Connecting atmospheric composition with climate variability and change

Connecting atmospheric composition with climate variability and change Seminar in Atmospheric Science, EESC G 9910 9/12/12 Overview 1. Loulergue et al. , Nature, 2008 Glacial to interglacial variability (methane) 2. Montzka et al. , Nature, 2011 Anthropogenic climate change (non-CO 2 gases)

Course Information Two motivating questions: 1) How does climate variability (and change) influence distributions of trace species in the troposphere? 2) How do changes in trace species alter climate? Weekly readings at www. ldeo. columbia. edu/~amfiore/eesc. G 9910. html

More than half of global methane emissions are influenced by human activities ~300 Tg CH 4 yr-1 Anthropogenic [EDGAR 3. 2 Fast-Track 2000; Olivier et al. , 2005] ~200 Tg CH 4 yr-1 Biogenic sources [Wang et al. , 2004] >25% uncertainty in total emissions Clathrates? Melting permafrost? PLANTS? BIOMASS BURNING + BIOFUEL ANIMALS 30 WETLANDS 90 180 60 -240 Keppler et al. , 2006 85 Sanderson et al. , 2006 10 -60 Kirschbaum et al. , 2006 0 -46 Ferretti et al. , 2006 GLOBAL METHANE SOURCES (Tg CH 4 yr-1) TERMITES RICE 40 20 LANDFILLS + WASTEWATER 50 GAS + OIL 60 COAL 30 A. M. Fiore

Loulergue et al. , Nature, 2008: Key points 1. Context for anthropogenic influence on atmospheric composition CH 4 was 350 -800 ppb over 800 kyr versus 1800 ppb today 2. ~380 year resolution, sufficient to identify orbital and millenial-scale features dominated by ~100, 000 glacial-interglacial cycles until 400 kyr precessional influence larger in 4 recent cycles CH 4 as an indicator of millenial-scale Temp variability over past eight glacial cycles Hypothesis: Methane budget controlled by changes in strength of tropical CH 4 wetland source and atmospheric oxidation possibly due to changes in monsoons / ITCZ northern wetlands contribute during terminations (overshoots every ~100 kyr)

Loulergue et al. : Motivation 1. Context for anthropogenic influence on atmospheric composition 2. Examine orbital and millenial-scale features 3. Advance understanding of “external forcings and internal feedbacks on the natural CH 4 budget… forecasting the latter in a warmer world”

Loulergue et al. : What is novel? 1. Longest CH 4 record ever derived from a single ice core -- Over 2000 measurements, ~3000 m core, ~380 kyr avg resolution 2. Doubled time resolution over previously measured 0 -215 kyr 3. New reference dataset (checked for consistency with Vostok (420 kyr) and with Greenland (~120 kyr)

Loulergue: Methods Two laboratories (U Bern and LGGE, Grenoble) analyze ice core samples from EPICA/Dome C • Melt-refreezing method under vacuum to extract air • Gas chromatography to analyze chemical composition • Calibration using standard methane gases • EDC 3 gas age scale (Analyseries) • Orbital components + residual (Analyseries) 1) precession, 2) obliquity, 3) ~100 -kyr ~ 10 ppb analytical uncertainty -- 1% error by not correcting for gravitational settling http: //cdiac. ornl. gov/trends/temp/domec. html

Loulergue: EDC 3 chronology -- snow accumulation + mechanical flow model -- pattern matching to absolutely dated paleoclimatic records or insolation variations -- matches Dome Fuji and Vostok within 1 kyr to 100 kyr. 3 kyr uncertainty for certain Periods -- 20% accuracy of event durations back to MIS 11 -- absolute ages back to 800 kyr with 6 kyr uncertainty

GC schematic http: //en. wikipedia. org/wiki/Gas_chromatography

Loulergue Figure 1 VOSTOK EDC Temperature proxy Oldest interglacial has higher CH 4 (740 ppb) than MIS 13 -17 CH 4 -temp: r 2=0. 82 warmer MIS 19 and 9 decoupled

Loulergue Figure 1 Rapid, large fluctuations ~8 kyr, 170 ppb Oscillation

Sources of variability SOURCES: 1. Wetlands: At present 2/3 tropics, 1/3 boreal; estimated at 170 -210 Tg CH 4 -- T and water table (seasonal, interannual) 2. Biomass burning 3. clathrate degassing (plant source receiving much hype likely not important) SINKS: Atmospheric Oxidation (primarily lower tropical troposphere) -- feeds back on any source change -- amplified by changes in biogenic VOC (but chemistry uncertain!) -- (note: other climate drivers of OH production not mentioned!)

Loulergue Figure 2: Spectral analysis Orbital periodicities were previously shown in shorter Vostok record 100 kyr dominates 400 -800 kyr 23 and 41 kyr approx equal for 0 -400 kyr

Loulergue Figure 2: Spectral analysis of CH 4 record combines 3 periodicities Tropical climate dominated by precession (supported by Asian summer monsoon reconstruction); CH 4 overshoots ~100 kyr due to N ice sheets/wetlands Residuals of similar amplitude To orbital components

Loulergue: The big picture Role for wetland response to: • Ice-sheet volume (peat deposition rate, thawing/refreezing, seasonal snow cover) high N lats • Monsoon systems (respond latitudinal / land-sea T gradients which change with orbital forcings) tropics • ITCZ position tropics Amplified OH sink (BVOCs? ) Overall: Dominant contribution of tropical wetlands, boreal source contributes as ice-sheets decay + OH sink feedback Supported by isotopically constrained budget for LGM early Holocene (Fischer et al. , Nature, 2008_ Needs testing with ESMs

Loulergue Figure 3: Propose high-res CH 4 records as a proxy for millenial temperature fluctuations ~74 millenial CH 4 changes (>50 ppb + associated With isotope maxima) Had been suggested (marine Records) that variability occurs when ice-sheet volume is Above some threshold These results cast doubt on a simple link between ice volume/Antarctic cooling and climate instabilities

Human influence: Recent trends in well-mixed GHGs http: //www. esrl. noaa. gov/gmd/aggi/

Some definitions WMO Scientific Assessment of Ozone Depletion 2010 • Ozone Depleting Substances (ODSs) – While there are natural O 3 depleters, ODSs are defined as those whose emissions come from human activities – Further restricted to those controlled under Montreal Protocol (thus some ozone depleters are not commonly lumped into ODS – Major ODSs include CFCs, HCFCs • HFCs do not deplete ozone (no chlorine) – Lifetime is comparable or longer than HCFCs – GWP is comparable or larger to HCFCs

Global Warming Potentials GWP attempts to account for different lifetimes of climate forcing agents by comparing the integrated RF over a specified period (e. g. 100 years) from a unit mass pulse emission, relative to CO 2. Time Horizon a = RF per unit mass increase i = species of interest r = CO 2 Problems with this approach? (e. g. CH 4 vs CO 2) [Section 2. 10. 1 of IPCC AR 4]

TABLE 2. 14 IPCC AR 4 Global Warming Potentials

Montzka et al: Estimating emissions (Box 1) • Bottom-up -- variable accuracy, uncertainties not well quantified -- infrequent updates, methodological changes • Top-down -- a priori assumptions influence results when measurements are limited -- assumes model transport is correct • Process-based approaches -- identify key sensitivities -- reconcile discrepancies in top-down/bottom-up

a et al Figure 1 Montzka et al. , 2011 Emissions derived from observed Mixing ratio changes in global Background atmosphere Assuming constant steady-state lifetime (No changes in sink or natural source) ODSs = CFCs+HCFCs CH 4 and N 2 O smoothed 4 -yr average To reduce influence of natural variability CFCs

Montzka et al. Figure 2 Methane: ANTHRO: 340 +/- 50 Tg CH 4 yr-1 (2/3 total) -- agriculture and fossil fuel ~230 Tg CH 4 yr-1 WETLANDS: 150 -180 Tg CH 4 yr-1 ; ~70% tropics (positive feedback to climate supported by ice core records) WILD CARDS: permafrost, Arctic clathrates

Chemical Feedbacks Methane and OH also affects lifetimes of HCFCs, HFCs t. CH 4 = • 80 -90 % of tropospheric methane loss by OH occurs below 500 mb • ~75% occurs in the tropics [Spivakovsky et al. , JGR, 2000; Lawrence et al. , ACP 2001; Fiore et al. , JGR, 2008] [OH] influenced by: + NOx sources (anthrop. , lightning, fires, soils) + water vapor (e. g. , with rising temperature) + photolysis rates (JO 1 D; e. g. , from declining strat O 3) - CO, NMVOC, CH 4 (emissions or burden)

Montzka et al. Figure 2 – N 2 O: 19% above preindustrial levels BUDGET: biogeochemical cycling + stratospheric loss (slow ~120 yr lifetime) ANTHRO: 6. 7 +/- 1. 7 Tg N yr-1 (~40% total) inorganic fertilizer, N-fixing crops, NOx deposition NATURAL: ~75% terrestrial (tropics); marine largest in upwelling regions -- feedbacks possible (ice cores) -- unintended consequences of mitigation: reduced C uptake? Uncertainties from Table 7. 7 IPCC AR 4 (Denman et al)

Montzka et al. Figure 2 – ODSs + substitutes CFCs + other primary ODSs decreased from 9 to 1 Gt. CO 2 -eq yr-1 since late 1990 s HCFCs and HFCs have increased; in 2008 0. 7 Gt and 0. 5 CO 2 -eq yr-1 Future impacts uncertain: 1) HFCs under Kyoto but being used as ODS replacements (developing nations) 2) Existence of “banks” 3) Depend on trends in OH (dominant sink) Uncertainties from Table 7. 7 IPCC AR 4 (Denman et al)

montzka Front page Print version Saturday (9/8)

“So since 2005 the 19 plants receiving the waste gas [[HFC-23]] payments have profited handsomely from an unlikely business: churning out more harmful coolant gas [[HCFC-22]] so they can be paid to destroy its waste byproduct. The high output keeps the prices of the coolant gas irresistibly low, discouraging air-conditioning companies from switching to less-damaging alternative gases. That means, critics say, that United Nations subsidies intended to improve the environment are instead creating their own damage. ”

“HFC-23, the waste gas produced making the world’s most common coolant — which is known as HCFC-22 — is near the top of the list, at 11, 700” GWP

Montzka et al. : RF from non-CO 2 LLGHGs constant -80% non. CO 2 -80% both “indirect influences” of CH 4, ODSs could increase 0. 2 -0. 4 W m-2 Some are offsetting Some accounted for in GWP so in translation to CO 2 -eq In absence of mitigation, LL non-CO 2 GHG RF could be ~1. 5 W m-2 in 2050 ~80% cut in CO 2 required to stabilize Stabilization not possible with cuts only in non-CO 2 GHGs Future estimates do not consider climate feedbacks from natural emissions (or losses)

Montzka et al: Impact of 25% reductions in all LLGHGs 25% reduction in Anthrop emissions (2009 -2020): Non-CO 2 RF peaks next decade mainly due to CH 4 reductions Relative RF: relative to 2009

Montzka et al. , Key points Non-CO 2 gases • About 1/3 total CO 2 -eq emissions so can lessen total future RF • 35 -40% total climate forcing from all LLGHGs • Co-benefits to air/water quality, less acid deposition • Shorter lifetimes offer an opportunity to lessen near-term forcing; potential to avoid tipping points; but time lags inherent in climate system • Stabilization requires CO 2 reductions • Advanced understanding of sensitivities of natural GHG fluxes to climate change more effective management (necessary? ) Call for… Process studies to inform inventories + initializing top-down estimates More measurements; better (inverse) modeling;