Connecting atmospheric composition with climate variability and change

Seminar in Atmospheric Science, EESC G9910

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-CO2 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/eescG9910.html

More than half of global methane emissions are influenced by human activities

~300 Tg CH4 yr-1 Anthropogenic [EDGAR 3.2 Fast-Track 2000; Olivier et al., 2005]

~200 Tg CH4 yr-1 Biogenic sources [Wang et al., 2004] >25% uncertainty in total emissions

ANIMALS90

LANDFILLS +WASTEWATER

50GAS + OIL60

COAL30RICE 40TERMITES

20

WETLANDS180

BIOMASS BURNING + BIOFUEL 30

GLOBAL METHANESOURCES

(Tg CH4 yr-1)

PLANTS?

60-240 Keppler et al., 2006 85 Sanderson et al., 200610-60 Kirschbaum et al., 2006 0-46 Ferretti et al., 2006

Clathrates?Melting permafrost?

A.M. Fiore

Loulergue et al., Nature, 2008: Key points

1. Context for anthropogenic influence on atmospheric composition CH4 was 350-800 ppb over 800kyr versus 1800 ppb today

2. ~380 year resolution, sufficient to identify orbital and millenial-scale features dominated by ~100,000 glacial-interglacial cycles until 400kyr precessional influence larger in 4 recent cycles CH4 as an indicator of millenial-scale Temp variability over past

eight glacial cycles

Hypothesis: Methane budget controlled by changes in strength of tropical CH4 wetland source and atmospheric oxidation

possibly due to changes in monsoons / ITCZ northern wetlands contribute during terminations (overshoots every

~100kyr)

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 CH4 budget… for forecasting the latter in a warmer world”

Loulergue et al.: What is novel?

1. Longest CH4 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 (~120kyr)

Loulergue: Methods

Two laboratories (U Bern and LGGE, Grenoble) analyze ice core samples fromEPICA/Dome C• Melt-refreezing method under vacuum to extract air• Gas chromatography to analyze chemical composition• Calibration using standard methane gases• EDC3 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/domec.html

Loulergue: EDC3 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 6kyr uncertainty

GC schematic

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

Loulergue Figure 1

warmer

VOSTOK

EDC

Temperature proxy

Oldest interglacial has higher CH4 (740 ppb) than MIS13-17

CH4-temp: r2=0.82MIS 19 and 9 decoupled

Loulergue Figure 1

Rapid, large fluctuations

~8 kyr, 170 ppbOscillation

Sources of variability

SOURCES: 1. Wetlands: At present 2/3 tropics, 1/3 boreal;

estimated at 170-210 Tg CH4-- T and water table (seasonal, interannual)2. Biomass burning3. 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 400-800kyr 23 and 41 kyr approx equal for 0-400 kyr

Loulergue Figure 2: Spectral analysis of CH4 record

Tropical climate dominated byprecession (supported by Asian summer monsoon reconstruction); CH4 overshoots ~100kyr due to N ice sheets/wetlands

Residuals of similar amplitudeTo orbital components

combines 3 periodicities

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 CH4 records as a proxy for millenial temperature fluctuations

~74 millenial CH4 changes(>50 ppb + associatedWith isotope maxima)

Had been suggested (marineRecords) that variability occurs when ice-sheet volume isAbove some threshold These results cast doubton a simple link between ice volume/Antarctic coolingand climate instabilities

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

Some definitions WMO Scientific Assessment of Ozone Depletion

2010

• Ozone Depleting Substances (ODSs)– While there are natural O3 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 CO2.

Problems with this approach? (e.g. CH4 vs CO2)

[Section 2.10.1 of IPCC AR4]

a = RF per unit mass increaseTime Horizon

r = CO2

i = species of interest

Global Warming PotentialsTABLE 2.14 IPCC AR4

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 observedMixing ratio changes in globalBackground atmosphereAssuming constant steady-state lifetime(No changes in sink or natural source)

CFCs

ODSs = CFCs+HCFCsCH4 and N2O smoothed 4-yr averageTo reduce influence of natural variability

Montzka et al. Figure 2

Methane: ANTHRO: 340 +/- 50 Tg CH4 yr-1 (2/3 total)-- agriculture and fossil fuel ~230 Tg CH4 yr-1 WETLANDS: 150-180 Tg CH4 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

• 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]

tropopause

surface

CH

CHOHk

B

]][[ 4

4tCH4=

[OH] influenced by:+ NOx sources (anthrop., lightning, fires, soils)+ water vapor (e.g., with rising temperature)+ photolysis rates (JO1D; e.g., from declining strat O3)- CO, NMVOC, CH4 (emissions or burden)

Montzka et al. Figure 2 – N2O

N2O: 19% above preindustrial levelsBUDGET: 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 depositionNATURAL: ~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 AR4 (Denman et al)

Montzka et al. Figure 2 – ODSs + substitutes

CFCs + other primary ODSs decreased from 9 to 1 GtCO2-eq yr-1 since late 1990sHCFCs and HFCs have increased; in 2008 0.7 Gt and 0.5 CO2-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 AR4 (Denman et al)

montzka

Front pagePrint versionSaturday(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-CO2 LLGHGs

“indirect influences” of CH4, ODSscould increase 0.2-0.4 W m-2

Some are offsetting Some accounted for in GWP

so in translation to CO2-eq

In absence of mitigation, LL non-CO2GHG RF could be ~1.5 W m-2 in 2050

~80% cut in CO2 required to stabilize

Stabilization not possible with cutsonly in non-CO2 GHGs

Future estimates do not considerclimate feedbacks from naturalemissions (or losses)

constant -80% non-CO2-80% CO2

-80% both

Montzka et al: Impact of 25% reductions in all LLGHGs

25% reduction in Anthrop emissions(2009-2020):

Non-CO2 RF peaks next decade mainly due to CH4 reductions

Relative RF: relative to 2009

Montzka et al., Key points

• About 1/3 total CO2-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 CO2 reductions

• Advanced understanding of sensitivities of natural GHG fluxes to climate change more effective management

(necessary?)

Non-CO2 gases

Call for… Process studies to inform inventories + initializing top-down estimatesMore measurements; better (inverse) modeling;