OVERVIEW & CHALLENGES

THE EARTH ENERGY BALANCE OVERVIEW & CHALLENGES

Karina von Schuckmann

Mercator Ocean international, France

Swiss National GAW/GCOS Symposium, 13-14 September 2021, Bern

The state, variability and change ofthe climate are to a large extentdriven by energy transfer betweenthe different components of theEarth's system.

Energy flows alter clouds, andweather and external and internalclimate forcing can temporarily alterthe Earth energy balance forperiods of days to several decades.

EARTH ENERGY BALANCE

The Earth energy balance is one of the most fundamental condition for making planet Earth conducive to sustaining life.

Earth’s energy budget is determined by the main flows of energy into and out of the Earth system.

von Schuckmann at al., 2016

Perturbations of the equilibrium Earth energy budget arise from internal or external climate variations and can create a postive or

negative Earth energy imbalance, manifested as a radiativeflux imbalance at the top of the atmosphere

EARTH ENERGY BALANCE at the top of the atmosphere

• Changes in atmospheric composition and land use (e.g. anthropogenic GHG emissions & emissions of aerosols and their precursors) affect climate through perturbations to Earth’s top-of-atmosphere energy budget

• How the climate system responds to a given forcing (equilibrium climate sensitivity & transient climate response) is determined by climate feedbacks associated with physical, biogeophysical and biogeochemical processes.

EARTH ENERGY BALANCE: Climate forcing

Variations of Earth’s energy budget are determined on how energy flows govern the climate response to a radiative forcing.

Gulev et al., 2021 (IPCC AR6, Chapter 2)

Understanding of changes in the Earth’s energy flows helps understanding of the main physical processes driving climate

variability & change

Dieng et al., 2017

d(OHC)/dt (in situ)d(OHC)/dt (satellite)Net flux at TOA (satellite)

EARTH ENERGY BALANCE: Climate forcing

Gulev et al., 2021 (IPCC AR6, Chapter 2)

Effective radiative forcing Earth energy imbalance

Subseasonal to decadal Decadal and longer

Changes in solar output (+/-) Milankovitch cycle (+/-) Human induced changes (+)

Climate variability (+/-)(e.g. ENSO, PDO)

Large volcanic eruptions (-)

Human-caused net positive radiative forcing causes an accumulation of additional energy (heating) in the climate system.

EARTH ENERGY BALANCE: Current status as assessed in IPCC AR6

Forster et al., 2021 (IPCC AR6, Chapter 7)

Estimates of the net cumulative energy change (ZJ = 1021 Joules) for the period 1971–2018

Heat inventory

Ener

gyC

hang

e (Z

J)

Radiative forcing

von Schuckmann et al., 2020

EARTH ENERGY BALANCE: Current status

IPCC AR6: • 1971–2006: 0.50 [0.32 to 0.69] Wm2

• 2006–2018: 0.79 [0.52 to 1.06] Wm2

Evolution of the Earth energy imbalance over time – published estimates


IPCC AR6 (1971–2018):

• Ocean: 91% • Land: 5%• Cryopshere: 3%• Atmosphere: 1%

Ocean heat uptake is by far the largest contribution, followed by land heating, melting of ice and warming of the atmosphere

EARTH ENERGY BALANCE: Earth heat inventory

Josey et al., 2015

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Earth surface budget

Radiation at TOA

Climate modelsEarth heat inventory

EARTH ENERGY BALANCE: How to monitor & evaluate?

Loeb et al., 2021

fundamental test of climate models and their

projectionsForster et al., 2021 (IPCC AR6, Chapter 7)

Josey et al., 2015

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Radiation at TOA



Loeb et al., 2021



EARTH ENERGY BALANCE: The global mean energy balance at the Earth’s surface

OLR: outgoing longwave rad.DLR: downward longwave rad.

ULR: upward longwave rad.OSR: outgoing solar rad.

DSR: downward solar rad.USR: upward solar rad.

P: precipitation rateSH: sensible heat flux

E: latent heat flux

after L’Ecuyer et al. 2015,updated based on Loeb et al. 2018 and Kato et al. 2018

Estimates of the current state of the energy cycle

(Wm-2)

ALL-SKY

The unconstrained view of the Earth’s energy budget does not balance

L’Ecuyer et al. (2015)


(Wm-2)

Earth’s energy budget with balance constraints imposed.

NEWS OriginalNEWS ConstrainedWm-2

341

17

184

333

239

Trenberth et al. (2009)

23

80

102

396

80

0.9

340 ± 0.1

24 ± 7

188 ± 7

346 ± 9

240 ± 3

Stephens et al. (2012)

23 ± 388 ± 10

100 ± 2

398 ± 5

0.6

88 ± 10

340

21

185

342

240

Wild et al. (2015)

2485

100

398

82

0.6


ALL-SKY

Earth Energy Budget closure at the surface: an integrated way forward

The global mean energy balance at the Earth’s surface: estimates of the current state of the energy cycle …

… subject of vigorous research for more thana century

… central for accurate observationally basedbenchmarks of energy flows to evaluate andrefine model physics

… Satellite observations with improvedcalibration and increased spatial and temporalresolution have played a central role in refiningreconstructions of Earth’s energy balance

… growing network of surface-basedmeasurements has provided substantiallybetter constraints

… improvements in global atmosphericreanalyses through both increased resolutionand the ability to assimilate extensive ground-based and satellite observations

Together, these advances have enabled new reconstructions of energy balance on combinationsof in situ observations, satellite

datasets, and reanalyses bring together

complementary expertise and datasets to provide a

comprehensive view of the Earth surface energy budget

(e.g. NASA NEWS type)


Key issues:

• Improve uncertainty understanding of the 10 Wm-2 to 15 Wm-2 global surfaceenergy balance residual (e.g. reduce the uncertainty in surface energy fluxes by reducinguncertainties in near surface properties (e.g. temperature, water vapor, wind speed).

• Investigation of surface energy budget at smaller temporal and spatial scales(e.g. monthly, regional)

• Adress and specify accuracy and stability requirements, which can widely varydepending on applications (climate change, regional, …), and by flux type(radiative fluxes & turbulent fluxes) in situ surface observations and surfaceflux data products (GCOS)

• Horizontal energy transport to achieve regional energy budget closure for theregional energy budget

Assessments & intercomparisons activities are taking place underGEWEX/GDAP.

EARTH ENERGY BALANCE: Key issues for the Earth surface budget: key issues

Josey et al., 2015

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Radiation at TOA



Loeb et al., 2021



EARTH ENERGY BALANCE: The Earth heat inventory

EEI can best be estimated from the Earth heat inventory, complemented byradiation measurements from space.

Combining multiple measurements in an optimal way holds considerable promise for estimating EEI and thus assessing the status of global climate change,

improving climate syntheses and models, and testing the effectiveness of mitigation actions. Progress can be achieved with a concerted international effort.

von Schuckmann at al., 2016

LAND OCEAN

CRYOSPHEREATMOSPHERE

HEAT

WHERE DOES THE ENERGY GO?

THE EARTH HEAT INVENTORY

HEAT AVAILABLE TO WARM LAND

ATMOSPHERIC HEAT CONTENTHEAT AVAILABLE TO MELT ICE

OCEAN HEAT CONTENT

Total heat gain of 358 ±37 ZJ during 1971-2018

HOW MUCH? WHERE?

89% OCEAN

6% LAND

4% CRYOSPHERE1% ATMOSPHERE




Total heat gain of 358 ±37 ZJ during 1971-2018

HOW MUCH? WHERE?

89% OCEAN

6% LAND

4% CRYOSPHERE1% ATMOSPHERE

RATE OF CHANGE IN TIME

1971-2018: 0.47 ± 0.1 W/m2

2010-2018: 0.87 ± 0.1 W/m2




The various facetsand impacts of

observed climatechange arise due to

the positive EEI, which thus representsa crucial measure of

the rate of climatechange.

The EEI is the most critical number defining the prospects for continued global warming and climate change. This simple number,

EEI, is the most fundamental metric that the scientific community and public must be aware of, as the measure of how well the world is doing in the task

of bringing climate change under control

The EEI is the portion of the forcing that the Earth has not yet been responded to(F- ∆T/S)

How much heat is ‘in the pipeline’ ?


THE EARTH HEAT INVENTORY: WHY SHOULD WE CARE?

Continued quantification and reduced uncertainties in the Earth heat inventory can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling,

as well as to establish an international framework for concerted multi-disciplinary

research of the Earth heat inventory

THE EARTH HEAT INVENTORY: FINAL COMMENTS

Major challenges / recommendations …. … Further unravel underlying uncertainties, identify biases and further advance on

observing system recommendations to fill critical measurement gaps

… Further foster multi-product approaches & physical budget constraints

… Advance on the role of internal vs. external variability

… Unravel heat re-distribution within different Earth system components at differenttime scales

… Explore potential new approaches to complement and cross-validate the Earthheat inventory approach

Josey et al., 2015

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Radiation at TOA



Loeb et al., 2021



The Earth energyimbalance budget

constraint

EARTH ENERGY BALANCE: The Earth energy imbalance (EEI)

Palmer and McNeal, 2014

Trend length [month]

Cor

rela

tion

Correlation of modelled EEI & OHC

Change in TOA net radiation and rate of global ocean heat storage from independent global climate observing systems should be in phase and of the same magnitude on annual and longer time scales (e.g. Hansen et al., 2005, 2011; Loeb et al., 2012; Palmer &

McNeal, 2014; von Schuckmann et al., 2016).

All other forms of heat storage are factors of 10 smaller at that time scale (e.g. Hansen et al., 2005, 2011; Trenberth et al., 2009; Loeb et al., 2012, Palmer and Mc Neal 2014, von Schuckmann et al., 2016).

Cheng et al., 2017

EARTH ENERGY BALANCE: The Earth energy imbalance (EEI) budget constraint

Loeb et al., 2021

Comparing net flux at TOA & Earth heat inventory

The GCOS components for the Earth energy imbalance budget constraint

The Earth energyimbalance (EEI) physical

budget constraint: a fundamental tool for

evaluation of the EEI and its uncertainties from the

underlying GCOS components

Heat has sequestered down into deeper ocean layers over the past 5 decades

Over the past decade (2010-2018), ocean warming rates have reached record values of 0.7 ± 0.1 (1.3 ± 0.3) W/m2 for the upper 700

(2000m) depth of the near-global (60°S-60°N) ocean EEI (1971-2018): 0.47 ± 0.1 W/m2; (2010-2018): 0.87 ± 0.12 W/m2


EARTH ENERGY BALANCE: Changes of the Earth energy imbalance (EEI)

EARTH ENERGY BALANCE: Changes of the Earth energy imbalance

Lui et al., 2020

Loeb et al., 2021

Kramer et al., 2021

How and why did EEI change over the past decade?

All-sky instantaneaous radiative forcing has increased by 0.53 ± 0.1 W/m2 from 2003 through 2018, accounting for a positive trend in the total planetary radiative imbalance due to a combination of rising concentrations of well-mixed GHG and recent reductions in aerosol emissions

Decadal increase in EEI from mid-2005 to mid-2019 of 0.5 ± 0.1 W/m2 from decreasedreflection of energy back into space by clouds& sea-ice, and increases in well-mixed GHG and water vapor.

EEI increase from 0.1 ± 0.61 W/m2 (1985-1999) to 0.62 ± 0.1 W/m2 (2000-2016), linked to changes in surface heat flux, planetary heat re-distribution and changes in ocean heat storage

W/m2

(rel. to 2001-2005)

A positive EEI of 0.2 W/m2 (for 10,000 y) during the deglaciation brought the climatesystem from the last ice age into the Holocene warm period.

The EEI varied significantly during thisperiod, with values up to 0.4 Wm−2 duringtimes of substantially reduced Atlantic Meridional Overturning Circulation net changes in ocean heat uptake, likely due to rapid changes in North Atlantic deep water formation and their impact on the global radiative balance,

changes in cloud coverage, albeit uncertain, may also factor into the picture.

Baggenstos et al., 2019

Reconstruction (noble gas) of the radiative imbalance for the last deglaciation, 20,000 to 10,000 y ago. importance of internal variability in the

Earth’s energy budget.

EARTH ENERGY BALANCE: Changes of the Earth energy imbalance (EEI)

Josey et al., 2015

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Radiation at TOA



Loeb et al., 2021



EARTH ENERGY BALANCE: The Earth heat inventory in CMIP5

radiative imbalance at TOA Earth heat inventory Ocean heat content

Simulated heat storage (1972–2005) from 30 CMIP5 GCM historical simulations

Assessment of the Earth heat inventory within CMIP5 historical simulations

The representation of terrestrial ice masses & the continental subsurface, as well as the response of each model to the external forcing, should be improved

in order to obtain better representations of the Earth heat inventory and the partition of heat among climate subsystems in global transient climate models

in comparison withrecent observations, the CMIP5 ensemble

overestimates the ocean heat content and underestimatesthe continental and

cryosphere heatstorage

Cuesta-Valero et al., 2021


Church et al., 2011

EARTH ENERGY BALANCE: The global energy balance in CMIP6

Wild, 2020

Global energy balance components are in better agreement with recentreference estimates compared to earlier model generations, particularly

for shortwave clear-sky budgets

However, substantial inter-model spread in the

simulated global meanlatent heat fluxes are present in the CMIP6

models, exceeding 20% (18 Wm−2)

CMIP6 has become the first model generation that largely remediates long-standing model deficiencies: overestimation in surface downward shortwave compensated by

an underestimation in downward longwave radiation (multi-model mean)

EARTH ENERGY BALANCE: Key messages

• The Earth energy balance is one of the most fundamental condition for making planet Earth conducive to sustaining life.

• Understanding of changes in the Earth’s energy flows helps understanding of the main physical processes driving climate variability & change

• The EEI is the most critical metric that the scientificcommunity and public must be aware as the measure for prospects of continued global warming and climate change and as the measure of how well the world is doing in the task of bringing climate change under control

• The EEI has increased over the past decade, and drivers for this change of anthropogenic and natural origin needfurther evaluation

EARTH ENERGY BALANCE: Synthesis of future opportunities

Advancements in uncertainty understanding & specify accuracyand stability requirements for all Earth energy budgetapproaches

Further advance on observing system recommendations, and fillcritical measurement gaps under a maintained GCOS

Further advance on the simulation of the global energy balance Investigations at different temporal and spatial scale through

regional energy budget closure approach Further advance on the role of planetary heat re-distribution and

their role in the Earth energy budget Further foster multi-product approaches & physical budget

constraints through concerted multi-disciplinary internationalcollaboration

THANK YOU

Any questions?

[email protected]

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OVERVIEW & CHALLENGES