IPCC WG1 AR5: Key Findings Relevant to Future Air Quality

1. IPCC WG1 AR5: Key Findings Relevant to Future Air Quality Fiona M. O’Connor, Atmospheric Composition & Climate Team, Met Office Hadley Centre

2. IPCC AR5 WG1 Report • WG1 Summary for Policy Makers released 27 Sept 2013 • WG1 Full Report published 30 Sept 2013 • WG1 provides the latest assessment of the physical science with respect to climate change • Observed changes are unprecedented and have been seen throughout the climate system • It is now possible to link observed changes in many climate components to human influence • Climate models have been improved, and can reproduce main features of observed multi-decadal warming • WG2 and WG3 on impacts and mitigation to be released in 2014

3. Outline of Presentation • Observed Changes in the Climate • What’s Causing these Changes? • Future Projections of Climate Change • Future Projections of Air Quality • Main Conclusions and Key Uncertainties

4. Part 1: Observed changes to the climate

5. Atmospheric CO2 levels are unprecedented for 800,000 yrs Atmospheric CO2 concentrations have • increased by about 40% since 1750, due to human activity • exceed values recorded in ice cores for the last 800,000 years

6. 2000s: warmest decade on record • Last 3 decades warmest in instrumental record. • From palaeoclimate records, in the NH, last 30 years likely (66-100%) the warmest period of the past 1400 years. • Very likely (90-100%) that number of warm days has increased and cold nights decreased globally

7. Almost the whole globe is warming Annual mean temperature (1901-2012) Most global land areas analysed have experienced significant warming including of both maximum and minimum temperature extremes since 1950 Despite robust multi-decadal warming since 1901, there is substantial decadal variability in the rate of warming with several periods exhibiting almost no linear trend.

8. Part 2: What are the causes of the changing climate?

9. Changes to Earth’s Energy Budget The AR5 estimate for 2011 is 44% greater than the AR4 estimate for 2005 because of: • Increased forcing from greenhouse gases • Revised estimate of aerosol forcing

10. Attribution of Radiative Forcing to Emissions

11. Radiative Forcing from Aerosols

12. Time Evolution and Spatial Heterogeneity in RF

13. Part 3: Future projections

14. Scenarios for future change • AR4: Special Report on Emission Scenarios (SRES) are four major families of GHG emission scenarios each making different assumptions for future greenhouse gas pollution, land-use and other driving forces • AR5: Representative Concentration Pathways (RCPs) are four GHG concentration trajectories, each describing a different future value of radiative forcing in 2100. RCPs aim to provide a range of climate model responses, rather than being derived from socio-economic storylines.

15. Projections of global average warming • By the end of the century, the increase of global mean surface temperature above 1986-2005 levels is projected to be: • 0.3-1.7˚C for RCP2.6 • 2.6-4.8˚C for RCP8.5 • Global warming >2˚C is likely (66-100%) for RCP6.0 and RCP8.5 • Global warming >4˚C is unlikely (0-33%) except for RCP8.5

16. Warming will not be the same everywhere • There is very high confidence that long-term warming will be larger over land than over the ocean, and that the Arctic region will warm most rapidly. • Ocean warming will continue for centuries, even if greenhouse gas emissions are decreased.

17. There will be large geographical variations in precipitation change • For the next few decades, changes in regional-scale precipitation will be strongly influenced by natural variability. • Contrast between wet and dry regions and seasons will increase over most of the globe, though there are regional exceptions. • Monsoon precipitation is likely to intensify, along with a lengthening of the monsoon season.

18. Projections of temperature over Europe 2016–2035 vs 1986–2005 ensemble mean results from the ENSEMBLES project Figure 11.18 Rajczak et al. (2013)

19. Part 4: Future Projections of Air Quality (O3 and PM2.5)

20. AQ Statements in Summary for Policy Makers • Range in projections of near-term AQ (surface O3 and PM2.5) • is driven primarily by emissions rather than by climate change • Globally, warming decreases background surface O3 but • high CH4 (RCP8.5) can offset this decrease • Higher surface temperatures in polluted regions will trigger • feedbacks in local chemistry and emissions, increasing peak • levels of O3 and PM2.5 • For PM2.5,climate change may alter natural aerosol sources • and wet removal, but no confidence level is attached to the • overall impact

21. Future Anthropogenic Emissions SRES vs RCPs Figure 8.2 AR5

22. Changes in Trop. O3 Burden Atmospheric Composition and Climate Model Intercomparison Project (ACCMIP) Young et al., ACP, 2013

23. Changes in Near-Term Surface O3 Figure 11.21 (adapted from Fiore et al., 2012)

24. Global and Regional Changes in Surface O3 Time series of O3 Figure 11.23a

25. Changes in OH/Reactivity Results from ACCMIP time slice experiments Voulgarakis et al., ACP, 2013.

26. Changes in Aerosol Optical Depth relative to Yr- 2000 Table AII.5.3

27. Changes in Surface PM2.5 Time series of PM2.5 Figure 11.23b

28. Extreme Weather and AQ • Extreme AP episodes are associated with changing weather • patterns, such as heat waves and stagnation episodes • Climate change has increased the near-term risk of heat waves • Projected changes in the frequency of regional air stagnation • events remain difficult to assess -> regional AP extremes • Projections show increases in extreme O3 pollution events over • US/Europe but lack of agreement at regional level

29. Longer-Term Feedbacks on Natural CH4 Emissions Figure 6.36 O’Connor et al., 2010

30. Summary on AQ • Lower background AP levels are projected following • the RCPs compared to SRES (high confidence) • Range in near-term projections of AQ is driven • primarily by emissions rather than by climate change • (medium confidence) • The total range in emissions — including the CLE and • MFR scenarios—is larger than spanned by the RCPs • Peak O3 and PM2.5 will increase with climate change

31. Key Gaps and Uncertainties • Uncertainties in Future Anthropogenic Emissions • Uncertainties in BVOC chemistry • Impact of climate change on BVOC emissions • Impact of climate change on natural CH4 emissions • Impact of climate change on transport pathways • Future Projections of Stagnation Events • Future Projections of Regional AQ • Future Projections of Regional OH • Recent and Future Trends in surface O3

32. Questions and answers