DARGAN M. W. FRIERSON DEPARTMENT OF ATMOSPHERIC SCIENCES DAY 2: 04/01/2010 ATM S 111, Global Warming: Understanding the Forecast
Dec 19, 2015
DARGAN M. W. FRIERSONDEPARTMENT OF ATMOSPHERIC SCIENCES
DAY 2 : 04 /01 /2010
ATM S 111, Global Warming: Understanding
the Forecast
My Recent Grant Applications
Hot in Herre: On Earth and in the ClubTiK ToK on the Clock: Neither the Party Nor
the Carbon Dioxide Emissions are Going to $top
The Hydrologic Cycle and Makin’ it Rain
How Grants Actually Work
I currently have 3 grants: Two from the National Science Foundation (NSF), one
from National Oceanic and Atmospheric Administration (NOAA) NSF #1: Tropical atmospheric circulation and global
warming NSF #2: Processes that determine the midlatitude
atmospheric vertical structure NOAA: Natural climate variability of the tropics (the
Madden-Julian Oscillation) There are plenty of important natural weather/climate
phenomena to worry about… Further, they’re reviewed by other scientists, so
exaggerating impacts doesn’t get you far
What Do Grants Pay For?
My grants pay almost exclusively for graduate students Tuition & salary for them Also undergrad research assistants
I get up to 3 months (summer) salary from grants, but having grants doesn’t increase my income Grants also pay for visits to conferences, publication
fees, research equipment, etc.Grants are a significant source of income for
the university as well UW took in over $1 billion in grant funds last year
(we’re #1 in the nation in federal grants)
Talk Tonight
Plastic Solar Cells? Challenges and Opportunities for Photovoltaics David Ginger (UW Chemistry Department) Kane 130, 6:30 PM Reserve a seat at
http://courses.washington.edu/efuture/
Reading Assignments
From last time: Make sure you’ve read Rough Guide p. 3-19 “Climate
Change: A Primer” The Big Picture The Outlook What Can We Do About It
Next reading assignment: Rough Guide p. 20-31 “The Greenhouse Effect” If it’s about hotels in Melbourne you might have
bought the wrong Rough Guide
Outline of This Lecture
Review of: How exactly the Sun heats the Earth How strong? Important concept of “albedo”: reflectivity
How the greenhouse effect works How the Earth cools And how greenhouse gases lead to less cooling
What are the main greenhouse gases? And which are changed by human activity?
How Does Energy Arrive From the Sun?
Energy from the Sun is called “shortwave radiation” or solar radiation
Radiation with shorter wavelengths is more energetic
This has long wavelength and low energy
This has short wavelength and high energy
Average Solar Radiation
Solar radiation at top of atmosphere is 1366 W/m2
Average solar radiation on Earth is 342 W/m2
Reason for seasons: Winter hemisphere is tilted away from the Sun, and gets less direct sunlight
Solar Radiation on Earth
30% is reflected back out to space Mostly by clouds, also some by the surface or by the
atmosphere20% is absorbed in the atmosphere50% is absorbed at the surface
Next: how does the Earth lose energy?
“Longwave Radiation”
The Sun is the energy input to the climate system
How does the Earth lose energy? Turns out it’s also by radiation! But it’s not visible light like
from the Sun, it’s infrared radiation AKA “longwave radiation”
Infrared satellite image
“Longwave Radiation”
Everything actually emits radiation Depends partly on the substance but mostly on
temperature
Infrared thermometerNeck = hotterHair = colder
Longwave Radiation
Higher temperature means more radiation
A WARM CAT….
IZ A HAPPY CAT
Eyes and inner ears are warmest: they radiate the most
Nose is the coldest: it radiates less
Thermal night vision technology detects longwave radiation
Temperature & Radiation
Higher temperature = more radiation and more energetic radiation (shorter wavelengths)
Explains the Sun’s radiation too Sun is really hot
It emits much more radiation It emits shortwave radiation instead of longwave
radiation like the Earth
Energy Into and Out of the Earth
Heating/cooling of Earth The Earth is heated by the Sun (shortwave radiation) The Earth loses energy by longwave radiation (out to
space)
“Energy Balance”
If the energy into a system is greater than the energy out, the temperature will increase A temperature increase then results in an increase of
energy out Hotter things radiate more
This will happen until:
When energy in equals energy out, we call this “energy balance”
Energy in Energy out
Energy Balance on Earth
If the solar radiation into Earth is greater than the outgoing longwave radiation, the temperature will increase A temperature increase then results in an increase of the
longwave radiation out (hotter things radiate more) This will happen until:
Global warming upsets the energy balance of the planet
Shortwave in Longwave out
Energy Balance with No Atmosphere
If there was no atmosphere, for energy balance to occur, the mean temperature of Earth would be 0o F (-18o C)
Missing piece: the greenhouse effect All longwave radiation doesn’t escape directly to
space
-18o C (0o F)
The Greenhouse Effect
Greenhouse gases block longwave radiation from escaping directly to space These gases re-radiate both upward and downward The extra radiation causes additional warming of the
surface
Extra downward radiation due to greenhouse gases
15o C (59o F)
The Greenhouse Effect
Greenhouse gases cause the outgoing radiation to happen at higher levels (no longer from the surface) Air gets much colder as you go upward So the radiation to space is much less (colder less
emission)
15o C (59o F)
The Greenhouse Effect
Greenhouse effect is intuitive if you pay attention to the weather! Cloudy nights cool less quickly
In the desert, temperatures plunge at night! No clouds & little water vapor in the desert: little
greenhouse effect
What are the Major Greenhouse Gases?
Our atmosphere is mostly nitrogen (N2, 78%), oxygen (O2, 21%), and argon (Ar, 0.9%) But these are not greenhouse gases
Molecules with 1 atom or 2 of the same atoms aren’t greenhouse gases though Just like the atmosphere is almost transparent to solar
radiation, the primary gases in our atmosphere are transparent to longwave radiation
If our atmosphere was only nitrogen, oxygen, and argon, this picture with no greenhouse effect would be accurate!
Greenhouse Gases
Polyatomic molecules are greenhouse gases Water vapor (H2O) Carbon dioxide (CO2) Methane (CH4) Nitrous oxide (N2O) Ozone (O3) Chlorofluorocarbons (the ozone depleting chemicals which
have been banned)
The fact that they can rotate and vibrate means they can absorb the right frequencies of longwave
Greenhouse Gases
All greenhouse gases are a rather small fraction of the atmosphere! Water vapor has the highest concentration: 0.4% CO2: 0.04% Methane: 0.0002%
“Trace gases” have a remarkable effect on the atmosphere E.g., ozone is less than 0.00001% of the atmosphere,
but absorbs essentially all harmful UV-B and UV-C radiation
Let’s discuss each gas separately
Water Vapor
Gas form of water AKA humidity Not the same as clouds – clouds are tiny droplets of
water suspended in airThe number one greenhouse gas!
Powerful because there’s a lot of itNot controlled by humans!
It’s a feedback not a forcing (topic of the next lecture)
Observed to be increasing with global warming
Carbon Dioxide
CO2
It’s what we breathe out, what plants breathe inThe primary contributor to the anthropogenic
(human-caused) greenhouse effect 63% of the anthropogenic greenhouse effect so far
Increases primarily due to fossil fuel burning (80%) and biomass burning (e.g., forest fires; 20%) Preindustrial value: 280 ppm Current value: 386 ppm
Carbon Dioxide
CO2 will also be the main problem in the future
It’s extremely long-lived in the atmosphere 50% of what we emit quickly gets taken up by the
ocean or land We’ll discuss this more later
Most of the rest sticks around for over 100 years Some of what we emit will still be in the atmosphere
over 1000 years from now!
Methane
CH4
Natural gas like in stoves/heating systems
Much more potent on a per molecule basis than CO2
Only 1.7 ppm though – much smaller concentration than CO2
Natural sources from marshes (swamp gas) and other wetlands
Increases anthropogenically due to farm animals (cow burps), landfills, natural gas leakage, rice farming
Methane
The lifetime of CH4 is significantly shorter than carbon dioxide Breaks down in the atmosphere in chemical reactions Lifetime of methane is only 8 years
Methane concentrations have been leveling off in recent years, possibly due to drought in wetlandsat high latitudes
Global Warming Potential
CO2 lifetime > 100 yearsMethane lifetime = 8 years
But methane is a much stronger greenhouse gasHow to put these on similar terms? Global
warming potential (or GWP) Global warming potential is how much greenhouse
effect emissions of a given gas causes over a fixed amount of time (usually 100 years) Measured relative to CO2 (so CO2 = 1)
Methane’s global warming potential is 25 Much more potent than CO2 (25 times more powerful)
even though it doesn’t stay as long
Nitrous Oxide
N2O Laughing gas
Also more potent on a per molecule basis than CO2
Global warming potential: 310Comes from agriculture, chemical industry,
deforestationSmall concentrations of
only 0.3 ppm
Ozone
Ozone or O3 occurs in two places in the atmosphere In the ozone layer very high up
This is “good ozone” which protects us from ultraviolet radiation & skin cancer
Remember ozone depletion is not global warming! Near the surface where it is caused by air pollution:
“bad ozone”Bad ozone is a greenhouse gas, and is more
potent on a per molecule basis than CO2
But very very short-lived Fun fact: Global warming potential for ozone is not usually
calculated – rather it’s wrapped into the GWPs of the other gases that lead to its chemical creation
CFCs
CFCs or chlorofluorocarbons are the ozone depleting chemicals Have been almost entirely phased out
CFCs are strong greenhouse gases Their reduction likely saved significant global
warming in addition to the ozone layer!Some replacements for CFCs (called HFCs)
are strong greenhouse gases thoughGlobal warmingpotentials of up to 11,000!
The Natural Greenhouse Effect
Contributions to the natural greenhouse effect: H2O (water vapor): 60% CO2 (carbon dioxide): 26% All others: 14%
These numbers are computed with a very accurate radiation model First running with all substances, then removing each
individual gas
The Unnatural Greenhouse Effect
Increasing levels of CO2 and other greenhouse gases leads to a stronger greenhouse effect With more greenhouse gases, it becomes harder for
outgoing radiation to escape to spaceIt’s like this same picture from before, but more.
More radiation is trapped before it gets out to space.
Longwave radiation is emitted from a higher (and colder) level on average.
The Unnatural Greenhouse Effect
Contributors to the “anthropogenic” greenhouse effect Numbers for the whole world up to this point:
Carbon dioxide: 63% Methane: 18% CFCs, HFCs: 12% Nitrous oxide: 6%
The Anthropogenic Greenhouse Effect
Contributors to the “anthropogenic” greenhouse effect Numbers for the US
based on current (2008)emissions
CO2 is the big problem in the US currently.
Note how much lower the HFCs are than on the previous slide. This is b/c we basically don’t emit CFCs any more.
From US EPA 2010 report (draft)
Summary
The Earth is heated by the Sun This is shortwave radiation Albedo: key factor that determines how much
radiation is absorbed vs reflectedEarth loses energy due to longwave
radiation The greenhouse effect causes less efficient heat loss
to space by longwave radiationGreenhouse gases:
Number one is water vapor Number two is CO2
Global warming potential: total warming caused over a fixed time period