Modern explorers have pushed into nearly every nook and cranny of the globe,frompolar Antarctica
to the depths of the Amazonian jungle.
Yet there’s land still to explore, and regularly comes news of unexpected and
wondrous findings — a mongooselike
carnivore spotted in Madagascar, a massive waterfall discovered in Peru.
Such is the state of climate science
today. In some respects its territory has
been thoroughly probed. Despite vigorous questioning of the premises and
conclusions of research into climate
change, reviews of the evidence consistently confirm the basic findings of
the United Nations’ Intergovernmental
Panel on Climate Change: The Earth’s
rising temperature cannot be explained
by natural processes alone. Emissions
of greenhouse gases from human activities, like burning fossil fuels, must be
included to account for the observed
warming. Policy makers will be building
on this firm foundation during meetings
in Cancun, Mexico, in late November
and early December to hammer out the
next global climate-control agreement.
But unexplored corners of global climate remain. The most recent IPCC
report, from 2007, acknowledged
this terra incognita: “There is still an
incomplete physical understanding of
many components of the climate system and their role in climate change.”
Such unknowns are fertile territory
They are now pushing, for example, into perhaps the least understood
aspect of observational climate science:
how tiny particles called aerosols influence climate. Some types of aerosols
cool the planet, while others warm it.
They also affect how many clouds form
and where, further redrawing the planetary climate picture. After decades of
effort, researchers are finally starting
to disentangle this particular unknown,
Predicting regional climate patterns,
such as droughts in Phoenix or flood-
ing in Pakistan (shown), remains a
major challenge for researchers.
in part thanks to fleets of airplanes,
satellites and other instruments
deployed to monitor aerosols.
Understanding the physical processes
that drive the climate system today is
one thing; figuring out how changes in
the system will influence people’s lives in
the future is another problem altogether.
Here, scientists focus on regional climate
prediction — zooming their computer
models down to ever-smaller scales to
understand how climate change might
alter local environments. Such work is
the only way to know how drought will
affect Phoenix or floods affect Pakistan.
While just beginning to map out the
thorniest problems in regional predictions, such as how to accurately model
short-term circulation patterns in the
atmosphere and ocean, researchers are
inking in the details using some promising approaches.
By the time the next IPCC report
is released, in 2013 or 2014, scientists
should have shortened — or at least sharp-
ened — their list of unknowns. “There’s a
whole lot of climate science that needs to
be done,” says climate researcher Noah
Diffenbaugh of Stanford University. And
while the new information might not
pacify climate change skeptics, it will
clarify key areas of uncertainty in the
climate system. It will also help fill in the
last details of the geography of climate,
giving society a guide for navigating the
shoals of future changes.
Aerosols, tiny as they are, have an outsized
influence on climate. These particles range
from fractions of a micrometer to several
micrometers across and come from both
artificial and natural sources — including
power plants, biomass burning, sea spray,
volcanic eruptions and even wildfires
(SN: 11/6/10, p. 28).
Most aerosols cool the planet, by acting as a sunscreen to reflect the sun’s
incoming rays back into space. The
1991 eruption of Mount Pinatubo in the
Philippines, for instance, spewed enough
sulfur and other particles to circle the
globe and drop temperatures worldwide
by about half a degree Celsius.
Climate scientists agree that without
aerosols, the Earth would have warmed
more than it has in recent decades.
Exactly the extent of the cooling effect,
though, is a matter of dispute. Even less
well understood are the indirect effects
of aerosols: They can change the size and
distribution of clouds around the globe.
Tiny particles called aerosols can have a big impact on climate, but their many roles have been
hard to disentangle. Most of the particles re;ect sunlight, keeping the atmosphere cool. But
black carbon, or soot, can absorb the sun’s rays and heat up the atmosphere. The role of aerosols in providing surfaces for cloud formation further complicates the climate picture.
Aerosols serve as
seeds for cloud
Darker aerosols absorb
and reemit light
Burning of biomass
into the air