Scientist says new data back humans as cause of warming
By Jan TenBruggencate
Advertiser Science Writer
Climate researchers who met last week in Honolulu are working on the latest assessment of where the world's climate is headed.
The scientists are part of Working Group 1 of the Intergovernmental Panel on Climate Change, which in its past assessments generated international furor by linking human activities to global warming.
The newest report will further support that position, said meeting organizer Gerald Meehl, senior scientist with the National Center on Atmospheric Research in Boulder, Colo. Last week's sessions were sponsored by the University of Hawai'i's International Pacific Research Center, which conducts climate research.
"In our previous assessment, we reported that most of the warming since the mid-20th century was from human activity. We have new and stronger evidence for that," Meehl said.
The new report, which will go through an international scientific and governmental review process before being made final in early 2007, is likely to fine-tune previous predictions, but the data he has seen so far indicate it will not contradict them, Meehl said. A key improvement will be an ability to establish probabilities.
"One new aspect is that we can for the first time talk about climate change in terms of probabilities, such as an 80 percent chance of 3 degrees of warming in a certain location," he said. "There will be much more probability information."
Meehl said researchers are getting a better understanding of some of the unexpected movements in global temperature during the past century. Extended periods in which the planet stayed cool despite rising greenhouse gases — notably during the first half of the 20th century — may have been associated with "a clustering of (eruptions of) big tropical volcanoes," he said.
The volcanic emissions help reflect the sun's rays, thus keeping temperatures cooler. Similarly, sulfate aerosols created by smokestack emissions helped reflect heat during part of the century.
But all the time, "greenhouse gases were relentlessly increasing, and by the time we got to the late 20th century, the greenhouse gases sort of overwhelmed everything," he said. That has resulted in most of the hottest years on record occurring in the past two decades.
Meehl said there is now an understanding that temperatures are warmer today than at any time in the past 1,000 years, including what scientists refer to as the medieval warm period. Warm temperatures during the 1200s roughly approximate the climate of about the 1940s, and in the decades since then, it has been warmer still, he said.
For oceanic regions such as Hawai'i, continued warming means residents can expect sea levels to continue rising. If oceans are warmer, it can mean that hurricanes can whip up both stronger winds and more rain, Meehl said.
The IPCC was created by the World Meteorological Organization and the United Nations Environmental Programme in 1988 to collect scientific information and assess the condition and prospects for the world's climate.
The group includes 150 scientists from around the globe who use complex computer models that crunch everything we know about past and present climate to predict the future of world temperatures, rainfall, storms, sea-level change and other factors.
The panel's Web site, which includes copies of its climate assessments, is www.ipcc.ch.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
