Global Change
Chapter 1: Some basics of the climate system
The difference between weather and climate:
- Weather is a momentary atmospheric condition at a given place
▪ Air T, precipitation, clouds, air pressure, wind speed, atmospheric humidity …
▪ It’s very chaotic => difficult to predict ~ Lorenz butterfly
- Climate is a mean and extreme conditions of the atmosphere, ocean, sea, ice … over a
longer period of time
▪ More easily predictable
Climate is de statistic of the weather. We can distinguish 5 types of spheres, being:
1. Atmosphere => air of the earth
2. Hydrosphere => oceans, sea …
3. Cryosphere => ice, snow, glaciers, permafrost …
4. Biosphere => plants and vegetation
5. Lithosphere => rocky outher part of the earth
The earth’s climate system is very
difficult. The equilibrium arrows
represent interactions between both
components, while the single
orientated arrows are forcing’s: the
change in 1 system will cause a change
in the other system too
Radiation balance of the earth
The law of energy conservation => incoming radiation = outgoing radiation. This law was
described by Stefan Boltzmann as follows:
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,The albedo is the reflection coefficient of the earth. Clouds, ice, deforestation … will change
this value. The effective emission the fraction of outgoing thermal radiation the reaches outer
space. This variable also represents the greenhouse effect. This equation can be solved in order
to calculate the T of the earth.
Different earth’s T can be obtained by changing the values of certain variables:
The T of a planet can be changed in 3 ways, as displayed above:
- Varying the effective emission
- Varying the incoming radiation (difficult)
- Varying the planetary albedo
The greenhouse effect
The greenhouse effect is caused by greenhouse gasses (CO2, O3 and H2O) and clouds. Some of
the solar incoming IR radiation is reflected by earth’s atmosphere, but some passes through.
Half of this radiation will be absorbed by earth and half will be re-emitted, but from this re-
emitted radiation fractions will be absorbed by those greenhouse gasses and clouds; these
greenhouse gasses will re-emitted the absorbed radiation in all directions, so also towards
earth again => cause global warming.
Earth’s T without greenhouse effect => - 19°C. Earth’s T with the natural greenhouse effect =>
15°C.
The absorption spectra of greenhouse gasses in the near IR:
The smooth lines => Planck curves of earth’s
radiation for a specific T. the jagged line is the
actual emitted radiation by earth. The larger the
difference between both lines, the greater the
greenhouse effect of the gas.
We can observe that CO2 displays the largest
difference => although it’s not the most abundant
one, it’s the most harmful one.
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,Water vapor contributes up to 60% of the greenhouse effect, CO2
up to 26%, O3 up to 8% and the rest is, but methane and NOX
gasses. But why do we always talk about carbon dioxide, if water
vapor contributes mostly to the greenhouse effect, the reason is
that the concentration of water vapor doesn’t change from itself.
Water vapor is a feedback and not a forcing! The CO2
concentration on the other hand increases due to human activity,
mostly from the burning of fossil fuels.
The concentrations of water vapor will vary in function of earth’s
T, hence global warming will increase the concentration of water
vapor, hence it’s greenhouse contribution will also increase =>
viscous circle.
What is the effect of doubling the CO2 concentration in our atmosphere?
The amount of incoming shortwave radiation = amount of outgoing long wave radiation. If the
CO2 concentration is doubled (b), the amount of outgoing longwave radiation will be smaller
than the incoming shortwave radiation, hence earth will warm (c) + radiation equilibrium is
restored. But this T increase will have a feedback effect (d), being the increased concentration
of water vapor, hence earth’s T will continue the increase.
The changes of the atmospheric concentrations of CO2, methane and NOX over the last 2000
years:
CO2 is mostly from fossil fuels, cement and deforestation.
Methane is from agriculture and waste (anaerobic
released), while NOX is from fertilizers and livestock.
Around the industrial revolution (1750) a significant
increase in all 3 gasses can be observed.
T
he above-mentioned gasses are anthropogenic gasses = man made. The carbon dioxide
concentrations have increased by almost 50% since the pre-industrial times. The atmospheric
CO2 concentration is around 415 ppm.
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, This concentration slightly fluctuates with the seasons. In the winter the reduced presence of
leaves causes an CO2 increase compared to the summer.
The concentration of methane and carbon dioxide from Antarctic ice cores (Dome C):
The red curve represents CO2, while de blue one
methane. We know that both greenhouse gasses are
more abundant than their natural range, but how do
we know that? By measuring the glacial-interglacial
ice cores => snow bubbles that contain air of that
period of time.
Measuring those concentrations and comparing them
with the contemporary ones will provide the
evidence.
The main anthropogenic source of CO2 is the combustion of fossil fuels. How do we know this?
The combustion of those fossil fuels will cause the release of C, that can react with O2 from the
atmosphere to form CO2. A decrease in the O2 and an increase in the CO2 concentrations can
be measured!
Fossil fuels compose 86% of the anthropogenic CO2 emission source. The remaining 14% are
from deforestation. The sinks for these emissions are the atmosphere, the terrestrial biosphere
and the ocean. Estimations provide a budget imbalance of 5% => 5% of the man-made emitted
CO2 does not get absorbed by nature.
Role of aerosols
Aerosols are suspended particles in the air, little droplets of liquids in a gas, that cause the
scattering of the incoming light. Anthropogenic aerosols originate from fossil fuel carbon &
biomass burning (soot). Natural aerosols originate from mineral dust (desert), sea-salt and
even volcano eruptions.
Aerosols cause global dimming (positive) due to the scattering and absorption of radiation. On
the other hand, they increase the albedo of the earth by increasing the lifetime of clouds due
to their cloud condensation nuclei.
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