Climate Change

Climate Change
June 29 th 2009
2

Lifetime of GHGs – CH 4
• Residence time of the “stuff in the box” that is
our atmosphere.
• CH 4 – How long would it last?
– It would last about 8-12 years in the atmosphere
• That means that the CH 4 we are emitting now
will leave the atmosphere after about 10 years.
So if we stop emitting CH 4 now the increase
should slow down ten years from now.
3

Lifetime of GHGs
• Other GHGs have much longer
lifetimes like SF 6 .
• Whatever amount we put into the
atmosphere, we’re condemning the
future population of the Earth to deal
with its radiative effects for another
3200 years!
4

Global Warming Potential
• Comparison between one molecule of some
GHG, like CH 4 , and one molecule of CO 2 .
• EX: How many molecules of CO 2 would have to
be put in the atmosphere to equal the radiative
effects of one molecule of CH 4 ?
• 1 CH 4 molecule --- 23 CO 2 molecules
5

Global Warming Potential
• EX: How many molecules of CO 2 would have to be put
in the atmosphere to equal the radiative effects of one
molecule of SF 6 ?
• 1 SF 6 --- 22,200 CO 2
• In the case of sulfur hexafluoride (SF 6 ) it is
equivalent to so many CO 2 molecules because it has a
very long life time giving it a greater potential to affect
the atmosphere. It is also much better at absorbing IR
radiation than CO 2 . The combination of these two
factors makes it a very potent GHG.
6

Radiative Forcing by Aerosol
• How do they affect the radiative balance of the
Earth?
• Definition of aerosol: Particles made of liquid
or solid (or both) suspended in a gas phase
• The ones we are concerned about here are
about 1 mm (or 0.000001 m) in diameter,
roughly 1/50th the width of a human hair.
7

Aerosol Types and Composition
• Sulfate aerosol – from SO 2 (g)
• SO 2 H 2 SO 4 (this is sulfuric acid and what is in acid
rain)
• Organic aerosols – from combustion of fossil fuels
(gasoline, coal) and biomass (forest fires and agricultural
burning)
• Black carbon – also called soot; the black stuff from
diesel engines and other combustion
• Sea salt
• Mineral dust – windblown dust
8

Two Types of Forcing
• Direct effect: aerosols scatter (reflect)
incoming sunlight back to space, which
causes a cooling.
• Indirect effects: anthropogenic aerosols
cause a change in cloud properties, which
lead to changes in cloud albedo.
9

Direct Effect in Action
• Particles (including aerosols) are reflecting
light and can block your view of some
distant objects like mountains or bridges.
10

Direct Effect in Action
• Previous pictures show a view of the San
Gabriel Mountians in Pasadena, CA.
• First picture: clear (small amount of
aerosol particles/haze)
• Second picture: very hazy obscuring the
view of the mountains.
13

Dust Storms
14

Direct Effect in Action
• Dust Storms – dust storms obscure the surface
of the Earth as seen from space. They are
brighter than the land and ocean around them
(slightly increasing the albedo of the Earth).
– Dust storms can extend over far distances. There
have been instances in which dust from China has
reached the western coast of North America (and in
some extreme cases reached Colorado). An example
of one of these big storms reaching the California,
Oregon and Washington coats occurred on April 25,
1998.
16

Industrial Pollution
17

Direct Effect in Action
• Pollution – industrial pollution can create similar
results to those of dust storms.
• An example is the heavy industrial pollution
seen over China.
• The pollution haze causes light to be reflected
away from the surface of the Earth and
causing it to be a little brighter than the land and
ocean underneath it.
18

Ship tracks19
19

More Ship Tracks
20

Indirect Effect in Action
• The way aerosols affect clouds can be seen by the
image of ship tracks.
• You can clearly see that the plumes cased by the ships
passing under the clouds are much whiter/brighter than
the surrounding cloud.
• This is due to the fact that the clouds have an
increased number of smaller droplets (and thus
more surface area) to reflect sunlight. This causes
them to appear brighter and to reflect more sunlight back
to space.
21

Shortwave (Albedo) as seen by satellites
• You see that clouds are responsible
for reflecting a lot of shortwave
radiation back to space.
• The bright line around the equator
(ITCZ – Inter-tropical convergence
zone) shows areas where lots of clouds
typically form.
• The bright patches over Northern Africa
and in Saudi Arabia are due to the
deserts which reflect a lot of radiation.
• Other bright areas over Eastern North
America, China and Europe are due to
industrial pollution and the haze that
reflect a lot of solar radiation. There
are also a lot of storms and cloudiness
in the southern hemisphere ocean.
22

Long wave (IR) emissions seen by satellites
• You see that there is a dark
band around the equator at
the same location as the big
clouds that reflect a lot of
shortwave radiation.
• This dark band shows that
what is doing the emitting at
the equator are the cold
tops of the clouds.
• These clouds are very high
and very cold so they emit
less longwave radiation then,
say, the oceans.
23

Radiative Forcings
Figure SPM.2
24

Radiative Forcings
• This is one of the most famous figures from the
IPCC (International Panel on Climate Change)
report.
• The Blue Oval identifies what we think the
indirect radiative forcing by aerosols (via
clouds) is doing.
• As you can see it is believed that it will cause a
cooling effect but just how much of a cooling
effect is unknown.
25

Global Climate Change Debate
• The real question is:
What is the change in temperature
given some change in radiative
forcing?
26

Global Climate Change Debate
• For example: Will a 2 W/m 2 increase in
radiation flux cause global temperature to
rise by 1 or 10ºC?
• This is something we’re not really sure
about, but we have some guesses.
27

Global Climate Change Debate
• What causes us to not be sure? Feedbacks!
• There are different types of feedbacks known as
positive feedbacks and negative feedbacks.
• It is possible to come up with hundreds of
different feedbacks related to even just one
phenomenon such as increasing the
temperature of the earth.
28

Example of a Negative Feedback
1. Temperature goes up due to GHGs.
2. This means more evaporation from oceans
3. This means more clouds
4. Clouds reflect sunlight, so more sunlight reflected.
5. Therefore temperature goes down again.
6. Negative feedback – the initial increase in
temperature in (1) leads to events that cause a
reduction in this temperature increase.
• e.g. GHGs cause an increase in T by 2 K, but the cycle
of evaporation and clouds causes a cooling by 1 K,
leading to an overall warming of only 1 K.
• Note: there is still a net T increase – its just smaller
than the initial T increase.
29

Example of a Positive Feedback
1. Temperature goes up due to GHGs.
2. This means more sea ice and glaciers melt.
3. Ice is very reflective.
4. Therefore, less sunlight is reflected.
5. Therefore more sunlight is absorbed, causing a further
incrase in temperature!
6. Positive feedback – the initial increase in temperature
in (1) leads to events that cause an amplification of this
temperature increase)
• e.g. GHGs cause an increase in T by 2 K, but the
melting ice scenario causes a further warming by 2 K,
leading to an overall warming of 4 K.
30

Predicting Climate Change
•The climate system exhibits countless
feedback cycles, some positive and some
negative.
• The sum of all of these feedbacks
determines what future temperatures
will be.
31

Predicting Climate Change
• However, accurately incorporating all of these
feedbacks into a computer model is a very large
challenge!
• Therefore, there is uncertainty in our
predictions of future climate.
• We don’t necessarily know all the stories
(feedbacks) that might be affecting climate.
Thus, we’re only taking our best guess with the
knowledge we currently have to predict what the
climate will be like in the future.
32

Past and Present Climate Change
• Questions to think about as we continue
the lecture:
• What are some of the uncertainties in
predicting what will happen in the
future (over the next 100 years or so)?
• What are predicted consequences of a
warming world?
33

Atmospheric CO 2 and Temp
• Temperature has
indeed varied in time
but that they appear
to be related to one
another.
• Clear correlation
between atmospheric
CO 2 and temperature
over last 160,000
years
34

Atmospheric CO 2 and Temp
• Current level of CO 2 is
outside bounds of natural
variability (meaning that
even though CO 2 has
varied in time the amount
it has increased is even
more than it has
increased in the past)
• Rate of change of CO 2 is
also unprecedented
Note: The graph does not prove causality. Temperature could increase for
some other reason and CO 2 could be responding to that.
35

Atmospheric CO 2 and Temp
• If nothing is done to slow greenhouse gas
emissions. . .
– CO 2 concentrations will likely be more than 700 ppm
by 2100
– Global average temperatures projected to increase
between 2.5 - 10.4°F
• This would be much greater level of CO 2 than
we have seen in the past. The higher
temperature would affect the earth’s climate
system in unknown ways.
36

Historical CO 2 Concentrations
You’ll need this slide, and the number in yellow for HW problem #3
37

Historical CO 2 Concentrations
• Data comes from a variety
of sources (red is the
Keeling Curve), others are
ice cores.
• Looking at the curve you
see that CO 2
concentrations were more
or less constant around 280
ppm until around 1800
when the industrial
revolution began. Our
current level is
approximately 380 ppm.
• This is an indication that the rise in CO 2 concentrations may
be directly the result of human activities, specifically those
involving combustion processes that give off green house
gases.
38

Historical Methane (CH 4 )
Concentrations
39

Historical Methane (CH 4 )
Concentrations
• The same bubbles used to get ancient air for CO 2
measurements can be used to measure methane.
• This plot is similar to the
one above for CO 2
except now we’re
looking at methane.
• You see the same rise
in concentration at
around 1800 when the
industrial revolution was
starting
• Similar techniques used
to measure CO 2 from the
past are used to
measure methane.
40

Earth’s Surface Temperature
0.2 C warmer
You’ll need this slide, and the number in yellow for HW problem #3
1990
41

Variation in Earth’s Surface Temp
• The temperature record in not nearly as smooth as the
GHG record. There is more variability in the temperature
record. The increase is something less than about 1ºC,
1.5ºF since pre-industrial times.
42

Earth’s Surface Temperature
You’ll need this slide, and the number in yellow for HW problem #3
This is the
1961-1990
Average!!
0.3 °C
colder!
43

Earth’s Surface Temperature
• A good thing to keep in mind is
that when we talk about the
earth’s surface temperature
we’re actually talking about a
global average.
• This means that the poles are
actually warming more than the
mid-latitudes and the equator.
If it gets a little warmer at the
equator it would not be as
noticeable.
• In the lower graph we see that the red part of the curve (the
instrumental record) shows a sharp increase after the year 1800.
The blue part of the curve corresponds temperatures obtained by
other methods (called proxies) including tree rings, and
foraminiferas.
44

Global Annual Temperature Trends
(1901-1990)
45

Global Annual Temperature Trends
(1901-1990)
• Red dots indicate warming
• Blue dots indicate cooling
• Note that warming is
indicated in most parts of
the world.
• There is notable cooling in
the North Atlantic.
• There is more prominent
warming occurring in
Siberia and Northern
Canada.
46

Global Precipitation Trend
Green dots are increasing precipitation
Brown dots are decreasing precipitation.
The size of the dot indicates the percentage of increase.
47

Global Precipitation Trend
• Precipitation is change in a more complicated way.
Precipitation trends don’t look like temperature trends.
• Typically, people believe that as global temperatures
increase so will precipitation, but the trick is that the
average precipitation is what is increasing.
• We also see precipitation decreasing in areas that are
already somewhat dry such as the Sahara desert. While
at first this doesn’t seem like a bad thing, it should be
noted that the area is expanding such that areas that
once could support crops may now be having problems
48

Changes of Note:
• Sub-Sahara Africa is seeing extreme droughts causing
famine and desertification of land that was previously
fertile.
• West Coast of South America is seeing drying as well.
• Precipitation is increasing in Australia, Siberia and
Canada.
49

• The changes show in the above picture could have
serious impacts on the water supply for many regions.
Adapting to changes in water supply will require changes
in lifestyle and changes in farming techniques.
• If on the average precipitation is increasing due to global
warming it sounds like it wouldn’t be so bad. BUT… it
really matters where this increase in precipitation is
occurring and the intensity of the precipitation.
50

Global Precipitation Trend
• Intensity
• Frequency
• Time of Year
• Location
– If your precipitation is too intense it will cause flooding.
– If your precipitation does not occur frequently you can’t grow
crops. For example if you have one big storm followed by long
periods of drought, this would be bad.
– If you precipitation does not come during the growing season
you’ll have less water to grow your crops (unless you use melted
snow that comes down through rivers from mountains)
– If precipitation is increasing, but not where you need it, than it
won’t do you any good.
51

Extreme Precipitation events in US
• Black line shows the mean value.
• Extreme precipitation
events in the US
have actually
increased (causing
flooding).
• Red bars show the
percent of events that
were considered
severe.
• There is an upward trend since the record began
in 1910.
52

Projection of Future Climate
53

Projections of CO 2
You’ll need this slide, and the number in yellow for HW problem #3
Black line =
doubling CO 2 =
560 ppm
54

Future CO 2 Emission Scenarios
• This plot shows future
CO 2 emission scenarios.
Each scenario estimates
the fuel usage:
• How much fuel will we
burn in the future?
• Since we don’t know
what we’re going to do
so we come up with
potential usage curves
for a bunch of options.
55

Future CO 2 Concentrations - Predictions
You’ll need this slide, and the number in yellow for HW problem #3
56

Future CO2 Concentrations -
Predicitons
• Scenarios (A1F1,
A1B, A1T…) are
based on projected
emissions of CO 2 .
• Even those based on
the most optimistic
fuel usage still result
in a doubling of CO 2
(560 ppm) by 2100.
57

Future CO2 Concentrations -
Predicitons
• If we continue to use fuel
in the same way (i.e.
“Business as Usual”)
we’re looking at almost
at tripling of CO 2 by
2100.
• 450-1200 ppm in the
range predicted if you
consider all of the
scenarios in the plot.
• The most likely scenarios
are the ones in the
middle.
58

Temperature Change Predictions
59

Temperature Change Predicitions
• They include different
emission scenarios and are
calculated using a variety of
different climate models.
• Everyone agrees that we’re
going to get warmer.
• The likely scenario (dark
purple) would result in a 2-
4.5 ºC (4.5-8 ºF) degree
warming for the next 100
years
60

Temperature Change Predicitions
• There is a big range of
possibilities.
• We’re headed way outside
the bounds of natural
variability (the grey stuff on
the left side of the plot with
the black line through it is
the natural variability going
back to year 1000 AD).
• The projected warming is
unprecedented for the last
10,000 (or more) years.
61

Radiative Forcing by well mixed
greenhouse gases
62

Radiative Forcing by well mixed GHGs
• The greatest increase in forcing occurs over 30ºN and
30ºS where deserts already occur.
• Increase in evaporation from oceans leads to an increase
of H2O in the atmosphere. H20 remember is a very good
GHG.
63

Radiative Forcing by well mixed aerosol
• By adding H 20 you get a much bigger GHG effect. This is a form of
a positive feedback.
• You’ll also notice that the pattern is relatively smooth with the
changes in radiative forcing being more or less latitudinal. This will
not be the case for some of the other things we will consider next.
64

Radiative Forcing by Sulfate
65

Radiative Forcing by Sulfate
• Sulfate aerosol cause cooling.
• They stay in the atmosphere for a week or so after they
get there.
• Sulfate aerosol causes local radiative forcing.
66

Radiative Forcing by Sulfate
• The cooling effect is only seen in regions where you
emit lots of particles like the Eastern US, Europe
(especially Eastern Europe) and China
• This may be one reason why we see cooling over the
Southeast US.
67

Other Aerosol Types
68

Other Aerosol Types
• It’s no longer a nice
smooth increase at 30ºN
and 30ºS. When we
account for a whole suite
of forcings we get a much
different picture.
• The Arctic sees a much
larger temperature
increase than the rest of
the earth.
• This is primarily due to sea
ice feedbacks.
69

Other Aerosol Types
• The closer you get to
the poles the more
pronounced the
temperature increase.
• The plot shows the
change of the
temperature (color
shading), units: °C) for
the period 2071 to
2100 relative to
1961to 1990.
70

Other Aerosol Types
• Aerosols are patchy (do not have nice longitudinal effect)
• Organic Carbon, Black Carbon and Biomass Burning are
important for cooling South America and Africa.
• Organic Carbon and Black Carbon from fossil fuel
burning are the predominant aerosols in the US, Europe
and Asia and cause warming.
71

Other Aerosol Types
• Anthropogenic Dust in China and the Sahara
cause a warming while it causing a cooling over
the Indian Ocean.
• The indirect effect (caused by clouds) causes
cooling in the Northeast US, Europe and Asia
72

Predicted % Change of
Precipitation
73

Predicted % Change in
Precipitation
• This plot is very complicated to
look at so we suggest just
looking at the colors and not at
the lines (other than the
continental boundaries of
course).
• Blues are wetter and orangepink
is drier.
• This plot shows the predicted
range of precipitation (color
shading, units of %), for the
period 2071 to 2100 relative to
1961 to 1990.
74

Predicted % Change in Precip
• We see that a wetter world
(on average) may not be a
wetter US.
• Some important regions
get drier (bread basket of
US, Europe, Brazil,
Australia)
• Wetter areas tend to be
near the equator where
it’s already wet. Thus, they
won’t see as much of a
different as it changes.
75

Predicted % Change in Precip
• You are seeing some rain
over deserts, but it
probably won’t be enough
to make it farmable.
• Canada, China, Antarctica,
and the Arctic all get
wetter.
• If you think about where
people live you can think of
this plot as a plot of water
resources
– Local precipitation will affect
local water resources
– If drier in well populated
areas it could be a serious
problem.
76

Change in Maximum and Minimum
Daily Temperature
• In the top plot we are looking
at the change in average daily
maximum temperature.
• Where green represents an
average increase of around 8
degrees C for the 20 yr period
of 2080-2100 (relative to the
average from 1975-1995).
• The bottom plot shows the
change in average daily
minimum temperature. What
we see in the bottom plot is
that warming is greatly
increased at night.
77

Change in Maximum and Minimum
Daily Temperature
• We’re getting warmer nights, especially in places like the
artic and the Southeast US. (Purple is warmer, Blue is
colder)
• This is important because:
• Frost will happen less often
• Frost kills off insects which are carriers of disease
• If you decrease frost events you increase the
amount of time during a year in which mosquitoes
can live increasing the potential for disease
transmission. The carriers can live year round.
78

Change in Maximum and Minimum
Daily Temperature
• To Summarize: Nighttime
temperature (lows) will
rise much more than
daytime highs!
• This is because at night
we have IR radiation from
GHGs. If we increase
GHG we increase the
amount of IR radiation at
night as well making it
warmer.
79

Potential Climate Change Impacts
(Temperature
Health
Weather-related
mortality
Infectious
diseases
Air-quality
respiratory
illnesses
Agriculture
Crop yields
Irrigation
demands
Climate Changes
and Precipitation and
Forest
Change in
forest
composition
Shift
geographic
range of forests
Forest health
and
productivity
Water
Resources
Changes in
water supply
Water quality
Increased
competition for
water
Sea Level Rise)
Coastal Areas
Erosion of
beaches
Inundation of
coastal lands
Costs to protect
coastal
communities
Species and
Natural Areas
Shift in
ecological
zones
Loss of habitat
and species
80

Change in Phenomenon
Higher max Temperature, more hot days
Higher min Temperature, fewer cold and frost days
Higher heat index (related to Temp and RH)
Intensity of Precipitation and storms
Increased summer continental dryness and associated
risk of drought
Increase in tropical cycle peak wind and precipitation
intensity.
Extreme Events
Confidence in Projected Change
Very likely (90-99%)
Very likely (90-99%)
Very likely (90-99%), over most areas
Very likely (90-99%), over many areas
Likely (66-99%), over most mid-latitude continental
interiors
Likely (66-90%) over some areas
81

Sea Level Rise Projection
• Global average sea level
is projected to rise by 4 to
35 inches between 1990
and 2100
• Projected rise is slightly
lower than the range
presented in the SAR (6
to 37 inches)
• Sea level will continue to rise for hundreds
of years after stabilization of greenhouse
gas concentrations!
82

Sea Level Rise Projection
• Note: Ice that is already suspended in the
ocean will not change sea level when it
melts. It is already displacing water by
being there.
• If you take ice from the continents
(Greenland or Antarctic) and melt it you
will raise sea level.
83

Sea Level Rise Projection
• Concept: If we have one cup of water with ice
and then let all the ice melt it would have the
same level before and after the ice melts.
• This applies to the Artic:
– Sea ice that is in this form will not affect sea level
because only ice that has been on land makes a
difference. This way Arctic ice can form and melt each
year and we don’t see a change in sea level.
84

Sea Level Rise Projection
85

Sea Level Rise Projections
• If we warm the Earth a little bit
– Ice melts, within a couple of 100 years all the
ice that could melt is done melting so sea
level will start to stabilize (the red line in the
previous diagram)
– As the ocean gets warmer, the water expands
• Thermal expansion (the green line in the previous
diagram) causes sea level rise too.
86

Sea Level Rise Projections
• At the beginning Sea Ice is responsible for
the big jump in sea level rise.
• As time passes the sea ice part becomes less
important and the thermal expansion effect
takes over.
• Even if there was no melting whatsoever you’d
still get rising due to thermal expansion.
87

Sea Level Rise Projections
• It takes 2000 years for the entire ocean to
experience the warming that is going on at
the ocean surface.
• Whatever warming we are doing now
will still be causing thermal expansion
of the ocean for the next 2000 years!
88

People at Risk (by 2080) – Sea Level Rise
89

People at Risk (by 2080) – Sea Level Rise
• Here we see that almost all of Africa, Japan, Southeast
Asia, India, Bangladesh, Scandinavia and the
Mediterranean would be affected by a rise in sea level.
• In the US, Mexico and Central America wetlands are
especially at risk.
90

People at Risk (by 2080) – Sea Level Rise
• In the US:
– Louisiana shoreline would change dramatically if there was a 20 in rise
in sea level. We basically wouldn’t have New Orleans unless new flood
control measures are put into place.
– South Florida would pretty much disappear if there was a 3 ft rise in sea
level. Bye bye Everglades National Park.
– Salt water would intrude into coastal aquifers (where the water that
comes out of wells is stored) severely limiting the water resources of
coastal areas. (Basically there would be less drinking water available.
91

Predicted Changes in Runoff by 2050
• This is a plot of the change in annual runoff in mm/year. Blue and
green colors for the increasing and orange though pink for
decreasing runoff.
92

Projected Changes in Runoff by 2050
• We can consider our available water. Most people get
their drinking water from runoff. What this means is that
water falls as precipitation (either snow or rain) and this
is collected and then used directly or stored in reservoirs.
• This means that water could be the biggest political,
social and environmental issue of the future since the
transportation of water is very difficult.
• We may be looking at “Water Wars” in the future.
93

Predicted Changes in Runoff by 2050
• In the plot above we see that there are large areas where people live
or grow food that could be facing severe decreases in runoff.
94

Crop Yield Change
• Percentage change in average
crop yields for the 2020s,
2050s, and 2080s.
• Effects of CO 2 are taken into
account. Crops modeled are:
wheat, maize and rice.
• What we are basically seeing is
that we’ll be able to grow more
crops in the more northern
latitudes (like Canada and
Siberia).
• But we may begin to have
severe trouble growing crops
in areas that we are currently
using (i.e. US bread basket).
95

Crop Yield Change
• The increases in crop yield
are primarily due to:
• Longer growing seasons
• Increased precipitation
• Warmer temperatures
• Most other places see a
decrease due to a
decrease in precipitation.
96

Impacts on Human Health
• Beneficial
– Reduced winter mortality in mid- and high- latitudes
• Adverse
– Increased mortality from heat stress
– Wider spread of infectious diseases
– Worsening air quality
– Decreased food supply in developing countries
– Many impacts from possibly increasing frequency and
intensity of storms, floods, droughts, and cyclones
97