UC Davis


Climate Warms, Trees Head Downhill?

Near Tioga Pass, Yosemite (Photo: Gretchen Weber)

As the climate warms, plants and animals will need to move uphill to more hospitable climes, right?  Some are — but it turns out that in other cases, the process seems to have shifted into reverse.

According to a new study published in the journal Science, some plants in Northern California are actually moving downhill in response to climate change.   Aided by historical data, researchers from UC Davis and the University of Montana determined that between 1930 and 2000, many California species shifted downward an average of 260 feet.

The reason, according to UC Remote Sensing scientist Jonathan Greenberg, is increased precipitation, which, in some cases is overriding temperature as the main driver for species distribution.

“These wetter conditions are allowing plants to exist in warmer locations than they were previously capable of,” said Greenberg in a press release about the study.

NPR’s Richard Harris has more on the study and on what it could signal for California’s changing ecosystems.

Another Climate Change Impact: Smog

Los Angeles cloaked in smog shortly after sunrise. (Photo: David McNew/Getty Images)

Air pollution, already a problem for much of central and southern California, will get worse as temperatures warm, according to a new report from scientists at UC Davis and UC Berkeley.

By mid-century, trouble spots like the Central Valley and Los Angeles could experience between six and 30 more days per year when ozone concentrations exceed federal clean-air standards, depending on how much temperatures rise, and assuming that pollutant emissions in the state remain at current levels, the scientists project. Continue reading

Western Lakes Warming Up Rapidly

Craig Miller

Lake Tahoe from above Emerald Bay. Photo: Craig Miller

Some lakes in Northern California and Nevada are warming twice as fast as the surrounding air temperature, raising concerns that climate change may be affecting aquatic ecosystems more rapidly than terrestrial ones, according to a recently published study.

Researchers from the Tahoe Environmental Research Center, UC Davis and NASA’s Jet Propulsion Laboratory in Pasadena, studied Lake Tahoe, Lake Almanor, Clear Lake, and Mono Lake in California, and Nevada’s Pyramid and Walker Lakes, by analyzing 18 years of temperature data from satellite sensors.

Long-established instrument buoys provided a flow of temperature data for Tahoe, dating back to 1968, which allowed the team to calibrate satellite readings, raising confidence in data gathered from the other lakes. Previous studies have documented the warming of Lake Tahoe but John Reuter, associate director of the Tahoe Environmental Research Center (TERC), says the new study takes that information one step further.

“This study really shows that this phenomenon is happening on a much larger scale than just Lake Tahoe,” said Reuter.

All of the lakes studied showed a strong warming trend among summer nighttime temperatures between 1992 and 2008.  The two lakes that warmed the most during that time, Almanor and Mono, warmed 4.3 degrees (F).  During that time Lake Tahoe’s surface waters warmed 3.7 degrees, averaging .23 degrees annually.  In contrast, Tahoe City’s air temperature increased just .1 degree each year.

TERC director Geoffrey Schladow, who co-authored the study, said there is no doubt in his mind that rising lake temperatures are related to climate change, and he expects that it’s happening across the world, not just in Northern California and Nevada.

“The significance of this study is that across the western United States these very different lakes are displaying signs of warming.  It’s not just a Tahoe issue, it’s a regional issue.  And in all likelihood, it’s a global issue,”said Schladow.

Over the next six months, researchers will be using the remote sensors to extend the study to 50 lakes across the world to evaluate whether or not large lakes everywhere are warming at similar rates.

Warmer temperatures can affect water circulation, which influences the amount of oxygen and nutrients available throughout the lake.  A 2008 study from TERC predicts that warming due to climate change could dramatically affect the amount of mixing in Lake Tahoe, which would deplete the bottom water of oxygen and drastically disrupt the food web.

“Temperature is one of the conditions that dictates who lives in the lakes,” said Schladow. “Warmer temperatures may make the lakes more hospitable to invasive species and put native species under stress.  I’m not saying this is happening yet, but it could.”

In his article about the study, Matt Weiser of the Sacramento Bee has some examples of how warmer temperatures can affect lake ecosystems. And KQED news editor Dan Brekke has assembled an interactive map (below), showing the locations and some temperature data for lakes in the study.

View California’s Warming Lakes in a larger map

Warmer Temperatures Threatening CA Fruit Crops?

Almond trees in winter, Photo by Sahsa Khokha

Almond trees in winter, Photo by Sasha Khokha

 Increasingly warmer temperatures  in the Central Valley could pose a serious threat to California’s  fruit and nut crops in the not-too-distant future, according to a new study out of UC Davis.   The study finds that winter chill, which is an important factor in the productivity of tree crops, is likely to decrease by more than 50% by 2100, making the region less hospitable for crops like walnuts, peaches, plums, and cherries, unless changes in growing techniques are adopted.

Tree crops go dormant in the winter when temperatures drop to a certain level for a certain period of time.  Each crop then needs a certain number of  ‘chilling hours’ – between 32 and 45 degrees Fahrenheit – in order to break dormancy and resume growth.  

If crops don’t recieve their specific chilling requirement during the winter,  problems arise.  Flowering time is disturbed, which could be devastating for crops such as walnuts and pistachios that depend on simultaneous male and female flowering for pollination.   And if crops don’t recieve enough winter chill to go dormant in the first place, they will continue producing buds and sprouting branches, but they may not yield fruit, having dire consquences for California’s $7.8 billion fruit and nut industry, explained study author Minghua Zhang.

“We hope that people will take this study as a wake up call,” said Zhang. “Crops are going to be seriously impacted.”

Zhang and her fellow reaserchers found that in certain parts of the Central Valley, winter chill declined by nearly 30% between 1950 and 2000.  They expect that the decline will be 60% by 2050 and 80% by the end of the century. 

“There is a problem coming up that we need to prepare for,” said Eike Luedeling, another of the study’s authors. “So far low chilling requirement haven’t even been a breeding goal, but we are going to need a long-term strategy to cope with this.”

The researchers found that by 2000, winter chill had declined to the point that only 4% of the Central Valley was suitable for growing apples, cherries, and pears, down from 50% earlier in the 20th century.  They predict that by the end of the century, the region might no longer be suitable for growing these crops as well as walnuts, pistachios, peaches, plums, and apricots.   Crops like almonds and pomegranates will most likely be affected the least, as they have low winter chill requirements.

Two Billion Cars

We already have one billion, worldwide. Transportation researcher Dan Sperling says that stands to double within about a generation, with unthinkable consequences for air quality and climate change.

But it’s his job to think about the unthinkable. Sperling is a founder of the UC Davis Institute of Transportation Studies and a member of the California Air Resources Board. He talks about his new book, Two Billion Cars, on today’s podcast of NPR’s Fresh Air.