Transcript December 3rd: Climate Change

AOS 100: Weather and
Climate
Instructor: Nick Bassill
Class TA: Courtney Obergfell
Miscellaneous
• New Homework
• “Forecasting” Assignment
• Exam Results
The Greenhouse Effect
• Atmospheric gases are generally transparent to
most incoming solar (shortwave) radiation, but
some are fairly opaque to outgoing terrestrial
(longwave) radiation
• This causes extra heat to be trapped in the
atmosphere, resulting in a warmer surface
temperature than would otherwise occur
• Some of the most common greenhouse gases
are Water Vapor, Carbon Dioxide, Ozone, and
Methane
http://en.wikipedia.org/wiki/Greenhouse_effect
Global Warming
• It’s intuitive that adding
additional greenhouse
gases to the atmosphere
would act to warm the
planet
• The plot on the right
indicates how much
carbon (i.e. carbon
dioxide, methane, etc.) has
been added to the
atmosphere, and from
what sources
From: http://en.wikipedia.org/wiki/Greenhouse_effect
From: http://en.wikipedia.org/wiki/Greenhouse_effect
So what have we actually
observed regarding global
temperatures ?
Observations
• On average, global temperatures have
undoubtedly warmed over approximately the last
century
• Now the question is whether this is a result of
anthropogenic (human) actions, or a result of
natural variability
• Given projections of population growth, land use
changes, greenhouse gas emissions, etc., we
can use computer models to attempt to predict
what will happen
Intergovernmental Panel on
Climate Change (or IPCC)
• As the name implies, the IPCC is an
organization composed of many nations and
hundreds of scientists
• It is designed to give policy makers the latest
knowledge about the state of climate change
• Every few years, they publish a report containing
the latest knowledge (including the latest model
predictions)
• http://www.ipcc.ch/index.htm
An example of what a doubling of
CO2 would do …
Feedbacks
• A “feedback” is what happens due to the
result of some action (sort of like cause
and effect)
• Feedbacks are extremely important when
discussing the Earth’s climate
• “Positive feedbacks” (those that cause a
continuation of the initial action) are
especially important
• Let’s look at some examples …
The Ice-Albedo Feedback
• Recall that snow and ice have a high albedo
(meaning it reflects a lot of sunlight)
• If we warm the Earth a little (the “cause” in this
example), then some of that snow and ice will
melt, leaving bare ground or water
• But ground and water do not reflect as much
sunlight as snow or ice, meaning that it absorbs
more radiation
• This means that it will get even warmer!
• This is an example of a positive feedback
Oceans and CO2
• Water can absorb some CO2 from the
atmosphere
• However, cold water can hold more CO2
than warm water
• These means that as the oceans warm,
they can’t take in as much CO2, meaning
that there’s more in the atmosphere
• And more CO2 leads to a warmer Earth,
meaning that this is another example of a
positive feedback
Volcanic Eruptions & Aerosols
• When a volcano erupts, it puts a lot of
“aerosols” (ash, smoke, and other
particulates) into the atmosphere
• These aerosols can help block sunlight
from reaching the Earth’s surface when
they are in the atmosphere
• However, over time they gradually fall out
of the atmosphere by themselves, or
carried down by rain and snow
An Example
Average Yearly Sea-level
Temperature