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

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

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

Part 1: Observed changes to the climate

Atmospheric CO 2 levels are unprecedented for 800,000 yrs Atmospheric CO 2 concentrations have increased by about 40% since 1750, due to human activity exceed values recorded in ice cores for the last 800,000 years

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

Almost the whole globe is warming 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. Annual mean temperature ( )

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

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

Attribution of Radiative Forcing to Emissions

Radiative Forcing from Aerosols

Time Evolution and Spatial Heterogeneity in RF

Part 3: Future projections

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 RCPs aim to provide a range of climate model responses, rather than being derived from socio-economic storylines.

Projections of global average warming By the end of the century, the increase of global mean surface temperature above levels is projected to be: ˚C for RCP ˚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

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.

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.

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

Part 4: Future Projections of Air Quality (O 3 and PM 2.5 )

AQ Statements in Summary for Policy Makers Range in projections of near-term AQ (surface O 3 and PM 2.5 ) is driven primarily by emissions rather than by climate change Globally, warming decreases background surface O 3 but high CH 4 (RCP8.5) can offset this decrease Higher surface temperatures in polluted regions will trigger feedbacks in local chemistry and emissions, increasing peak levels of O 3 and PM 2.5 For PM 2.5,climate change may alter natural aerosol sources and wet removal, but no confidence level is attached to the overall impact

Future Anthropogenic Emissions SRES vs RCPs Figure 8.2 AR5

Changes in Trop. O 3 Burden Atmospheric Composition and Climate Model Intercomparison Project (ACCMIP) Young et al., ACP, 2013

Changes in Near-Term Surface O 3 Figure (adapted from Fiore et al., 2012)

Global and Regional Changes in Surface O 3 Figure 11.23a Time series of O 3

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

Changes in Aerosol Optical Depth relative to Yr RCP2.6-14%-26% RCP4.5-4%-18% RCP6.0-12%-23% RCP8.5-4%-14% Table AII.5.3

Changes in Surface PM 2.5 Figure 11.23b Time series of PM 2.5

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 O 3 pollution events over US/Europe but lack of agreement at regional level

Longer-Term Feedbacks on Natural CH 4 Emissions Figure 6.36 O’Connor et al., 2010

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 O 3 and PM 2.5 will increase with climate change

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 CH 4 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 O 3

Questions and answers