Lecture 07

1. Lecture 07 Climate Change

2. A perspective • Change is normal • Seasonal • Yearly: El Nino/La nina • Mid-term: • Medieval warming  little ice age • Long term: Milankovitch Cycles • Induced by major events/disturbances

3. El Niño Southern Oscillations “The Christ Child” • Prevailing condition: east-to-west trade winds push warm surface water westward  upwelling off coast of Peru • El Nino conditions: winds drop/cease  Fishers in Peru, Ecuador and Chile get some time off!

5. An El Niño winter - unusual weather patterns all over the world http://www.osdpd.noaa.gov/ml/ocean/index.html http://www.noaanews.noaa.gov/stories2009/20090709_elnino.html

6. La Niña • Not as well known as El Niño • Causes extreme effects that are nearly opposite to those of El Niño • In the US, effects are more apparent in winter • Northwest is wetter and cooler than normal • Southeast is dryer and warmer than normal

7. Global temperatures have fluctuated in the past • Ice age temps 4 – 5 C cooler • Past 1000 years: • Warm periods: + 0.5C • Cool periods: -0.5C

8. Medieval Warming: roughly AD 950-1250 • Global nature debated • Warmer in Europe, drier middle east, western NA • Probably impacted China • Probably not associated with changes in atmospheric CO2 levels • Mechanism associated with changes in sea surface temperatures and wind patterns

9. Long-term Climate Trends – Milankovitch Cycles • Summer-winter flux due to inclination of axis of earth • Orbit of earth more elliptical that circular • Periodic coupling of inclination with eccentric orbit means ~ 100,000 to 400,000 year variation in intensity of solar radiation at 65N latitude  warming/cooling at polar latitides

11. Catastrophic events and Climate Change: • Volcanic eruptions, meteor strikes • Alterations in atmospheric gas composition

12. atmospheric concentration of CO2: 25 percent increase over the past 100 years • Continuous observations of atmospheric CO2 started in 1958 • Earlier evidence from air bubbles trapped in the glaciers of Greenland and Antarctica • Exponential rise since mid-19th century

13. Evidence For Climate Change Temperature records Phrenological indicators Melting of ice fields and glaciers Reduction in size of ice caps

14. Sea/land surface temperature anomaly: difference between 29 year average (1951-80) and annual temperatures (fig b shows 2010 in text)

15. Atmospheric CO2 and Global Warming • Minor component • 180 ppm during cooler periods • 270 ppm during warmer periods • Historical association with changes in global temperatures • Current levels ~ 375ppm

16. Long-term Climate Trends • Human observational records: 200-500 yrs • Other sources: • Tree ring/growth • Isotopic analysis • Pollen analysis of sediments • ice core analysis • Fossil evidence

19. Uptake of carbon dioxide by marine ecosystems: • The rate of diffusion of CO2 is a function of the diffusion gradient • Although the oceans have the potential to absorb most atmospheric carbon derived from fossil fuel combustion and deforestation, this does not happen • Thin layer of warm water floating on a much deeper layer of cold water • Mixing of CO2 does not extend into the deep waters because of the thermocline

20. Greenhouse gases • Water vapor ~ 60% of effect • CO2 ~ 20% of effect • Others ~ 20% of effect • Methane • N2O • Various man made gasses • Greenhouse effect • The average surface air temperature of the earth is 30°C higher than it would be without the absorption and reradiation of thermal energy • Since the industrial period began, the concentrations of greenhouse gases in Earth’s atmosphere have increased dramatically

21. Contributers to Greenhouse Effect

22. Positive Feedback : Occurrence of an effect further strengthens effect

23. Positive Feedback : Occurrence of an effect further strengthens effect • Positive Feed Back Effects • Atmospheric water vapor • Albedo • Decreased reflectance • Release of methane from permafrost and methane hydrate in deep sea waters • http://www.youtube.com/watch?v=Wofv9o0j1Ew • Increase in detrital food chain processes  more CO2 • forest growth decline due to environmental factors • Decrease in effectiveness of marine food chains in absorbing atmospheric CO2 •  adds uncertainty to General Circulation Models

24. Projections for temperature rise

25. General Circulation Models – or - Global Climate Models • Sophisticated numerical mathematical models used to predict future changes in climate • 3 dimensional aspect – consider potential positive and negative feedback factors • Make various assumptions • Provide basis for most climate models • Unknown or problamatic factors: • Positive and negative feedbacks • Changes in ocean circulation patterns • Tipping points

26. Ecosystem Effects • Major focus: Alpine and arctic ecosystems • Expectations for the future: • Shifts in vegetation communities up-slope • Decreased winter snow pack and consequent drier/longer summer period • Decreased ‘island’ effect • GLORIA: Global Observation Research Initiative in Alpine Environments

28. Shifts in precipitation

29. Sea level rise – an ice free planet

31. Indicators of Climate Change in California • Rising sea levels, temperatures and dropping pH • Rise in lake temperatures • Decline in spring runoff, glacier melt and decrease in salmon runs • Changes in vegetation patterns in the Sierra • Massive wild fires