Short-Term Data Clouds the Climate Picture

Two established climate scientists have issued a warning about using short-term data in arguments over climate change. This is such a common point of confusion that I’ve published the news release from Lawrence Berkeley National Lab, in its entirety:

BERKELEY, CA – In the hotly debated arena of global climate change, using short-term trends that show little temperature change or even slight cooling to refute global warming is misleading, write two climate experts in a paper recently published by the American Geophysical Union–especially as the long-term pattern clearly shows human activities are causing the earth’s climate to heat up.

In their paper “Is the climate warming or cooling?” David R. Easterling of the National Oceanographic and Atmospheric Administration’s National Climatic Data Center and Michael Wehner of the Computational Research Division at the Department of Energy’s (DOE) Lawrence Berkeley National Laboratory note that a number of publications, websites and blogs often cite decade-long climate trends, such as that from 1998-2008, in which the earth’s average temperature actually dropped slightly, as evidence that the global climate is actually cooling.

However, Easterling and Wehner write, the reality of the climate system is that, due to natural climate variability, it is entirely possible, even likely, to have a period as long as a decade or two of “cooling” superimposed on the longer-term warming trend. The problem with citing such short-term cooling trends is that it can mislead decision-makers into thinking that climate change does not warrant immediate action. The
article was published April 25 in Geophysical Research Letters.

“We wrote this paper, which was carefully reviewed by other researchers and is scientifically defensible, to clearly show that even though our climate is getting warmer, we can’t expect it to do so in a monotonic way–or that each year will be warmer than the preceding year,” said Wehner. “Even with the climate changes caused by human activity, we will continue to see natural variability including periods of cooler temperatures despite the fact that globally averaged temperatures show
long-term global warming.”

“It is easy to ‘cherry pick’ a period to reinforce a point of view, but this notion begs the question, what would happen to the current concerns about climate change if we do have a sustained period where the climate appears to be cooling even when, in the end, the longer term trend is warming?” write Easterling and Wehner.

The research was funded by the DOE Office of Science’s Office of Biological and Environmental Research through its Climate Change Prediction Program.

Citing an accepted climate modeling scenario in which no efforts are made to reduce the amount of greenhouse gases released into the atmosphere, the earth’s climate is expected to warm by 4 degrees Celsius (7.2 degrees Fahrenheit) by the end of the 21st century. The authors point out that this is consistent with other simulations contained in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC 2007), which was recognized with the 2007 Nobel Peace Prize.

“Climate scientists pay little attention to these short-term fluctuations as the short term ‘cooling trends’…are statistically insignificant and fitting trends to such short periods is not very meaningful in the context of long-term climate change,” the authors write. “On the other hand, segments of the general public do pay attention to these fluctuations and some critics cite the most recent period as evidence against anthropogenic-forced (human-induced) climate change.”

The authors used both observed climate data from 1901-2008 and a series of climate model simulations performed on supercomputers to study the occurrence of decade-long trends in globally averaged surface air temperature. They found that it is possible, and indeed likely, to see periods as long as a decade in the recent past which do not show a warming trend. The authors even found that running computer simulations for the 21st century with significant increases in greenhouse gas emissions showed some decades with lower or static average temperatures. One such example can be found by looking at data from 1998 to 2008, which shows no real trend, even though global temperatures remain well above the long-term average.

According to the authors, the unusually strong 1997-98 El Niño contributed to unusual warmth in the global temperature for 1998, so that without similar dramatic changes, the following decade does not appear to be warming. A similar interpretation can be made by looking at the short-term data from 1977-85 or 1981-89, “even though these periods are embedded in the 1975-2008 period showing a substantial overall
warming,” Easterling and Wehner write. In the first example, dropping data from 1998 and looking at 1999-2008, the researchers found a strong warming trend.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Editors’ Note: Of course, this cuts both ways. Though it may be tempting to do so, it’s no more legitimate to point to the latest heat wave or a single fire season as proof of global warming. This is a conundrum that makes it difficult to find consensus on pubic policy. There are additional links posted with the full news release at the LBNL site.

Early Runoff More than Theory

This post has been modified based on clarifications by the study’s lead author, which are outlined in her comment, below.

A recent study seems to confirm what many have already surmised: The spring melt from the Sierra snowpack is happening sooner.

To get a handle on the timing of mountain runoff, a team led by Iris Stewart of Santa Clara University pulled together data from 52 stream gauges up and down California. For her study, Stewart says she chose only water courses unaffected by dams and diversions, with at least 20 years of continuous data.

Stewart’s data shows that over the 60 years spanning 1948-2008; 80% of the gauges show the “stream pulse” that accompanies peak runoff, coming consistently sooner in the season–an average of about 10 days sooner, though at least one location had shifted up by more than a month. In fact, combining all of the metrics in the study, Stewart says only one gauge showed a later trend.

The trend seems remarkably consistent. Stewart says that despite a warming trend over the past ten years, she has not seen any acceleration of the trend within that period.

Stewart cautions that there’s more work to do on this and was reluctant to draw broad inferences from the study. Runoff in a particular stream is affected by many factors, including the elevation, slope, aspect (which direction it’s facing), vegetation cover and soil composition. Stewart says further study of these variables will better help identify the most vulnerable streams. But the latest results seem consistent with an earlier study in which Stewart found “earlier runoff on a continental scale.”

Scientists are concerned that as average temperatures rise, California’s mountains will see more rain, less snow–and what snow there is will melt off sooner. Reservoirs can only retain so much runoff at once, so if more of the “frozen reservoir” dissipates earlier in the season, farms and cities stand to be caught short of water before the rains return.

Stewart, an assistant professor at SCU’s Environmental Studies Institute, presented her findings this morning to researchers at the Pacific Climate Workshop (known as PACLIM, the conference does not have a website), a semi-annual gathering of climate scientists doing front-line research around North America. The conference in Pacific Grove is organized by the USGS office in Menlo Park.

Over the course of four days, about 60 researchers will hear findings on the climatic implications for fire, fog, glaciers, the ocean and wildlife, among other topics.

Climate Debate Runs Hot and Cold

We see occasional references in our discussions here to a “cooling phase” over the past decade or so. It’s often evoked in arguments against the case for global warming. Of course, in the centuries-long span of the Earth’s climate patterns, a decade or so is a mere blip on the screen.

Now a climatologist at Lawrence Berkeley National Lab has co-authored a paper that warns against using “periods of a decade or two” to argue the case one way or the other (we also often hear people use temperature data from recent hotter years as evidence for global warming).

Andrew Revkin summarizes the findings in his blog for the New York Times.

Wehner works in the Computational Research Division at LBNL and co-authored the paper with NOAA scientist David Easterling of the National Climatic Data Center, in Ashville, NC. Easterling wrote the Center’s FAQ page on global warming, in which he includes this answer to the question of whether the global climate is warming:

Global surface temperatures have increased about 0.74°C (plus or minus 0.18°C) since the late-19th century, and the linear trend for the past 50 years of 0.13°C (plus or minus 0.03°C) per decade is nearly twice that for the past 100 years. The warming has not been globally uniform. Some areas (including parts of the southeastern U.S. and parts of the North Atlantic) have, in fact, cooled slightly over the last century. The recent warmth has been greatest over North America and Eurasia between 40 and 70°N. Lastly, seven of the eight warmest years on record have occurred since 2001 and the 10 warmest years have all occurred since 1995.”

As for the geographic fluctuations, Robert Bornstein of San Jose State has produced data showing a general cooling trend along the California coast over the past 30 or 40 years. But he’s quick to point out that the anomaly is most likely a result of, not an argument against the broader global warming trend.

Ag Rules: Heading Off the Heat

Water cooler imprinted with heat safety tips. Photo: Sasha Khokha

Water cooler imprinted with heat safety tips. Photo: Sasha Khokha

It was like a pageant of farmers in plaid shirts; nearly a dozen speakers  in a Fresno County meeting hall, surrounded by vineyards. Farm leaders offered glowing praise of Cal OSHA’s new guidelines and training seminars that will help them comply with the state’s first-in-the nation heat safety rules–passed three years ago.

The love-fest with Cal-OSHA sets a new tone for agriculture. Growers have traditionally been at odds with the agency tasked with protecting the state’s workers. Farmers have challenged fines and complained about inspections. But despite the regulations,  six workers died last summer, including a pregnant teenage farmworker (some of the victims worked in construction or other outdoor jobs).

Part of the problem was that neither Cal-OSHA inspectors nor farmers had a very clear understanding of how to implement the rules. Is it enough to have an umbrella folded up in the back of a pickup in case it got hot? How hot? How much shade and water is enough?

Today, Cal-OSHA chief Len Welsh made it clear: when it’s 85 degrees or hotter, shade tents or umbrellas have to go up. And that shade should be no more than a two-and-a-half-minute walk away, according to the rules, which also require enough shade so that one-in-four employees are protected from the sun at any given time.

That’s still worrisome for leaders of  the United Farmworkers Union, who were conspicuously absent from the press conference. There are times, they say, when the temperature soars well above 100 or spikes suddenly and everybody should get a break. The UFW says the new guidelines are too vague, and Cal-OSHA’s publicity campaign to educate farmers isn’t enough. Union leaders say the state should impose more fines and criminal penalties when workers die in the heat.

Was 2008 Relatively Warm or Cool?

Answer: Both. It depends on your historical time frame.

With a global average surface temperature of 79 degrees Fahrenheit, 2008 was the coolest year since 2000, according to climatologists at the NASA Goddard Institute for Space Studies (GISS). But it’s also the ninth-warmest year since 1880, so it’s probably not time to invest in a ski resort just yet.

Including the 2008 dip, the 10 warmest years on record (since 1880) have all occurred between 1997 and 2008, according to NASA.

The NASA scientists attribute 2008’s relatively lower temperature to a cooler Pacific Ocean, due to a strong La Nina pattern in the first half of 2008. La Nina and El Nino are opposite phases of a natural oscillation of  upwelling and subsequent temperatures in the equatorial Pacific Ocean.

2008 temperatures in the United States were cooler than any other year this decade, but, as illustrated on the map below, other parts of the world such as Eurasia and the Arctic were exceptionally warm.

Director of GISS James Hansen predicts that because a shift to El Nino is expected to start this year or next, it “still seems likely” that we’ll see a new record high for the average global surface air temperature in that time frame.


The End of Ag? Chu Drops a Climate Bomb

arizona-drought-small.jpgHigher temperatures and drier conditions could destroy California’s vineyards by the end of the century if Americans do not act fast to slow global warming, Secretary of Energy Stephen Chu said Tuesday in his first interview since joining the Obama cabinet.  Chu, a California native, warned that increased water shortages in the West and a loss of up to 90 percent of the Sierra snowpack are likely to have a severe impact on the state’s agricultural industries as well as California’s cities.

“I don’t think the American public has gripped in its gut what could happen,” Chu told the Los Angeles Times.  “We’re looking at a scenario where there’s no more agriculture in California.”

Californians may appreciate this kind of attention in Washington to what is shaping up as potentially the worst drought in the state’s history.  The California Department of Water Resources reports $308.9 million in agricultural losses last year due to drought in the state, and if January was any indication of what’s to come, that number will be even higher for 2009.  The Santa Rosa Press Democrat reports that grape growers in the counties of Sonoma and Mendocino are facing a difficult choice this month as they decide whether to use some of their reduced water allotments for frost protection. With such a rapidly dwindling supply, water used now could mean none for irrigation later in the season.

This morning on KQED’s Forum, California water experts discussed the direness of the situation and the probability of water rationing and other measures to deal with it.

The California Department of Water Resources website has extensive information about drought conditions and mitigation efforts across the state, including this fact sheet updated for January 2009.

Photo by Reed Galin

A New Slogan for Reno

Reno, NV has long laid claim to being “The Biggest Little City in the World.” Now it could claim to be one of the fastest-warming towns in America.

Reno Arch

According to a survey of US cities from Environment America,  Reno averaged 4 degrees (Fahrenheit) above”normal” for the calendar year 2007. Citing data from the National Climatic Data Center, the report said that temperatures tended above normal for most of the nation (“normal” is defined as the 30-year average from 1971-2000), but few cities made the exclusive plus-four-degree club.

More telling, perhaps, is the average minimum temperature (overnight low), which clocked in at an eyebrow-raising 5.5 degrees above normal in Reno. Climatologists have noted that throughout the West, “T-minimums” (overnight lows) have been rising almost twice as fast as daytime highs, partially obscuring for many the sensation that things are warming up.

Environment America can be justifiably challenged for implying that one year’s worth of temperature records is any indication of generalized long-term warming. It isn’t. The group takes the position that the warm 2007 was part of a broader trend:

“Between 2000 and 2007, the average temperature was at least 0.5 degrees F above the 30-year average at 228 (89%) of the stations examined (nationwide).”

Reno also made the hot list for cities that showed the most deviation from normal (3.5 degrees F), during the eight-year period 2000-2007. Of all the data collected in the report, this is the most useful number to use in making a case for a persistent warming trend. Skeptics might argue that even eight years of data can be misleading and they’d be right–but other studies have been more than sufficient to confirm that the West is warming. The debate has largely shifted to what to do about it.

Photo courtesy of: RSCVA & VisitRenoTahoe.com.

In CA's Future: More Hay, Less Lemonade?

Climate change might actually help California’s agriculture industry, according to preliminary research findings by one of today’s speakers at the California Climate Change Conference in Sacramento. UC Santa Barbara professor Charles Kolstad described his current research assessing potential future effects of weather and climate on different California agricultural crops such as broccoli and lettuce. His team compiled historical data on farm revenues, crop production, soil quality, and weather, and applied it to two of the standard scenarios provided by the IPCC; A2 (“business as usual”) and B1 (“more moderate change in climate”). Kolstad found “a clearly positive effect [of climate change] on profits” that is mostly due to temperature changes. Precipitation changes had a lesser effect on the results.

However, before you fire up the Farmall (that’s a tractor, for you city folk) and head for the fields, it’s important to note that the study does not account for future water availability and price, which obviously will have a huge impact on the future of agriculture in the state. When one conference attendee took issue with the study, calling it “completely wrong” based on several factors, Kolstad said he was aware that water availability and prices could “swamp these results,” but said that the study was focused on just one piece of a complicated issue.

Of course, not all crops will benefit from increased temperatures. According to the study, cotton and hay will see some of the biggest gains, but food crops like table grapes and lemons will suffer. So at least the horses of the future will be well fed…or not.