CLIMATE CHANGE AND ENERGY

Juan Carlos de ObesoOctober 12 2013

Climate System

What is Climate?• Climate is the characteristics of the environment, defined over

a finite time interval, at a given location.- This includes the mean values or the range of values or even frequency of events for weather variables, such as wind, temperature, precipitation, humidity, cloudiness, pressure, visibility, and air quality.

• A complete description of the climate system and the understanding of its characteristics and change require the study of the physical properties of the high atmosphere, deep ocean, and the land surface, and sometimes the measurement of their chemical properties.

• Climate is a quantitative science, involving the understanding and modeling of the transfer of energy from the sun to the earth, from earth to space, and between atmosphere, ocean, and land, all under fundamental physical laws such as conservation of mass, heat, and momentum.

Sept. 9, 2009

What is evident from this graphs?

1958-2012?1700-2012?

Source:http://keelingcurve.ucsd.edu/

Latest CO2 Reading

393.28 ppmOctober 09, 2013

Modeling the Climate

Sept. 7, 2010

Models• Conceptual

Illustrate principal relationships or balances

• Empirical/statisticalDescribe relationship between observed parameters (e.g. sea surface temperature and rainfall)

• Numerical/dynamicalBased on set of mathematical equations describing physical processes, that allow the system to evolve in time

Sept. 7, 2010

How do we model climate?[physically]

• Physical/dynamical equations- 3-D equations of motion (conservation of momentum)- Continuity equation (conservation of mass)- Thermodynamic equation (conservation of energy)- Equation of state for air- Balance equation for water vapor

• ParameterizationsSmall-scale processes that are treated statistically and their effects related to average conditions over much longer periods of time and larger space scalese.g. clouds, radiative transfer, turbulence

Sept. 7, 2010

Sept. 9, 2009

Weather & Climate PredictionClimate Change

Unce

rtain

ty

Time Scale, Spatial Scale

CurrentObserved

State

Initial & ProjectedState of Atmosphere

Initial & Projected

Atmospheric Composition

Decadal

Initial & Projected

State of Ocean

Sept. 14, 2009 EESC W4400x

Global Climate Change Projections

Source: IPCC 4th Assessment Report, Working Group 1: The Physical Science Basis for Climate Changehttp://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-1-3.html

Surface Energy Budget

How is energy/temperature transferred from surface to atmosphere?

Ground

Atmos.

Net Solar Radiation(SW)

4TRadiative Heat Flux Sensible Heat Flux

( )sfc airu T T Latent Heat Flux

( )sfc airu q q

GH Effect(LW)

- - - - Radiation - - - - Conduction/Convection

Blackbody: DefinitionA blackbody is a hypothetical body made up of molecules that absorb and emit electromagnetic radiation in all parts of the spectrum

– All incident radiation is absorbed (hence the term black), and– The maximum possible emission is realized in all wavelength

bands and in all directions

In other words…A blackbody is a perfect absorber and perfect emitter of radiation with 100% efficiency at all wavelengths

Planck Function & Blackbody Radiation

• The radiation emitted by a blackbody can be described mathematically by the Planck Function.

• Relates the the intesity of radiation from a bb to it’s wavelength or frequency.• Mathematically complicated (we will skip).• But will help us derive a simple model of Earth’s energy balance.• Wein’s Law (flux of radiation emitted by a bb reachest its peak value at wavelength (picture

b)• Sun is at ~ 5780 K. What is max wavelength? (Think about this).

Blackbody emission curves for the Sun and Earth. The Sun emits more energy at all wavelengths.

Note logarithmicscales

Electromagnetic Spectrum

Sensitivity of human eyes to EM radiation Definition of visible spectrum

1st Law of ThermodynamicsΔEint = Q – W

Earth’s atmosphere: (1) Constant volume: W=0 (in equilibrium) (2) Sun is approx. constant

ΔQin = 0 (although Qin > 0)(3) dEint = 0, over long time periods,

at least before the anthropocene

If Earth’s [effective] temperature is constant (dE = 0) then how does surface temperature increase?Hint: What about Qout?

EESC W4400x

Blackbody Equilibrium(Energy Conservation)

Energy In

Sept. 14, 2010

Effect of latitude on solar flux

1

2

The solar flux of beam 1 is equal to that of beam 2. However, when beam 2 reaches the Earth it spreads over an area larger than that of beam 1. The ratio between the areas (see figure above) varies like the inverse cosine of latitude, reducing the energy per unit area from equator to pole. What happens at the pole?

The effect of the tilting earth surface is

equivalent to the tilting of the light source

Blackbody Equilibrium(Energy Conservation)

Energy In = Energy Out

Emitted“Earthlight”

4πR2Earth x SEarth

EESC W4400x

Blackbody Equilibrium(Energy Conservation)

Energy In = Energy Out

Emitted“Earthlight”

4πR2Earth x SEarth

Consider albedo

Sept. 14, 2010

Reflection of Solar Radiation: The Earth’s Albedo

•The ratio between incoming and reflected radiation at the top of the atmosphere (TOA) is referred to as the planetary albedo.•The albedo varies between 0 and 1.

Components of the Earth’s albedo and their value in % and the processes that affect incoming solar radiation in the

Earth’s atmosphere

Emission Temperature of a PlanetSolar radiation absorbed = planetary radiation emitted

Ein = Eout = S (1-A) p R2 = T4 4p R2

using: A = 0.3; S = 1370 W/m2; = 5.67 10-8 W/m2/K4

T ~ 255 °K ~ -18 °C [ T0]

Is that an reasonable answer?

=> T4 = S (1-A) / (4)

Greenhouse Effect

Te is the “effective” or “emitting” temperature of the planet.

Incomingsolar radiation

Reflection

Transmission

Surface Emission

Atmos. Emission

Atmos. Emission

The simple model has one layer of greenhouse gases that are transparent to short wave radiation but absorb all long wave radiation.The temperature of the absorbing layer is Te

The temperature at the surface is Ts

Energy in = πr2 S, which is spread over the earth having area 4πr2 so we have πr2 S/4πr2 = S/4 for the incoming radiation (W/m2)

Greenhouse EffectIR-Opaque Atmosphere

Te is the “effective” or “emitting” temperature of the planet.

Incomingsolar radiation

Reflection

Transmission

Surface Emission

Atmos. Emission

Atmos. Emission

Top of the atmosphere balance:

(S/4) (1-A) = σTe4

Te4 = S (1-A) / (4σ)

IR Absorbing Layer:2 σ Te

4= σ Ts4

Earth’s surface budget:S (1-A)/4 + σTe

4 = σTs4

Ts = 2(1/4) Te

Greenhouse Effect IR-Opaque Atmosphere

Incomingsolar radiation

Reflection

Transmission

Surface Emission

Atmos. Emission

Atmos. Emission

End Result (assuming atmos. absorbs all IR): Ts

= 2(1/4) Te =1.19 Te

Substituting previous results Te

4 = S (1-A) / (4) using: A = 0.3; S = 1370 W/m2

Te ~ 255 K ~ -18 C T0 Ts =1.19*Te ~ 303 K ~ 30 C T1

very warm Earth !

Greenhouse EffectIR-Opaque Atmosphere

Tobserved 288K = 15 C

so

T0 (-18C) < Tobs < T1 (+30C)

What are we missing?

OK, we are missing almost everything, but what is important?

Sept. 16, 2009 EESC W4400x

Absorption of Infrared (Longwave) Radiation in Earth’s Atmosphere

Absorption of 100% means that no radiation penetrates the atmosphere. The nearly complete absorption of radiation longer than 13 micrometers is caused by absorption by CO2 and H2O. Both of these gases also absorb solar radiation in the near infrared (wavelengths between about 0.7 μm and 5 μm). The absorption feature at 9.6 micrometers is caused by ozone.

Acrobat Document

Absorption of Infrared (Longwave) Radiation in Earth’s Atmosphere

Emissivity

From http://m-w.com (similar info from wikipedia)

So, if atmosphere behaved like a blackbody, it would absorb all incoming radiation at all wavelengths, and emit at all wavelengths (appropriate to its temperature)

Greenhouse EffectIR-Semi-Opaque Atmosphere

Ts(obs) = 288K, ε=0.77

ε is the atmospheric emissivity

(1-)σTs4

σTs4

σTs4

σTa4

σTa4

with an atmosphere that is not 100% opaque

4

4

4

𝑆4 =

𝐴𝑆4 + (1−𝜀 )𝜎𝑇𝑠4+𝜎𝑇𝑎4

𝜀𝜎 𝑇𝑠4=2𝜎𝑇𝑎4∨𝑇𝑎4=𝜀𝑇𝑠4

2

(1− 𝐴)𝑆4

+𝜎𝑇𝑎4=𝜎𝑇𝑠4𝑜𝑟 (1−𝐴 )𝑆4

+𝜎 𝜀𝑇𝑠4

2=𝜎𝑇𝑠4

Earth’s Globally Averaged Atmospheric Energy Budget

All fluxes are normalized relative to 100 arbitrary units of incident radiation. Values are approximate. Figure 3-19

(Kump et al)

Greenhouse Effect

The difference between the longwave radiation from the Earth’s surface and OLR is the greenhouse effect. Note the strong GH effect in areas which are dominated by deep tropical clouds that precipitate a lot (above). These clouds reach high into the atmosphere (more than 10 Km) where the temperature is low, thus the radiative longwave flux from their tops is relatively small. At the same time the surface underneath is warm and the surface emitted longwave radiation is almost entirely trapped in the cloudy atmosphere.

Example 1: Increase planetary albedo

-- Decrease absorbed solar

-- Emitted thermal exceeds

absorbed solar -- Temperature must decrease to

restore balance.

Climate change occurs when either side of energy balance is perturbed.

Climate change occurs when either side of energy balance is perturbed.

Example 2: Increase greenhouse gases

Decrease IR radiation to

space Absorbed solar exceeds

emitted thermal Temperature must increase

to restore balance.

Climate Feedbacks: The Ice Albedo Feedback

Precipitation Changes

Climate Trends: Sea Level Rise

I present multiple lines of evidence indicating that the Earth’s climate is nearing, but has not passed, a tipping point, beyond which it will be impossible to avoid climate change with far ranging undesirable consequences. The changes include not only loss of the Arctic as we know it, with all that implies for wildlife and indigenous peoples, but losses on a much vaster scale due to worldwide rising seas. Sea level will increase slowly at first, as losses at the fringes of Greenland and Antarctica due to accelerating ice streams are nearly balanced by increased snowfall and ice sheet thickening in the ice sheet interiors. But then the balance will tip toward ice loss, thus bringing multiple positive feedbacks into play and causing rapid ice sheet disintegration. The Earth’s history suggests that with warming of 2-3°C the new equilibrium sea level will ……. raising sea level of the order of 25 meters (80 feet).Contrary to lethargic ice sheet models, real world data suggest substantial ice sheet and sea level change in centuries, not millennia. The century time scale offers little consolation to coastal dwellers, because they will be faced with irregular incursions associated with storms and with continually rebuilding above a transient water level.The grim “business-as usual” climate change is avoided in an alternative scenario in which growth of greenhouse gas emissions is slowed in the first quarter of this century, primarily via concerted improvements in energy efficiency and a parallel reduction of non-CO2 climate forcings, and then reduced via advanced energy technologies that yield a cleaner atmosphere as well as a stable climate.

The Ocean induces a lag in response – as it slowly warms up and then releases the heat to the atmosphere

Approaching the warmest period in almost a million years