Radiation and Climate Change FS 2018 Martin Wild Exam information Exam, 1. 6. 2018 • Takes place in RZ F21, approx. 60 - 70 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 simple laws and formulas, but not the more complex ones • 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.
37
Embed
Radiation basics lecture9 18May2018final forpdf · • global dimming counter-balances increasing longwave downward radiation • Surface radiative heating is not increasing Wild
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Radiation and Climate Change FS 2018 Martin Wild
Exam information
Exam, 1. 6. 2018• Takes place in RZ F21, approx. 60 - 70 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 simple laws and formulas, but not the more
complex ones• 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.
Radiation and Climate Change FS 2018 Martin Wild
7. Decadal changes in Earth radiation balance and climate response
Radiation and Climate Change FS 2018 Martin Wild
Radiative forcing over past 100 years
Radiative imbalance currently
estimated at 0.85 W/m-2
(0.75 W/m-2 over 1993-2003)
From Hansen et al. (2004)
Model simulations
Radiation and Climate Change FS 2018 Martin Wild
Radiative imbalance at TOA 1860-2100
Slingo and Webb 1997, QJRMS
Model simulations
Radiative imbalance: where does the energy go?
Radiation and Climate Change FS 2018 Martin Wild
0.75 Wm-2
Measurements of Ocean Heat Content
Radiation and Climate Change FS 2018 Martin Wild
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
Radiation and Climate Change FS 2018 Martin Wild
Von Schuckmann et al. JGR 2009
Radiation and Climate Change FS 2018 Martin Wild
Additional reading
Available on the course website:http://www.iac.ethz.ch/edu/courses/master/modules/radiation-and-climate-change.html
Radiation and Climate Change FS 2018 Martin Wild
Response of the climate system to radiative forcings
Radiation and Climate Change FS 2018 Martin Wild
Climate sensitivity is a measure of the equilibriumglobal surface air temperature change for a particularradiative forcing, usually given as a °C change perW/m2 forcing.
A standard experiment to determine this value in aclimate model is to look at the doubled CO2 climate,and so equivalently, the climate sensitivity is oftengiven as the warming for doubled CO2 (i.e. from 280ppm to 560 ppm)(“2xCO2 climate sensitivity”)
Climate sensitivity
Radiation and Climate Change FS 2018 Martin Wild
Equilibrium 2 x CO2 temperature response
IPCC TAR
GCMs with mixed layer ocean calculated into equilibrium under 2 x CO2 forcing
Radiation and Climate Change FS 2018 Martin Wild
Equilibrium 2 x CO2 temperature response
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
Radiation and Climate Change FS 2018 Martin Wild
Radiative forcing and climate sensitivity (I)
TOA radiation balance: N = SW - LWWhere N = TOA Net Radiation (“imbalance”), SW = absorbed solar radiation, LW = longwave outgoing radiation
Planet in radiative equilibrium:N = SW - LW = 0
Climate change:Apply radiative forcing F, climate system responds by a change in Temperature and resulting change in longwave emitted flux (Temperature dependent)N= F – l D T (“imbalance = forcing – response”)wherel= climate feedback parameter (Wm-2/�C)
Radiation and Climate Change FS 2018 Martin Wild
Equilibrium surface temperature response to imposed radiative forcing:At new equilibrium N=0DT= l-1 Fwhere F = Radiative forcing (Wm-2)l-1 = equilibrium climate sensitivity parameter (°C/Wm-2)DT= Equilibrium surface temperature response (°C)
Example: Climate sensitivity to doubling CO2
F = 4 Wm-2 (2 x CO2 radiative forcing)DT= 3°C=> l-1 = DT/F = 0.75°C / Wm-2
Radiative forcing and climate sensitivity (II)
Radiation and Climate Change FS 2018 Martin Wild
Equilibrium 2 x CO2 temperature response
IPCC TAR
GCMs with mixed layer ocean calculated into
equilibrium under 2 x CO2 forcing (ca. 4 Wm-2)
l-1= DT/F=2°C/4Wm-2
= 0.5°C/Wm-2
l-1= DT/F=5°C/4Wm-2
= 1.25°C/Wm-2
Radiation and Climate Change FS 2018 Martin Wild
Decadal changes in surface radiation
Changes in downward longwave radiation
most directly affected by changes in atmospheric greenhouse gases
expected to undergo largest changeof all energy balance componentsin coming decades
CMIP5 models suggest increase of 6 Wm-2 since 1870
Only monitored since the initiation ofBSRN in the early 1990s
Downward longwave radiation in CMIP5 models
Greenhouse Gases
6 Wm
-2
1870-2005
Wild et al. 1997 J. Climate / Wild 2016, AIP proc.
Increasing greenhouse effectat the surface
Radiation and Climate Change FS 2018 Martin Wild
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
Radiation and Climate Change FS 2018 Martin Wild
Philipona et al. 2004
Wild et al. 2016
Widespread increase in observed downward longwave radiation
South Pole
Observed increase at all BSRN sites since 1992: +2 Wm-2/decade