Featured Research

from universities, journals, and other organizations

Falloff In Freezes: NCAR Study Projects Decrease In Frost Days

Date:
August 26, 2004
Source:
National Center For Atmospheric Research
Summary:
Days and nights when the air temperature dips below freezing will become increasingly less common by the late 21st century across much of the world, according to a modeling study by scientists at the National Center for Atmospheric Research (NCAR).

Credit: Photo courtesy of National Center For Atmospheric Research

BOULDER -- Days and nights when the air temperature dips below freezing will become increasingly less common by the late 21st century across much of the world, according to a modeling study by scientists at the National Center for Atmospheric Research (NCAR). The reduction in 24-hour periods with freezes (frost days) is projected to be most dramatic across the western parts of North America and Europe.

In a paper published in the August 20 online edition of Climate Dynamics, NCAR scientists Gerald Meehl, Claudia Tebaldi, and Doug Nychka examine the factors that have led to a reduction in frost days in many areas over the last 50 years. The authors then use the Parallel Climate Model, developed by NCAR and the U.S. Department of Energy, to simulate day-to-day temperature changes across the globe for the years 2080 to 2099. NCAR's primary sponsor, the National Science Foundation, and the DOE funded the study, with additional support from NCAR's Weather and Climate Impact Assessment Initiative.

Over the last half-century, many weather stations across the western United States reported a decrease of 10 or more frost days per year, mostly the result of warmer conditions in springtime. Little change in frost-day frequency has been reported across the upper Midwest and Northeast.

Until now, most modeling studies of future climate change have focused on average temperatures rather than day-to-day variations, says Meehl. “For many years, a lot of the models didn’t even have diurnal [24-hour] cycles,” Meehl says.

With increased computer power and more complex software, scientists can now simulate and study changes in potential day-to-day weather events far into the future. This study is the first to examine trends in frost days using a global climate model.

Meehl and colleagues found the frost-day trends over the last 50 years intensifying during the next century. Nearly all of the United States and Canada show losses in frost days in 2080-2099 compared to 1961-1990.

“In general, there is a gradient from west to east across the continent, with greater decreases in frost days in the western regions,” says Meehl. The biggest decrease is from the Great Plains westward, where the model produces more than 20 fewer frost days in a typical year by 2080-2099. More than 40 fewer frost days per year are projected along and near the Pacific coast from Washington State north into British Columbia.

The factors at work

The cause of this pattern, according to the authors, is a shift in atmospheric circulation.

* In northwestern North America, low-level winds are projected to blow more frequently from the Pacific, bringing relatively mild air during the winter.

* Eastern North America is projected to receive more wintertime flow of cold Canadian air. This partially cancels out the decrease in frost days that results from overall climate warming.

* A similar pattern produces greater reductions in frost days across western and northern Europe than over northeast Asia.

Although the model warms polar regions the most (as measured by average daily minimum temperatures), these areas do not show the largest decrease in frost days. The difference is in part because winter nights are so cold at high latitudes that even a century of warming fails to bring the averages above freezing.

Changes in soil moisture and cloud cover can also affect overnight low temperatures. However, the changes in atmospheric pressure and circulation were the dominant factors in producing the frost-day reductions for all locations the authors studied.

Implications for agriculture

Frost days are obviously related to the growing season, but a reduction in frost days does not necessarily mean a longer season for crops. For example, the average dates for the first and last freeze might not change even if there are fewer intervening freezes.

The authors compared the 2080–2099 model results to 1961-1990 data for one common measure of the growing season: the number of days between the first six-day spring stretch with average daily temperatures above 41F and the first six-day autumn period with averages below 41F. Although the length of the growing season increases in all regions examined, the authors found only a weak statistical relationship between this result and the changes in frost days.

“This tells us that other factors, in addition to frost days, contribute to the length of the growing season,” says Meehl. The NCAR team plans to examine growing seasons in more detail in a future study.

The frost-day study, as well as a related effort examining heat waves, was produced in preparation for the next assessment by the Intergovernmental Panel on Climate Change, which is expected in 2007.


Story Source:

The above story is based on materials provided by National Center For Atmospheric Research. Note: Materials may be edited for content and length.


Cite This Page:

National Center For Atmospheric Research. "Falloff In Freezes: NCAR Study Projects Decrease In Frost Days." ScienceDaily. ScienceDaily, 26 August 2004. <www.sciencedaily.com/releases/2004/08/040826083225.htm>.
National Center For Atmospheric Research. (2004, August 26). Falloff In Freezes: NCAR Study Projects Decrease In Frost Days. ScienceDaily. Retrieved August 30, 2014 from www.sciencedaily.com/releases/2004/08/040826083225.htm
National Center For Atmospheric Research. "Falloff In Freezes: NCAR Study Projects Decrease In Frost Days." ScienceDaily. www.sciencedaily.com/releases/2004/08/040826083225.htm (accessed August 30, 2014).

Share This




More Earth & Climate News

Saturday, August 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Volcano Erupts on Papua New Guinea

Raw: Volcano Erupts on Papua New Guinea

AP (Aug. 29, 2014) Several communities were evacuated and some international flights were diverted on Friday after one of the most active volcanos in the region erupts. (Aug. 29) Video provided by AP
Powered by NewsLook.com
Killer Amoeba Found in Louisiana Water System

Killer Amoeba Found in Louisiana Water System

AP (Aug. 28, 2014) State health officials say testing has confirmed the presence of a killer amoeba in a water system serving three St. John the Baptist Parish towns. (Aug. 28) Video provided by AP
Powered by NewsLook.com
Scientists Have Figured Out Why Rocks Move In Death Valley

Scientists Have Figured Out Why Rocks Move In Death Valley

Newsy (Aug. 28, 2014) The mystery of the moving rocks in Death Valley, California, has finally been solved. Scientists are pointing to a combo of water, ice and wind. Video provided by Newsy
Powered by NewsLook.com
Big Waves, Minor Flooding from Hurricane

Big Waves, Minor Flooding from Hurricane

AP (Aug. 27, 2014) Thundering surf spawned by Hurricane Marie pounded the Southern California coast Wednesday, causing minor flooding in a low-lying beach town. High surf warnings were posted for Los Angeles County south through Orange County. (Aug. 27) 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