Dit document omvat een samenvatting van het vak Global Change, gegeven door prof. Philippe Huybrechts aan de VUB. Dit document bevat alle lectures, en is volledig uitgewerkt met behulp van lesnotities en de slides.
Dit document is bevat lecture 1 (climate change, the physical science basis), le...
CLIMATE CHANGE: THE PHYSICAL
SCIENCE BASIS
1. SOME BASICS OF THE CLIMATE SYSTEM
The weather and the climate are two different things.
The weather is the condition of the atmosphere at a given moment, at a given place. The weather
depends on many feedbacks and interactions in the atmosphere, so the weather can’t be predicted for
more than 14 days ahead. If the initial conditions are changed a little, the outcome will be very different.
We call this the Lorenz butterfly effect”: if butterfly flap sits wings in the Amazon, it may cause a
thunderstorm somewhere else.
The climate is looking at the average condition of the atmosphere over a longer period, mostly over 30
years. We can conclude that climate is the statistic of the weather.
Interactions between the hydrosphere, the cryosphere, the biosphere and the lithosphere are crucial to
understand the climate system. The hydrosphere includes the fluid water on the earth’s surface, the
cryosphere includes the frozen water on the earth’s surface, the biosphere includes the plants on the
earth’s surface and the lithosphere is the earth itself.
,The earth’s climate system is a very complex system, because of all the different interactions. We
distinguish two types of interactions: components that influence other systems (single arrows) and
components that influence each other (double arrows).
The law of conservation of energy also applies to earth: the incoming radiation must be equal tot he
outgoing radiation. This means that the energy the earth receives from the sun, must be equal tot he
outgoing radiation.
We can conclude that the mean global temperature depends on the solar radiation, the planetary albedo
ad the effective emissivity of the atmosphere. This shows the importance of the greenhouse effect of
the earth’s atmosphere. The earth’s temperature with natural greenhouse effect is 15 degrees, the
earth’s temperature without greenhouse effect would be -19 degrees.
,The greenhouse effect is caused by some gases, which occur at very low concentrations in the
atmosphere. They let incoming short-wave radiation from the sun come through, but absorb and re-emit
the outgoing long-wave radiation towards the surface.
In the figure below we can see the absorption spectra of greenhouse gases in the near infrared. The
smooth lines are ‘Plack’ curves, this is the theoretical emission in case there wouldn’t be a greenhouse
effect. The jagged line is the actual radiation emitted by the earth. The difference between both lines,
indicates the absorption in the atmosphere.
,Carbon dioxide is unlike what most people think, not the biggest contributor to the greenhouse effect.
CO2 is only responsible for 26% of the greenhouse effect. Water vapour, on the other hand, is the most
important contributor to the natural greenhouse effect with a percentage of 60%.
But why are we focusing on carbon dioxide, when water vapor is the biggest contributor to the
greenhouse effect? Water vapor is internal to the climate system, it can’t be changed by mankind.
Carbon dioxide on the other hand, can be changed by mankind (through burning fossil fuels).
Water vapour is a feedback, not a force. When the carbon dioxide concentration increases,
the temperature of the atmosphere will increase. This temperature increase, causes an
increase in the amount of water vapour. This, in turn, will increase the radiation. We can
conclude that the initial effect from CO2 doubles.
On the left side we see the pre-industrial situation. There is a balance between incoming
radiation and outgoing radiation, which gives a mean annual temperature of 15 degrees. When
the concentration of CO2 rises, there will be more outgoing long-wave radiation than incoming
short-wave radiation. This causes an imbalance: the restore the balance, the temperature must
rise.
,2. CHANGES IN HUMAN AND NATURAL DRIVES
The figure below illustrates the changes of the atmospheric concentrations of carbon dioxide, methane,
and nitrogen oxide over the last 2000 years. After 1750, the period of industrial revolution, we notice an
increase in concentration. Based on a Hawaiian study, we can conclude that the carbon dioxide
concentration is increased by almost 50% since pre-industrial times.
The next figure illustrates the evolution of atmospheric CO2 during the last 3.6 million years. The
concentrations are constantly changing over time, but the current concentration isn’t been experienced
for at least 2 million years. We are experiencing very exceptional times in the climate system.
The increasing CO2 concentrations in the atmosphere arise primarily from the combustion of fossil fuels.
Note that the rise of carbon dioxide concentration is accompanied by a decrease of oxygen
concentration. This is because, in order to create CO 2, we need C and link it with O2 from the
atmosphere.
, The emitted carbon dioxide goes into 3 ‘sinks’: 44% remains in the atmosphere, 29% is taken out by
plants, and 23% is taken out by the ocean. We can conclude that only 44% of the emitted carbon dioxide
causes the global warming.
Carbon dioxide isn’t the only factor, aerosols also play an important role in the global warming. These
can be natural or anthropogenic: they can come from fossil fuel carbon, biomass burning, sea salt,
volcanic eruptions, etc. Aerosols have a cooling effect on climate and have a short lifetime.
They have a direct effect on the earth’s balance by absorbing short wave and long wave radiation ; and
have an indirect effect on the earth’s balance by modifying the radiative properties, amount and the
lifetime of clouds. Clouds increase the earths albedo and reflect incoming short-wave radiation.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller cursusdienst. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $10.25. You're not tied to anything after your purchase.
