Global Climate Change. The sky is falling! The sky is falling!

Transcription

1 Global Climate Change The sky is falling! The sky is falling! 1

2 Global Climate Change Radiative Equilibrium, Solar and Earth Radiation Atmospheric Greenhouse Effect Greenhouse Gases Global Climate Change Predictions: Temperature, Sea Level Feedback Effects Alternative Causes Historical Climate Trends Remediation: Greenhouse Gas Emission Reduction 2

3 Radiative Equilibrium Absorption Emission Radiative Equilibrium: amount of EMR absorbed equals amount of EMR emitted 3

4 Sun and Earth are both near-blackbodies I Sunlight Terrestrial radiation Sun, 6000K: emits mostly visible light Earth, 255K: emits mostly infrared radiation λ 4

5 Atmospheric Absorption Earth s atmosphere is a selective absorber (not a BB) Transmits visible light (such as sunlight) Absorbs infrared radiation (such as terrestrial radiation) 5

6 The Atmospheric Greenhouse Effect S E 6

7 The Atmospheric Greenhouse Effect S E A 7

8 Greenhouse Gases These are gases that are transparent to visible light, partially opaque to infrared radiation Earth s major greenhouse gases: Water vapor Carbon dioxide Methane CFCs Nitrous oxide Ozone 8

9 Global Warming Potential (GWP) related to amount of predicted warming ( radiative forcing ) from a unit increase in gas concentration GWPs relative to carbon dioxide: Carbon dioxide 1 Methane 21 Nitrous oxide 310 Chlorofluorocarbons

10 Sources Water Vapor (H 2 O) Evaporation of oceans, land surface water Anthropogenic emissions (insignificant) Sinks Condensation, precipitation Largely out of the control of humans; at higher air temperatures, water vapor content is often higher than at lower temperatures 10

11 Carbon Dioxide (CO 2 ) Sources Aerobic respiration Outgassing by land and oceans Fossil fuel combustion Sinks Green plant photosynthesis Dissolution in oceans 11

12 Carbon Cycle Atmosphere Plants Animals Land Oceans Fossil Fuel Deep Ocean Sediments 12

13 Anthropogenic Carbon Dioxide Inventory Cement Production 2% Deforestation 25% Fossil Fuel Combustion 73% 13

14 Methane (CH 4 ) Sources Cellulose digestion/breakdown Organic decay Sinks Chemical reactions Soil uptake Recent rapid increase due to food production and gas field leaks 14

15 Nitrous Oxide (N 2 O) Sources Soil bacteria Oceanic outgassing Combustion, atmospheric chemical reactions Sinks Chemical reactions in stratosphere Very slow increase over time (until recently); linked to agricultural production 15

16 Chlorofluorocarbons (CFCs) Sources Industrial/consumer leakage, direct emission (all anthropogenic) Sinks Chemical reactions in stratosphere Concentration trend dependent on production of CFCs and regulation in developed and less-developed countries 16

17 Global Change Climate change due to anthropogenic greenhouse gas emissions Assume: carbon dioxide mixing ratio doubles in next years 17

18 Sea level rises from: Polar ice cap melt Thermal expansion of sea water Vegetation loss from drought, weather changes Uncertainties: Effect of non-co 2 greenhouse gases with higher GWPs Emission forecasts Feedback effects Limited numerical forecast models 18

19 Feedback Effects Enhance Cause Effect Suppress Positive feedback: the effects enhance or reinforce the cause, resulting in increased effect (the vicious circle ) Negative feedback: the effects suppress the cause, decreasing the effect ( selfcorrecting or thermostatic ) 19

20 Albedo Reflectivity of a surface Higher albedo = less absorption of EMR Less EMR absorption = lower temperatures Overall albedo of Earth-atmosphere system: 30% 20

21 Feedbacks Sea level and ice cover changes Melting ice delays onset of atmospheric warming Rising sea level and receding ice cover decreases albedo enhancing warming (positive feedback) 21

22 Water vapor and cloud cover changes Warmer air can contain more water vapor positive feedback Cloudiness may increase when water vapor content increases Precipitation patterns altered vegetation coverage changes Affects amount of carbon dioxide sink capacity Affects albedo 22

23 Other Possible Causes of Climate Change Sunspot cycle (approx. 22 years long) Longer cycle = lower solar intensity Intensity variation less than 0.5% Natural variations in solar activity (flares, prominences, general increase/decrease in intensity) Small and unpredictable General intensity change usually over geologic time 23

24 Earth s Climatological Record Natural carbon dioxide concentration and temperature appear correlated do humans really affect global temperature? 24

25 Year to Year Variation 25

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29 What We Know Humans are increasing the atmospheric carbon dioxide content About C increase in global temperature during the last 100 years The major greenhouse gas concentrations will continue to rise Increasing greenhouse gas concentrations tend to warm the planet 29

30 What is Likely Scientific analysis shows a high likelihood of a connection between anthropogenic increases in greenhouse gas concentrations and the observed warming trend 30

31 What is Not Certain How much warming will occur in the future and how quickly Feedback of warming on other climatic features (e.g., precipitation) and the Earth System Need more information about natural variations, solar variation, impacts of clouds and land use, relative contribution of human activities vs. natural influences, future greenhouse gas emissions 31

32 Reduction of GH Gas Emissions and Accumulation Why bother? Purpose: risk reduction Decrease fossil fuel usage Reduce forest clearing Increase plant biomass (?) Carbon dioxide controlled by these measures, but what about methane and nitrous oxide? Difficult agricultural link 32

33 Biomass Non-Fossil Energy Sources Nuclear Fission Geothermal Heat Solar Heat Collection Wind Power Hydroelectric Power Photovoltaic Cells Hydrogen Fuel Cells 33

34 Biomass Non-Fossil Energy Sources Nuclear Fission Geothermal Heat Solar Heat Collection Heat Steam Electricity 34

35 Non-Fossil Energy Sources Wind Power Hydroelectric Power Kinetic energy Electricity 35

36 Non-Fossil Energy Sources [Energy] Electricity Photovoltaic Cells Hydrogen Fuel Cells 36

37 Regulated Carbon Markets Set emissions quota, divide into chunks ( emission credits ), allocate to polluters Unused credits can be sold in open market Depending on pollutant, ability to sell or buy may be regulated Quota reduced year-to-year Subject to political abuse 37

38 Engineering Climate Change (or Unchange) Problem: Carbon dioxide emission rate exceeds carbon dioxide sink rate Natural Anthropogenic Natural Solutions: Sources Sinks Decrease source rate Add anthropogenic sinks Alter the physical environment 38

39 Carbon Sequestering Grow biomass, then bury it deep in the ground Pump carbon dioxide to bottom of ocean, letting pressure liquify the CO 2 In both techniques, the point is to keep the carbon dioxide in the ground/ocean, and out of the atmosphere CO 2 39

40 Altering the physical environment: Increase planetary albedo Install mirrors in the atmosphere or on Earth s surface Distribute light-colored dusts in the air 40