Earth’s Radiative Forcing

Given the data: Can you close the energy

budget?

Alex, Elizabeth, & Tyreke

Kevin Trenberth• works for NCAR

• lead author for IPCC reports in 1995, 2001, 2007

• father of energy balance figure

• fun fact: in 2009’s “climategate,” quoted for not being able to account for hiatus and missing energy

(Calvin, 2005)

Norman G. Loeb

• works for NASA, principal investigator of CERES

• focuses on remote sensing

• plays basketball in free time

(NASA, 2011)

Data Analysis vs. Modeling-Data analysis: observations-Physical model that has been

constructed. Think: Matlab

http://www.mathworks.co.uk/

Balanced? Energy Budget In steady state, energy

follows energy balance model:

CHANGE IN STORAGE = IN – OUT

These papers discuss an imbalance in this equation, which results in missing energy

(Trenberth & Fasullo, 2012)

Incoming Shortwave Radiation

• yellow: total solar irradiance that reaches TOA

• red: radiation that penetrates through atmosphere to sea level

• spaces: irradiance absorbed by gases in atmosphere

Most of radiationfrom the sun reaches theEarth’s surface (EPS 22, 2014)

Greenhouse Gases and Atmospheric Transmissivity

• longwave effects: increasing GHG emissions lower the transmissivity of the atmosphere and trap outgoing radiation

• Graphs show percent of solar radiation absorbed at each wavelength• Breaks down atmosphere

into constituentsTake home: very little longwave radiation escapes

Atmospheric Constituents and their Effect on Radiative

Forcing

Relative forcing for:Greenhouse gases trap

longwave radiation (positiveRadiative effects)

Stratospheric Ozone lowers transmissivity of incoming UV radiation

Aerosols reflect solar shortwave radiation back to space (negative radiative effects)

Data Sources measuring TOA radiation

• ERBE (Earth’s Radiant Energy Budget Experiment)o conducted from 1985-1989 -- when TOA values were

assumed to be in balance

• CERES (Clouds and the Earth’s Radiant Energy System)o continuation of ERBE, December 1999- presento Objectives

to continue ERBE, increase accuracy, provide long-term global estimates, bridge gap between clouds and radiative fluxes

Data Sources: Through the Atmosphere

• Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals

❏ captures data in 36 spectral bands (0.4 µm to 14.4 µm)

❏ measures changes in cloud cover, radiation budget, and oceanic/atmospheric processes

Photos based on observations from MODIS

Data Sources: Precipitation

• Global Precipitation Climatology Project (GPCP) o Develop a temporal and spatial

understanding of global precipitation

o Network of ~6,000 stationso contains error (undercatch and

sampling), but considered to be most reliable (Trenberth et al. 2007b)

Data Sources: CloudSat and GRACE

• CloudSato measures altitude and

properties of cloudso to add info. on the

relationship between clouds and climate

• Gravity Recovery and Climate Experiment (GRACE) o Shows increase in mass of

ocean since 2003 La Niña

Trenberth PaperMotivation: After 2004, the energy balance model

is unbalanced and this missing energy is unaccounted for in the climate system

Contends the energy is unbalanced and looks to find it by incorporating analysis of subsurface ocean data

Used model to suggest what is the main sink: the ocean below 275 meters

Ocean Heat Content Has Increased Over Time

blue bars: 1961-2003

burgundy bars: 1993-2003

• positive energy content change = increase in stored energy

• (Total) oceans account for most energy uptake (90%)

(Trenberth & Fasullo, 2012)

• “natural climate variability has a cause”o external to the climate system (volcanic eruption)o internal

• heat once sequestered can resurface at later time

ENSO: An Example of Natural Variability

NOAA / PMEL / TAO Project Office, Dr. Michael J. McPhaden, Director

Increased Heating After 2008 La Niña

(Trenberth & Fasullo, 2012)

• ENSO (°C) drives net increase in energy imbalance

• Cloud cover decreases• Lagged decrease of

outgoing longwave radiation (W/m2) to cooler conditions and increase in ASR

• Extra TOA energy absorbed (W/m2)Net Radiation (RT)=ASR-OLR

--Left axis

Rate of Increase in Surface Temperaturein Relation to Sea Level and CO2

(Trenberth & Fasullo, 2012)

T(sfc): 12-month global mean surface temperature anomalies relative to 1901-2000

Thick line: data normalized to decadalEl Niño (1997-98)La Niña (2007-08)

Atmospheric carbon dioxide concentration and sea level are increasing ~ linearly Rate of temperature increase appears to slow after 2003

Missing Energy in the Global Net Energy Flux

(Trenberth & Fasullo, 2012)

Solid black line: original satellite dataDotted black line: EBAF Ed2.5 is revisited satellite data

• Currently, we are not accounting for all missing energy

• The ocean is the main energy sink

• Additional energy sinks (e.g. ice) make 0.6 W/m2 of total warming

• Sun changes reduce net heating

Storage of Energy Entering Climate System

• 1993-2003 residual only is 0.7 W/m2

• 2004-2008 >50% of energy entering system is residual

(Trenberth & Fasullo, 2012)

Model: NCAR CCSM version 4

• Released May 2010

• Modeling temperature for 21st century

• Coupled atmospheric and land-surface model

Global Mean Surface Temperature

(Trenberth & Fasullo, 2012)

Black: average of 5 runs

Blue: moments of surface warming stasis

Modeled Perturbations of 21st Century Ocean Heat Content

(Trenberth & Fasullo, 2012)

• top left: net radiation at TOA (RT) increases

• top right: ocean heat content increases at depth as surface heat content decreases

• lower panel: ocean heat content modeled Gray: stasis in global mean surface temperature

Strengths: Trenberth• Effectively discusses history of data analysis

and how this information is interpreted in the context of the CCSM model

• Makes a strong argument for why we should be concerned with missing energy: need to track global energy to understand how hard we are driving the climate system. If we ever want to make predictions it is necessary to better understand and balance the energy budget.

Weaknesses: Trenberth• Current observations and analyses either:

o Provide an incoherent narrativeo Have huge error

• Does not discuss the switch in ocean surveying (to ARGO) in 2004 and its implications on accuracy.

Loeb Paper• Obtained most of data from CERES then

applied adjustment of heat uptake using ARGO and ice melt data

• Finds imbalance from 2001-2008 to be 0.50±0.42 W/m2 (confidence of 90%)

• Motivation: to decrease uncertainty by estimating warming rates over longer periods of time

Great Uncertainty in Upper Ocean Warming Rates

• uncertainty declines in recent years after transition of technology

• shows ocean warming of 0.64±0.11 W/m2 between 1993 and 2008

(Loeb et al. 2012)

Ocean Heat Rate (W/m2)

Great Uncertainty in Upper Ocean Warming Rates

Loeb et al. finds decline in heating rates after 2004 statistically insignificant

(Loeb et al. 2012)

Mean and Uncertainty of Ocean Heating Rates at 90% Confidence Level

Variations in Radiation Correlated with ENSO Cycle

Tropics Global

(Loeb et al. 2012)

Earth energy anomalies (ASR, NET, OLR) correlate to El Niño and La Niña conditions. Positive anomalies with La Niña. Negative with El Niño years.

gray is ENSO index:

positive el niño phase

negative la niña phase

TOA Flux vs Ocean Heating Rates

(Loeb et al. 2012)

CERES does not show a sharp decline during the XBT to Argo transition (2002-2005)

CERES and PMEL/JPL/JIMAR have r ~ 0.46

CERES and ERA-Interim show consistency

Interannual variability of net TOA ranges from 0.09-1.5Wm2

No statistically significant heating rate decline

Energy is continuing to accumulate in the oceans

Applying Loeb’s Errors to Trenberth’s Image

Strengths: Loeb• clearly states Trenberth and others hypothesis on

missing energy and reruns and reinterprets data

• argues strength of newer measurements (Argo v XBF) and reevaluates error measurements

• identifies concrete sources of uncertainty

Weaknesses identified in Trenberth’s email regarding Loeb’s paper

Trenberth’s Response to Loeb (email)

● Main point of original Trenberth paper: to challenge the OHC and CERES communities to do better

● Trenberth accuses Loeb of having uncertainties too large to confine to “within uncertainty.”

● Large discrepancies between OHC data sets hamper current studies.

Summary of Debate: Trenberth

● Missing heat being deposited in ocean: ○ Below 700 meters○ in the Pacific○ between 40°S and 30°N○ it is associated with the negative phase

of the Pacific Decadal Oscillation and/or La Nina events

Summary of Debate: Loeb• New satellite and ocean data have improved

measurements

• No statistically significant decline in ocean heating rate

• There may not be “missing energy” in the climate system, energy is continuing to accumulate in the oceans

Given the data: Can you close the energy

budget?