Climate Change: What We Know and What We need To Learn

1. Climate Change: What We Know and What We need To Learn Science on Saturday March 26, 2006 Dave Bader, LLNL Barry Marson, Tokay High School UCRL-PRES –220136 Work supported by the Office of Science, US Department of Energy ay the University of California Lawrence Livermore National Laboratory Under Contract W-7405-Eng-48

2. Brazil Canada China France Germany India Italy Japan Russia United States United Kingdom Climate Change: What Do We Know?Joint science academies’ statement:Global response to climate changeJune 2005(http://nationalacademies.org/onpi/06072005.pdf)Signed by the Presidents of the National Science Academies of:

3. “Climate change is real” • The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems. • It is likely that most of the warming in recent decades can be attributed to human activities. • This warming has already led to changes in the Earth's climate .

4. What is Climate? • Simplest definition: The average weather • More complicated answer: The statistics of weather at a location or over a defined area • Weather • Is it raining now? • The temperature outside. • There is a snowstorm in Reno. • Climate • The average temperature for Pleasanton in July • The average yearly snowfall in Yosemite • The probability that there will be another flood in Napa next winter

5. Weather vs Climate

6. Weather and Climate are Driven by the Earth’s Energy and Water Cycles • The sun transfers energy to the earth (warming) • The earth transfers energy to outer space (cooling) • The heating and cooling is unevenly distributed over the Earth’s surface • Atmospheric motions (weather) and ocean circulations result from this uneven heating and cooling

7. The Sun’s Energy Drives the Climate

8. Demonstration 1 IR Thermometer

9. Visible and Infrared Satellite images of the Western Hemisphere Energy In Energy Out

10. Greenhouse Gases Affect the Infrared Radiation Part of the Energy Balance • Greenhouse Gases absorb some of the energy radiated from the surface and release heat to the air • Primary Greenhouse Gases are CO2 , O3 and water vapor • CO2 evenly distributed throughout the troposphere and slowly increasing • Water vapor highly variable in space in time, but total is nearly constant • O3 nearly constant in stratosphere, highly variable in troposphere

11. Annual Average Energy Budget Terms

12. Incoming and Outgoing Energy Budget Differences

13. Heat Transport • Atmosphere • Warm air rises, cold air sinks (warm air is less dense) • Water absorbs heat when it evaporates and melts, releases heat when it condenses and freezes • Motions are influenced by the Earth’s rotation • All weather results from these processes • Minutes to weeks • Ocean • Ocean circulations result from differences in salinity and temperature • Ice is less dense than water • 4° C water is most dense • Warm fresher water rises, cold salty water sinks • Motions are influenced by the Earth’s rotation • Days to centuries

14. Demonstrations • Air convection • Water convection • Evaporative cooling

15. Source: IPCC 2001

16. Quicktime Ocean clip available at:http://sos.noaa.gov/movies/index.htmlunder “Sea Current Simulation”

17. Average Circulation

18. Atmosphere is Thin Shell Surrounding the Earth

19. Most of the Mass and Water in Troposphere (lowest 15 km)

20. Water Cycle

21. Thunderstorm Convection

22. Animation available at : http://www.vets.ucar.edu/vg/CCM3T170/index.shtml

23. Climate Change is Caused by Changes in the Energy Balance

24. Climate Change ResearchWhat We Need to Learn • System is unobservable over the time scales required for experiments – decades to millenia • Models are substitutes – numerical “laboratories” • Effects of a small change have big impacts from a human perspective • Very complex problem because of feedbacks • Positive Feedback Examples • Snow-Ice Cooling • Water Vapor Warming • Negative Feedback Examples • High Cloud Cooling

25. Natural Climate Change • Large volcanic eruptions eject tiny dust particles into the stratosphere that stay suspended for several years and reflect sunlight • Changes in the amount of sunlight received by Earth • Orbital changes occur slowly over hundreds of centuries • Solar output cycles produce small changes over a few years, e.g.sunspots

26. Annual Average Energy Budget Terms

27. Ice Ages At the peak of the last ice age (18,000 years ago), the temperature was only 4-5 °C colder than it is today, and glaciers covered much of North America!

28. Greenland Ice Sheet

29. “Anthropogenic” Climate Change • Earth’s energy budget changed rapidly since the mid-1800s because of human activities • Emissions of CO2 from fossil fuel combustion • Increased from 270 ppm in the 1800s to over 370 ppm today • Estimates are that 90% of warming since 1850 results from the radiative effects of CO2 concentration increases • Air pollution of other gases and small aerosol particles • Changes in land use • Farms replace forests • Urbanization • Many others

30. Annual Average Energy Budget Terms

31. Carbon Dioxide and Temperature

33. Changes in Ocean Temperature

34. Snow line elevation increases and alpine glaciers melt Much of the world depends on snowpack for water storage. Winter snows support summertime irrigation

35. Impacts of Climate Change Snowpack Temperature Observed Change 1950-1997 (- +) (-+)

36. Future Climate Change? • CO2 Greenhouse Gas Warming Theory is over 100 years old (1896). Postulated that doubling of concentrations would result in 5-6° C global surface temperature rise. • Changes observed are consistent with theory • Nighttime temperatures increase more than daytime • Polar regions warm faster than tropical regions

37. Model formulation Y= f(x,y,z,t) Real system Approximations Assumptions (errors) Approximations Assumptions (errors) Approximations Assumptions (errors) Computer code DO K=1,NZ U(I,J,K)=U(I,J,K)+DELU(K) ENDDO Numerical model DY=F(Dx,Dy,Dz ,Dt ) Approximations Assumptions (errors) Experiment design DELX=100.,DELY=100,….. Modeled System

38. Test Models with Observations

40. What Happens Next? • CO2 concentrations will continue to increase • Rate and amount depend on energy sources and consumption and natural processes • Model simulations suggest that increasing CO2 concentrations to 540 ppm will raise global temperatures 1.7-4.1°C • Climate will continue to change • Feedbacks unknown and potentially large • Ice-free summertime Arctic Ocean? • Melting of Ice Sheets • Melting of Greenland Ice Sheet will raise sea-level 7 meters (23 feet)

41. Sea-ice from Climate Model Animation available at: http://www.vets.ucar.edu/vg/categories/globalchange.shtml

42. Sea-Ice and Climate Change