* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download PPT
Soon and Baliunas controversy wikipedia , lookup
Numerical weather prediction wikipedia , lookup
Climate change mitigation wikipedia , lookup
Effects of global warming on human health wikipedia , lookup
2009 United Nations Climate Change Conference wikipedia , lookup
Low-carbon economy wikipedia , lookup
Climate change adaptation wikipedia , lookup
Intergovernmental Panel on Climate Change wikipedia , lookup
Climate change in Tuvalu wikipedia , lookup
Climate engineering wikipedia , lookup
Mitigation of global warming in Australia wikipedia , lookup
Fred Singer wikipedia , lookup
Economics of climate change mitigation wikipedia , lookup
Climate governance wikipedia , lookup
Climate change and agriculture wikipedia , lookup
Citizens' Climate Lobby wikipedia , lookup
Climatic Research Unit documents wikipedia , lookup
Economics of global warming wikipedia , lookup
Atmospheric model wikipedia , lookup
Media coverage of global warming wikipedia , lookup
Global warming controversy wikipedia , lookup
Effects of global warming wikipedia , lookup
Climate change in the United States wikipedia , lookup
Effects of global warming on humans wikipedia , lookup
Climate change and poverty wikipedia , lookup
Scientific opinion on climate change wikipedia , lookup
Climate change, industry and society wikipedia , lookup
Global warming hiatus wikipedia , lookup
Criticism of the IPCC Fourth Assessment Report wikipedia , lookup
Physical impacts of climate change wikipedia , lookup
Public opinion on global warming wikipedia , lookup
Surveys of scientists' views on climate change wikipedia , lookup
Carbon Pollution Reduction Scheme wikipedia , lookup
Instrumental temperature record wikipedia , lookup
Global warming wikipedia , lookup
Politics of global warming wikipedia , lookup
Effects of global warming on Australia wikipedia , lookup
Solar radiation management wikipedia , lookup
Business action on climate change wikipedia , lookup
Attribution of recent climate change wikipedia , lookup
General circulation model wikipedia , lookup
Climate sensitivity wikipedia , lookup
Near-term climate forcers and climate policy: methane and black carbon Daniel J. Jacob Atmospheric black carbon: absorber of solar radiation diesel engines residential fuel open fires freshly emitted BC particle Global BC emission [Wang et al., 2014] Loss of BC is by wet deposition (lifetime ~ 1 week) Gorillas and chimpanzees of climate change CO2: the 800-lbs gorilla Methane and BC: the chimps Do we care about the chimps? Radiative forcing of climate change Terrestrial flux Fout =σ T 4 Solar flux Fin • Global radiative equilibrium: Fin = Fout • Perturb greenhouse gases or aerosols radiative forcing F = Fin - Fout • Global equilibrium surface temperature responds as To ~ F Radiative forcing referenced to emissions, 1750-2011 • Radiative forcing from methane emissions is 0.97 W m-2, compared to 1.68 W m-2 for CO2 • Radiative forcing from black carbon aerosol (BC) is 0.65 W m-2, highly uncertain • Together methane and BC have radiative forcing comparable to CO2 • But atmospheric lifetimes of methane (10 years) and BC (~1 week) are shorter than CO2 (> 100 years) • What does that mean for priorities in controlling future emissions? [IPCC, 2014] Climate policy metrics consider the integrated future impact of a pulse unit emission of a radiative forcing agent Inject 1 kg of agent X at time t = 0 Concentration C(t) from pulse time Impact from pulse = f(C(t)) time Discount rate Climate metric = 0 time (impact)(discount rate)dt …usually normalized to CO2 Standard IPCC metric: Global Warming Potential (GWP) Integrated radiative forcing over time horizon [0, H] Radiative forcing F vs. time for pulse unit emission of X at t = 0 CO2 methane BC H AGWP(X) ΔFX (t )dt 0 GWP(X) AGWP(X) AGWP(CO2 ) Discount rate: step function H IPCC [2014] GWP for methane vs. chosen time horizon: 28 for H = 100 years 1 Tg CH4 = 28 Tg CO2 (eq) GWP is easy to compute, but it does not correspond to any physical impact New IPCC metric: global temperature potential (GTP) Global mean surface temperature change at t = H CO2 methane BC GTP ( X ) Temperature change vs. time for pulse unit emission at t = 0 ΔTo , X (H ) ΔTo ,CO 2 (H ) Discount rate: Dirac function H IPCC [2014] Temperature response to actual 2008 emissions taken as a 1-year pulse Methane as important as CO2 for 10-year horizon, unimportant for 100-year horizon Why does methane cause only a short-term temperature response? Fin Fout To To t<0 t=0 climate equilibrium emission pulse F = 0 F > 0 To + To t = 20 years climate response F < 0 To t = 100 years back to original equilibrium F = 0 Simple calculation of Global Temperature Potential (GTP) Use impulse response function of surface To to pulse F of 1 W m-2 at time t = 0: 0.63 0.43 To (t ) ( exp[ t / 8.4] exp[ t / 410]) 8.4 410 t in years obtained by fitting results of HadCM3 climate model GTP is then given by H To ( H ) F (t ) T ( H t )dt 0 Boucher and Reddy [2008] Implication of GTP-based policy for near-term climate forcers Consider a policy aiming to restrict warming to 2oC in 100 years Start controlling methane 40 years before target, BC 10 years before target IPCC [2014] Controlling methane and BC should be part of climate policy … but for reasons totally different than CO2 • • • • • • It addresses climate change on time scales of decades – which we care about It offers decadal-scale results for accountability of climate policy It is less sensitive to arguments over what discount rates should be used It is an alternative to geoengineering by aerosols It has important air quality co-benefits BC has additional regional, hydrological impacts Trend in Arctic sea ice volume Geoengineering: cloud seeding Black carbon in the atmosphere diesel engines residential fuel open fires freshly emitted BC particle Global BC emission [Wang et al., 2014] Loss of BC is by wet deposition (lifetime ~ 1 week) BC exported to upper troposphere is major component of forcing …because it’s above white clouds instead of dark surface Integral contribution To BC forcing • • Export to upper • deep troposphere convection • Global mean BC profile (chemical transport model) • • 50% from BC > 5 km scavenging • • •• • • • • • ••• • • ••• • • • • • • •• • frontal lifting BC source region (combustion) BC forcing efficiency Ocean Samset and Myhre [2011] Multimodel intercomparisons and comparisons to observations AeroCom chemical transport models (CTMs) used by IPCC overestimate BC by order of magnitude in upper troposphere Pressure, hPa TC4 aircraft campaign (Costa Rica) Observed Models Such large overestimate must be due to model errors in scavenging BC, ng kg-1 Pressure, hPa HIPPO aircraft campaign over Pacific obs models 60-80N BC, ng kg-1 obs models 20S-20N BC, ng kg-1 Koch et al. [2009], Schwarz et al. [2010] Previous application to Arctic spring (ARCTAS) BC/aerosol scavenging in GEOS-Chem CTM Cloud updraft scavenging Anvil precipitation Large scale precipitation IN+CCN CCN+IN, impaction entrainment detrainment CCN • Meteorological data including convective mass fluxes from NASA GEOS assimilation system • Aerosols are scavenged in cloud by similarity with condensed water • Additional scavenging below cloud by rain/snow • In-cloud scavenging efficiency from freezing/frozen clouds is highly uncertain • Additional uncertainty for BC is its efficiency as cloud condensation nucleus (CCN) and ice nucleus (IN) BC lifetime in GEOS-Chem is 4 days (vs. 7±2 days in AeroCom models) GEOS-Chem BC simulation: source regions and outflow Tests sources, export Observations (circles) and model (background) Wang et al., 2014 Normalized mean bias (NMB) in range of -30% to +10% NMB= -27% surface networks NMB= 6.6% AERONET BC optical depth NMB= -32% Aircraft profiles in continental/outflow regions Asian outflow HIPPO US observed (A-FORCE) (HIPPO) model (US) Arctic (ARCTAS) NMB= -12% Comparison to HIPPO BC observations across the Pacific Model PDF PDF, (mg m-3 STP)-1 Observed • Model doesn’t capture low tail, is too high at N mid-latitudes • Mean column bias is +48% • Still much better than the AeroCom models Wang et al., 2014 BC top-of-atmosphere direct radiative forcing (DRF) Absorbing aerosol optical depth (AAOD) DRF = Emissions X Lifetime X Mass absorption Forcing X coefficient efficiency Global atmospheric load Emission Global load Tg C a-1 (mg m-2) This work 6.5 AeroCom [2006] 7.8 ±0.4 Bond et al. 17 [2013] [% above 5 km] BC AAOD x100 Forcing efficiency (W m-2/AAOD) Direct radiative forcing (W m-2) fuel+fires 0.15 [8.7%] 0.17 88 0.19 (0.17-0.31) 0.28 ± 0.08 [21±11%] 0.22±0.10 168 ± 53 0.34 ± 0.07 0.55 0.60 0.88 147 • Our best estimate of 0.19 W m-2 is much lower than IPCC recommendation of 0.65 (0.25-1.1) W m-2 or the Bond et al. review • IPCC value is from models that greatly overestimate BC in upper troposphere Better understanding of BC scavenging is critical for radiative forcing estimates Wang et al., 2014