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Lecture 1

ENVIRON 157 Lecture Notes - Lecture 1: Black-Body Radiation

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Anupom Ganguli

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PUB POL 461 Week 1 Lect 1
What is Climate Change?
What do we know? What do we not know? Why is it urgent to take immediate action?
What goes in depends on the temperature of the sun. And the radiation is blocked by the atmosphere.
What goes out of the Earth is in the form of infinite radiation. Like standing in front of a hot stove.
Cannot control water vapor because it is naturally occurring.
The rock that covers the surface of the earth is a great insulator. When a volcano erupts, it is actually a
good source of energy.
Earth receives an average of 342 watts of incoming solar energy per square meter (yellow paths,
showing shortwave energy). Of that amount, about 30 percent (107 watts per square meter) is reflected
back to space, about 20 percent (67 watts per square meter) is absorbed within the atmosphere, and
about half (168 watts per square meter) is absorbed by Earth’s surface.
Earth, like all bodies, seeks to be in a temperature equilibrium with its environment. So, much of the
solar energy that Earth absorbs is emitted back to space in the form of heat (red paths, showing
longwave energy). Much of the heat energy emitted from the surface is absorbed and then re-emitted
by gases in the atmosphere so that, effectively, these so-called “greenhouse gases” slow the rate of
Earth’s cooling.
Over the course of a year Earth would typically reflect and emit about the same amount of energy that it
receives from the Sun. Thus, our world’s energy budget would be in balance. However, if any of the
mechanisms influencing Earth’s energy budget should change significantly, it would tip the balance in
either a warming or a cooling direction (depending upon the nature and the magnitude of the change).
We get more energy from the sun in an hour than the gases we release in a year
Energy is absorbed or re-radiated. And it is
exercised by greenhouse gases
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