1 MET 112 Global Climate Change Dr. Craig Clements San José State University MET 112 Global Climate Change - Lecture 1

2 MET 112 Global Climate Change What is weather vs. climate?  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

3 MET 112 Global Climate Change Climate vs. Weather WeatherClimate Shorter-term fluctuationsLonger-Term Changes in atmospheric environmentbroad composite of average (or mean) (e.g., temp, press, ws, wdir,condition of a region (e.g., temp, rainfall, rainfall amount, etc)snowfall, ice cover, winds) Hours, Days, WeeksYears (and longer) Specific location for specific timeMean state of a specific region (e.g., continent, ocean, or entire planet)

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5 Climate Change?  Climate Change: – Changes in climate of the past, present or future associated with natural or anthropogenic (human) factors  Global Warming: – Warming of the 20 th and 21 st century associated with anthropogenic activities.

6 MET 112 Global Climate Change 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

7 MET 112 Global Climate Change 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?

Three temperature scales: KelvinKelvin CelsiusCelsius FahrenheitFahrenheit What does temperature mean physically?What does temperature mean physically? What does 0° K mean?What does 0° K mean? °K= °C+273

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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11 MET 112 Global Climate Change The Solar System  “The nine planets”The nine planets

12 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?

13 MET 112 Global Climate Change Source of Energy: The Sun Sun radiates energy; Energy “radiates out” with distance

14 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.

15 MET 112 Global Climate Change Earth and Venus Venus Earth Sunlight striking Venus is 93% stronger than sunlight striking Earth, thus we would expect Venus to be warmer Based on solely the position of Venus and the Earth, which planet would be warmer?

16 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 …

17 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

18 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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21 MET 112 Global Climate Change Comparison of Earth and Venus Venus is completely covered by highly reflective clouds; Earth is partially covered by clouds. Which planet has a higher albedo? _______________ Venus Earth Venus

22 MET 112 Global Climate Change Comparison of Earth and Venus  Earth’s albedo is 30%  Venus’ albedo is 70% Earth absorbs70% of the sunlight that strikes it. Venus absorbs30% of the sunlight that strikes it. Let’s re-examine the surface temperatures with this information.

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 absorbs100 x 0.70 = 70units Venus absorbs193 x 0.30 =58units Thus, Earth absorbs sunlight at a greater rate than Venus does!

24 MET 112 Global Climate Change 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.

25 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?

26 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

27 MET 112 Global Climate Change Atmospheres of Earth and Venus (Gases)  Earth 1.Nitrogen (N 2 ) 2.Oxygen (O 2 ) 3.Argon (Ar) 4.Water Vapor (H 2 O) 5.Carbon Dioxide (CO 2 )  Venus 1.Carbon Dioxide 2.Nitrogen

28 MET 112 Global Climate Change Principal Atmospheric Gases Earth Venus GASMASS Nitrogen 3870 (75%) Oxygen 1185 (23%) Argon 67 (1%) Water Vapor 17 (0.3%) CO 2 3 (0.06%) TOTAL 5140 GASMASS CO 2 ~500, 000 (96%) N2N2 ~20, 000 (4%) TOTAL520, 000 Unit: g Compare the amount of CO 2

29 MET 112 Global Climate Change Comparison of Atmospheres Conclusions: 1.Venus has a much more massive atmosphere than Earth. 2.Venus’ atmosphere is mostly CO 2. 3.The mass of CO 2 in Venus’ atmosphere is almost 100 times greater than the total mass of Earth’s atmosphere.

30 MET 112 Global Climate Change Why is CO 2 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