Transcript Introduction - Department of Meteorology and Climate Science

MET 112 Global Climate Change - Lecture 1
Dr. Craig Clements
San José State University
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MET 112 Global Climate Change
Definitions
 Weather:
– the state of the atmosphere at a particular point
in time.
 Climate:
– the accumulation of daily or seasonal weather
events over a longer time period.
 Meteorology and Climatology represent the
study of weather and climate respectively, but are
each components of Atmospheric Science and
are dealt with in this course
MET 112 Global Climate Change
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Climate vs. Weather
Weather
Shorter-term fluctuations
Climate
Longer-Term Changes
in atmospheric environment
(e.g., temp, press, ws, wdir,
rainfall amount, etc)
broad composite of average (or mean)
condition of a region (e.g., temp, rainfall,
snowfall, ice cover, winds)
Hours, Days, Weeks
Years (and longer)
Specific location for specific time
Mean state of a specific region
(e.g., continent, ocean, or entire planet)
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MET 112 Global Climate Change
Definitions
 Climate Change:
– Changes in climate of the past, present or
future associated with natural or anthropogenic
(human) factors
 Global Warming:
– Warming of the 20th and 21st century
associated with anthropogenic activities.
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MET 112 Global Climate Change
Change in surface temperature in 20 th century
Observed temperature changes
Units
 Our class will use both English and Metric unit
systems.
 Most important:
– Distance (kilometres and miles)
– Temperature (ºC and ºF)
 Conversions:
1.6 km = 1 mile; 1 km = 0.61 miles
(9/5 x ºC) + 32 = ºF
(ºF – 32) x 5/9 = ºC
MET 112 Global Climate Change
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Unit Review
 What was today’s low temperature in ºC?
 California is about 800 miles long (from Oregon
to Mexico). How many kilometers is that?
 If you were told that the average high
temperature in Sydney Australia at this time of
year is 26ºC, what temperature is that in ºF?
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MET 112 Global Climate Change
Three temperature
scales:
•Kelvin °K= °C+273
•Celsius
•Fahrenheit
•What does
temperature mean
physically?
•What does 0° K mean?
Temperature
Is the measure of the average heat or
thermal energy of the particles in a substance.
(How fast the atoms/molecules are moving)
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MET 112 Global Climate Change
The Solar System
 “The nine planets”
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MET 112 Global Climate Change
Average Surface Temperature of Earth
and Venus: Factors to consider



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MET 112 Global Climate Change
Average Surface Temperature of Earth
and Venus: Factors to consider
 Which planet is closer to the Sun?
 Which planet is more reflective?
 Which planet has a larger ability to absorb and
retain solar energy?
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MET 112 Global Climate Change
Source of Energy:
The Sun
Sun radiates energy;
Energy “radiates
out” with distance
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MET 112 Global Climate Change
The intensity or amount of radiant energy decreases with distance.
* The same amount of energy is spread over a larger area.
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MET 112 Global Climate Change
Earth and Venus
Venus
Earth
Based on solely the
position of Venus and
the Earth, which planet
would be warmer?
Sunlight striking
Venus is 93% stronger
than sunlight striking
Earth, thus we would
expect Venus to be
warmer
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MET 112 Global Climate Change
Temperature Based Only on Distance to
the Sun
 Based only on distance to the sun,
– Venus would be somewhat warmer than
Earth
 Average surface temperatures would be as
follows if the planets absorbed all of the
incoming sunlight:
– Earth: 5°C
– Venus: 55°C
 However …
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MET 112 Global Climate Change
 Venus and Earth do not absorb all of the
incoming sunlight
 Part of the incoming sunlight is reflected back
into space
 Earth reflects 30%
 Venus reflects 70%
 This leads to an important concept
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MET 112 Global Climate Change
Definition
 Albedo: The fraction of light reflected by
an object or a surface
 White objects have high albedos
 Black objects have low albedos
Increasing albedo
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MET 112 Global Climate Change
Comparison of Earth and Venus
Venus
Earth
Venus is completely covered by highly reflective
clouds; Earth is partially covered by clouds. Which
planet has a higher albedo? _______________
Venus
MET 112 Global Climate Change
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Comparison of Earth and Venus
 Earth’s albedo is 30%
 Venus’ albedo is 70%
Earth absorbs 70 % of the sunlight that strikes it.
Venus absorbs 30 % of the sunlight that strikes it.
Let’s re-examine the surface temperatures with this
information.
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MET 112 Global Climate Change
Absorption of Solar Radiation Taking
into Account Distance to Sun and
Albedo
 Let intensity of sunlight striking Earth be denoted by
100
 In these units, intensity of sunlight striking Venus is
193
Earth absorbs
100 x 0.70 = 70 units
Venus absorbs 193 x 0.30 =58 units
Thus, Earth absorbs sunlight at a greater
rate than Venus does!
Temperature Taking Into Account
Distance to Sun and Albedo
 If a planet’s mean surface temperature were
determined solely by the rate of absorption of
solar radiation,
– Venus would be colder than Earth.
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MET 112 Global Climate Change
Actual Surface Temperatures
 Based on average measurements combining
surface air temperature and sea surface
temperatures:
– Earth’s mean surface temperature is about
15°C
– Venus’ mean surface temperature is 480°C!




So…
Venus absorbs less sunlight than Earth, yet
Venus’ surface is much hotter than Earth’s
Why?
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MET 112 Global Climate Change
Recap
 Rate of absorption of sunlight can be calculated
from outer space; distance to sun and albedo
are all that are required
 Surface temperature is not correctly predicted
from rate of absorption of sunlight
 What could cause such a difference?
 The respective atmospheres of the Earth
and Venus
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MET 112 Global Climate Change
Atmospheres of Earth and Venus
(Gases)


Earth
1.
2.
3.
4.
5.
Nitrogen (N2)
Oxygen (O2)
Argon (Ar)
Water Vapor (H2O)
Carbon Dioxide
(CO2)
Venus
1. Carbon Dioxide
2. Nitrogen
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MET 112 Global Climate Change
Principal Atmospheric Gases
Venus
Earth
GAS
MASS
Nitrogen
3870 (75%)
Oxygen
1185 (23%)
Argon
67
(1%)
Water Vapor
17
(0.3%)
CO2
3
(0.06%)
TOTAL
5140
GAS
MASS
CO2
~500, 000 (96%)
N2
~20, 000
TOTAL
520, 000
(4%)
Compare the
amount of CO2
Unit: 1018 g
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MET 112 Global Climate Change
Comparison of Atmospheres
Conclusions:
1. Venus has a much more massive atmosphere
than Earth.
2. Venus’ atmosphere is mostly CO2.
3. The mass of CO2 in Venus’ atmosphere is
almost 100 times greater than the total mass
of Earth’s atmosphere.
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MET 112 Global Climate Change
Why is CO2 So Important?
 Carbon Dioxide is a greenhouse gas.
 Greenhouse gases are those gases that cause
the greenhouse effect.
 The greenhouse effect makes a planet’s
surface temperature warmer than it would
otherwise be.
 The stronger the greenhouse effect, the warmer
the surface (other factors being equal).
 Consider the blanket analogy
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MET 112 Global Climate Change
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MET 112 Global Climate Change