ATM S 111, Global Warming: Understanding the Forecast

DARGAN M. W. FRIERSONDEPARTMENT OF ATMOSPHERIC SCIENCES

DAY 2 : 04 /01 /2010

ATM S 111, Global Warming: Understanding

the Forecast

A Confession…

It’s all made up

We did it for the grant money

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 in

The 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: 310

Comes from agriculture, chemical industry, deforestation

Small 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

Extra Credit Questions

Climate change vs global warming? And ATM S 211 “Climate Change” vs ATM S 111

“Global Warming”?Painting buildings white to increase albedo &

cool cities?Why does the Earth continue to warm even if

CO2 remains fixed?