- As we go on pumping carbon dioxide into the air, we might
borrow a line from financial planners. Past performance is no guide to
- The buildup of carbon dioxide (CO2) is forcing scientists
to rethink their expectations - not only about the buildup of heat on Earth
but also about the implications for the natural world far beyond warming.
- Take those powerful Alaskan earthquakes. We expect land
to rise as the weight of glaciers melts away. Should we also adjust our
assessment of earthquake risk?
- Two geophysicists say "yes." Glaciers hold
down earthquake action even in a seismically active region like Alaska,
argue Jeanne Sauber with NASA's Goddard Space Flight Center in Greenbelt,
Md., and Bruce Molnia with the US Geological Survey in Reston, Va. They
use history and current data to make their case.
- For example, earthquake action picked up in places where
the ice masses retreated some 10,000 years ago, Dr. Sauber notes. Scandinavia
had major quakes back then. Canada also had many moderate quakes as its
- Melting glaciers do not cause earthquakes: Quakes are
created when forces within the crust build up strain in rock until something
slips. Alaska is seismically active because a North Pacific crustal plate
is ramming into southern Alaska, creating pressures that must be relieved
at some point.
- However, these pressures do push up high mountains where
glaciers form - and the weight of the glaciers pushing down can stabilize
the situation, if not eliminate the risk altogether. Remove that weight,
and the likelihood of a quake goes up as the strain accumulates.
- That's what happened with the 7.2 magnitude quake in
Alaska's St. Elias region in 1979, Sauber and Dr. Molnia believe. Photographs
show how glaciers in the fault area had thinned substantially during the
80 years since the previous earthquake activity.
- Sauber says it now is clear that "in areas like
Alaska where earthquakes occur and glaciers are changing, their relationship
must be considered to better assess earthquake hazard." She adds that
satellites are helping seismologists do this "by tracking the changes
in extent and volume of the ice and movement of the Earth."
- Another nonwarming implication of global warming is plant
growth. Because plants use the carbon in CO2 to make their food and structures,
they should grow faster as concentrations of the greenhouse gas go up.
Many experts hope this will take some of the excess CO2 out of the air.
They count on increased nitrogen fixation to supply the extra nitrogen
to fertilize the plants.
- Not so fast, warn Bruce Hungate at Northern Arizona University
in Flagstaff. The experiments of Dr. Hungate and his collaborators show
that this expected boon soon turns sour.
- After burgeoning for a couple of years, the nitrogen
fixers begin to lose their fixing ability. It looks as though molybdenum
- a key nutrient - becomes less available as elevated CO2 levels change
- "Our results ... caution against expecting increased
biological [nitrogen] fixation to fuel terrestrial [carbon] accumulation,"
the team warned in reporting its results in the journal Science last spring.
The results also show the need for scientists to broaden their perspective
when trying to foresee how Earth's ecosystems will respond to global change,
the team added.
- To adapt the financial guru's mantra, the way things
worked in the past is an unreliable guide for expectations of how our planet
will respond as humans force more unnatural change upon it.
- Copyright © 2004 The Christian Science Monitor.
All rights reserved.