Week four Flashcards
Global Energy Balance
We can measure or calculate a global energy budget: an accounting of all
the energy flows into and between the surface and the atmosphere.
This includes both radiative and non-radiative (i.e. physical motion)
transfers of energy.
The budget for the entire earth-atmosphere system
is balanced.
Energy Balance
The energy budget of the Earth is naturally in balance.
Solar energy input = Radiative output from the
surface and the atmosphere back to space
The Greenhouse Effect
Some of the longwave radiation emitted by the Earth is absorbed by gases in
the lower atmosphere and emitted back to the Earth.
These gases are called infrared (IR) active and commonly referred to as
greenhouse gases
Longwave absorption
(Atom / gas types)
The molecules that constitute the bulk of the
lower atmosphere (O2, N2, Ar) are IR-inactive.
Water vapour, CO2 and O3 are the dominant longwave absorbers / emitters.
Living in a greenhouse?
People say the atmosphere is like the glass in a greenhouse: mostly transparent to short-wave radiation but mostly opaque to long-wave radiation.
The Earth is warmer (~ 33 K) than it would be without this radiation trapping by the atmosphere.
FACT TWO
Greenhouse gases have increased
Increase in greenhouse gas levels
CO2 concentrations have increased since the mid-1800s due to fossil fuel use (~75-90%) and land-use change
FACT THREE
Temperature has increased
Fact 1-3
FACT ONE: Greenhouse gases warm the Earth’s atmosphere
FACT TWO: Human activity has increased the level of atmospheric greenhouse gases
FACT THREE: The climate has warmed
Attribution of climate change
We have done “detection”. Now the hypothesis is:
The global climate has warmed since the Industrial Revolution due to the emission of greenhouse gases by human activity.
H0: Not due to human activity (e.g. other factors at play)
Ha: Due to human activity
FACT FOUR
Multiple lines of evidence related to the pattern of warming and the magnitude of
“natural forcings” suggests humans are the primary cause
Two approaches:
Mitigate – reduce emissions
Adapt – prepare for climate change
Counteract – “Geoengineering”
Atmospheric Pressure
Atmospheric pressure (or air pressure) is the force produced by the weight of a column of air above a unit area of surface.
Measurements
A barometer is used to measure air pressure.
Pressure normally ranges from 1050 mb to 950 mb (or 105 to 95 kPa).
The lowest pressures occur at the centre of tropical storms. The record low is 870 mb (87kPa).
Winds and pressure gradients
Wind
horizontal motion across the Earth’s surface – is created by gradients in air pressure (or air density).
