EVSC 305: Climate Change – the Science and Local Impact on a Global Environmental Crisis

1. EVSC 305: Climate Change – the Science and Local Impact on a Global Environmental Crisis

2. EVSC 305… • This introductory course will give students an integrated overview of the science of climate change and an analysis of the implications of this change for patterns of daily life in their own circumstance and around the world

3. EVSC 305 • Your reader… • Additional readings… • The website (www.greenresistance.wordpress.com) • Set up your own research database

6. EVSC 305 • 4 objectives • Science of Climate Change • Impacts of Climate Change • Policy Analysis • Mitigation Objectives

7. Writing Assignment 2 page paper on recent news of climate change. Reference. Grammar. Your analysis. Due via email on Friday October 8

8. EVSC 305: Climate Change – the Science and Local Impact on a Global Environmental Crisis Chapters 1 and 2

9. The start… • Climate is dynamic • Nothing simple about how the climate changes: the behavior of the Earth’s climate is governed by a wide range of factors all of which are interlinked in an intricate web of physical processes • What are the factors that most matter? • What is climate change? • What is climate?

10. Weather and Climate: what is the difference? • “Weather is what we get; climate is what we expect. Weather is what is happening to the atmosphere at any given time; climate is what the statistics tell us should occur at any given time of the year” • Emphasis on average conditions • In considering climate change: we are concerned about the statistics of the weather phenomena that provide evidence of longer term changes

11. Climate variability – climate change • Climate variability - the way climatic variables (such as temperature and precipitation) depart from some average state, either above or below the average value. (Although daily weather data depart from the climatic mean, we consider the climate to be stable if the long-term average does not significantly change.) • Climate change - a trend in one or more climatic variables characterized by a fairly smooth continuous increase or decrease of the average value during the period of record.

12. Climate variability – climate change • One basic interpretation: climate variability is a matter or short-term fluctuations; climate change: longer-term shifts. • Potentially oversimplifying • (1) no reason why the climate should not fluctuate randomly on longer timescales; major challenge is to recognize this form of variability • (2) climate change may occur abruptly • Detecting fluctuations in the climate involves measuring a range of past variations of meteorological parameters around the world over a wide variety of timescales • Unfortunately – variety in quality

13. Connections, timescales and uncertainties • Golden rule: do not oversimplify the workings of the climate • Need to understand feedback processes (a perturbation in one part of the system may produce effects elsewhere that bear no simple relation to the original stimulus) – positive and negative feedback processes • Positive: warming  reduction in snow cover in winter  more sunlight absorbed at the surface  more warming • Negative: warming  more water vapor in the atmosphere  more clouds  more sunlight reflected into space  less heating of the surface • [supporting material on feedback systems on http://greenresistance.wordpress.com/climate-change-evsc-305/]

14. Challenge: which processes matter most involves: (1) knowing how a given alteration may disturb the climate; (2) knowing how different timescales affect the analysis of climate • Thus: need to know how changes occur and how they are linked to one another • Continental drift – crucial when interpreting geological records; more immediate consequences (volcanism) more dramatic impact on interannual climate variability • Fluctuations in the output of the Sun

15. Big picture… • Everything in the system is connected to everything else • There is no simple answer to any issue associated with climate change • How do the changes in every aspect of the Earth’s physical conditions and extraterrestrial influences combine? • Atmospheric motions (ever-changing); variations in land surface (…); sea-surface temperatures; pack-ice extent in polar regions; deep-ocean currents; ocean productivity; carbon dioxide levels in the atmosphere; and…

16. Chapter 2: Radiation and the Earth’s energy balance • Essential driving process: supply of energy from the Sun • Properties of solar radiation and how the Earth re-radiates energy to space; • How the Earth’s atmosphere and surface absorb or reflect solar energy and also re-radiate energy to space; • How all these parameters change throughout the year and on longer timescales

17. Solar and terrestrial radiation • Radiative balance of the Earth: over time the amount of solar radiation absorbed by atmosphere and the surface beneath it is equal to the amount of heat radiation emitted by the Earth to space • Global warming: retains some solar energy in the climate system

18. What is radiation? • electromagnetic waves • Characteristics of a wave …

19. What are typical wavelengths of radiation? • units of micrometers are often used to characterize the wavelength of radiation • 1 micrometer = 10-6 meters

20. Radiation laws • Any object not at a temperature of absolute zero (-273.16 C) transmits energy to its surroundings by radiation in the form of electromagnetic waves travelling at the speed of light and requiring no intervening medium • Black body: a body which absorbs all the radiation and which, at any temperature, emits the maximum possible amount of radiant energy; no actual substance is truly ‘black’ • Snow absorbs very little light but is highly efficient emitter of infrared radiation • object does not have to appear "black" • sun and earth's surface behave approximately as black bodies

21. Radiation laws • Spectrum: wavelength dependence of the absorptivity and emissivity of a gas, liquid, or solid • Radiative properties of the Earth are made up of the spectral characteristics of the constituents of the atmosphere, oceans, and land surface

22. Black body…Stefan-Boltzmann law • Black body: the intensity of radiation emitted and the wavelength distribution depend only on the absolute temperature • Expression for emitted radiation is the S-B law: flux of radiation from a black body is directly proportional to absolute temperature • E=sT4 • E/F = flux of radiation • T = absolute temperature (K) of object • s= constant called the Stefan-Boltzman constant = 5.67 x 10-8 Watts m-2 K-4

23. Consider the earth and sun: • Sun: T = 6000 K • so E = 5.67 x 10-8 Watts m-2 K-4 (6000 K)4 = 7.3 x 107 Watts m-2 • Q: is this a lot of radiation??? Compare to a 100 Watt light bulb..... • Earth: T = 288K • so E = 5.67 x 10-8 Watts m-2 K-4 (288 K)4 = 390 Watts m-2 • Q: If you double the temperature of an object, how much more radiation will it emit?  • A: 16 times more radiation

24. Wien displacement law: • Wavelength at which a black body emits most strongly is inversely proportional to the absolute temperature • the hotter the body, the shorter the wavelength of peak emission. • Most objects emit radiation at many wavelengths • However, there is one wavelength where an object emits the largest amount of radiation

25. Weins law • This wavelength is found with Weins Law: lmax = 2897 mm / T(K) • At what wavelength does the sun emit most of its radiation? – 0.5 micrometers • At what wavelength does the earth emit most of its radiation? – 10.0 micrometers

26. Radiative equilibrium • If the temperature of an object is constant with time, the object is in radiative equilibrium at its radiative equilibrium temperature (Te) • Q: What happens if energy input > energy output?  • A: object will be warmer • Q: What happens if energy input < energy output?  • A: object will be cooler • Q: Is the earth in radiative equilibrium?  • A: Earth’s global average is constant with time

27. So… • If the Earth were a black body and the Sun emitted radiation as a black body of temperature 6000 K, then a relatively simple calculation of the planet’s radiation balance produces a figure for the average surface temperature of 270 K • Observed value is about 287 K • Why? • Earth does not absorb all the radiation from the Sun; in principle, should be even cooler – at around 254 K – i.e. FROZEN • Reason for the difference: properties of the Earth’s atmosphere, aka Greenhouse Effect

28. How does the build up for radiatively active gases in the atmosphere alter the temperature? • To understand that… • As the density of the atmosphere decreases rapidly with altitude, any absorption of terrestrial radiation will take place principally near the surface • Since the most important absorber is water vapor, which is concentrated in the lowest levels of the atmosphere, the greatest part of the absorption of terrestrial radiation emitted by the Earth’s surface occurs at the bottom of the atmosphere • In achieving balance between income and outgoing radiation  the surface and lower atmosphere are warmed and the upper atmosphere cooled

29. Interaction of Long Wave Radiation and the Atmosphere • Some of the long-wave radiation emitted by the earth escapes to space • Some of the long-wave radiation is absorbed by gasses in the atmosphere • These gasses then re-emit some of the long wave radiation back to the ground • The additional long-wave radiation reaching the ground further warms the earth • This is known as the "greenhouse effect" • The gasses that absorb the LW emitted by the earth are called "greenhouse gasses"

30. Greenhouse Gases • Methane (CH4) • Carbon Dioxide (CO2) • Ozone (O3) • Water Vapor (H2O) • Nitrous Oxide (N2O)

31. the wavelengths over which the Sun and Earth emit most of their radiation. • The Sun being a much hotter body emits most of its radiation in the shortwave end and the Earth in the longwave end of the spectrum. • The division between shortwave and longwave radiation occurs at about 3 micrometers.

32. Terrestrial radiation • The principal atmospheric gases (oxygen and nitrogen) do not absorb appreciable amounts of infrared radiation • Radiative properties of the atmosphere are dominated by certain trace gases (water vapor, carbon dioxide, ozone) – which interact with infrared radiation in their own way  modifying surface radiation by absorption and re-emission in the atmosphere

33. Remember…Greenhouse Gases • Methane (CH4) • Carbon Dioxide (CO2) • Ozone (O3) • Water Vapor (H2O) • Nitrous Oxide (N2O)

34. How to quantify the impact of the naturally occurring radiatively active gases? • What is their contribution to the warming of the Earth above the figure of 254 K? • Water vapor  21 K • Carbon dioxide  7 K • Ozone  2 K • Note: if the climate warms - the amount of water vapor in the atmosphere will increase. A positive feedback. • Methane, oxides of nitrogen, sulphur dioxide and CFCs also modify the radiative properties of the atmosphere

35. Terrestrial radiation • Where are these greenhouse gases – how are they distributed in the atmosphere? • Most trace constituents are relatively uniform; • water vapor and ozone have a more complicated distribution • Hydrological cycle… • Photochemical process…

36. Hydrological cycle

37. Questions re: H20 cycle • What is the extent to which global warming will alter the [ ] of water vapor in the atmosphere? • Water vapor is dependent on the surface temperature of the Earth  expected to impact future warming (+ive feedback) – depends on whether in a warmer world the increase in water vapor will occur throughout the troposphere • Also: most complicated absorption spectrum

38. Ozone • Majority of ozone is created by photochemical action of sunlight on oxygen in the upper atmosphere • Depends on the amount of sunlight – thus have a marked annual cycle (esp at high latitudes); + pollution in urban areas can produce conditions for photochemical production of ozone  significant widespread increases in lower atmosphere over much of the more populated parts of the world

39. Energy balance of the Earth • Earth’s orbit around the Sun • Earth’s own rotation about its tilted axis

40. Energy budget • Overall – the total incoming flux of solar radiation is balanced by the outgoing flux of both solar and terrestrial radiation

43. Energy budget Key: amount of energy absorbed or reflected is dependent on the surface properties • Snow: high proportion of incident sunlight reflected • Moist dark soil: efficient absorber of sunlight

44. Snow: selective absorption • Snow is a poor absorber of solar radiation, but is a great absorber and therefore emitter of long-wave radiation • during the daytime - snow surface stays cool

45. Selective Absorption - Snow during night time • during night time, snow is only emitting long wave radiation, and is doing it very effectively • so, snow covered surface gets quite cold at night • ski areas in the spring • thin snow cover in the late fall

46. Energy budget • Albedo: amount of solar radiation reflected or scattered into space w/o any change in wavelength (global albedo = ~30%) [yes, know table 2.1] • Eg: what are the implications of this new discovery? – twice as much sunlight is reflected back to space by snow-covered croplands and grasslands as is reflected by snow-covered forests • Solar radiation is absorbed differently on land and at sea • Land: most of the energy absorbed close to the surface, warms up rapidly, increases amount of terrestrial radiation leaving the surface • Sea: solar radiation penetrates deeper; more than 20% reaching 10 m depth; more energy stored in top layer of ocean; less lost to space

47. Clouds and Climate Change • Some clouds help cool the Earth, but other clouds help keep Earth warm – in part depending on how high up they are in our atmosphere. • So: what is the role of low-cloud cover? • Will climate change dissipate clouds, which would effectively speed up the process of climate change, or increase cloud cover, which would slow it down? • One study (July 2009, Science) level clouds tend to dissipate as the ocean warms — which means a warmer world could well have less cloud cover. … A positive feedback • Remember water vapor? The transition betw clouds and vapor … • “The physics of clouds is the greatest obstacle to improving predictions of climate change.” • Data from satellites (data only a few decades old) • Human observations (data back to the 1950s) • Read the scientific article

48. Clouds and Climate Change • a growing consensus among climate modelers is that clouds will increase, rather than hold back, the warming triggered by greenhouse gases. That’s largely because water vapor itself is a powerful greenhouse gas, which means that clouds should trap more heat than they are likely to reflect back into space. • But uncertainty remains • what types of clouds will form and at what altitude? • what particles will the clouds form around? • how can modelers go from predicting the ways any given bank of clouds might behave as opposed to forecasting how the effects on systems of clouds on a regional or global scale? • Plus incomplete cloud observations

49. Role of particulates • Better reflectors of sunlight than they are absorbers of terrestrial radiation • Impact: reduce the net amount received  cooling effect • [eg: dust from drought-prone areas]

50. Role of oceans • Not separate from the atmosphere • Continual exchange of energy • In the form of heat, • momentum as winds stir up waves, • moisture in the form of both evaporation from the oceans to atmosphere, and • precipitation from atmosphere to oceans