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ATM S 111, Global Warming: Understanding the Forecast

ATM S 111, Global Warming: Understanding the Forecast. Dargan M. W. Frierson Department of Atmospheric Sciences Day 2: 04/01/2010. A Confession…. It’s all made up We did it for the grant money. My Recent Grant Applications. Hot in Herre: On Earth and in the Club

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ATM S 111, Global Warming: Understanding the Forecast

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  1. ATM S 111, Global Warming: Understanding the Forecast Dargan M. W. Frierson Department of Atmospheric Sciences Day 2: 04/01/2010

  2. A Confession… • It’s all made up • We did it for the grant money

  3. My Recent Grant Applications • Hot in Herre: On Earth and in the Club • TiK ToK on the Clock: Neither the Party Nor the Carbon Dioxide Emissions are Going to $top • The Hydrologic Cycle and Makin’ it Rain

  4. How Grants Actually Work • I currently have 3 grants: • Two from the National Science Foundation (NSF), one from National Oceanic and Atmospheric Administration (NOAA) • NSF #1: Tropical atmospheric circulation and global warming • NSF #2: Processes that determine the midlatitude atmospheric vertical structure • NOAA: Natural climate variability of the tropics (the Madden-Julian Oscillation) • There are plenty of important natural weather/climate phenomena to worry about… • Further, they’re reviewed by other scientists, so exaggerating impacts doesn’t get you far

  5. What Do Grants Pay For? • My grants pay almost exclusively for graduate students • Tuition & salary for them • Also undergrad research assistants • I get up to 3 months (summer) salary from grants, but having grants doesn’t increase my income • Grants also pay for visits to conferences, publication fees, research equipment, etc. • Grants are a significant source of income for the university as well • UW took in over $1 billion in grant funds last year (we’re #1 in the nation in federal grants)

  6. Talk Tonight • Plastic Solar Cells? Challenges and Opportunities for Photovoltaics • David Ginger (UW Chemistry Department) • Kane 130, 6:30 PM • Reserve a seat at http://courses.washington.edu/efuture/

  7. Reading Assignments • From last time: • Make sure you’ve read Rough Guide p. 3-19 “Climate Change: A Primer” • The Big Picture • The Outlook • What Can We Do About It • Next reading assignment: • Rough Guide p. 20-31 “The Greenhouse Effect” • If it’s about hotels in Melbourne you might have bought the wrong Rough Guide

  8. Outline of This Lecture • Review of: How exactly the Sun heats the Earth • How strong? • Important concept of “albedo”: reflectivity • How the greenhouse effect works • How the Earth cools • And how greenhouse gases lead to less cooling • What are the main greenhouse gases? • And which are changed by human activity?

  9. How Does Energy Arrive From the Sun? • Energy from the Sun is called “shortwave radiation” or solar radiation • Radiation with shorter wavelengths is more energetic • This has long wavelength and low energy • This has short wavelength and high energy

  10. Average Solar Radiation • Solar radiation at top of atmosphere is 1366 W/m2 • Average solar radiation on Earth is 342 W/m2 Reason for seasons: Winter hemisphere is tilted away from the Sun, and gets less direct sunlight

  11. Solar Radiation on Earth • 30% is reflected back out to space • Mostly by clouds, also some by the surface or by the atmosphere • 20% is absorbed in the atmosphere • 50% is absorbed at the surface • Next: how does the Earth lose energy?

  12. “Longwave Radiation” • The Sun is the energy input to the climate system • How does the Earth lose energy? • Turns out it’s also by radiation! • But it’s not visible light like from the Sun, it’s infrared radiation AKA “longwave radiation” Infrared satellite image 

  13. “Longwave Radiation” • Everything actually emits radiation • Depends partly on the substance but mostly on temperature Neck = hotter Hair = colder Infrared thermometer

  14. Longwave Radiation • Higher temperature means more radiation Eyes and inner ears are warmest: they radiate the most Nose is the coldest: it radiates less A WARM CAT…. IZ A HAPPY CAT Thermal night vision technology detects longwave radiation

  15. Temperature & Radiation • Higher temperature = more radiation and more energetic radiation (shorter wavelengths) • Explains the Sun’s radiation too • Sun is really hot  • It emits much more radiation • It emits shortwave radiation instead of longwave radiation like the Earth

  16. Energy Into and Out of the Earth • Heating/cooling of Earth • The Earth is heated by the Sun (shortwave radiation) • The Earth loses energy by longwave radiation (out to space)

  17. “Energy Balance” • If the energy into a system is greater than the energy out, the temperature will increase • A temperature increase then results in an increase of energy out • Hotter things radiate more • This will happen until: • When energy in equals energy out, we call this “energy balance” Energy in Energy out

  18. Energy Balance on Earth • If the solar radiation into Earth is greater than the outgoing longwave radiation, the temperature will increase • A temperature increase then results in an increase of the longwave radiation out (hotter things radiate more) • This will happen until: • Global warming upsets the energy balance of the planet Shortwave in Longwave out

  19. Energy Balance with No Atmosphere • If there was no atmosphere, for energy balance to occur, the mean temperature of Earth would be 0o F (-18o C) • Missing piece: the greenhouse effect • All longwave radiation doesn’t escape directly to space -18o C (0o F)

  20. The Greenhouse Effect • Greenhouse gases block longwave radiation from escaping directly to space • These gases re-radiate both upward and downward • The extra radiation causes additional warming of the surface Extra downward radiation due to greenhouse gases 15o C (59o F)

  21. The Greenhouse Effect • Greenhouse gases cause the outgoing radiation to happen at higher levels (no longer from the surface) • Air gets much colder as you go upward • So the radiation to space is much less (colder  less emission) 15o C (59o F)

  22. The Greenhouse Effect • Greenhouse effect is intuitive if you pay attention to the weather! • Cloudy nights cool less quickly • In the desert, temperatures plunge at night! • No clouds & little water vapor in the desert: little greenhouse effect

  23. What are the Major Greenhouse Gases? • Our atmosphere is mostly nitrogen (N2, 78%), oxygen (O2, 21%), and argon (Ar, 0.9%) • But these are not greenhouse gases • Molecules with 1 atom or 2 of the same atoms aren’t greenhouse gases though • Just like the atmosphere is almost transparent to solar radiation, the primary gases in our atmosphere are transparent to longwave radiation If our atmosphere was only nitrogen, oxygen, and argon, this picture with no greenhouse effect would be accurate!

  24. Greenhouse Gases • Polyatomic molecules are greenhouse gases • Water vapor (H2O) • Carbon dioxide (CO2) • Methane (CH4) • Nitrous oxide (N2O) • Ozone (O3) • Chlorofluorocarbons (the ozone depleting chemicals which have been banned) The fact that they can rotate and vibrate means they can absorb the right frequencies of longwave

  25. Greenhouse Gases • All greenhouse gases are a rather small fraction of the atmosphere! • Water vapor has the highest concentration: 0.4% • CO2: 0.04% • Methane: 0.0002% • “Trace gases” have a remarkable effect on the atmosphere • E.g., ozone is less than 0.00001% of the atmosphere, but absorbs essentially all harmful UV-B and UV-C radiation • Let’s discuss each gas separately

  26. Water Vapor • Gas form of water • AKA humidity • Not the same as clouds – clouds are tiny droplets of water suspended in air • The number one greenhouse gas! • Powerful because there’s a lot of it • Not controlled by humans! • It’s a feedback not a forcing (topic of the next lecture) • Observed to be increasing with global warming

  27. Carbon Dioxide • CO2 • It’s what we breathe out, what plants breathe in • The primary contributor to the anthropogenic (human-caused) greenhouse effect • 63% of the anthropogenic greenhouse effect so far • Increases primarily due to fossil fuel burning (80%) and biomass burning (e.g., forest fires; 20%) • Preindustrial value: 280 ppm • Current value: 386 ppm

  28. Carbon Dioxide • CO2 will also be the main problem in the future • It’s extremely long-lived in the atmosphere • 50% of what we emit quickly gets taken up by the ocean or land • We’ll discuss this more later • Most of the rest sticks around for over 100 years • Some of what we emit will still be in the atmosphere over 1000 years from now!

  29. Methane • CH4 • Natural gas like in stoves/heating systems • Much more potent on a per molecule basis than CO2 • Only 1.7 ppm though – much smaller concentration than CO2 • Natural sources from marshes (swamp gas) and other wetlands • Increases anthropogenically due to farm animals (cow burps), landfills, natural gas leakage, rice farming

  30. Methane • The lifetime of CH4 is significantly shorter than carbon dioxide • Breaks down in the atmosphere in chemical reactions • Lifetime of methane is only 8 years Methane concentrations have been leveling off in recent years, possibly due to drought in wetlands at high latitudes

  31. Global Warming Potential • CO2 lifetime > 100 years • Methane lifetime = 8 years • But methane is a much stronger greenhouse gas • How to put these on similar terms? Global warming potential (or GWP) • Global warming potential is how much greenhouse effect emissions of a given gas causes over a fixed amount of time (usually 100 years) • Measured relative to CO2 (so CO2 = 1) • Methane’s global warming potential is 25 • Much more potent than CO2 (25 times more powerful) even though it doesn’t stay as long

  32. Nitrous Oxide • N2O • Laughing gas • Also more potent on a per molecule basis than CO2 • Global warming potential: 310 • Comes from agriculture, chemical industry, deforestation • Small concentrations of only 0.3 ppm

  33. Ozone • Ozone or O3 occurs in two places in the atmosphere • In the ozone layer very high up • This is “good ozone” which protects us from ultraviolet radiation & skin cancer • Remember ozone depletion is not global warming! • Near the surface where it is caused by air pollution: “bad ozone” • Bad ozone is a greenhouse gas, and is more potent on a per molecule basis than CO2 • But very very short-lived • Fun fact: Global warming potential for ozone is not usually calculated – rather it’s wrapped into the GWPs of the other gases that lead to its chemical creation

  34. CFCs • CFCs or chlorofluorocarbons are the ozone depleting chemicals • Have been almost entirely phased out • CFCs are strong greenhouse gases • Their reduction likely saved significant global warming in addition to the ozone layer! • Some replacements for CFCs (called HFCs) are strong greenhouse gases though • Global warming potentials of up to 11,000!

  35. The Natural Greenhouse Effect • Contributions to the natural greenhouse effect: • H2O (water vapor): 60% • CO2(carbon dioxide): 26% • All others: 14% • These numbers are computed with a very accurate radiation model • First running with all substances, then removing each individual gas

  36. The Unnatural Greenhouse Effect • Increasing levels of CO2 and other greenhouse gases leads to a stronger greenhouse effect • With more greenhouse gases, it becomes harder for outgoing radiation to escape to space It’s like this same picture from before, but more. More radiation is trapped before it gets out to space. Longwave radiation is emitted from a higher (and colder) level on average.

  37. The Unnatural Greenhouse Effect • Contributors to the “anthropogenic” greenhouse effect • Numbers for the whole world up to this point: • Carbon dioxide: 63% • Methane: 18% • CFCs, HFCs: 12% • Nitrous oxide: 6%

  38. The Anthropogenic Greenhouse Effect • Contributors to the “anthropogenic” greenhouse effect • Numbers for the US based on current (2008) emissions CO2 is the big problem in the US currently. Note how much lower the HFCs are than on the previous slide. This is b/c we basically don’t emit CFCs any more. From US EPA 2010 report (draft)

  39. Summary • The Earth is heated by the Sun • This is shortwave radiation • Albedo: key factor that determines how much radiation is absorbed vs reflected • Earth loses energy due to longwave radiation • The greenhouse effect causes less efficient heat loss to space by longwave radiation • Greenhouse gases: • Number one is water vapor • Number two is CO2 • Global warming potential: total warming caused over a fixed time period

  40. Extra Credit Questions • Climate change vs global warming? • And ATM S 211 “Climate Change” vs ATM S 111 “Global Warming”? • Painting buildings white to increase albedo & cool cities? • Why does the Earth continue to warm even if CO2 remains fixed?

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