Craig Miller

Sunset on San Pablo Bay. Coastal areas saw a balmy end to September, accompanied by air quality alerts.

The Great American Heat Wave of 2012 arrived later in California than in many parts of the country — and it’s in no hurry to leave.

Having nudged the upper 90s on Sunday, Sacramento closed out the month of September with a record 26 days of 90-plus highs, surpassing the 1974 record of 24 days. The trend is forecast to continue into the first several days of October, with a chance of hitting 100 for the first time since mid-August. Farther north, Sacramento Valley towns like Redding and Red Bluff are suffering similar bake-offs.

Dry heat persisted up and down California, accompanied by red-flag warnings for fire danger along the South Coast. Of course, it’s that time of year, when the sea breeze backs around and “offshore flows” become the dreaded Santa Anas (in the south) and Diablos (in the north), notorious for fanning catastrophic wildfires. Air quality suffers during these periods, even without fires. Air quality regulators placed a Spare-the-Air Alert in effect for Monday in the San Francisco Bay Area.

For a vivid visual review of the world’s extreme weather in 2012, the World Resources Institute constructed a timeline of major events, which currently runs through August and WRI says it plans  to continue updating.

Josh Simerman, Flickr

Hot Creek, near Mammoth Lakes, was one of 20 streams in the Western U.S. examined in a study by Oregon State researchers who found no clear relationship between increasing air temperatures and stream temperatures.

Rising sea levels, melting glaciers, intensifying storm events – evidence is mounting that the effects of a warming planet will be far-reaching and potentially catastrophic. But one natural system may be more resilient than others when it comes to global warming: mountain streams.

Researchers from Oregon State University report in the journal Geophysical Research Letters that small streams in the western United States have not heated up in response to the region’s warming air temperatures.

Water temperature is a critical variable for aquatic ecosystems. Some fish, for example, time egg-laying to minute changes in water temperatures; in other species, stream temperatures are a key factor in determining the sex of juvenile fish.

The Oregon State team’s findings are based on an analysis of temperature data from 20 streams in seven western states, including California’s Hot Creek, a waterway fed by geothermal springs in Inyo National Forest, near Mammoth Lakes. (More than 600 streams were originally considered but that set was winnowed down, taking into account only streams with few human impacts and  records spanning more than 12 years.)

“It is a small set and we are trying not to extrapolate too much from this data. But some streams in our study seem to be getting warmer,” lead author Ivan Arismendi told me. “Others are getting cooler and some have not changed much at all. But our data suggests that warming air temperatures are not having a corresponding effect on streams.”

The question, of course, is why. Arismendi explains that a number of factors in addition to ambient air temperature influence — and may buffer — stream temperatures, including wind and humidity, timing of snow melt, interaction with groundwater, and variations in solar radiation.

Other studies, such as a 2010 report published in the journal Frontiers in Ecology and the Environment, have suggested that streams and rivers in the U.S. are warming up along with the climate. But Arismendi points out that many of the waterways in those studies had lots of human influences such as stormwater runoff, impoundments and diversions. All can drastically influence water temperature, he adds, which makes it impossible to determine if it is the air or some other host of factors causing the rising water temperatures.

Arismendi says the research will continue, focusing on current computer models used to predict how streams will respond to a warming climate.  “Most of the predictions in the models are based on a correlation [between air and stream temperature],” says Arismendi. “So we are trying to test how good those models are for specific sites.”

Craig Miller

Rain comes late to Northern California: A March storm front hovers over San Pablo Bay, north of San Francisco.

Last week’s State of the Climate report issued by the National Oceanic and Atmospheric Administration found that this winter is stacking up as the warmest since 2000 and the fourth warmest on record in the contiguous United States.

According to NOAA, 47 of 48 states experienced above-average temperatures in the period between December and February, with the greatest increases seen in the Northeast and Midwest.

Only New Mexico saw below-average temperatures.

In spite of the Bay Area’s balmy winter, California’s average temperatures during the three-month span were only slightly above average — and .2 degrees Fahrenheit cooler than last year during the same period.

NOAA

Deke Arndt, chief of NOAA’s Climate Monitoring Branch, said the nation’s warmer weather is partly attributable to a phenomenon known as the Arctic Oscillation, or AO, which is a determinant in how far north or south the jet stream will be situated. “This year’s index was ‘positive’ for most of the winter,” Arndt told me. “This is an indicator that the jet stream will stay further north.”

Arndt compared the influence of the Arctic Oscillation to playing with a jump rope. The more positive the index, he said, the more the rope is pulled taut. “There is a stronger pressure gradient between the mid and upper latitudes, which means that the jet stream tends to get ‘locked’ further north and cold air from the arctic does not penetrate as far into the interior of North America.” Conversely, Arndt said, last year’s wild winter can be partly attributed to a “negative phase” of the oscillation, he said, which contributes to greater variability in the latitude of the jet stream and increased likelihood of arctic air being drawn over the continental U.S.

Arndt noted, however, that there is a complex set of factors at play in determining temperature including this winter’s ocean conditions in the Pacific — known as La Niña — and feedbacks from long-term warming. “Rarely does a single factor dominate all results in all places,” he said.

NOAA

Kelly Redmond, a climatologist with the Western Regional Climate Center, cautioned against extrapolating too much from the data. “From winter to winter, the warm areas tend to move around a bit,” Redmond wrote.  “With La Niña we tend to see cool and wet/snowy conditions along the northern tier states and warmer, drier conditions along the southern tier.”

The last three months have not merely been warm but dry, particularly in the Pacific Northwest and California, which, according the report, is in the grip of its second driest recorded winter. “Storms coming onto the West Coast have either been shunted north, or torn apart before reaching California,” wrote Redmond. “We look to be in a respectable wet pattern later this week. Maybe the wettest episode of the winter for the northern half of the state and mountains.”

One study cited in the NOAA report, published by the Rutgers Global Snow Lab, pointed out that the area of snow cover across the U.S. was the third smallest it’s been in 46 years of satellite data.

According to the report, a full 39% of the country was in the midst of a drought. However, the percentage classified as D4 or “exceptional” drought shrunk, from 3.2 to 2.5%, largely the result of a spate of recent wet weather in Texas and the Southern Plains.

Overall, 2011 was the 11^th warmest year globally since record-keeping began in 1880.

By Katrina Schwartz

Just as many Californians are puzzling over winter-like weather in June, climate scientists are saying hotter days are ahead for most of the West. According to a new Stanford study (available soon at this link), we may be in for permanently hotter summers sooner than expected. Of course, for climatologists, “sooner” is a relative term.

Photo: Craig Miller

Plenty of climate scientists have studied the relationship between climate change and extreme temperature shifts, but until now no one has tried to pinpoint a moment when summer temperatures will permanently shift into a new “heat regime”, in which the coolest summer temperatures will be hotter than the hottest summer temperatures of the previous regime. Findings by the Stanford team suggest that the shift will likely happen sooner and be more widespread than expected.

The research team led by Noah Diffenbaugh of the university’s Climate and Earth System Dynamics Group analyzed more than 50 climate model simulations and estimated a 50% likelihood that a permanent shift will happen in tropical parts of the globe in the next twenty years. In middle latitudes like Europe and North America that shift will likely happen in 40 to 50 years, the study suggests. The authors say that because temperatures don’t vary as widely near the Equator, it won’t take as much warming to bump those regions into a new “seasonal envelope”— a completely new summer temperature range.

The Stanford team applied the same climate models to historical data to see how well they could predict what actually happened between 1979 and 2008. They concluded that many areas of the globe are already experiencing these permanent heat shifts. In central Africa, the authors conclude, 40% of the land area has already experienced a permanent upward shift. The climate models were able to predict the same results, making the observable reality match the simulated prediction. This correlation gives Diffenbaugh confidence in his team’s predictions for the future.

The study has potentially dramatic effects on humans. Drastically warmer temperatures adversely affect human health and agriculture. Morbidity and mortality rates rise. The demand for energy increases while the ability to supply it decreases. Many crops important to the economy of the western United States like grapes, corn, soybeans, and cotton cannot handle extreme heat. While the study found that only the eastern and western parts of the U.S. would experience permanent summer temperature increases, Diffenbaugh was quick to point out to me that his team studied the most dramatic shift possible — a complete shift upward in temperature into a new seasonal range. He says that the effects on areas that don’t experience a permanent shift in the next 50 years — like the Midwest — could still be significant.

Diffenbaugh says he was intrigued by the wintertime comparisons in the study. He explained that the relative seasonal sameness of the tropics causes the bump up in temperature to happen quickly. In the mid-latitudes, however, the move into hotter regimes takes much longer because of overlays like arctic air movement that occur simultaneously to an overall warming trend.

Katrina Schwartz is former KQED News intern, now a freelance contributor to Climate Watch.

The scientists analyzed 100 years of temperature data collected in downtown Los Angeles  and found that between 1906 and 2006 the average number of extreme heat days – those over 90 degrees – increased from 2 per year to more than 25 per year.  In that time, the average maximum daytime temperature for the city climbed 5 degrees.  Heat waves have also increased, from 2-day events to sweltering stretches that last for 1-2 weeks. The scientists predict that in the coming decades, 10-14 day heat waves will be the norm. 

The bottom line? Even though this summer was a cool one, Southern California is going to get warmer, for longer periods of time. ”Our snow pack will be less, our fire seasons will be longer, and unhealthy air alerts will be a summer staple” said study co-author Bill Patzert, a NASA climatologist and oceanographer.

The scientists assert that the main cause of this increase in temperature and heat days in Los Angeles is due the “urban heat island effect,” which makes urban areas 2-10 degrees Fahrenheit warmer than the surrounding rural areas.

Check out a historical temperature chart for downtown Los Angeles and a full report on the study here.