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

……………………….