THE ANTHROPOCENE - Plastics and Environmental Sustainability - page 31

of the environment (say, air) only to increase its concentration in another
(say, the ocean) is of no practical benefit. For instance, remediation of
groundwater contaminated with fuel (perhaps from a leaking fuel tank) by
air stripping to volatilize the hydrocarbons merely shifts the problem from
one medium to another. The argument that in an alternative medium the
pollutant will have a reduced risk is not a robust one. Emphasis needs to be
on pollution prevention in industrial processes to make sure that less waste
is generated, emitted, and waste does poses the minimum damage to the
environment.
1.3.2 Climate Change and Global Warming
The temperature at the Earth's surface depends on how much solar
radiation reaches the surface and how much of it is reemitted back into
space. Only about half the incoming solar radiation reaches Earth's surface
due to scattering by clouds and absorption by atmosphere. A fraction of
the incoming radiation absorbed by the Earth is emitted back as
longer-wavelength heat into the atmosphere. Some of this is reflected back
into space. It is the delicate balance between the incoming radiation
absorbed by Earth and that emitted back into space that maintains the
average temperature at Earth's surface within a hospitable range. How well
theemittedheatcantraversetheatmosphereandescapeintospacedepends
on the composition of the atmosphere. Molecules such as water vapor, CO 2 ,
and CH 4 , the GHGs, are in the upper atmosphere, impair this process,
and the heat is reflected back toward the Earth's surface. It is this natural
“greenhouse effect” that maintains the temperatures at Earth's surface
within a range that supports life . 26
However, the levels of these contaminants in the environment, especially
that of CO 2 and methane emissions from human activity, have steadily
increased by about 40%, from 280 ppm, at the time of industrial revolution,
to about 337 ppm today (see Fig. 1.11 ). Higher levels of CO 2 have not been
seeninEarth'satmospherefornearlythelastonemillionyears!Inresponse,
the average global temperature rose by 0.8°C over the last century. In the
twenty-first century, it can increase by a further 1.5-6.1°C, depending on
how well we control the emission of these gases (Solomon et al., 2007). The
potential of a gas to cause global warming (GWP) depends on its lifetime
in the atmosphere and how well it absorbs the infrared radiation (especially
in a wavelength window where the atmosphere itself does not absorb such