While leading climate scientists have been reluctant to link regional heat
waves with rising temperatures in the world's atmosphere and oceans, they say
the recent weather patterns are consistent with computer projections for global
warming.
In the United States, the first six months of 2006 were the hottest
recorded in more than a century, according to the National Oceanic and
Atmospheric Administration's National Climatic Data Center. Canada reported the
hottest winter and spring since it started keeping track about a half-century
ago, while England, Germany and France are sweltering, and the Netherlands is
recording the hottest month since temperatures were first measured 300 years
ago.
"The current heat waves throughout much of North America and Europe are
consistent with the predictions of our global climate models," said physicist
John Harte, a professor and researcher in UC Berkeley's Energy and Resources
Group and the Ecosystem Sciences Division.
"In the future, we can expect more intense, more long-lasting, and more
frequent heat waves as a consequence of global warming. If you warm the planet
as a whole, as we've been doing, it's likely that any particular heat wave is
going to be hotter with global warming, and any hurricane will be more intense.
You warm the whole, and you warm the parts," Harte said.
Temperature trends for the rest of the world won't be known until the end
of the year.
In Northern California, it was hotter for longer than ever on record,
hitting 110 degrees four consecutive days in the nine-county Bay Area. Towns
from Rio Vista in the Sacramento-San Joaquin River Delta to Modesto in the
Central Valley, Danville in the East Bay and Palo Alto on the Peninsula had
temperatures in the triple-digits.
The heat wave was blamed or suspected in the deaths of at least 126 people
in the region, while livestock died, crops burned up, power failed and energy
bills soared.
Every hot spell can't be blamed on global climate change, scientists say.
But the planet's dramatic warming over the past 50 years has made matters
worse, and the continuing rate of discharge from carbon dioxide, methane and
other heat-trapping gases will keep raising the world's temperatures throughout
the rest of the century and beyond, they say.
"But you can't predict where those parts will be," said Harte, who is
cautious about the ability of regional models to forecast the weather in areas
the size of California.
On a larger scale, the current pattern of warming is consistent with what
scientists have projected would happen in global climate models, as an
oversupply of greenhouse gases from industrial and traffic sources trap some of
the heat that once radiated into space.
The warming has been the greatest in the Arctic regions, particularly
Alaska, Siberia and Scandinavia, as melting ice and snow reflect less sunlight
back into the atmosphere and expose more land to heat and warmth. Antarctica
also has warmed. Within the United States, the warming is greater in the West
than in the East.
"This is expected," said James Hansen, director of the National
Aeronautics and Space Administration's Goddard Institute for Space Studies. The
subtropics, which include the American Southwest and the Mediterranean regions,
become hotter and drier with increasing greenhouse gases, he said.
"Weather will fluctuate a lot from year to year. But the situation this
year is of the nature of the expected trend. So get used to it," Hansen said.
While most global-climate modelers say they can' t yet correctly predict
patterns of regional climate change, they say high latitudes should warm more
than low latitudes, and the land should warm more than the ocean, Hansen said.
The higher temperatures being recorded around the world are consistent with
those predictions, he said.
During the past century, global surface temperatures have increased 1.2
degrees Fahrenheit, according to weather records. But within the century, the
past 25 to 30 years have been even hotter, leading scientists to calculate that
over a century the rate would be 3.2 degrees, with some of the highest
increases occurring in the high latitudes, according to NOAA's National
Climatic Data Center.
Three degrees might not seem like much, but it represents more than the
annual average temperature difference between San Francisco and Santa Barbara,
said Christopher Field, director of the Department of Global Ecology at the
Carnegie Institution of Washington's branch at Stanford University.
Most of the world's leading climate experts agree that the current warming
is not part of Earth's natural fluctuations. They base conclusions on studies
that assess carbon dioxide and temperature levels from borings of Antarctic ice
cores carrying trapped gaseous bubbles. The cores date 650,000 years, covering
six periods of ice ages and warming periods.
Carbon dioxide in the atmosphere has increased 35 percent since before the
Industrial Revolution, from about 278 parts per million to 378.9 parts per
million in 2005, the highest level on record.
Harte, in collaboration with Margaret Torn, a staff scientist at the
Lawrence Berkeley National Laboratory, added insight to global climate models
in May in a paper based on the ice-core data and published by the American
Geophysical Union.
They concluded that temperatures by the end of the century will be even
hotter than the models currently predict because of the heretofore uncalculated
feedback effects of global warming brought about by increasing amounts of
greenhouse gases.
If emissions from the burning of fossil fuels continue as expected, and
carbon dioxide levels reach 560 parts per million by 2060 as projected,
temperatures could increase by 12 degrees Fahrenheit above pre-industrial
global temperatures, the study found. Current models project a rise of 8
degrees.
"These findings add to the sense of urgency that we do something about the
problem," said Harte. "The predicted warmer future is not inevitable."
Regulating energy efficiency in transportation and deploying solar and wind
energy, he added, "can greatly reduce the threat of global warming."
20 hottest years on record
Rank Year
1 2005
2
1998
3 2002
4 2003
5 2004
6 2001
7 1997
8 1990
9 1995
10 1999
11 2000
12 1991
13 1987
14 1988
15 1994
16 1983
17 1996
18 1944
19 1989
20 1993
Source: World Meteorological Organization
Chronicle
Global mean temperature over land and ocean
John
Blanchard / The Chronicle
This article appeared on page A - 1 of the San Francisco Chronicle
