climate change andrew levan – department of physics
TRANSCRIPT
Climate ChangeAndrew Levan – Department of Physics
OutlineSetting the temperature of the planet
Out of balance
Projections of the future
Weighing the impacts
A need for action?
The Earth is heated from above
Outward heat from molten core (~0.2 W/m2)
Incoming solar radiation (1370 W/m2 at equator, 342 W/m2 on average)
Reflected (107 W/m2 )
Absorbed (235W/m2 )
Re-radiated (235.2 W/m2 )
Equilibrium Temperature In general Energy in = Energy out
Equilibrium Temperature In general Energy in = Energy out
Earth is approximated as a perfect absorber and emitter of radiation, a so called black-body, accounting for reflection
Equilibrium Temperature In general Energy in = Energy out
Earth is approximated as a perfect absorber and emitter of radiation, a so called black-body, accounting for reflection
Ein = 1370 W m2 x Area of disc of Earth x (1-Albedo)
Eout = Surface area of Earth x constant x Temperature4
Equilibrium Temperature In general Energy in = Energy out
Earth is approximated as a perfect absorber and emitter of radiation, a so called black-body, accounting for reflection
Ein = 1370 W m2 x Area of disc of Earth x (1-Albedo)
Eout = Surface area of Earth x constant x Temperature4 2 2 4(1 ) 4 eR S A R T
Equilibrium Temperature In general Energy in = Energy out
Earth is approximated as a perfect absorber and emitter of radiation, a so called black-body, accounting for reflection
Ein = 1370 W m2 x Area of disc of Earth x (1-Albedo)
Eout = Surface area of Earth x constant x Temperature4
Re-arranging can give an expression for the expected temperature of the Earth (or any other planet).
The Earth should have an average temperature of -18 degrees
2 2 4(1 ) 4 eR S A R T
Equilibrium Temperature In general Energy in = Energy out
Earth is approximated as a perfect absorber and emitter of radiation, a so called black-body, accounting for reflection
Ein = 1370 W m2 x Area of disc of Earth x (1-Albedo)
Eout = Surface area of Earth x constant x Temperature4
Re-arranging can give an expression for the expected temperature of the Earth (or any other planet).
The Earth should have an average temperature of -18 degrees
2 2 4(1 ) 4 eR S A R T
Energy balance Incoming energy from the sun has a
“temperature” of 6000 degrees. Mostly optical light
Outgoing energy from the Earth has a temperature of -18 degrees. Infrared light
The atmosphere has a profound impact.
Wavelength
Intensity
IncomingOutgoing
Optical Infrared
Transp
are
nt
Opaqu
e
http://www.giss.nasa.gov/research/briefs/schmidt_05/
A greenhouse
Earth Surface
in-coming Re-radiated
Greenhouse gasE E
E
E
½ E
½ E
Energy in = Energy out
Anthropogenic greenhouse gases
Energy is trapped here, it warms upEnergy doesn’t reach here, it cools down
Eventually both troposphere and stratosphere will warm more to restore equilibrium
Radiative forcing Imbalance in incoming and outgoing radiation
Earth surface
Top of tropospher
e
240 240
x2 CO2
240 236 240 240
T=15 oC T=15 oC T=15+1.5 oC (2.5 oC including feedbacks)
Pre-industrial CO2 = 280 ppm, now = 400 ppm
Radiative forcing arises from all greenhouse gases, and can be assessed via global warming potential
(W/m2)
“Real” Climate Sensitivity
No feedback
With feedback(e.g. ice melt, water vapour etc)
Risks Health
Increased deaths from heat stress Spread of vector borne diseases (e.g. Malaria)
Food security Changes in crop production/locations Lack of fish breeding grounds Freshwater availability
Migration/Immigration Flooding of low-lying coastal regions (e.g. Ganges/Nile Delta) – loss of
living space
Infrastructure Flooding Energy
Weather is not climate
Daily Express 2013
Daily Express (yesterday)
Projections to the future
Business as usual
Ocean Atmosphere General Circulation Models (OAGCM)
AIM: To enable projections of future climate
IPCC 2013
Setting a target Avoid the risks of irreversible damage to the
climate system – permafrost metling, gulf stream shut-off etc
Allow unavoidable climate changes to happen at rate at which ecosystems can adapt
Food production should not be threatened
Economic development (particularly in the developing world) must be sustainable.
Possible at Kyoto? Possible now?
SolutionsMitigation vs AdaptationMitigation is probably cheaper than adaptation,
but the money must be spent now (few % of GDP now and forever – Stern) Renewables Changing lifestyle Etc
Adaptation is more expensive, but can be done downstream (Discounting rate? Technological solutions?)
www.withouthotair.com
The big problems….
Poverty
Ebola
Terrorism
Health
Population
Resource exhaustion
Economic growth (too much and too little)
Climate
……………………….