To the teenage hoopsters he is said to have run ragged on the
basketball court, he became known as Dr. J.
His friends acknowledge that Jerry Mahlman comes by the nickname
honestly. He plays an intense game of basketball. His first name
starts with J. And he holds a PhD in atmospheric science.
On Oct. 1, Jerry Mahlman, retires as head of one of the world's
leading climate-modeling centers, the National Oceanic and
Atmospheric Administration's Geophysical Fluid Dynamics Lab (GFDL).
During his tenure, the lab has been credited with developing new,
more accurate hurricane-forecasting tools, as well as models to
forecast El Nio outbreaks up to a year in advance.
But the rise of climate change as a global issue also has placed
the lab and its director at the center of what he calls
"potentially the defining problem of the 21st century."
In an interview conducted during a two-day symposium earlier this
month honoring his contributions to climate science, Mahlman
summarized recent signs that he says boost his confidence that
human-induced climate change is underway.
These signs range from Earth posting its warmest year on record
and perhaps the warmest year in the past 1,000 years to recent
paleoclimate research that tracks temperatures since AD 1000, using
several natural "thermometers." At the start of the period, he
says, the data show "very, very slow cooling - with lots of
uncertainty in the data. Then about 1760, warming takes off. You
can take different parts of the data set and get basically the same
answer. It's an extraordinarily careful piece of research."
Temperatures are warming the fastest in high, northern latitudes,
the part of the world models point to as the regions of most
pronounced change, he adds.
He acknowledges that uncertainties remain in computer simulations
of climate, fueled by gaps in researchers' understanding about key
aspects of climate - most notably the role clouds play. The
problem, he notes, lies in a poor grasp of cloud physics as well as
in the fact that clouds act on much smaller scales than computer
models can now capture.
"Some people say that the fundamental uncertainties haven't
changed in 20 years," he continues. This assertion, he says, is
based in part on global temperature-increase estimates that have
hovered for 20 years at a range of 1.5 to 4.5 degrees Celsius.
Yet, what has changed, he adds, is the confidence many
researchers have in the temperature range. What was once a 66
percent chance that temperature increases would lie within that
range has grown to a 90 to 95 percent chance as understanding of
earth's climate system has improved.
Questions of certainty versus uncertainty continue to bedevil
efforts to come up with a new consensus report on the science of
climate change. …