Preserving Life on Planet Earth
Frederik Lichtenberg and Barb Gottlieb
February 3, 2012
This is the last of four blog posts by PSR intern
Frederik Lichtenberg and
Environment & Health director Barbara Gottlieb,
reflecting on a recent article by NASA climatologist James Hansen.
their article, “Perceptions of Climate Change: The New Climate Dice,” Hansen
and his coauthors ask an important question:
If we want to identify changes in the world’s climate, what do we
compare current temperatures against?
What is the right base period to examine? The question matters. After all, if we adopt as our norm a time
period where changes in climate are already in place, we will fail to recognize
just how large recent changes have been.
10,000 years, big changes
argues that when choosing a base period, it is sensible to pick one that
represents the climate conditions that have existed for most of humanity’s life
on Earth: the past ten thousand
years. Over that period, known as the
Holocene period, the climate remained relatively stable. In contrast, the planet has warmed
considerably in just the past thirty years.
This is reflected in the fact that the major ice sheets in both the
northern and southern hemispheres are melting much more rapidly, and that sea
level is rising more rapidly, than at any previous point in the Holocene.
Baseline: Comparing to what?
picks as his baseline a time period that precedes those recent, rapid
changes. His choice: 1951-1980, a period which represents the
climate that life on Earth has adapted to, and for which we have reliable
researchers have chosen as their base period the past three decades, 1981-2010.
While it’s reasonable to look at a recent multi-decade period, the problem with
this choice, as Hansen et al explain, is that those years had already
experienced an increase in average temperatures of about 0.5°C. Picking a warmer period as the basis for
defining “normal” serves to disguise the fact that today’s normal is
significantly higher than the norm just two generations ago.
fact, the changes witnessed in the years 1981-2010 already indicate the rapid
changes in climate that humankind will likely have to adjust to in the very
in the water cycle
changes arising from increasing global temperatures will have their biggest
impacts on the hydrological cycle. Hot and dry places are expected to become
even drier. At the same time, unusually heavy rainfall and floods will also
become more common. Since warm air
masses can store more water than cool ones, the total amount of water vapor
held by the atmosphere will soar as temperatures rise, leading to more
precipitation falling in extreme events. Formerly ‘100-year’ and ‘500-year’
storms and floods will lose their historic character as their frequency surges
in the future.
data already show increases of such events over many areas of the Northern
Hemisphere as well as in the tropics. Studies link this trend to human-induced
on insects, disease vectors
and his co-authors stress that climatic changes are manifested not only by
droughts, floods and other extreme events. There are numerous subtler
indicators of climate change, including effects on animals, birds, insects and
plants. These include the epidemic of
pine bark beetles destroying forests in Canada
and the U.S. Rockies, and the geographical spread of such diseases as West Nile virus and chikungunya.
certain species, including those that transmit disease, spread with global
warming, other species, especially those habituated in the tropics, are likely
to go extinct. If indeed the mean global
temperature increases by about 3°C, it is estimated that 21 to 52 percent of
all species on our planet will vanish.
is extraordinary, since many animal species migrate long distances in order to
stay in their preferred and needed climatic zone. However, for many species it
will be impossible to survive such a harsh and rapid increase in temperature.
Survival: Still possible
is still possible to avoid such an alarming scenario by taking the appropriate
measures to fight global warming. Dramatically increasing energy efficiency and
conservation, replacing fossil fuels with non-polluting forms of energy, and
slashing carbon emissions where fossil fuels are burned would all move the
world in the right direction.
That would allow us to limit global warming to
less than one degree Celsius, preserving life as we have come to know it on
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