Featured Research

from universities, journals, and other organizations

Human Activities Contribute To California's Global Warming

Date:
January 23, 2008
Source:
DOE/Lawrence Livermore National Laboratory
Summary:
Over the past 85 years, humans have helped shape California climate during certain seasons. But that's not necessarily good. Recent research shows that California temperatures have jumped statewide by more than 2.1 degrees Fahrenheit between 1915 and 2000. This warming is likely related to human activities.

Center pivot irrigation system, Northern California. The team found the lack of a trend in summertime maximum temperatures may be associated with the rapid expansion of large-scale irrigation during the 20th century, an important factor in California that is not accounted for in the climate models.
Credit: NASA

Over the past 85 years, humans have helped shape California climate during certain seasons. But that’s not necessarily good.

Recent research by scientists at the Lawrence Livermore National Laboratory, the University of California, Merced and the National Center for Atmospheric Research shows that California temperatures have jumped statewide by more than 2.1 degrees Fahrenheit between 1915 and 2000. This warming is likely related to human activities.

Using data from up to eight different observational records, the team found the warming has been fastest in late winter and early spring.

“The trends in daily minimum and maximum temperatures over the last 50 and 85 years are inconsistent with current model-based estimates of natural internal climate variability,” said lead researcher Cιline Bonfils, a former UC Merced postdoc now working at Lawrence Livermore.“It’s pretty clear that natural causes alone just can’t cut it and external factors such as greenhouse gases and urbanization come into play.”

California is not alone when it comes to warming trends. Late winter and springtime temperatures have increased in nearly all of western North America. They have been associated with a large change in atmospheric circulation in the northern Pacific, likely resulting from greenhouse gas-induced warming.

But all California climate trends during the 20th century aren’t so clear.

For example, less warming is observed in summer. This warming, which mainly occurs at night but not during daytime, is not well explained by historical climate simulations.

“We looked at observations and models and they don’t concur,” said Phillip Duffy, part of the Livermore team and a UC Merced adjunct professor. “One possible reason for this is that most models don’t include factors such as irrigation, which can influence regional climate.”

The team found the lack of a  trend in summertime maximum temperatures may be associated with the rapid expansion of large-scale irrigation during the 20th century, an important factor in California that is not accounted for in the models.

“We found empirical evidence that irrigation has a large cooling effect on local summer daytime temperatures but minimal effect on nighttime temperatures,” said Bonfils, who investigated that issue in another Livermore study published in Proceedings of the National Academy of Sciences earlier this year.

Until now, cooling from irrigation may have counteracted the daytime warming from mounting greenhouse gases and urbanization.

“If this hypothesis is verified, the acceleration of CO2 emissions combined with a leveling of irrigation may result in a rapid summertime warming in the Central Valley in the near future,” said David Lobell, co-author in both studies.

What does this mean for the future climate in California? “The 21st century may be less climatically complex than today,” Bonfils said. “Greenhouse warming is likely to be the dominant factor over today’s many climate influences.”

“Our study represents a credible first step toward the identification of the effects of human activities on California climate,” said Benjamin Santer, also part of the Livermore team.

An increase in California temperatures could have dire consequences for the state’s water system. “If human-induced climate change is occurring, societal impacts – such as impacts on our water supply – cannot be far behind,” Duffy said.

The research, funded by the California Energy Commission, and including contributions from Livermore scientists Thomas Phillips and Charles Doutriaux, appears in the Dec. 19 online edition of the journal Climatic Change. The research also was included in the “Report to the Governor and Legislature on Climate Change.” California temperature trends also are discussed in a recent article in the American Geophysical journal, Eos, written by Duffy, Bonfils and Lobell.


Story Source:

The above story is based on materials provided by DOE/Lawrence Livermore National Laboratory. Note: Materials may be edited for content and length.


Cite This Page:

DOE/Lawrence Livermore National Laboratory. "Human Activities Contribute To California's Global Warming." ScienceDaily. ScienceDaily, 23 January 2008. <www.sciencedaily.com/releases/2008/01/080118093350.htm>.
DOE/Lawrence Livermore National Laboratory. (2008, January 23). Human Activities Contribute To California's Global Warming. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2008/01/080118093350.htm
DOE/Lawrence Livermore National Laboratory. "Human Activities Contribute To California's Global Warming." ScienceDaily. www.sciencedaily.com/releases/2008/01/080118093350.htm (accessed July 31, 2014).

Share This




More Earth & Climate News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) — Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Florida Panther Rebound Upsets Ranchers

Florida Panther Rebound Upsets Ranchers

AP (July 31, 2014) — With Florida's panther population rebounding, some ranchers complain the protected predators are once again killing their calves. (July 31) Video provided by AP
Powered by NewsLook.com
Big Waves In Arctic Ocean Threaten Polar Ice

Big Waves In Arctic Ocean Threaten Polar Ice

Newsy (July 30, 2014) — Big waves in parts of the Arctic Ocean are unprecedented, mainly because they used to be covered in ice. Video provided by Newsy
Powered by NewsLook.com
Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) — Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins