Radiation basics lecture8 17May2019forpdf · Global dimming versus greenhouse warming 1950s to 1980s • global dimming counter-balances increasing thermal downward radiation •

Radiation and Climate Change FS 2019 Martin Wild

Exam information

Exam, 31. 5. 2019• Takes place in RZ F21, approx. 60 Min.• Covers all material discussed in the lectures and in the computer lab• No supporting material allowed (keine Hilfsmittel), except a simple pocket

calculator with trigonometric and power functions (no calculators on smartphones, no pocket computers). We will provide a number of TI30 calculators, if you cannot bring an appropriate calculator.

• Emphasis is on understanding of concepts• You should know the more simple laws and formulas (e.g. the Stefan

Boltzman law), but not the complex ones (e.g. the solution of the Schwarzschild Equation).

• Not necessary to learn by heart values of the constants in the equations• Please be here at 8 15, we will need some time to check your IDs and

possibly the pocket calculators, and start the exam towards 8 30.• Additional reading material on website is not part of exam

6. Radiation and climate change on different timescales



• Radiative forcings over 109 Years: Climate change on geological timescales: faint Sun, snowball Earth

• Radiative forcings over 106 Years: Ice age cycles

• Radiative forcings over 104 Years: Holocen climate change

• Radiative forcings over 103 Years: Millenium climate change

• Radiative forcings over 102 Years: Multidecadal climate change

Radiative forcings over Earth’s history


Orbital parameters that determine changes in solar radiation relevant for glaciation and ice ages cycles

Radiative forcing over past million years

100’000 yearsperodicity




Radiative forcing over past million years

Milutin Milankovitch (1879-1958) - astronomical theory (1940): realized importance of summertime insolation changes in high latitudes for ice sheet melt.

Radiative forcing over past 10‘000 years

Holocene dominated by Precession (20‘000 years periodicity)


N-Summer in Perihel

N-Summer In Aphel

Inso

latio

n (W

m-2

) Dec

embe

r 45°

Inso

latio

n (W

m-2

) Dec

embe

r 0° Insolation (W

m-2) July 0

°

Insolation (Wm

-2) July 45°

Radiative forcing over past 10‘000 years

Holocene dominated by Precession (20‘000 years periodicity)


Northern Hemisphere

Insolation past 1300 years

Radiative forcing over past 1000 years


Temperature past 1000 years

Variations in solar output relevant

Little ice age caused by weak solar forcing

Painting of the frozen Thames 1683 by Jan GrifierRadiation and Climate Change FS 2019 Martin Wild


Solar activity also documented in sunspot number observations

Radiative forcing over past hundreds of years






Radiative energy imbalance currently estimated at ~0.8 W/m-2

Hansen et al. (2004) Model simulations

?=

“radiative energy imbalance”


Additional reading

Available on the course website:http://www.iac.ethz.ch/education/master/radiation_and_climate_change/

http://www.iac.ethz.ch/education/master/radiation_and_climate_change


Radiative energy imbalance at TOA 1860-2100

Slingo and Webb 1997, QJRMS

Model simulations

“radiative energy imbalance”

Radiative imbalance: where does the energy go?


0.8 Wm-2

Measurements of Ocean Heat Content


Argo: • Global array of 3800 floats provides since 2003

100,000 temperature/salinity profiles and velocity measurements per year distributed over the global oceans at about 3°degree spacing.

• Floats cycle to 2000m depth every 10 days.

Measurements of Ocean Heat Content


Von Schuckmann et al. JGR 2009


Additional reading

Available on the course website:http://www.iac.ethz.ch/edu/courses/master/modules/radiation-and-climate-change.html


Forcing and Energy Imbalance

From Murphy et al 2009

Apply step-function radiative forcing (e.g., instantaneous doubling of CO2: system responds by change in temperature and resulting change in emitted longwave radiation)

TOA Imbalance

Outgoing longwave radiation

(imbalance)

Forcing

Response


Decadal changes in surface radiation balance

Changes in downward longwave radiation

most directly affected by changes in atmospheric greenhouse gases

expected to undergo largest change of all energy balance components in coming decades

CMIP5 models suggest increase of 6 Wm-2 since 1870

Only monitored since the initiation of BSRN in the early 1990s

Downward longwave radiation in CMIP5 models

Greenhouse Gases

6 Wm

-2

1870-2005

Increasing greenhouse effect at the surface



What can we see in currently available records

of downward longwave radiation?Baseline Surface Radiation Network (BSRN)

Observed changes in downward longwave radiation

Longterm monitoring of downward longwave radiation is acentral objective of BSRN


Philipona et al. 2004

Wild et al. 2016

Widespread increase in observed downward longwave radiation

Ny-Alesund Spitzbergen

Alpine sites

Greenhouse Gases

Observed changes in downward longwave radiation

25 Wm

-210 Wm

-2

RCP 8.5

RCP 4.5

CMIP5 projections 21th century 10 CMIP5 Models

Future changes in downward longwave radiation

Wild et al. 1997 J. Climate / Wild 2016, AIP proc.

25 Wm

-210 Wm

-2

RCP 8.5

RCP 4.5

CMIP5 projections 21th century

2010-2030: RCP8.5:+2.2 Wm-2/decRCP4.5:+1.7 Wm-2/dec

Observed: +2 Wm-2/dec

10 CMIP5 Models

Future changes in downward longwave radiation

Wild et al. 1997 J. Climate / Wild 2016, AIP proc.

“dimming”

Potsdam, Germany 1937 – 2014

Inso

latio

n an

omal

ies

(Wm

-2)

Decadal changes in surface solar radiation

Surfa

ce s

olar

radi

atio

n (W

m-2

)

Wild et al. 2005, ScienceWild 2016, WIREs Clim Change

“dimming” “brightening”

Wild, M. 2012: Enlightening Global Dimming and Brightening. Bull. Amer. Meteor. Soc., 93

“global dimming” “brightening”

Decadal changes in surface solar radiation

Numbers: changes in Wm-2/decade


Additional reading



Periodic sunspots > active sun

What causes dimming and brightening?

Can variations in solar activity explain dimming/brightening?

0.1 %

Variations in solar activity CANNOT explain dimming/brighthening

Variations in solar output, measured from satellites

Periodic sunspots > active sun

Number of sunspots



From ISCCP (NASA/ Bill Rossow)

Anomalies in global cloud cover from satellite 1983-2002

International Satellite Cloud Climatology Project


Wild et al, 2005, Science

Recent recovery in atmospheric transmission in line with reduced emissions

“dimming” “brightening”

Atmospheric clear-sky transmission

Data source: Stern, 2005

Global AnthropogenicSulfur Emissions

Changes in cloud-free atmosphere 1950-2000



Both direct and indirect aerosol effects (cloud albedo/cloud lifetime) reduce the amount of solar radiation reaching the ground

Direct and indirect aerosol effects

Direct effects Indirect effects: cloud albedo and lifetime

Less precipitation > longer lifetime



- +

Global dimming versus greenhouse warming

1950s to 1980s• global dimming counter-

balances increasing thermal downward radiation

• Surface radiative heating is not increasing

Wild et al. (2004) GRL 32Wild (2012) Bull. Amer. Meteorol. Soc.

- +-xsince 1980s• Absence of global

dimming no longer masks thermal greenhouse effect

• Surface radiative heating increases significantlyWild et al. (2005) Science 308Wild (2012) Bull. Amer. Meteorol. Soc.

Dimming BrighteningDimming / brightening modulates decadal warming rates

Observed Northern HemisphereTemperature change

Data source:CRU

2m T

empe

ratu

re a

nom

alie

s (C

)

Deviation from 1960-1990

-0.002°/ decade 0.29°/decade

Global dimming versus greenhouse warming

Radiation and Climate Change FS 2019 Martin Wild Wild 2012, BAMS


DTR as proxy for surface insolation changes

From Liu et al. 2004, J. Climate

Correlation of surface insolation and DTR in Europe

Correlation of surface insolation and DTR in China

From Makowski et al. 2009, JGR

Daily maximum temperature dominated by surface solar radiation

Daily minimum temperature dominated by thermal radiation

DTR:Diurnal Temperature Range=T max – T min

R=0.87


Observation data: CRU dataset

Wild et al. 2007, Geophys. Res. Lett.

Units °C/decade

1958-1985“dimming”

1985-2002“brightening”

T max -0.04 +0.37

T min 0.11 +0.40

DTR -0.15 -0.03

Observed DTR Land Mean 1958-2000s

Linear regression slopes land mean DTREvidence for large scale change in surface radiative forcings

Asymmetric hemispheric pollution

Emissions show trend reversal in NH, but not in SH

Anthropogenic sulfur emission 1950-2000

Source: Stern (2005)

Northern Hemisphere

Southern Hemisphere

Globe

Wild, BAMS 2012Radiation and Climate Change FS 2019 Martin WildWild 2016, WIREs Clim Change

2m T

empe

ratu

re (C

)“dimming” “brightening”

Temperature changeNorthern Hemisphere

2m T

empe

ratu

re (C

)

Wild 2016, WIREs Clim Change

Temperature changeSouthern Hemisphere

Sulfur Emissions since 1950

Reversal in Temperature trends in Northern Hemisphere, but not in Southern Hemisphere > fits to emissions

Deviations from 1960-1990 Deviations from 1960-1990

Asymmetric hemispheric warming


Impact on mountain glaciers

Swiss Glaciers area reduction:

“Dimming phase“1973 - 1985: -1 %“Brightening phase“1985 - 2017: -33 %F. Paul. Personal communication

Swiss glaciers only retreated

after transition from dimming to brightening

Negative surface net radiation

Positive surface net radiation

Observed precipitation NH mean landData source:

GHCN

Wild, BAMS 2012

Impact on the global water cycle


Variations in precipitation quantitatively consistentwith variations in surface net radiation

Dimming total radiationdiffuse fraction

Brightening total radiationdiffuse fraction

Dimming and brightening affects quantity & quality of radiation

Abakumova et. al. 1996

Total solar radiation

Direct solar radiation

Diffuse solar radiation

Solar radiation during dimming phasein Odessa 1960-1986

More pollution leads to less direct and more diffuse solar radiation

Impact on carbon uptake and plant growth

Total radiation= Direct + DiffuseDiffuse fraction= Diffuse / Total

total radiation --- reduces plant photosynthesis

diffuse fraction --- enhances plant photosynthesis

Global-Dimming period

Mercado et al. 2009 Nature

Direct radiation: Can only be used by uppermost leaves for photosynthesis

Diffuse radiation: penetrates deeper into canopy - can be more effectively used for photosynthesis by many plants

Modeling studies: Effect of diffuse fraction increase dominates=> Increased carbon uptake and plant growth during dimming

Impact on carbon uptake and plant growth

Impact of dimming on PV production in China

Sweerts et al. Nature Energy (in press)

PV electricity potential decreased by 11-15% between 1960 and 2015 due to the reduction in surface solar radiation

In 2017 China accounted for over half of global PV capacity additions

Reverting back to 1960s radiation levels could yield additional electricity generation of 14 TWh with PV capacities as installed in 2016 and 51 –74 TWh in 2030. The corresponding economic benefits could amount to 1.9 billion USD in 2016 and 4.5 – 6.5 billion USD in 2030.


Additional reading



Documents

Radiation basics lecture8 17May2019forpdf · Global dimming versus greenhouse warming 1950s to 1980s • global dimming counter-balances increasing thermal downward radiation •