1. Modern Climate Change Darryn Waugh waugh@jhu.edu OES Summer Course, July 2015

2. IS THE EARTH’S TEMPERATURE CHANGING? Focus on last 160 yrs

3. Climate over last 160 Years Surface measurements show clear warming over last 100 yrs. Last decade warmest on record. Annual average Temperature ( relative to 1961-1990 )

4. Climate over last 160 Years

5. Past Climate: Last 2000 years Large uncertainty in temperature before 1850s, but all reconstructions show that global temperatures over last 30- 40 years have not occurred in at least 2000 years.

6. Spatial Variations in Temperature Trends Although global warming has occurred, this does not mean warming everywhere. More rapid warming over land than oceans. [IPCC AR5]

7. WHAT ARE OTHER CHANGES IN THE CLIMATE SYSTEM?

8. Ocean Heat Content & Sea Level [IPCC AR5]

9. Arctic Sea Ice

10. [IPCC AR5] Land Surface Temp. Sea Surface Temp. Marine Air Temp. Sea Level Arctic Sea Ice NH Snow Cover Glacier Mass Balance Specific Humidity Ocean Heat Content Tropo- spheric Temp.

11. Reading Material Homework [IPCC AR5] Observed Changes in Climate System

12. Positive Proof

13. WHAT ARE THE CAUSES OF MODERN CLIMATE CHANGE ? What has caused for the observed warming over the last 160 yrs?

14. WHAT HAS CAUSED THE RECENT CHANGE IN EARTH’S TEMPERATURE? The suspects: –Orbital variations –Volcanoes –Solar Irradiance –Internal variability –Greenhouse gases

15. The suspects: –Orbital variations –Volcanoes –Solar –Internal variability –Greenhouse gases For last 50 yrs N time scale too long (>10,000 yrs) N no sustained forcing (2-3 yrs) N no trend since 1960s N inconsistent with last 2000 yr record Y time scale correct + consistent with theory and measurements. WHAT HAS CAUSED THIS CHANGE IN EARTH’S TEMPERATURE?

16. Surface Temperature and Solar Variations No trend in solar irradiance in recent decades => Changes in solar irradiance can not explain increase in surface temperature over this period.

17. IPCC, 2007 Greenhouse Effect

18. Absorption by Gases

19. Atmospheric CO 2 : 1958 to present Surface CO 2 measurements show long-term increase + annual cycle Mauna Loa South Pole

20. Atmospheric CO 2 : 1000 to present

21. Greenhouse Gases (GHGs) Concentrations of CO 2, N 2 O, CH 4 (“Greenhouse Gases”) have increased dramatically over last 150 yrs.

22. Temperature and CO 2 20001000 1st Oil Well

23. Attribution Need to also consider changes in aerosols, clouds and land surface (as well as solar, volcanic eruptions, etc.) for a quantitative understanding of cause of warming. Increases in GHGs has been major contributor to warming.

24. WHAT MIGHT HAPPEN IN THE FUTURE? To make projections of the future climate need 1. Numerical models to integrate together different components and processes, and 2. Projections of future emissions of greenhouse gases (and changes in land use), which depends on human behavior and activities.

25. Climate Models

26. Predicting Future Emissions Future emissions of greenhouse gases (and changes in land use) will depend on several on different factors. E.g. Global Population trends World Economic Growth Source of Energy Technological Trends Policies Historical events (wars, political transitions). All above are affected by human behavior and activities.

27. CO 2 Emission Scenarios A1B - balance between fossil and non-fossil fuels. A1F1 - fossil fuel intensive. A1T - large shift to non-fossil fuel. B1 - sustainable development A2 - heterogeneous would. [IPCC 2001] Projections since 2001

28. Temperature Projections: 2005-2100 High Emissions Low Emissions

29. Temperature Changes: Spatial variations Warming is largest in NH high latitudes (ice feedback) and larger over land than oceans (heat capacity). Minimum over North Atlantic Ocean and Southern Ocean High EmissionsLow Emissions

30. Sea Level Rise High Emissions Low Emissions

31. Sea Ice Predictions All models predict continued retreat of Arctic sea ice. Some predict complete ice free summers by end of the century.

32. Rainfall Less rain in dry regions - Droughts More rain in wet regions - Floods. High EmissionsLow Emissions

33. Heat Stress

34. “Global Climate Change Impacts in the US” Report from US Global Change Research Program http://www.globalchange.gov Impacts separated by Regions and Sectors

35. Impacts of Climate Change

36. “What’s the worst that could happen?” [A rational response to climate change debate] Greg Carven http://www.youtube.com/watch?v=zORv8wwiadQ http://manpollo.org/education/videos/how_it_all_ends/how_it_all_ends.html

37. Areas of Response Geoengineering Mitigation - reduce the emissions of GHGs that cause climate change. Geoengineering - manipulate the climate system to offset climate effects of increased GHGs. Adaptation - adjust human society to changing climate to reduce resulting harms.

39. Stabilization Wedges

40. TAKE-HOME MESSAGES Restatement of IPCC (2013) conclusions: We know that the climate is warming. We’re very sure humans are to blame. The future is hard to predict, but it’s certainly possible that “business as usual” will lead to a catastrophic warming. Contact: Darryn Waugh waugh@jhu.edu 410-516-8344.