A World Of Change: Climate Yesterday, Today, and Tomorrow

1. A World Of Change: Climate Yesterday, Today, and Tomorrow Susan Solomon Senior Scientist, NOAA, Boulder and ex-co chair IPCC WG1 IPCC, post-IPCC, irreversibility, and other key aspects of what we know about climate change

2. The World Has Warmed 2008: 10th warmest Widespread warming has occurred. Globally averaged, the planet is about 0.75°C warmer than it was in 1860, based upon dozens of high-quality long records using thermometers worldwide, including land and ocean. IPCC WG1 (2007)

3. 1997-2008 1987-1996 1977-1989 Global Average Climate Change Ups and downs from year to year? Yes, true. Relevant? No. See Easterling et al., GRL, 2009

4. Our lives are heavily influenced by local weather. It’s important to distinguish between weather and climate. Fronts move air from one region to another (e.g., winter cold fronts) and cause large local variability. Averaging over space and/or time is critical to deducing meaningful climate changes.

5. Canada China Near Paris Australia Near Denver, CO Global Average Local And Global Changes (from NCDC data) http://www.ncdc.noaa.gov/gcag/index.jsp Fewer cold extremes

7. Many Changes Signal A Warming World Rising atmospheric temperature And…… • Atmospheric water vapor increasing • Glaciers retreating • Arctic sea ice extent decreasing • Extreme temperatures increasing • …………. Warming is Unequivocal Rising sea level Reduction in NH snow cover IPCC WG1 (2007)

8. Human Drivers of Climate Change: Unprecedented • CARBON DIOXIDE • • A critical greenhouse gas • • Dramatic increase in industrial era, ‘forcing’ climate change • • Higher concentration than for more than 600,000 years IPCC WG1 (2007)

9. Carbon Dioxide at Mauna Loa The biosphere ‘breathes’ every year in its growing cycle, but the human trend is clear. Big natural fluxes? Yes. Relevant? No http://www.esrl.noaa.gov/gmd/ccgg/trends/

10. Forcing of Climate Change [1750 to Present-day] CO2 is largest Solar brightness effect small Carbon dioxide is causing the bulk of the forcing, and it lives a long time in our atmosphere (some of it lives for more than 1000 years). Every year of emission means a commitment to climate change for more than 30 generations. Global-average Radiative Forcing (RF) (W m-2) IPCC WG1 (2007)

11. Are Humans Responsible? Natural and human effects Natural forcings only Pinatubo Agung Chichon IPCC (1995): “Balance of evidence suggests discernible human influence” IPCC (2001): “Most of global warming of past 50 years likely (odds 2 out of 3) due to human activities” IPCC (2007): “Most of global warming of past 50 years very likely (odds 9 out of 10) due to human increases in greenhouse gases” Observations Volcanoes: proof of principle that forcing changes climate. GHG increases dominate forcing and climate changes of past 50 years. IPCC WG1 (2007) ch 9 and summary

12. Are Humans Responsible? Why can we say it’s very likely (90% odds) that most of the warming is due to increased greenhouse gases? High statistical confidence based on multiple fingerprints in time and space. IPCC WG1 (2007) ch 9 & summary

13. The Pine Beetle Perfect Storm Reduced moisture, trees stressed; esp. lodgepole pine Longer beetle breeding season (two cycles, not one) Fewer extreme cold snaps to kill beetle in winter (below -20°F) Photo http://www.for.gov.bc.ca Photo by Ken Papaleo / The Rocky Mountain News See, recent papers by Kurz et al in Nature and Mantgen et al in Science.

14. A different climate on each continent by 2050 A changing world for everyone, including science and scientists. What about smaller scales? IPCC WG1 (2007) ch 11

15. A World of Change: More Rain for Some, Less for Others Regional changes (+/-) of up to 20% in average rainfall. At mid to low latitudes, dry get drier, wet get wetter. Dust bowl and other major droughts of the past: 5-15% less rain over 10-20 yrs. (2090s: medium emissions scenario; highest confidence in stippled areas) DJF seasonal precipitation IPCC WG1 (2007) SPM

16. A World of Change: Less Rain for Some, More for Others Dry regions in the “subtropics”, wet regions at higher latitudes; basic pattern is linked to fundamental physics

17. UNFCCC and Science This part of the talk: irreversible changes that can be expected with high scientific confidence. • observed changes are already occurring, and there is evidence for anthropogenic contributions to these changes • the phenomenon is based upon physical principles thought to be well-understood • projections are broadly robust across available models [“Geoengineering” to remove carbon or artificially cool not considered here.] High confidence, well quantified information: Very useful.

18. Beyond the 21st Century EMICs: New Tool to Probe the Very Long Term UNFCCC Article 2: Stabilization of GHG at a level that avoids ‘dangerous interference’. Article 3: emphasizes “serious or irreversible damage” IPCC, WG1 (2007), chapter 10

19. Stop Emissions Completely: Can The World Return to A Natural State? One test: ramp towards 750 stabilization, then stop. ≈450 ppmv left in 3000 Warming remains constant ±0.5°C for more than a thousand years. IPCC, WG1 (2007), chapter 10

20. Carbon Cycle: It Really Is A Cycle Some man-made CO2 goes (in the short-term) from the atmosphere to vegetation, surface ocean. Long term sink is deep ocean. It’s very slow.

21. Carbon Dioxide Is A Unique Gas: Multiple Timescales CO2 dissolves in seawater to acidify the ocean (1). Dissolution is limited by buffering. Added carbonate (eg rock weathering) can very slowly dissolve more (2). (1) CO2 + H2O <-> H+ + HCO3- (2) CO2 + H2O + CO3-2 <-> 2HCO3- Initial step ~100,000 years Archer (many papers); review in Solomon et al., PNAS, 2009

22. Carbon Cycle: Back to Basics (Revelle and Suess, 1957) • Isotopes: ocean sink and speed • Long-term: 20% of human Gts input retained (Revelle factor)

23. Carbon Cycle: Gts And ppmv • Half of human CO2 emissions (Gts) retained in atmosphere each year (airborne fraction or ‘instantaneous Revelle factor’). • Long-term human CO2 Gts retained will be 20%, due to well understood processes in the ocean (Revelle factor). • Long-term concentration retained will be 0.2/0.5, or about 0.4 of the peak concentration enhancement above pre-industrial value of 278 ppmv. Solomon et al., PNAS, 2009

24. Carbon Sink and Heat Transport: Links to Deep Ocean Linked physics and relationship to timescales for carbon and climate system inertia (also SLR due to thermal expansion).

25. Carbon Sink, Heat Transport, Climate Change, and Sea Level Rise Due to Thermal Expansion Broad range of test cases: • Every year of climate change that occurs (warming, precip, snow cover, sea ice retreat, ocean acidification, etc…) due to carbon dioxide increases is irreversible for at least 1000 years. • Sea level rise is slower, but is irreversibly linked to the peak CO2 we reach. Solomon et al., PNAS, 2009

26. Irreversible Precipitation Changes • 5 to 10% per degree of warming in e.g., Southern Europe, North Africa, Western Australia, SW North America, South Africa in the respective dry seasons. ≈Forever. • Compare to ‘dust bowl’ or other major droughts, typically 5-15% over ≈10-20 years. White: fewer than 2/3 of the models agree; colors and gray >2/3 Solomon et al., PNAS, 2009

27. Precipitation Change: How Far Will We Go? Best estimate of 21st century choices. The longer we wait to act, the more rainfall change we will be locked into. Solomon et al, PNAS, 2009

28. Irreversible Sea Level Rise: How Far Will We Go? Thermal expansion only: 0.2-0.6 m/°C Locked in during 21st century add glaciers (0.2-0.7m) add ice sheets? Solomon et al., PNAS, 2009

29. Add Ice Sheets? How Quickly Do They Melt? Charbit et al., GRL, 2008 Can ice sheets outlast the carbon for some levels of perturbation? How much?

30. Sea level rise of 0.5-1.0 meter would have large impacts in many parts of the world. [From IPCC WG2 (2001).]

31. Us Carbon Dioxide Emission From Fossil Fuel Burning Who? Source: Energy Information Agency, DOE

32. Why: Going, Doing, Making, Being Comfortable….. In short, just about everything.

33. Carbon Dioxide Emission From Fossil Fuel Burning 5.5 B people now in the developing world emit about 5x less fossil CO2 per person than the 1B in the developed world

34. Changes in Total and Per Capita Emissions of Carbon Dioxide From Fossil Fuel Burning in China and the USA Last decade: China is getting richer, and emitting more CO2 Kyoto Protocol? Source: Energy Information Agency, DOE

35. 5/6 of the people now emit 5x less per person than 1/6 Climate And Bathtubs: A Poorly-Understood Principle • Stabilization of CO2 would require 50% emissions reductions (for a few decades) and then 80% • Geoengineering? Cool the planet? Real and ‘artificial’ trees?

36. How Far Will We Go? The longer we wait to act, the more climate change we will be locked into. Image: Socolow and Pacala

37. Some Possible Future Choices: Just Illustrations 50x wind or 700x current solar 60 mpg cars Successful tests completed Reduce deforestation Double current capacity There are no silver bullets but there is much silver buckshot. Technology matters.

39. Some Things I Hope You’ll Remember About Climate Change • -Caused mainly by different long-lived gases produced by people via a well understood physical mechanism. CO2 from fossil fuel burning is (by far) the main climate change agent. • -Abundant data for at least a century, carefully calibrated, show the changes in the industrial era. • -Temperatures are rising globally. There is local variability. • -Young people today will live in a world some 5-10°F warmer by the time they are old men and women, if emissions continue ramping. • Rainfall changes with climate change would affect many people and ecosystems. Droughts like the dust bowl would be widespread. • Climate changes from CO2 emissions should be expected to last more than 1000 years (unless we find a ‘miracle cure’ to remove CO2) • -Climate change challenges us to think beyond our own backyards.

40. Thanks for your attention

41. Additional Slides (not for presentation)

42. Rainfall Changes with Warming • 22 AR4 models • Regional averages over the respective dry seasons (not JJA, DJF, etc.), relative to 1900-1950 baseline • Future changes dominated by GHG in these runs Solomon et al., PNAS, 2009

43. Context: 5-15% less rain is a lot

45. Structures Greenland ice sheet? Toxicology, epidemiology Uncertainty, Risk, and Confidence Climate change: A mix of things we now know quite well, and other things that represent high-impact but highly uncertain risks. Do more to identify what is well known…..separate from the much more uncertain risks to aid clarity and consensus. Stock markets?

46. How Accurate Are Model Simulations of Rainfall? Observed annual average precipitation (cm/year), 1980-1999; CMAP climatology Multi-model average IPCC WG1 (2007), chapter 8

47. La Nina The World Is Still Warm (post-IPCC 2007) Short-term variations (e.g., volcanoes, El Nino/La Nina in some years) don’t change the global ‘big picture.’ From www.realclimate.org

48. Some Key Underpinnings: Held and Soden; Seidel et al Change in obs bigger than models…. •expansion of tropics • mean rainfall trends • heavy rain

49. Carbon Sink, Heat Transport, Climate Change, and Sea Level Rise Due to Thermal Expansion Broad range of test cases: • Every year of climate change that occurs (warming, precip, snow cover, sea ice retreat, ocean acidification, etc…) due to carbon dioxide increases is irreversible for at least 1000 years. • Sea level rise is slower, but is also irreversibly linked to the peak CO2 we reach. Solomon et al., PNAS, 2009

50. “Realized” Warming During the period of CO2 rise, the realized warming fraction is about 50-60% of the climate sensitivity. After emissions stop, warming remains 50±10% of that for equilibrium relative to CO2 peak value. Actual and equilibrium temperatures, relative to CO2 change. Solomon et al., PNAS, 2009