Page 244 - James Rodger Fleming - Fixing the sky

Ratcheting up the sense of urgency, in 2005 Hansen warned that the Earth’s
climate is nearing an unprecedented “tipping point”—a point of no return that
can be avoided only if the “growth of greenhouse gas emissions is slowed” in the
next two decades:

The Earth’s climate is nearing, but has not passed, a tipping point beyond which
it will be impossible to avoid climate change with far-ranging undesirable conse-
quences. These include not only the loss of the Arctic as we know it, with all that
implies for wildlife and indigenous peoples, but losses on a much vaster scale due
to rising seas. . . . This grim scenario can be halted if the growth of greenhouse gas
emissions is slowed in the first quarter of this century. 6

According to Hansen, tipping points occur because of amplifying feedbacks,
including loss of sea ice, melting glaciers, release of methane in warming per-
mafrost, and growth of vegetation on previously frozen land. These surface and
atmospheric changes increase the amount of sunlight absorbed by the Earth and
amplify the warming effect of carbon dioxide produced by burning fossil fuels.
Hansen’s brief statement, widely distributed by the press, clearly struck a cultural
nerve. It acknowledged undesirable and inadvertent human influence on the cli-
mate system and pointed to a possible remedy. In the interest of impact, how-
ever, Hansen avoided complexities. For example, it is highly unlikely that merely
slowing the growth of emissions would be a very effective policy. Hansen may be
right: we may be approaching the physical tipping point of climate, or, as James
Lovelock argued in his book The Revenge of Gaia, we may already have passed
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it, with catastrophic consequences for humanity. More likely, Hansen, Lovelock,
and many others are trying to add the weight of their opinions to a second kind
of “tipping point,” a behavioral change in which humanity decides to live with
only clean energy and takes concerted action against harming the climate system.
There is also a third “tipping point”—one that has been reached by a handful of
geoengineers who are so concerned about climate change that they are proposing
purposeful, even reckless, intervention.
The following discussion will define geoengineering, review its recent his-
tory, and provide a critique of current proposals and practices by revealing
their assumptions and values. It is an occasion to reflect on the precedents that
brought us to this point and to identify a “middle path” of mitigation and adap-
tation located between doing too little and doing too much. It is offered in the
hope that the study of a checkered past can help us avoid a checkered future and
with the conviction that if we are indeed facing unprecedented challenges, it is
good to consider historical precedents.

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