APS March 2015 – Talk D33.00002

Observational Determination of

Surface Radiative Forcing by CO2 and CH4

Daniel Feldman

Lawrence Berkeley Lab

William Collins, and Margaret Torn

Lawrence Berkeley Lab

With assistance from

Jonathan Gero

University of Wisconsin, Madison

Eli Mlawer

Atmospheric and Environmental Research

Timothy Shippert

Pacific Northwest National Laboratory

GHG Concentrations and Forcing

IPCC AR5

• While the concentrations are observed,

these forcings are strictly modeled.

• Can we observe climate forcing?

CO2 Infrared Absorption

• CO2 symmetric molecular structure leads to a series of infrared

absorption features that absorb the energy the Earth emits.

• Databases tabulate these features but are periodically updated as

measurements and theory improve.

Rothman, 2013

3

Goody and Yung, 1989

Radiative Forcing and Climate Models

HITRAN Line

Parameters

Climate Model

Integrations

Radiative Transfer

Code

Radiative

Forcing

Line Mixing,

Continuum Absorption

4

Objectives of This Study

• Determine whether the basis of climate change

projections, namely GHG forcing, can be

observed outside the laboratory.

• Provide direct observational evidence how

changes in GHGs are altering the

surface energy balance.

• Determine whether climate models are

reproducing surface forcing from WMGHGs

(other work).

0

1

2

3

4

5

6

3 3.2 3.4 3.6 3.8 4 4.2 More

Fre

qu

en

cy

Forcing ( W / m 2 )

2 xCO2 Forcing in I PCC Models

Collins et al, 2005

Rasch et al, 2014

ARM Sites

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The Atmospheric Radiation Measurement (ARM) program run by the

US Department of Energy has sponsored decades of intensive

measurements at sites in Alaska and Oklahoma

The Data and Tools We Use

In situ data on WMGHGs Active Remotely-Sensed Cloud Locations

Radiosonde Atmospheric Profiles

AERI

Microwave Water Retrieval

The Role of Simulations

90% of energy within 3σ Noise-Equivalent Radiance

The Spectral Fingerprint of CO2

Trend is zero based on linear least-squares fit and a χ2 test at the 0.01 level.

1st Detection of CO2 Surface Forcing

(a) (b)

(c) (d)

• First empirical confirmation of surface radiative forcing:

(from 23 ppmv increase in atmospheric CO2 from 2000-2010).

SGP

NSA

Task 1 CO2 Time Series Task 4 CO2 Forcing Time Series and Power Spectra

Feldman et al, 2015

0.2 W/m2/decade

0.2 W/m2/decade

Growing Surface CH4 Forcing?

Methane growth rate by latitude

E G Nisbet et al. Science 2014;343:493-495

Recent global methane concentrations

• We can use an analogous procedure to derive CH4 surface longwave forcing.

CH4 Time Series at ARM Sites

• North Slope of Alaska site shows clear CH4 hiatus in 2000s ending ~ 2005.

• Southern Great Plains shows much higher CH4 concentrations than NSA.

1st Detection of CH4 Surface Forcing

Observational Determination of:

• Time series of radiative forcing by CH4: Signals of “hiatus” and recent rise.

• Quantification of impact of CH4 on the Earth’s surface energy budget

• Determination of the radiative signal from seasonal cycle.

• We have quantified trends in

surface radiation from ΔCO2 and

from ΔCH4.

• Trends in forcing:

• CO2: 0.2 + 0.05 Wm-2 / decade

• CH4: 0.2 + 0.1 Wm-2 / decade

• We have independently determined

the increasing greenhouse effect

due to rising CO2 and CH4.

• We find the basis for climate forcing

by GHGs to be robust and

consistent with observations.

• For more details, see:

Nature (2015) doi:10.1038/nature14240

Backup Slides

Global Sources of Methane

Anthropogenic sources (70%) • Fossil fuel 100 Tg CH4 yr-1 • Ruminant animals 80 Tg CH4 yr-1

• Rice agriculture 60 Tg CH4 yr-1 • Landfills 60 Tg CH4 yr-1 • Biomass burning 50 Tg CH4 yr-1

Natural sources (30%) • Wetlands 100 Tg CH4 yr-1 • Termites 20 Tg CH4 yr-1

• Geological 10 Tg CH4 yr-1

• Hydrates 5 Tg CH4 yr-1 • Oceans 4 Tg CH4 yr-1

• Wildfires 2 Tg CH4 yr-1

Denman et al. (2007) (IPCC, Ch. 7)

Thanks to I. Simpson, UC Irvine

Global Sources of Ethane

Anthropogenic sources • Fossil fuel 8-9 Tg yr-1 • Biomass burning 2-3 Tg yr-1

• Biofuel 2-3 Tg yr-1

Minor sources • Oceans 0-0.5 Tg C yr-1 • Vegetation Negligible

Xiao et al. (2008); Pozzer et al. (2010)

• Ethane has a fairly simple source budget

• Ethane’s major sources are shared with methane

Thanks to I. Simpson, UC Irvine

Using Ethane to Understand Methane

Ethane + methane sources: • Fossil fuel • Biomass burning

Methane-only sources: • Wetlands • Rice paddies • Ruminants • Landfills

Time Time

Co

nce

ntr

atio

n

Co

nce

ntr

atio

n Methane Methane

Ethane

Ethane

Thanks to I. Simpson, UC Irvine

Evidence for Joint (M)Ethane Source

• High correlation with ethane in Oklahoma.

• Low correlation with ethane on Alaska coastline.

Absence of Combustion Signatures

• Little correlation with CO, a product of combustion.

• Negligible correlation with AOD, including smoke AOD.

Signals of Other Agents in CH4 Band

• Methane forcing signal is convolved with effects of N2O, H2O, and T (of course).

• Uncertainties in non-CH4 agents introduce large uncertainties in FLBLRTM (t,t0).