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NATS 101 Lecture 34 Anthropogenic Climate Change

NATS 101 Lecture 34 Anthropogenic Climate Change. Anthropogenic Climate Change. The data indicate that global-mean land and sea-surface temperatures have warmed about ~0.6 o C during the last century. Is this the start of a man-made global warming? Two main anthropogenic forcing mechanisms:

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NATS 101 Lecture 34 Anthropogenic Climate Change

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  1. NATS 101Lecture 34Anthropogenic Climate Change

  2. Anthropogenic Climate Change The data indicate that global-mean land and sea-surface temperatures have warmed about ~0.6oC during the last century. Is this the start of a man-made global warming? Two main anthropogenic forcing mechanisms: Greenhouse gas concentrations => rising. Aerosol concentrations => also increasing. We will focus attention on CO2 increases.

  3. CO2 and the Greenhouse Effect If the atmosphere were dry, we could predict with high confidence that a doubling of CO2 (likely before 2100) would increase the global mean surface temperature by ~2C. The presence of oceans, ice, water vapor and clouds complicates the analysis significantly. Ahrens, Fig 2.10

  4. There is a very strong relationship between CO2 levels and past global temperatures. CO2 levels are now higher than during any period of the past 450,000 years. Will global temperatures responding accordingly? Global Temperatures and CO2

  5. Currently, 7 gigatons per year of CO2 are injected into the air by burning fossil fuels (80%) and forests (20%). • Half accumulates in atmosphere, where it resides for 50+ years. • If the burning fossil fuels and forests totally ceased, it would still take 50 years for CO2 levels to return to 50% above pre-industrial levels.

  6. CO2 makes the biggest contribution to the climate forcing

  7. US (5% of world population) now causes 20-25% of total pollution.

  8. Projections of Global Warming • Coupled Atmo-Ocean models are run for hundreds of years to get future climates • We assume continued increases in the levels of greenhouse gasses in the atmosphere. • The models have sophisticated physics… But they have coarse grid separations! Atmosphere: 250 km horizontal, 30 levels vertical Ocean: 125-250 km horizontal, 200-400 m vertical

  9. Performance Varies by Weather Element In general… Excellent for Surface Temperature Skillful for Sea-Level Pressure (SFC Winds) Marginal Skill for Precipitation How Well Do Models Capture Current Observed Climate? Fig. 8.4 IPCC Report

  10. Assume CO2 levels rise at current rate of 1% per year until 2070. Good agreement for past climate and CO2 levels leads to high confidence. Rather close agreement among models. Consensus of several model runs indicates an average warming of 2oC Global Temperature Outlook Fig. 9.3 IPCC Report

  11. Marginal performance for past climate and CO2 levels means low confidence in outlook. Large differences exist among models. Consensus of several model runs indicates an average increase of 2% in global precipitation Global Precipitation Outlook Fig. 9.3 IPCC Report

  12. Regional Consistency: Warming Fig. 10.1.1 IPCC Report A + or - symbol denotes 7 out of 9 models agree. A2: no sulphate aerosols; B2: has sulphate aerosols

  13. Regional Consistency: Rainfall Fig. 10.1.2 IPCC Report A + or - symbol denotes 7 out of 9 models agree. A2: no sulphate aerosols; B2: has sulphate aerosols

  14. GDFL Model Lets look at some details from a 500-year simulation by a specific climate model. Examine Two Scenarios: 1% CO2 increase per year for 70 years 2X Total Increase in CO2 1% CO2 increase per year for 140 years 4X Total Increase in CO2

  15. Good agreement for CO2 levels of the past 150 yrs Mandatory before use as global warming model www.gfdl.noaa.gov

  16. CO2 Increases 1% per Year Average Global Surface Temperatures… Warm 2oC for 2X CO2 Warm 4o C for 4X CO2 Sea Level Rises… Equilibrium Not Reached until after 500 years North Atlantic Ocean… Circulation Weakens www.gfdl.noaa.gov

  17. CO2 Increases 1% per Year • Surface Temperatures for GFDL Model 2X CO2 Temperature Animation Remote 2X CO2 Temperature Animation Local Disk BIG File (8.2 MB)!!!

  18. 4X CO2 Sea Ice Animation 4X CO2 Sea Ice Local Link www.gfdl.noaa.gov

  19. CO2 Increases 1% per Year July Temperature over Southeastern U.S. • Warms 5-9oC July Heat Index over Southeastern U.S. • Rises 7-14oC due to increase H2O vapor Consistent Signal Warmer Southern U.S. www.gfdl.noaa.gov

  20. CO2 Increases 1% per Year Soil Moisture • Much Drier over U.S. 60% Soil Moisture Decrease Higher Evapo-Transpiration Altered Balance between Evaporation-Precipitation • Agricultural Implications How do we feed ourselves? www.gfdl.noaa.gov

  21. (Excludes Melting of Ice) Sea Level Rises: Consistent Model Signal h=.000210T  Depth =.0002101C 4000m =0.8m www.gfdl.noaa.gov

  22. 1 meter 2 meters www.gfdl.noaa.gov 4 meters 8 meters

  23. Increases in the frequency and/or the intensity of extreme weather events is a likely consequence of global warming.GFDL Super Typhoon Hurricane Intensities Increase by 10% Reason: Warmer Sea Surface Temps www.gfdl.noaa.gov

  24. Key Points: CO2 Warming • CO2 levels are rising and will likely double by 2070. • The greenhouse relationship between higher CO2 levels and warmer temperatures is indisputable. • Even with perfect knowledge of future CO2 levels, there is significant uncertainty about how much warming would occur and how fast it would occur. • Model results suggest a 2oC global warming, with strongest warming in polar regions, and an overall increase in global precipitation. • Shifts in precipitation are much more uncertain.

  25. What MightWeDo? • Common sense precautionary measures suggest that we begin to reduce emissions before enormous changes to the climate and ecosystems could occur. • Greenhouse warming is internationally recognized as a serious problem. • Kyoto Protocol is a good start, but the Congress and Administrations have refused to ratify it or to support attempts to curb greenhouse emissions. • Consider supporting leaders and organizations who provide vision and can make tough decisions.

  26. What CanYOUDo? • Nothing, after all you might be gone by 2070! Or… • Insist on Energy Efficient Appliances-Merchandize • Limit Heating and Air Conditioning Programmable Thermostats • Think Alternative Transportation Bicycles, Walking, Public Transportation • Practice Smart Use of Personal Automobiles Carpool, Combine Errands, Lighter Loads, Slow Down Consider Fuel Efficient or Hybrid Vehicles

  27. Assignment for Next Lecture • Will Send Information Via Email?

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