the greenhouse effect & global warming

CO2 Variations, 1999 Mauna Loa, Hawaii

The Greenhouse Effect&Global Warming

Lecture 14: Atmospheres

Section 1: Measurements of the Temperature and CO2 in the Earths atmosphere.

1Welcome to Lecture 13 of The Planets. This is the second lecture on the Atmospheres of the Terrestrial Planets.This lecture is on the Greenhouse Effect and Global Warming on the Earth and Other terrestrial worlds. In the first section, well be discussing how certain molecules in the Earths atmosphere absorb infrared light.Global Temperature: Past 130 years

Average Temperatureduring the 20th CenturyThe Greenhouse Effect: Trapping IR Thermal Emissionfrom the planetWhat is the greenhouse effect?What is the cold evidence for Global Warming?What different types of data indicate Global WarmingIs it good, bad, or both . . .How would planets be different without the greenhouse effect?Compare the greenhouse effect on Venus, Earth, and Mars.Questions:3

Planet Earth: 4 Billion years of a stable environment4Charles Keeling

1958Mauna Loa,Hawaii

Develops techniquefor measuringcarbon dioxide inthe atmosphere.

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A reduction in carbon dioxide occurs every spring and summer each year as plant growth increased in the land-rich northern hemisphere, consuming CO2 by photosynthesis..6Arctic Ice:Storing CO2 for 400,000 Years

The Vostok ice cores provide the longest continuous record of Antarctic climatic history. Cores go to a depth of 3350 meters, representing approximately 440,000 years of climate history.Vostok ice core drilling site in Antarctica

Snow falls year after year, forming stratified layers in ice. Trapped within these layers are small air bubbles that get trapped during snow falls. These air bubbles contain samples of atmospheric composition.

Cutting an ice coreto analyze the CO2 trapped inside.7

CO2 in atmosphere, measured in thick arctic ice.CO2 Since the Year 1000 AD8FAQ 2.1, Figure 1

9FAQ 2.1, Figure 1. Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample. (Data combined and simplified from Chapters 6 and 2 of this report.)

Ice Cores:Deuterium and 18Oxygen isotopes Correlate with Air Temperature

Fractional Increase in DeuteriumTemperature (oC)ChangeIn18O

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Variations of deuterium (D) in antarctic ice, which is a proxy for local temperature, and the atmospheric concentrations of the greenhouse gas carbon dioxide (CO2). Note the correlation.Temperature and CO2 concentration in the atmopshereDuring the past 400,000 years (from the Antarctic Ice cores)CO2(ppm)TEMP(oC)11

Earths Temperature Increased 0.9 C in the Atmosphere and Ocean since 1880.12Figure TS.6

Patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere from satellite records (right). Grey indicates areas with incomplete data. (Bottom) Annual global mean temperatures (black dots) with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right hand axis shows estimated actual temperatures, both in C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100 (magenta) and 150 years (red). The smooth blue curve shows decadal variations (see Appendix 3.A), with the decadal 90% error range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76C 0.19C.Global Averaged Temperature13Figure TS.6. (Top) Patterns of linear global temperature trends over the period 1979 to 2005 estimated at the surface (left), and for the troposphere from satellite records (right). Grey indicates areas with incomplete data. (Bottom) Annual global mean temperatures (black dots) with linear fits to the data. The left hand axis shows temperature anomalies relative to the 1961 to 1990 average and the right hand axis shows estimated actual temperatures, both in C. Linear trends are shown for the last 25 (yellow), 50 (orange), 100 (magenta) and 150 years (red). The smooth blue curve shows decadal variations (see Appendix 3.A), with the decadal 90% error range shown as a pale blue band about that line. The total temperature increase from the period 1850 to 1899 to the period 2001 to 2005 is 0.76C 0.19C. {FAQ 3.1, Figure 1.}

Change in Temperature from 1960 to 200015Since 1850: Atmospheric CO2 has increased by 25% Increase in Temperature tracksIncrease in Greenhouse GasesYear18502000

Temperature vs Time

16Earth Data: CO2 and Temperature

17Carbon Dioxide:Humans are putting CO2into our Atmosphere

Worldwide CO2 ProductionBy fuel type: 1970 - 2020Burning coalGasolineNatural gasFact, not speculation.

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The Greenhouse Effect&Global Warming

Lecture 13: Atmospheres

Section 3: Glaciers are Retreating Feedback Mechanisms of the Greenhouse Effect Projections for the Future of our Atmosphere19Franz Josef Glacier In Retreat

195119601964193920Muir Glacier, Alaska

1941200421McCarty Glacier - Alaska

22Retreat of Glaciers

19482002Trift Glacier, Gadmental, Berner, Oberland Switzerland200623Mt. Hood, Oregon

1984200224

A 2003 photograph of the ~2.9 square kilometer Easton Glacier on Mount Baker in Washington State. Between ~1890 and 1950, this glacier retreated ~2400 meters. It subsequently expanded 600 meters during a locally cold period between 1950 and 1979. Since then, it has again retreated 315 meters (as of 2002) with 150 meters lost solely between 1997 and 2002.[1]. The extent of the glacier in 1985 is indicated in the figure.Easton Glacier25

All survey regions except Scandinavia show a net thinning. This widespread glacier retreat is generally regarded as a sign of global warming. During this period, 83% of surveyed glaciers showed thinning with an average loss across all glaciers of 0.31 m/yr. 26Retreating GlaciersGlacier Mass

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The Greenhouse Effect&Global Warming

Lecture 13: Atmospheres

Section 2:The Physics of Infrared Absorption by Molecules 28Earth Data: CO2 and Temperature

Why is Temperature closely related to CO2 ?29Vibrational Modes for CO2COOCOOOOCn1 symmetricn2 bending absorb 15 mm asymmetric absorb 4.3 mmGreenhouse effect caused by CO2: CO2 molecules absorb infrared light at specific wavelengths, trapping that energy in the Earths atmosphere. 30Other Greenhouse GasesOOOOHHwaterozoneNNOCHHHHmethanenitrous oxideThese molecules in Earths atmosphere absorb IR light31

Absorption in the Earth's atmosphere (middle panel) and the effect that this has on both solar radiation and upgoing thermal radiation (top panel). Individual absorption spectrum for major greenhouse gases plus Rayleigh scattering are shown in the lower panel.

Both the Earth and the Sun shine by thermal emission of light. For the sun, these emissions peak in the visible region and correspond to a temperature of ~5500 K. Emissions from the Earth vary following variations in temperature across different locations and altitudes, but always peak in the infrared. The Earth has an average emission temperature of about 250 K (-20 C).

The wavelengths of absorption bands are determined by the chemical properties of the gases present. Water vapor is the most significant of these greenhouse gases, followed by carbon dioxide.Percent AbsorptionLight Absorbed by the AtmosphereAbsorption by gases In the Earths Atmosphere32Absorption by different molecules l = 0-15 m

AbsorptionTransmissionPeak thermal emission at T=300KCO2BendingMode33How Greenhouse Gases Warm the Troposphere

CO234The Greenhouse Effect

Visible Sunlight passes through a planets atmosphere.Some of this light is absorbed by the planets surface.Planet warms. Emits its own light: thermal radiation, as infrared (IR) light - back out to space.IR light is absorbed by the molecules and sent back to Earth !Result: the temperature is higher than if there were no atmosphere at all.35What Determines a Planets Surface Temperature?Greenhouse Effect cannot change incoming Sunlight, so it cannot change the total energy returned to space.it increases the energy (heat) trapped in lower atmosphereit works like a blanket

In the absence of the Greenhouse Effect, what would determine a planets surface temperature?the planet's distance from the Sunthe planets overall reflectivity, albedo (fraction reflected)the higher the albedo, the less light absorbed, planet cooler

Earths average temperature would be 17 C (1 F) without the Greenhouse Effect !36DataCO2 Levels are higher than in the past 400,000 years.

Temperature rose 0.9 C since 1860.

CO2 correlates with Temperature for 400,000 years.

Data: CO2 and Temp. are Rising.

Physics: Temp. Related to CO2, by the Greenhouse Effect.Global Warming Dataand Physics. 37Feedback: Declining Arctic IceCauses less reflectivity (Albedo)

38Is the Sun to Blame ? No. Luminosity has been constant.Sunlight hitting Earth:

11 year Sunspot cycle Offsets among instruments No trend

Percentage change in monthly values of the total solar irradiance composites of Willson and Mordvinov (2003; WM2003, violet symbols and line) and Frhlich and Lean (2004; FL2004, green solid line).

(Solar max)39Global WarmingMade a political issue by certain people.