Question of the Day • Based on energy balance models, we would expect the average surface temperature of the earth to be only –18oC. However the temperature is actually about 15oC. Hmm…what gives?
The Greenhouse Effect • Solar radiation reaches the Earth’s surface as UV and visible light • Some is absorbed by the surface • Some of this is then re-radiated as IR • But some of the IR can’t get back out of the atmosphere, and is reflected back to the earth • So the earth’s temperature is higher than you would otherwise expect – and we can live here!
The Earth’s Energy Balance Greenhouse effect Our atmospheric gases trap and return a major portion of the heat radiating from the Earth. It is a natural, necessary process.
http://www.planetguide.net/book/chapter_3/greenhouse_effect.htmlhttp://www.planetguide.net/book/chapter_3/greenhouse_effect.html Web-based Animations of the Greenhouse Effect
Molecules: How They Shape Up • Molecular shape will affect whether a molecule is a ‘greenhouse gas’ (GHG) • Shape can be determined using Lewis Structures or molecular models • Reminder: The most stable molecular shape is the one in which the bonding or nonbonding electron groups attached to any atom are as far from each other as possible • Example: Water
CO2 and CH4 Molecules The two most important greenhouse gases!
Molecular response to different types of radiation Greenhouse effect Ozone Cooking
Trends in Global Temperature ISAT 112
1997 1995 1998
Average global surface temperatures have increased since 1880. The red bars indicate average temperatures for the year while the black error bars show the range for each year. The blue line is the 5-year moving average.
Weihenstephen Brewery in Freising starts, 1040! More Temperature Trends…
Comparison of Greenhouse Gases Gas Factor Abundance% Impact • CO2 1 3.7*10-2 1 • CH4 30 1.8*10-4 .145 • N2O 160 3.1*10-5 .132 • O3 2000 4.0*10-6 .22 • CCl2F2 25,000 5.2*10-8 .035 These gases have the ability to capture outgoing IR radiation from the earth, absorb that radiation, and re-radiate it back to the earth. The greenhouse effect!
2005: 379.5 ppm 2010: 392.9 ppm CO2 Measurements - Hawaii
The concentration of carbon dioxide (blue) and the global temperature (red) are well correlated over the past 400,000 years as derived from ice core data.
The Vostok ice core goes back 400,000 years. The current concentration of atmospheric carbon dioxide is 100 ppm higher than any time in the last million years.
Causes of GG increase Increased combustion Industrial revolution Fossil fuels Deforestation Amazon rainforest = 4,224,905 football fields/yr 8 football fields/minute Agriculture Melting of permafrost
CO2 Emissions by Country:Total emissions since 1950 (b tons) Graphic from: Michael Glantz, “What Makes Good Climates Go Bad? … and … “Why Care?” USAEE/IAEE Meeting, 9-19-05.
What might be true: • CO2 and other gases generated by human activity contribute to the temperature increase. In a recent poll, 97% of climate scientists believe that this is true. (http://www.sciencedaily.com/releases/2009/01/090119210532.htm) • The average global temperature will continue to rise as emissions of anthropogenic greenhouse gases increase.
Projected future regional patterns of warming based on three emissions scenarios (low, medium, and high growth). Source: NASA Earth Observatory, based on IPCC Fourth Assessment Report (2007)
Temperature projections to the year 2100, based on a range of emission scenarios and global climate models.
Global Climate Change bottom line • There is ample evidence that • the Earth experiences (and we rely on) the “greenhouse effect” • carbon dioxide is a “greenhouse gas” • the temperature of the atmosphere has been rising over the past century • the concentration of carbon dioxide is also rising, and correlates both to this increase in temperature and the use of fossil fuels • What is debated is whether humans are causing these changes • The Intergovernmental Panel on Climate Change (IPCC) has said yes for years, and the Kyoto Protocol was intended to address this
Sources of CO2 Fig. 3.17
One Gallon Gas = 20 lbs CO2 • Is this right? What do we need to know to prove it? • What is the basic formula for gasoline? • What is its density? • How much carbon is in the gasoline? • What are the products of its combustion? • What is the ratio of CO2 produced to carbon burned?
Analysis • 8 pints/gal * 0.8 lb gas /pint = 6.4 lbs gas/gal • C8H18 = 114 g/mol, 84.21% C • 6.4 lb gas/gal * 1000 g/2.2lbs = 2910 g gas • 2910 g gas * .8421% C = 2450 g C • 2450 g C/gal * 44 g/mol CO2/12 g/mol C = 8983 g CO2/gal • 8983g CO2 * 2.2lb./1000g = 19.76 lb CO2/gal gas
Some Questions about Global Warming • Does increased CO2 in the atmosphere really induce growth? • Can forests and soils sequester enough carbon to offset anthropogenic sources? • How much proof is needed to recognize and act on a problem like global warming? • What should we/can we do at the individual level?