Presentation on theme: "The Greenhouse Effect & Global Warming Lecture 14: Atmospheres Section 1: Measurements of the Temperature and CO 2 in the Earth’s atmosphere."— Presentation transcript:
The Greenhouse Effect & Global Warming Lecture 14: Atmospheres Section 1: Measurements of the Temperature and CO 2 in the Earth’s atmosphere.
Global Temperature: Past 130 years Average Temperature during the 20 th Century
The Greenhouse Effect: Trapping IR Thermal Emission from the planet What is the greenhouse effect?What is the greenhouse effect? What is the cold evidence for Global Warming?What is the cold evidence for Global Warming? What different types of data indicate Global WarmingWhat different types of data indicate Global Warming Is it good, bad, or both...Is it good, bad, or both... How would planets be different without the greenhouse effect?How would planets be different without the greenhouse effect? Compare the greenhouse effect onCompare the greenhouse effect on Venus, Earth, and Mars. Venus, Earth, and Mars. Questions:
Planet Earth: Planet Earth: 4 Billion years of 4 Billion years of a stable environment a stable environment
Charles Keeling 1958 Mauna Loa, Hawaii Develops technique for measuring carbon dioxide in the atmosphere.
A reduction in carbon dioxide occurs every spring and summer each year as plant growth increased in the land-rich northern hemisphere, consuming CO 2 by photosynthesis..
Arctic Ice: Storing CO 2 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 core to analyze the CO 2 trapped inside.
CO2 in atmosphere, measured in thick arctic ice. CO 2 Since the Year 1000 AD
Ice Cores: Deuterium and 18 Oxygen isotopes Correlate with Air Temperature Fractional Increase in DeuteriumTemperature ( o C) Change In 18 O
Variations of deuterium ( δ D) in antarctic ice, which is a proxy for local temperature, and the atmospheric concentrations of the greenhouse gas carbon dioxide (CO 2 ). Note the correlation. Temperature and CO 2 concentration in the atmopshere During the past 400,000 years (from the Antarctic Ice cores) CO 2 (ppm) TEMP ( o C)
Earth’s Temperature Increased 0.9 C in the Atmosphere and Ocean since 1880.
Figure 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 0.76°C ± 0.19°C. Global Averaged Temperature
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.. The extent of the glacier in 1985 is indicated in the figure.kilometerMount BakerWashington Stateglaciermeters Easton Glacier
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.Scandinaviaglacier retreatglobal warming
The Greenhouse Effect & Global Warming Lecture 13: Atmospheres Section 2: The Physics of Infrared Absorption by Molecules
Earth Data: CO 2 and Temperature Why is Temperature closely related to CO 2 ?
Vibrational Modes for CO 2 C O O C OO OOC symmetric bending absorb 15 m asymmetric absorb 4.3 m Greenhouse effect caused by CO 2 : CO 2 molecules absorb infrared light at specific wavelengths, trapping that energy in the Earth’s atmosphere.
Other Greenhouse Gases O OO O HH water ozone NNO C H H HH methane nitrous oxide These molecules in Earth’s atmosphere absorb IR light
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.Earth's atmospheresolar radiationthermal radiation greenhouse gasesRayleigh scatteringEarthSunvisibleKinfraredCchemicalWater vaporcarbon dioxide. Percent Absorption Light Absorbed by the Atmosphere Absorption by gases In the Earth’s Atmosphere
Absorption by different molecules = 0-15 µm Absorption Transmission Peak thermal emission at T=300K CO 2 BendingMode
The Greenhouse Effect Visible Sunlight passes through a planet’s atmosphere. Some of this light is absorbed by the planet’s 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.
What Determines a Planet’s 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 increases the energy (heat) trapped in lower atmosphere it works like a blanketit works like a blanket In the absence of the Greenhouse Effect, what would determine a planet’s surface temperature? the planet's distance from the Sunthe planet's distance from the Sun the planet’s overall reflectivity, “albedo” (fraction reflected)the planet’s overall reflectivity, “albedo” (fraction reflected) the higher the albedo, the less light absorbed, planet coolerthe higher the albedo, the less light absorbed, planet cooler Earth’s average temperature would be –17º C (–1º F) without the Greenhouse Effect ! –17º C (–1º F) without the Greenhouse Effect !
Data CO 2 Levels are higher than in the past 400,000 years. Temperature rose 0.9 C since 1860. CO 2 correlates with Temperature for 400,000 years. Data: CO 2 and Temp. are Rising. Physics: Temp. Related to CO 2, by the Greenhouse Effect. Global Warming Data and Physics.
Feedback: Declining Arctic Ice Causes less reflectivity (Albedo)
Is 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 Fröhlich and Lean (2004; FL2004, green solid line). (Solar max)
Global Warming Made a political issue by certain people. Three Facts are Absolute: 1.Earth has warmed by 0.5 C in past 50 years. Temperature rise greatest in past 10 years. 2.Humans are increasing by 30-50% the CO 2 in the atmosphere. 3.Rising CO 2 will cause rising temperatures Only Question: Not Whether, but by how much are humans contributing to Global Warming ?
Feedback Proceses: Positive and Negative Suppose Temp rises ==> Evaporation of ocean water. Evaporation of ocean water.Feedback: H 2 O is a greenhouse gas ==> Earth gets even Warmer ! Earth gets even Warmer ! But clouds may form, increasing albedo. ==> Earth cools.
The Arctic: Positive Feedback Process Temp rise causes polar cap ice to melt. Artic ground exposed: dirt absorbs more sunlight (lower albedo). Ground warms up more: Earth gets hotter. More polar cap ice melts. Earth gets even hotter.
Consequences of Global Warming 1.More evaporation of oceans: More storms, and more severe storms. 2.Water in oceans expand with rising Temp. Sea level has already risen 20 cm in past 100 years. Coastal regions and islands flood. 3.Polar caps and Glaciers melt: Causes rising ocean levels. 4. Change in ocean current patterns. Desserts may get rain; Farmland may get none.
Consequences of Global Warming According to the UN report: The world will be a much hotter place by 2100. Coral reefs almost extinct In North America, a new dust-bowl brings deserts to life in the high plains states, centered on Nebraska, but also wipes out agriculture andcattle ranching as sand dunes appear across five US states, from Texas in the south to Montana in the north.Rising sea levels accelerate as the Greenland ice sheet tips into irreversible melt, submerging atoll nations and low-lying deltas. In Peru, disappearing Andean glaciers mean 10 million people face water shortages. Warming seas wipe out the Great Barrier Reef and make coral reefs virtually extinct throughout the tropics. Worldwide, a third of all species on the planet face extinction+3.4 ｡ : Rainforest turns to desert The Amazonian rainforest burns in a firestorm of catastrophic ferocity, covering South America with ash and smoke. Once the smoke clears, the interior of Brazil has become desert, and huge amounts of extra carbon have entered the atmosphere, further boosting global warming. The entire Arctic ice-cap disappears in the summer months, leaving the North Pole ice-free for the first time in 3 million years. Polar bears, walruses and ringed seals all go extinct. Water supplies run short in California as the Sierra Nevada snowpack melts away. Tens of millions are displaced as the Kalahari desert expands across southern Africa. Melting ice caps displace millions Rapidly-rising temperatures in the Arctic put Siberian permafrost in the melt zone, releasing vast quantities of methane and CO2. Global temperatures keep on rising rapidly in consequence. Melting ice-caps and sea level rises displace more than 100 million people, particularly in Bangladesh, the Nile Delta and Shanghai. Heatwaves and drought make much of the sub-tropics uninhabitable: large-scale migration even takes place within Europe, where deserts are growing in southern Spain, Italy and Greece. More than half of wild species are wiped out, in the worst mass extinction since the end of the dinosaurs. Agriculture collapses in Australia+5.4 ｡ : Sea levels rise by five metresThe West Antarctic ice sheet breaks up, eventually adding another five metres to global sea levels. If these temperatures are sustained, the entire planet will become ice-free, and sea
Predictions of temperatures next 100 years DEPENDS ON MAGNITUDE OF FEEDBACK AND RATE OF INCREASE OF GHG. IN 100 YEARS, FORCED CLIMATE CHANGE WILL MOST LIKELY EXCEED NATURAL VARIABILITY
The Greenhouse Effect & Global Warming Lecture 13: Atmospheres Section 4: Comparison of Atmospheres: Earth to Venus and Mars
4.6 Billion Years Ago... (150 million km from Sun) 1 AU0.7 AU1.5 AUSUNVenusEarthMars
Temperature: Top of Atmosphere Temperature (Celsiu) 500 300 10 0 0 -100 decreases with distance from Sun 5500 o C Earth -18 o C (0 o F) Venus Distance From Sun Mars 0 0 0 300 500 200 100 -100 400 Temperature (C)
Clue: atm composition 500 300 100 0 -100 Temperature (Celsius) EARTH EARTH: Surface 15 o C (60 o F) Top of Atm: -18 o C (0 o F) All three phases of water Surface warmer than top of atm Greenhouse Effect Surface No Greenhouse
Climate History of Venus Venus should have outgassed as much H 2 O as Earth. Early on, when the Sun was dimmer, Venus may have had oceans of waterEarly on, when the Sun was dimmer, Venus may have had oceans of water Venus’ proximity to the Sun caused all H 2 O to evaporate. H 2 O caused runaway greenhouse effectH 2 O caused runaway greenhouse effect surface heated to extreme temperaturesurface heated to extreme temperature CO 2 released from rocks: Adds to greenhouse effectCO 2 released from rocks: Adds to greenhouse effect UV photons from Sun dissociate H 2 O; H 2 escapes, O is strippedUV photons from Sun dissociate H 2 O; H 2 escapes, O is stripped If Earth moved to Venus’ Orbit
Venusian Weather Today Venus has no seasons to speak of.Venus has no seasons to speak of. rotation axis is nearly 90º to the ecliptic planerotation axis is nearly 90º to the ecliptic plane Venus has little wind at its surfaceVenus has little wind at its surface rotates very slowly, so there is no Coriolis effectrotates very slowly, so there is no Coriolis effect The surface temperature stays constant all over Venus.The surface temperature stays constant all over Venus. thick atmosphere distributes heat via two large circulation cellsthick atmosphere distributes heat via two large circulation cells There is no rain on the surface. it is too hot and Venus has almost no H 2 Oit is too hot and Venus has almost no H 2 O Venusian clouds contain sulfuric acid! implies recent volcanic outgassing?implies recent volcanic outgassing?
Mars’ Thin Atmosphere Martian sunset illustrates just how thin the Martian atmosphere is.
The Earth is Changing Rapidly Who Speaks for Earth? Who is the steward, the shepherd, the parent of our home planet? CO 2 is higher than at any time in recorded history. Global Temperatures are rising Humans are changing the planet Earth, for the first time in history. for the first time in history. We don’t know the outcome of our experiment with our planet. Maybe everything will be perfectly OK. But Venus offers pause.
Martian Weather Today Seasons on Mars are more extreme than on EarthSeasons on Mars are more extreme than on Earth Mars’ orbit is more ellipticalMars’ orbit is more elliptical CO 2 condenses & vaporizes at opposite polesCO 2 condenses & vaporizes at opposite poles changes in atmospheric pressure drive pole-to-pole windschanges in atmospheric pressure drive pole-to-pole winds sometimes cause huge dust stormssometimes cause huge dust storms