1. http://forecast.uchicago.edu/lectures.html Watch chapter 7 lecture using the link above 2. read the pdf lecture note on climate feedback You are expected to submit a summary of a current climate / environmental-related article from the mainstream pr

Geograph110_16_ClimateFeedbacks3
 

1. http://forecast.uchicago.edu/lectures.html

Watch chapter 7 lecture using the link above

2. read the pdf lecture note on climate feedback

You are expected to submit a summary of a current climate / environmental-related article from the mainstream press, along with your personal evaluation / reflection. Using a recent news article from a reliable source, please feel encouraged to explore topics that include extreme weather (e.g. winter storms, drought), climate change, energy (e.g. decreases in crude oil price, fracking, coal mining, nuclear power plants, alternative energy, etc), adaptation of animal behavior to recent climate change (including mammals, insects, fish, etc), policy related topics (international climate change conferences), and more. Due by April 5th.

Guidelines of this assignment are:

• Article summary: Your own summary – do not copy from an original source (1 page).
• Reflection: Your own discussion about the topic(s) of the article. Please apply your knowledge from this course and incorporate it into your discussion (1 page)
• Font type and size: Times New Roman/Times, 12-point size, double spaced
• Data (optional): include source data 
• Figures and Tables (optional): include source data
• List of reference(s)

You are expected to submit a summary of a current climate / environmental-related article from the mainstream press, along with your personal evaluation / reflection. Using a recent news article from a reliable source, please feel encouraged to explore topics that include extreme weather (e.g. winter storms, drought), climate change, energy (e.g. decreases in crude oil price, fracking, coal mining, nuclear power plants, alternative energy, etc), adaptation of animal behavior to recent climate change (including mammals, insects, fish, etc), policy related topics (international climate change conferences), and more. Due by April 2nd.

Guidelines of this assignment are:

Article summary: Your own summary – do not copy from an original source (1 page).
Reflection: Your own discussion about the topic(s) of the article. Please apply your knowledge from this course and incorporate it into your discussion (1 page)
• Maximum pages: 2

Font type and size: Times New Roman/Times, 12-point size, double spaced
Data (optional): include source data 
Figures and Tables (optional): include source data

• List of 4 reference(s)
• 2 references to the course materials
• at least 600 words

Climate �feedbacks�

We talked briefly about the positive feedback processes of climate
change in previous lectures. What is “feedback”?

Feedback is a concept that explains the interaction of the climate
system that alters changes in climate. When the rate of climate change
is amplified (either by warming or cooling), the process is called
“positive feedback”. The upper figure demonstrates the basic way that
these feedbacks operate.

On the other hand, when the rate of climate change is suppressed, then
the process is called “negative feedback” (lower figure).

Primary Climate System Feedbacks
• Radiation feedback (hotter planet radiates

more energy out to space, E=sT4)

• Snow/ice-albedo feedback

• Water Vapor feedback

• Cloud feedback (high versus low clouds)

So, climate feedbacks are a loop of cause and effect; positive (amplifier) and
negative feedbacks (stabilizer). Some feedback processes are more
complicated than others. Here are a few important feedbacks that affect our
climate system.

Temperatureà radiation feedback
Energy emitted = σT4

éTemperature

éradiation to
space

éCO2

êTemperature

The temperature of the Earth is increasing due to a rise in greenhouse gases in
the atmosphere. Thus, how will the climate feedback system change with this
temperature increase?

First, increases in temperature will alter radiation feedback because the energy
emitted from a blackbody is proportionate to its temperature to the fourth (σT4).
Feedback process: Increasing CO2 concentration in the atmosphere – increasing
temperature – increasing associated energy radiation to space – decreasing
temperature

Thus, increasing CO2 is a negative feedback process in the long term. However,
this feedback process in the climate system is far more complex. This is not the
only feedback loop that we know of.

Snow/sea ice albedo feedback

Melting of snow/sea ice directly affects the
albedo of the Earth (less ice = decrease in albedo)

Measuring Earth’s Albedo
https://earthobservatory.nasa.gov/IOTD/view.php
?id=84499

https://earthobservatory.nasa.gov/IOTD/view.php?id=84499

Also, we have seen how
recent warming has
been impacting the
arctic sea ice (see the
following two slides)

Polar amplification!

Global temperature departures from average
during January through May 2020, compared
with a 1951-1980 average. (Berkeley Earth).

Greater climate change observed near the pole responds to changes in the
radiation balance (e.g. intensified greenhouse effect). This phenomenon is
known as “polar amplification”.

Melting sea ice in the Arctic decreases the Earth’s albedo. Changes in albedo are
likely contributing to significant temperature increases in the northern
hemisphere. The increase in surface temperature is observed mainly in the
higher latitude in the northern hemisphere, where most sea ice is, and where
there is a greater continental distribution (more continent is located in the
northern hemisphere than in the southern hemisphere. continent heat capacity
is lower than the water body – ocean).

Polar Amplification

“Over the past 100 years, it is possible (33-66% confidence)
that there has been polar amplification, however, over the
past 50 years it is probable (66-90% confidence)”
[The Arctic Climate Impacts Assessment (ACIA), 2005, p22]

Although polar amplification has been a known phenomenon for over 100 years,
such amplification has been more and more prominent in the recent past.

Further reading:
Polar amplification effect
http://ossfoundation.us/projects/environment/global-warming/arctic-polar-
amplification-effect

IPCC AR5 report about polar regions
(https://unfccc.int/files/science/workstreams/research/application/pdf/5_wgiar
5_hezel_sbsta40_short )

Snow/sea ice albedo feedback
éTemperature

êsnow and ice

éCO2

Melting of snow/sea ice directly affects the albedo of the Earth (less ice =
decrease in albedo).

Feedback process: Increasing CO2 concentration –> increasing temperature –>
melting snow/sea ice –> decreasing albedo –> less energy reflected to the
space –> further increasing temperature

Water vapor feedback

http://water.usgs.gov/edu/watercyclecondensation.html

http://water.usgs.gov/edu/watercyclecondensation.html

Clausius-Clapeyron relationship

Warm air holds
more water vapor!

NASA: Sea Surface Temperature vs Water Vapor
https://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYD28M&d2=MYDAL2_M_SKY_WV

http://www.atmo.arizona.edu/students/co
urselinks/fall16/atmo336/lectures/sec1/ev
ap_cond.html

https://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYD28M&d2=MYDAL2_M_SKY_WV

Clausius-Clapayron relationship is a way of characterizing discontinuous
phase transition between two phases of a matter of a single constituent. This
concept explains the relationship between the temperature and water
vapor, which is by far the most concerning greenhouse gas in Earth’s
atmosphere. This figure shows how the water-holding capacity of the
atmosphere (water vapor pressure) increases by 8% per temperature
increase in Celsius. Importantly, this relationship is mainly a function of
temperature, and not directly dependent on other parameters like pressure
or density.

What does this figure tell us?
“warm air hold more water vapor!”

Measures of Humidity

(a)

(b)

The same concept can be explained by “relative humidity” and “water vapor
capacity”.
• Vapor pressure – contribution of water vapor to total atmospheric pressure
• Humidity – amount of water vapor in the air

Imagine you have a balloon that is perfectly sealed. No air or water vapor goes in
or out of this balloon. In this figure, “water vapor capacity (red solid line)”
indicates that your balloon is “saturated (= relatively humidity 100%)” at the
temperature and the amount of water vapor that exists in the balloon. Now, your
balloon is first saturated at 16 degree Celsius or 60 degree Fahrenheit with 10g of
water vapor per cubic meter. How can you change the saturation status? It is easy
– you just need to change its temperature! If you heat up your balloon, for
instance, to 100F, your balloon will no longer be saturated (a). Instead, to
saturate this warm balloon (100F to be exact), you need 4 times more water
vapor (b)!

Measures of Humidity
• Relative humidity – how close the air is to saturation
– Saturation represents the maximum amount of water

vapor the air can hold
– Saturation depends on temperature
– Saturation vapor pressure

In this figure, water vapor capacity is depicted in the yellow circle. The
amount of water vapor in the atmosphere does not change regardless of
the temperature (blue circle). Instead, water vapor capacity increases with
increasing temperature. Therefore, relative humidity decreases when you
increase the temperature.

• Temperature and relative humidity are inversely related

Measures of Humidity

This relationship is rather obvious if you plot the typical hourly temperature
with the relative humidity for 24 hours. Temperature increases in the morning
at around 8 am. You observe the highest temperature of the day in the
afternoon. The temperature decreases when the sun sets. As you can see,
relative humidity is almost a mirror image of temperature. The relative
humidity is highest in the early morning when the temperature is the lowest,
and is at its minimum when the temperature is at the highest of the day.

• Temperature and relative
humidity are inversely
related

• Dew point temperature

Measures of Humidity

You must have seen dew in the grass or a windshield in the early morning, when
the temperature is lowest. This is because the air becomes saturated and the
excess amount of water is condensed to form moisture! When the temperature is
close to freezing level, the dew turns into frost. Both are exactly the same
phenomenon.

Dew point temperature—the critical air temperature at which saturation is
reached.

Also, when warm air rises, the temperature decreases adiabatically. At some
point, the air becomes saturated, and the excess amount of water is
condensed. This is called cloud!

Water vapor feedback

ñTemperature

ñH2O vapor

ñCO2

Feedback process: Increasing CO2 concentration – increasing temperature – high
temperature can hold more H2O vapor (which is a greenhouse gas!) – further
increasing temperature

Studies show that water vapor feedback roughly doubles the amount of warming
caused by CO2!
Further reading:
https://www.skepticalscience.com/water-vapor-greenhouse-gas.htm

Cloud Feedback

Cloud feedback is the coupling between cloudiness and surface air
temperature in which a change in radiative forcing perturbs the surface air
temperature, leading to a change in clouds, which could then amplify or
diminish the initial temperature perturbation.

Cloud feedbacks are more complicated

éTemperature

éclouds

éCO2
or

êTemperature

Feedback process:
Increasing CO2 concentration –> increasing temperature –> enhance cloud
formation (due to enhanced evaporation from the ocean) –> clouds emit
infrared radiation back to the Earth’s surface (positive feedback)

Or

– cloud reflects sunlight (negative feedback)

Condensation
• Conversion of vapor to

liquid water
• Surface tension makes it nearly

impossible to grow pure water
droplets

• Need supersaturated air
• Need particles to grow droplets

around, a cloud condensation
nuclei

• Liquid water can persist at
temperatures colder than 0�C
without a nuclei – supercooled

How big does a rain drop need to be to reach
Earth without evaporating?

The drop would have to be approximately .2 mm
or larger in diameter. Typical rain drops are 2
mm in diameter.

• Lifting condensation
level (LCL)

Adiabatic Processes

Large masses of air can be cooled to the dew point ONLY by expanding as they
rise. Because of this limitation, adiabatic cooling is the only prominent
mechanism for development of clouds and production of rain.

When warm air rises, it cools down. This is called adiabatic cooling. When the
air cools, it holds less moisture (capacity decreases). As a result, relative
humidity increases. The altitude at which air becomes saturated (100%
relative humidity) is called lifting condensation level (LCL).

Perhaps you have seen clouds like those shown in the slide – tall puffy clouds
with a flat bottom. This happens because rising warm air continuously brings
moisture to higher altitudes and, at a given point, air becomes saturated
(LCL).

Clouds

will form above the LCL.

Lenticular clouds

Examples of cloud formation
due to atmospheric lifting!

– Cirrus clouds
– Cumulus clouds
– Stratus clouds

Clouds
Not all clouds precipitate, but all precipitation comes from clouds!

The Oxford English Dictionary:
(Cloud is) “a visible mass of condensed
watery vapor floating in the air at
some considerable height above the
general surface of the ground.”

At any given time, about 50 percent of Earth is covered by clouds. Clouds play an
important role in the global energy budget.

• Cloud types
– High clouds (over 6 km)
– Middle clouds (from 2 to

6 km)
– Low clouds (less than

2 km)
– Clouds of vertical

development
• Grow upward from

low bases to heights
of over 15 km
occasionally

Cloud Families

Cloud categories are largely based on altitude:
• High clouds—Altocumulus clouds—found above 6 kilometers (i.e., cirrus

clouds)
• Middle clouds—between about 2 and 6 kilometers (i.e., altocumulus and alto

stratus).
• Low clouds—below 2 kilometers (i.e., stratocumulus and nimbostratus).
• Clouds with vertical development (i.e., cumulus clouds).

Clouds
– Cirrus clouds (high clouds)

Feathery appearance.

Cirrus: Detached clouds in the form of white, delicate filaments, mostly
white patches or narrow bands. These clouds may have a fibrous (hair-
like) and/or silky sheen appearance. Although cirrus clouds may look less
dense, considering that they form in the high altitude, they are always
composed of ice crystals. Since ice crystals are a blackbody that absorb
and re-radiate outgoing infrared radiation, having more cirrus clouds
contribute to warming (positive feedback)!

– Cumulus clouds (middle to low
clouds)

Puffy white cloud that forms from
rising columns of air.

– Stratus clouds (low clouds)
Low clouds, usually below 6500
feet, that sometimes occur as
individual clouds but more often
appear as a general overcast.

Clouds

Cumulus: Detached, generally dense clouds and with sharp outlines that
develop vertically in the form of rising mounds, domes or towers with
bulging upper parts often resembling a cauliflower. The sunlit parts of these
clouds are mostly brilliant white while their bases are relatively dark and
horizontal. Precipitation of showers or snow may be associated with cumulus
clouds.

Stratus: A generally gray cloud layer with a uniform base which may, if thick
enough, produce drizzle, ice prisms, or snow grains. When the sun is visible
through this cloud, its outline is clearly discernible. Often when a layer of
stratus breaks up and dissipates blue sky is seen. We also call stratus clouds
as overcast.

Both cumulus and stratus clouds are middle to low clouds and can block sun
light from reaching the ground. (Imagine an overcast day. You will feel cold
because there is less energy from the sun on ground.) With this, having more
cumulus and stratus clouds contribute to a cooling effect (negative
feedback)!

Contrails: Man-made clouds

http://water.usgs.gov/edu/watercyclecondensation.html

Jet contrails = condensation trails caused by the exhaust from airplanes that
contain water vapor, and are not much different from natural clouds. If the air is
very cold (which it often is at high altitudes), then the water vapor in the exhaust
will condense out into what is essentially a cirrus cloud.

Sailors have known for some time to look specifically at the patterns and
persistence of jet contrails for weather forecasting. On days where the contrails
disappear quickly or don’t even form, they can expect continuing good weather.
While on days where they persist, a change in the weather pattern may be
expected.

Contrails: Man-made clouds

http://www.wrh.noaa.gov/fgz/science/contrail.php?wfo=fgz

If contrails persist for a long enough period of time, they can spread out

across the sky due to the prevailing winds at the level at which they

formed. The two figures show how contrails generated on this particular

day spread out fairly quickly due to the stronger jet stream of air aloft.

Persistence of contrails is neither an indication that they contain some kind

of chemical, nor that it is some kind of spray. It is simply an atmospheric

condition.

Contrails are a concern in climate studies as increased jet traffic may result

in an increase in cloud cover (specifically, cirrus cloud coverage). It has been

estimated that in certain heavy air-traffic corridors, cloud cover has

increased by as much as 20 percent. However, the world’s goals for

reducing aircraft emissions are still unclear as strategies vary by nation.

Below, I am sharing an interesting and informative reading about the

unknowns of contrails and the complicating relationship with jet fuel

exhaust.

Greening the Friendly Skies
By Mark Betancourt, 4 November 2020

https://eos.org/features/greening-the-friendly-

skies?mkt_tok=eyJpIjoiTkRZeU1XWm1ObUZpWkdZMCIsInQiOiIzeE9BNGxoaD

gzWFYrMVhiaGkrQ0s3YlVuMU9STHo2XC9GNlZwWlM2NWlMb1NZQmxYcmlw

TnFPV1lrbGxjOWx1Mnk5QlJQb0dJUzRBK1BLNVVkZW5NdmZwMFk0UldBaTB

BM3lYTTJtc1lYSDJnWG5Tdjk3d3RscVRcL1wvTjU5dWt2dyJ9

The Coming Surge of Rocket Emissions

The launch plume from a test missile, photographed on 10 October 2013 by
astronaut Luca Parmitano, diffuses into the middle and upper atmosphere
during the first several minutes after launch. As the number of rocket
launches increases in the future, rocket engine emissions will increase
proportionally. Credit: © European Space Agency/NASA

By Martin N. Ross and Darin W. Toohey 24 September 2019, EOS

Due to the unique nature of the
combustion chemistry, it turns
out that rocket engines emit
even larger amounts of black
carbon than a modern jet
engine. This means that it is
more potent than contrails!

“With 114 launches in 2018, the
number of launches has been
growing at an average rate of
about 8% per year for the past
decade. Rocket emissions have
also been growing.” (EOS)

mailto:martin.n.ross@aero.org

Cloud feedbacks are more complicated
Because cloud feedbacks are more complicated than other feedbacks, it is likely that it

causes uncertainty in climate predictions.

éTemperature
éclouds
éCO2
or
êTemperature