1) The Earth heats up as it absorbs radiant energy from the Sun.

1
How the greenhouse effect occurs
1) The Earth heats up as it absorbs radiant
energy from the Sun. 2) The warmed Earth
re-emits energy as infrared radiation. 3)
Greenhouse gases are gases that absorb in the
frequencies of IR that the Earth emits and
re-emits some of it back to the surface of the
earth. 4) They also block the Earth from
releasing some of its input energy. Thus the
Earth reaches a higher T than before and its
released energy matches the solar input and the T
stabilizes.
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So where does the real debate lie?

• We know we are adding greenhouse gases
• The real question is what is the change in
  temperature given some change in GHG? i.e. will a
  50 increase in GHG cause global temperature to
  rise by 1oC or 10oC?
• This is something were not really sure about,
  but we have some guesses.
• What causes us to not be sure? Feedbacks!

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Example of negative feedback (GOOD CHANCE TO BE
ON FINAL)

• 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.

4
Example of positive feedback (GOOD CHANCE TO BE
ON FINAL)

• 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 increase 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.

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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.
• 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.
• Questions to Think About Especially for the
  FINAL
• 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?

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CO2 Recent Times
The Keeling curve shows the change in carbon
dioxide since 1860 from a combination of ice core
data and from the observation station at Mauna
Loa. The higher resolution data from Mauna Loa
clearly shows the breathing of the Earth during
which the CO2 concentrations increase in the
winter when fewer plants are taking in CO2 and an
decrease in CO2 when plants and trees are in full
bloom (spring and summer). Considering both
records there has been an indisputable increase
in CO2 concentration worldwide.
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Temp change Recent Times

• The global Average Temperature has also increased
  over the same time period.
• The change has not been as steady and even.
• These temperature fluctuations are due primarily
  to feedbacks within the climate system that are
  very difficult to predict.
• Even including all the short term increases and
  decreases in temperature we see a definite
  increase in global average temperature between
  1860 and 2000 of about 0.9C.

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CO2 and Temp longer time scale
Clear correlation between atmospheric CO2 and
temperature over last 160,000 years over last
160,000 years Current level of CO2 is outside
bounds of natural variability natural
variability Rate of change of CO2 is also
unprecedented This plot goes back much farther
than the previous two. We can obtain much longer
records by using ice cores, lake sediments,
tree-rings and other types of proxy records.
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CO2 and Temp longer time scale
This curve shows how the temperature deviation
from the mean is much greater now then it has
ever been as far back as 1000 years. This
says something about how extreme the temperature
changes actually are.
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CO2 and SO2 in the 21st century

• - For a) the bottom most line represents the
  most ideal case in which we reduce our CO2
  emissions drastically and eventually have a
  decline in emissions by the year 2050. The top
  most dotted line shows the most pessimistic case
  in which we dont reduce our emissions and they
  get way out of control.
• - For b) we see that the case in which we
  decreased our emissions has the lowest CO2
  concentrations by 2100 (500ppm). This makes
  sense because if were emitting less there wont
  be as much hanging around in the atmosphere. We
  also see that the case where we were spewing CO2
  into the air at an alarming rate we have the
  highest CO2 concentrations by 2100 (1000ppm)
• - For c) were looking at SO2 and we see that
  its not as easy to predict what will happen.
  There is a very wide spread by most show a
  decline in emissions. This is because we have
  been (and will probably continue) to get better
  and burning fossil fuels and our emissions will
  consequently contain less and less SO2.

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Three other important Gases
Indicators of the Human influence on the
atmosphere during the Industrial Era. We can
look at three gases - Carbon Dioxide went
from 280ppm to approximately 360ppm in 2000
(parts per million). - Methane went from
750ppb to 175-ppb (parts per billion) - Nitrous
Oxide went from 270ppb to 310ppb by 2000 (parts
per billion) All of which has shown a dramatic
increase in concentration since the beginning of
the industrial revolution.
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Temperature Predictions

• Global average temperature is projected to
  increase by 2.5 to 10.4F from 1990 to 2100
• Projected temperature increases are greater than
  those in the SAR (1.8 to those in the SAR (1.8 to
  6.3F) 6.3F)
• Projected rate of warming is unprecedented for
  last 10,000 years

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Variations of the Earths Surface Temperature
1000-2100

• 1000 to 1861, N. Hemisphere, proxy Hemisphere
• This is the wider looking, relatively steady line
  with the wiggling black line in the middle.
  These data are probably a collection of tree
  ring, lake sediment, floral, ocean core and ice
  core temperature estimates.
• 1861 to 2000, Global, instrumental
• From 1861 on we have temperature data from
  instruments recorded all over the globe. Of
  course our data has gotten better, as has our
  coverage over time.
• 2000 to 2100, SRES projections. These are the
  model projections of temperature that we saw in
  the previous figure. You can see how the
  temperatures are so much higher than anything we
  have instrumentally recorded or that we can
  deduce from other records.

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Projected Changes in Annual Temperatures for the
2050s

• The projected change is compared to the present
  day with a 1 in equivalent increase per year in
  equivalent CO2
• As you can see the temperature changes are not
  the same all over the globe. WE get more warming
  at the poles than we do at the equator.
• We also get less warming over the oceans than we
  do on land.

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Potential Climate Change Impacts due to

• Temperature, Precipitation and Sea level rise
• Health Weather-related mortality, infectious
  diseases, Air-Quality and respiratory illnesses.
• Agriculture crop yields, Irrigation demands
• Forests Change in forest composition, shift in
  geographic range of forests, Forest health and
  productivity will change.
• Water Resources Changes in water supply, Water
  quality, Increases competition for water.
• 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.

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Extreme Events
Change in Phenomenon Confidence in projected change
Higher maximum temperatures, more hot days Very Likely
Higher minimum temperatures, fewer cold days and frost days Very Likely
Increase of heat index Very likely, over most areas
More intense precipitation events Very likely, over many areas
Increased summer continental drying and associated risk of drought Likely, over most mid-latitude continental interiors
Increase in tropical cyclone peak wind and precipitation intensities Likely, over some areas
Judgmental estimates of confidence by IPCC
very likely 90-99 chance, likely 66-60 chance.
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Sea- Level Rise Projections

• Global average sea level is projected to rise by
  4 t0 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.

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Sea-level Rise Commitment

• Thermal expansion and land ice melt after an
  initial 1 increase in CO2 for 70years.
• If you look at the x-axis you see that time scale
  is on the order of 1000 years. This is consistent
  with the fact that the ocean takes about 1000
  years to circulate.
• Changes we are making now will not affect the
  deep ocean for about 1000 years. If we keep
  adding CO2 to the atmosphere and increasing
  global surface temperature we may not see the
  really dramatic ocean results for over 1000
  years.

• What a great thing to leave you
  great-great-great-great-great. Grandchildren.

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Crop Yield Change

• Maps show the percentage change in average crop
  yields for the 2020s, 2050s, and 2080s. Effects
  of CO2 are taken into account. Crops modeled
  are wheat, maize and rice.
• As you can see, most of the world would
  experience a decrease in crop yield.
• Canada is lucky and experiences an increase in
  crop yield due to the increased length of the
  growing season. So Canada is the place to go
  farming by 2080.
• Areas that are particularly hard hit are Mexico,
  some African countries, Saudi Arabia, India,
  Pakistan and other countries in that area.
• Youre basically making dry places even drying
  and less likely to be able to support crop
  growth.

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Projected Changes in Runoff by 2050

• We care about runoff because it is a major source
  of freshwater.
• It is prohibitively expensive to desalinate sea
  water (essentially boil sea water it all the
  water evaporates and leaves salt behind,
  collecting the evaporated water and then
  re-condensing it now that its salt free.
• By looking at the maps you can (sort of) see that
  it is more difficult to calculate how the runoff
  patterns will change. Some areas rain more
  runoff while others very close are experiencing
  extreme decreases.
• As we decrease the availability of freshwater we
  are also likely to decrease the quality of the
  fresh water we do have.
• Areas that are particularly hard hit are the
  Amazon, parts of tropical Africa, the Eastern US
  and Europe.
• Many places still use runoff as a main fresh
  water supply. You can imagine that reducing the
  availability of fresh water can have many
  negative impacts.

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Impacts of Clime Change on Human Health

• Beneficial
• - Reduced winter mortality in mid- and high-
  latitudes
• 1) Due to warmer winter temps
• Adverse
• - Increased mortality from heat stress
• 1) Due to warmer summer temps
• 2) More very hot days
• - Wider spread of infectious diseases
• 1) Longer growing seasons
• 2) More very warm areas
• 3) And fewer places that experience frost
  increase the locations insects that carry
  infectious diseases can breed
• - Worsening air quality
• 1) Increased atmospheric content of CO2, CH4
  and NO2, and O3 probably
• - Decreased food supply in developing countries
• 1) Think about the changes in crop yields and
  remember which countries where going to be hit
  the hardest, those in the Middle East, Africa and
  India.
• - Many impacts from possibly increasing
  frequency and intensity of storms, floods,
  droughts, and cyclones.