come up hot. This will make conditions like those that caused California’s current record-breaking drought return more often as the planet keeps warming.

California temperature (°F) and precipitation (inches) anomalies from January 1895 to November 2014, plotted as 3-year anomalies relative to 1901–2000 mean. Data from the National Climatic Data Center nClimDiv dataset.  Source: PNAS; Mann & Gleick (2015).

The PNAS paper summarizes the significance of these findings.

California ranks first in the United States in population, economic activity, and agricultural value. The state is currently experiencing a record-setting drought, which has led to acute water shortages, groundwater overdraft, critically low streamflow, and enhanced wildfire risk ... we find that human emissions have increased the probability that low-precipitation years are also warm, suggesting that anthropogenic warming is increasing the probability of the co-occurring warm–dry conditions that have created the current California drought.

Mann and Gleick similarly note that the Golden State is quickly becoming an arid brown state, but that we still have an opportunity to stop this dangerous transition.

As drought has taken hold, the Golden State is slowly becoming a more arid, brown state, where constraints on water availability threaten a large and growing population (up nearly 80% since the severe drought of 1976–77), unique ecological resources, a major source of agricultural produce, and one of the largest economies in the world ... That might sound like bad news, and certainly the trends are moving rapidly in the wrong direction. The good news, however, is that this is only one possible future. If society works to limit global warming to under 2 °C, which is still possible (1), then we can likely avoid committing to a brown California. California still has a chance to remain the Golden State.

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Comments 1 to 13:

  1. One aspect that has not been looked at and should is the contribution of SE Asian aerosol loading as a contribution to the 'RRR'.  This was implicated in the GEOmip analyses.  For example:  Moore et. al. (2013)


    The negative PNA-like pattern in G1-piControl is associated with a westward shift of the jet stream toward East Asia, blocking activity over the high latitudes of the North Pacific Ocean, and a strong split-flow configuration over the central North Pacific Ocean. Figure 7 displays these features with a decreased jet speed over central, west Pacific region (with across-model differences, Figure S7), and the 200 hPa geopotential height map also shows a “blocking” high pressure over the northern North Pacific under G1.

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  2. I like the cold/hot/dry/wet graph!  A nice representation that says much.  Thanks.

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  3. "The good news, however, is that this is only one possible future. If society works to limit global warming to under 2 °C, which is still possible (1), then we can likely avoid committing to a brown California."

    If California is experiencing such a drought with global warming at a mere 0.8 °C, how is this "good news" assertion justified?

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  4. saileshrao,

    Reviewing the chart plot of all the years shows 2014 to be a dramatic change from 2012 and 2011. And 2013 is not even at the fringes of data points in the Dry, Hot quadrent.

    If the global warming is kept to levels below 2 C then these drought events will still happen, and be more frequent or more extreme or longer lasting, but they will not be an almost permanent condition of drought that varies from "Very Dry and Hot" to "Never previously experienced Dryness and Heat".

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  5. one planet @4

    The temperature effects that the earth is experiencing today is at the emissions levels from 2005.  This is without considering the substantial dimming and albedo effects of short-lived anthropogeic aerosols.  If you include those factors the earth system response may well be operating at forcing values consistent with 1994 levels, when Russia had its emissions slowdown.
    It is extremely unlikely that, in the face of rapid 'catch-up' of recent emisisons increases and the reduction of chinese aerosols due to economic cycles and pollution mitigation efforts, that the Summer Arctic Sea ice will last the next 10 years. 
    This will produce a significant northern push of the Hadley Cell and exacerbate the perpetual drought that the U.S. southwest has experienced these last 15 years.

    For more info see:

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    Moderator Response:

    [JH] Link activated.

  6. One suggestion that would greatly improve the ability of that scatter plot to convey information: Color code the dots along a spectrum from the earliest year to the latest year. That way it's obvious at a glance if there is an overall trend.
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  7. Think about this - the current drought is compared to drought 1000 years ago by looking at tree rings.  Obviously, some trees lived through the drought then, because there are trees 2,000 years old and more in California.  So, devastating as this worsening climate change heat and drought will become, it isn't anything SO FAR trees couldn't survive before.  The question should be, why did they ALL start dying prematurely several years ago - why is the entire state brown?  Live oaks, Monterey Cypress, all sorts of conifers, every species in, say, the Santa Cruz Arboretum, even those that are extremely drought resistent imported from Australia have been dying prematurely for several years - why is there an unstoppable epidemic of beetles?

    Could it be that the foresters are missing a huge piece of the puzzle??

    Why are Europeans and the Chinese so much more willing to examine the underlying cause?

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  8. This reminds me of a saying they have here in Australia: if you want to see a good Gum(tree) don't look for it in Australia.

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  9. "if you want to see a good Gum(tree) don't look for it in Australia."

    Reminds me of a strange travel experience. Driving through southern Portugal when suddenly all we could smell was Australia - Gum-Trees everywhere.

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  10. Cool,.. but did they look healthy? More to the point: did they look like the healthiest gum-trees you've ever seen?

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  11. @witsend

    Is it possible that you are reading something into this article that was neither stated or intended? When a paper talks about California being "in the midst of its worst drought in over 1,200 years", that doesn't necessarily mean things were worse just over 1,200 years ago. (Or that 2,000 year old trees must therefore have lived through worse times.)

    Over the 2013/14 winter, the UK experienced the exact opposite of the Golden/Brown State, and we had record levels of precipitation. However, the amount of misinterpretation surrounding the reporting of this event was simply jaw-dropping. How much was deliberate, and how much was accidental, is open to conjecture.

    The longest running temperature & precipitation dataset from a fixed location anywhere in the UK, is that from the Radcliffe Meteorological Station at Oxford University. Although not completely continuous, this, nonetheless, has data stretching back to 1767.

    Apart from some newspapers (and individuals) not appreciating the difference between a national record, and a merely local record, many people appeared confused by the phrase "wettest since 1767". In many quarters, this was immediately taken to mean that 1766 must, perforce, have been wetter still.

    Some of the blame must be laid at the door of jounalists who are either too lazy, or too incompetent, to address any ambiguity. However, the onus is also on the reader not to extrapolate beyond what was said.

    On the other hand, if it was specifically spelled out somewhere that things were worse 1,000 or 1,200 years ago, and I simply failed to notice that, then it looks like I need to arrange a visit to the optician. (And that, of course, would also mean that it was mea culpa time yet again.)


    cheers     bill f

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  12. Perhaps they should start thinking about sea water greenhouses.

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  13. Recommended supplemental reading:

    California Tuolumne snowpack 40 percent of worst year by By Alan Buis,
    Jet Propulsion Laboratory, NASA Global Climate Change News, Apr 2, 2015  

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