Chapter 23: The Atmosphere, Climate and Global Warming

1. Chapter 23: The Atmosphere, Climate and Global Warming

2. The Origins of the Global Warming Issue • Concern arises from two kinds of evidence: • Increase in average surface temperature of the Earth from 1860 to the present • Increase in carbon dioxide concentrations in the atmosphere. • Measured on Mauna Loa in Hawaii by Charles Keeling

5. The Origins of the Global Warming Issue • Relationship between chemistry of planet’s atmosphere and planet’s surface temperature. • Certain gases trap heat energy and warm the plant • Since this idea was first introduce has stirred controversy

6. Structure of the Atmosphere • Made up of several layers • Troposphere- bottom layer • Where weather occurs • Temperature decrease w/ elevation • At the top is tropopause- acts as a lid • Stratosphere- above the troposphere • Stratospheric ozone layer just above the tropopause • Protects again UV radiation

8. Atmospheric Processes • Pressure and temperature – These components of atmosphere are physically related to one another. • Pressure is force per unit area. • Caused by the weight of overlying atmospheric gases on those below • Decreases w/ altitude • Low pressure systems usually bring clouds • High pressure systems usually bring clear skies

9. Atmospheric Processes • Atmosphere moves because of the Earth’s rotation and differential heating. • Produce global patterns of prevailing winds and latitudinal belts of high and low pressure

11. What Makes the Earth Warm • Almost all the energy from the sun. • Sunlight comes in a wide range of electromagnetic radiation. • Long to short wavelengths • Most of the radiation that reaches the Earth is in the infrared and visible wavelengths

15. Weather and Climate • Weather is what’s happening now w/ the atmosphere near the ground. • Its temperature, pressure, cloudiness, precipitation, winds – Very LOCAL • Climate is the average weather – GLOBAL and Regional • Usually refers to long periods of time • Classified mainly by latitude and amount of precipitation

17. The Climate is Always Changing • Climate has warmed and cooled many times in Earth’s history • Times of high temp involve relatively ice free periods • Times of low temp involve glacial events

19. Causes of Climate Change • Three kinds (non-anthropogenic) of changes occur to cause climate change: • (1) Earth is unable to keep its poles at a constant angle in relation to the sun. The wobble makes a complete cycle in 26,000 years. • (2) The tilt of wobble also varies over a period of 41,000 years • (3) The elliptical orbit around the sun also changes. Sometimes it is a more extreme ellipse; other times it is closer to a circle and this occurs over 100,000 years.

22. Causes of Climate Change • The combination of these lead to periodic changes in the amount of sunlight reaching the Earth. • Milankovitch showed that these variations correlated w/ the major glacial and interglacial periods. • Called Milankovitch cycles • Don’t account for all climate variations

24. Solar Cycles • The Sun Goes Through Cycles Too • Sometimes hotter, sometimes cooler • Documented by differing amounts of isotopes trapped in glacial ice • Appears that variability of solar input of energy explains some of the climatic variability too.

25. Atmospheric Transparency Affects Climate and Weather • How transparent the atmosphere is to radiation coming into it affects the temp of the Earth • From the sun and from the Earth’s surface • Dust and aerosols absorb light • Volcanoes, forest fires and farming put dust into the atmosphere • Chemical and physical composition of atmosphere can make it warmer or cooler

26. The Green House Effect • Each gas in the atmosphere has its own absorption spectrum • Certain gases are especially strong absorbers in the infrared • They absorb radiation emitted by the warmed surfaces of the Earth • They then re-emit this radiation • Making the Earth’s surface warmer

28. The Green House Effect • Coined because of the way a greenhouse traps heat • Major green house gases are • Water vapor • Carbon dioxide • Methane • Some oxides of nitrogen • CFCs

29. The Roles of Major Greenhouse Gases In Affecting Climate • Nobody doubts that the greenhouse effect exists and affects planets. • The puzzle arises on the Earth about relative importance of greenhouse gases in affecting climate. • Evidence indicates that carbon dioxide, methane, and temperature rise and fall together. • From this most scientists conclude that greenhouse gases are causing climate change.

30. Positive and Negative Feedbacks • The atmosphere and its interactions w/ the ocean and land surfaces experience positive and negative feedbacks. • Negative feedback • Warms temps warm air and lead to increased evaporation • Evaporation leads to more cloud formation which reflects more sunlight which could cool the surface.

31. Positive and Negative Feedbacks • Positive feedback • Warms temps warm air and lead to increased evaporation but instead of clouds forming remain as water vapor. • Water vapor is a greenhouse gas. The warmer it gets the more water vapor, and the process continues. • The warmer it gets, the more people use their AC – thus increasing demand for electricity that increases CO2 levels and temperature

32. The Ocean’s Effect on Climate Change • Water has the highest heat capacity of any compound. • Large amount of heat energy can be stored in oceans • Ocean can absorb CO2 • As CO2 increases in atmosphere it also increases in the oceans (increasing acidity – or “lowering” the pH)

33. The Ocean’s Effect on Climate Change • Part of what drives the climate system is the ocean conveyor belt. • A global circulation of ocean waters • If the conveyor was shut down, major changes in climate would occur because of the capacity the ocean have to “move” heat from one part of the planet to another

35. El Niño and Climate • El Niño refers to a certain kind of periodic variation of currents in the Pacific Ocean. • Under non-El Niño conditions • Trade-winds blow west across the tropical Pacific • Warm surface water pile up in W. Pacific

36. El Niño and Climate • During El Niño years • Trade winds weaken • Western moving current weakens or reverses • As a result eastern equatorial ocean being unusually warm • High rates of precipitation and flooding in Peru • Changes global atmospheric circulation • Causes changes in weather in regions that are far removed from tropical Pacific

37. El Niño and Climate • Rise in temp of sea surface waters off the SA coast (west side near Peru and Ecuador) inhibits the upwelling of nutrient-rich cold water from deeper levels. • Upwelling releases carbon dioxide • El Niño events reduce the amount of oceanic carbon out-gassing

40. What a Global Warming World Might be Like • Global surface temp has increased 0.2°C/ decade in the past 30 years. • Since 1998, the ten warmest years have occurred. • Continued warming of 0.2°C /decade is projected.

41. What a Global Warming World Might be Like • By 2030 the concentration of CO2 in the atmosphere will have doubled from pre–Industrial Revolution concentrations. • The average global temperature will have risen approximately 1° to 2°C • W/ greater temperature increases toward the poles. • Polar amplification

42. Artic sea ice coverage receding sequentially

43. Potential Environmental, Ecological, and Human Effects of Global Warming • Changes in River Flow • Melting of glacial ice and reductions in snow cover are anticipated to accelerate throughout the twenty-first century. • Rainfall will likely increase, but runoff will be more rapid than if snow slowly melts. • Reservoirs will fill sooner and more water will escape to the ocean.

44. Potential Effects of Global Warming • Rise in Sea Level • A major warming could increase sea levels because of • 1. Expansion of liquid water as water warms (a physical relationship) • 2. Melting of ice sheets on LAND whose waters then flow into the ocean. (This is unlike sea ice melt) • About half the people on Earth live in the coastal zone. • Sea level and population rising, the number of people vulnerable to coastal flooding increases.

45. Potential Effects of Global Warming • Rise in sea level could: • Threatens island nations • Increase coastal erosion on open beaches and cause property loss. • Cause landward progression of estuaries and salt marshes • Lead to lost of coastal wetlands • Threaten ground water supply in coastal communities

47. Potential Effects of Global Warming • Glaciers and Antarctic Ice Cap • Many more glaciers in the world are retreating than advancing. • Not all due to global warming • E.g. Mt. Kilimanjaro • Northern Hemisphere sea ice coverage has declined an average of 10.7% / decade since 1970s

49. Potential Effects of Global Warming • The central ice cap on Antarctica is growing • This is consistent w/ prediction of global climate change models. • As Earth warms, more snow falls on Antarctica. • The rate of melting of the Greenland ice sheet has doubled since about 1998.

50. Potential Effects of Global Warming • Changes in Biological Diversity • The Intergovernmental Panel on Climate Change (IPCC) report states that • “approximately 2–20% of species assessed so far are likely to be at increased risk of extinction as global mean temperatures exceed a warming of 2 to 3°C above preindustrial levels.”