Geoscience Reference
In-Depth Information
pansion, and new technologies are affecting the earth's climate. This
will change ecosystems, land use, and water fl ows in ever-larger ways.
Over the next century or so, human infl uences will almost certainly
push global temperatures beyond the top of the scale shown in Figure
10. In doing so, we will probably alter the earth system beyond the bio-
physical limits within which human civilizations have developed and
thrived.
2
I have primarily discussed climate models up to this point. But the
cutting-edge models in this area now include far more than the atmo-
sphere. They integrate the oceans, terrestrial systems, and ice sheets. In
addition to the large models surveyed previously, more detailed models
examine the dynamics of large ice sheets, the genesis of hurricanes,
patterns of river runoff, and similar features. All these studies taken
together help inform scientists about not only temperature trends, but
also precipitation, drought, snow packs, and potential tipping points in
the earth system, to which I turn next.
TIPPY CANOE AND CLIMATE TOO
If you look at the jagged climate history shown in Figure 10, you
might wonder why the earth moves so erratically from cold period to
warm period and back again. Is the earth on some kind of slippery
slope? Are we like skaters on a frozen pond who might break through if
we unwittingly move onto thin ice?
This is the domain of tipping points—an analysis that examines
whether climate change might trigger instabilities in the earth's sys-
tems. A tipping point comes when a system experiences a sharp discon-
tinuity in its behavior. We are familiar with tipping points from our
daily lives. For example, if you are sitting in a canoe and lean to one
side, you eventually will pass the tipping point. The canoe will fl ip over
and dump you into the water. On more than one embarrassing occa-
sion, I have tipped over a canoe—but I am here to tell the tale because
the outcome was not disastrous.
Financial specialists are familiar with tipping points as well. One
well-studied example is the phenomenon of bank runs, which were
