Earth System and Climate: Introduction (ESC-I) Coordinators: V. Valsala, R. Murtugudde and M. Baba.

Earth System and Earth System and Climate: Introduction Climate: Introduction

(ESC-I)(ESC-I)

Coordinators: Coordinators:

V. Valsala, R. Murtugudde and M. BabaV. Valsala, R. Murtugudde and M. Baba

Contents of ESC-Intro. course:• Earth System Science and Global Climate ChangeG

• Global Energy Balance P

• Global Carbon Cycle C

• Recycling of Elements; C, N, O2, O3 depletion C

• Global Biogeochemical Cycle- oceans C/B

• Short-term Climate variability, Global Warming P/C/BShould be covered in 7-hours

Where does the energy for earth system come from?

© http://en.wikipedia.org/wiki/Solar_System

Continuous supply of energy for Continuous supply of energy for the earth systems- Solar Energythe earth systems- Solar Energy

The solar energy drives the earth’s atmosphere and ocean.

Energy from sun’s radiation.

Nearly all the energy being at wavelengths 0.2µm to 4µm

Electro Magnetic spectrum of solar radiation

-----40% of energy------ -----10% of energy--

---------50% of energy------

Blackbody radiation fluxWein’s law λmax = 2898/TStefan-Botlzmann law F = σT4

Amount of radiation receives at surface of Earth

Solar constant (S ~ 1368 W/m2)

•S definition; Average energy ‘flux’ from the sun at a mean radius of earth

Latitude

Sola

r h

eat

flu

x

Reflectivity of earth surface and atmosphere Albedo.•Albedo The relative amount of solar

insolation reflected back to the space by means of reflection by the earth surface as well as the atmosphere.

Average albedo of earth ~ 0.3.Therefore net heat flux received from sun = 240W/m2

With an average of 240w/m2 influx from the sun, how much would be the atmospheric temperature?

Earth withno-atmosphere.

E = σT4

E = 240 w/m2 σ = 5.7x10-8 W/m2/k4 T = 250 Kelvin (~ -200C)

Earth withatmosphere.

E = σT4

E = 240 w/m2 = 5.7x10-8 W/m2/k4

T = 300 Kelvin (~ 150C)

Green house effect

The Green house effect.

Earth

Sun

Short w

ave

Long w

ave

(hea

t)

GH-effect helpsthe atmosphere tobe warm at 150C

The one-layer atmosphere model of Green-house effects

Adopted from Lee Kump book

Ts = 1.19*TeFor average Te=255k,Ts = 303KΔTg = Ts- Te

Summary of Greenhouse heat budget (w/m2)

Source: IPCC-AR4 report, 2007 http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml

Heig

ht

http://en.wikipedia.org/wiki/Atmosphere_of_Earth

Composition of the atmosphere.

Atmospheric Structure

How atmospheric pressure varies with altitude

P = F/A (Pressure = Force exerted on unit area)

The pressure exerted by atmosphere at sea-level is defined as one atmosphere (atm)

The SI unit of pressure is Pascal (Pa).

1 Pa = 1x10-5 bar = 9.9 x 10-6 atm.

Atmospheric pressure decreases with height.

Atmospheric Structure

Atmospheric pressure decreases by a factor of 10 for every 16 km increase in altitude.

1 atm at surface0.1 atm at 16 km0.01 atm at 32 km …

The vertical structure of the Atmospheric temperature.

Vertical distribution of Ozone.

Percentage of radiation absorbed in the atmosphere.

Physical causes of greenhouse effect

Molecules absorbs incident atmospheric radiation by mean of increasing its rotation.

Example: Water vapor.

Physical causes of greenhouse effect

Molecules absorbs incident atmospheric radiation by mean of vibration or bending. Example: CO2

But diatomic symmetric molecules have little capacity to absorb electromagnetic radiation. Therefore N2 and O2 are not greenhouse gases

Effects of clouds on radiation

Types of clouds:(a) Cumulus clouds: white

puffy clouds that look like balls of cotton. They are composed of water droplets and formed by convective activities.

(b) Cumulonimbus clouds: Tall cumulus clouds giver rise to thunderstorms.

(c) Stratus clouds: They are gray low-level water clouds that are more ore less continuous

Various type clouds with altitude and temperature

Opposing climate effects of cloud

Have you noticed cloude days are colder whereas cloudy nights are warmer?

oAlbedo

oGreenhouse effect

Vertical “gradient” of atmospheric temperature

• Lapse rate:Definition: “rate at which the temperature of the atmosphere decreases with height”

• Stability of the atmosphere:Warm air is lighter than hot air leads tovertical motion by virtue of buoyancy (gravity).

Warm air

Cold air

Cold air

Warm air

heig

ht

Unstable Stable

Lapse rate• Dry (adiabatic) lapse rate• Moist (adiabatic) lapse rate

Radiative-Convective equilibrium;-No- horizontal motion models.

Radiative-Convective equilibrium;with green house effect & no climatefeed backThese model predicts the green house warming ΔTg = 33 0Ci.e. with CO2 = 300 ppm

In test simulations with doubling the CO2, i.e. with 600 ppm (expected true value in near future), the additional ΔTg = 1.2 0C

Why doubling CO2 produce meager changes in temperature?Radiation absorption spectrum by CO2 and other greenhouse gases (H20 vapor) are different

Radiative-Convective equilibrium;with climate feedbacks

Climate feedbacks are extremely important because they can either amplify or moderate the radiative effect of changes in greenhouse gas concentrations.

We examined the feedbacks in chapter-2 in an imaginary “Daisy world”

We analogically attribute such feedbacks to the earth system here.

Water vapor feedback

o Water vapor is an excellent absorber of IR radiation.

o Unlike CO2, water vapor are at the edges of condensation, and if condenses and rain-out, the average vapor concentration in atmosphere reduces. This can cause reduction in GH-warming

o On the other hand, if average surface temperature increases by global warming, water vapor concentration increases and that will increase GH-warming further.

Observed Climate changes.Satellite derived water vapor (total column water vapor) 1988-2004

Trend

Anomaly

© IPCC-AR4

Ts Atm.H2O

GH-effect

(a) Water vapor feed back

+ve

Radiative-Convective equilibrium;with water vapor feedbackso Average surface temperature changes

in doubling the CO2 experiment without climate feedback was 1.2 0C.

o Whereas the above experiment with watervapor feedback causes the surface temperature rise by additional 1.2 0C.

o Therefore the total change in temperature with water vapor feedback is 2.4 0C.

o The feedback factor = 2.4/1.4 = 2 (strong positive feedback).

Snow-ice albedo feedback

Ts Snow and Ice

Albedo

+ve

Snow-ice feedbacko If surface Ts increases snow melts and albedo decreases

o If albedo decreases surface temperature increases

o This leads to a positive feedback loop which is unstable.

Infrared-flux and Temperature feedback

o If surface temperature Ts increases, the outgoing long wave radiation (infrared-flux increase)

o This tends to cool down the surface temperature

Ts Long-wave

Longwave-Temperature feedback

-ve

Climate feed backs of radiation-convection

Ts Atm.H2O

GH-effect

(a) Water vapor feed back

Ts Snow and Ice

Albedo

+ve +ve

(b) Snow-ice feedback

Ts Long-wave

(c) Longwave-Temperature feedback

-ve

Conclusion

o Green house and radiation budget.

o Earth is warmed by green house effect (from -15 0C to 15 0C)

o H2O and CO2 are major GH-gaseso Clouds affect radiation budget

both by reflection and GH-effect.o Water vapor feedback (+)o Snow-ice feedback (+)o Outgoing Longwave Radiation (IR

flux) – surface temperature feedback (-)

Assignment 1. Surface heat budget.(a) Plot the global and annual mean shortwave radiation reaching the earth surface(b) Plot the global and annual mean outgoing longwave radiation(c) Plot the global and annual mean sensible heat flux(d) Plot the global and annual mean latent heat flux(e) Plot the global and annual mean Precipitation rate(f) Plot the global and annual mean Evaporation rate

(g) From figure a to f, comment the total balance of heat fluxes on annual mean time-scale.

(h) From figure a to f, discuss on the symmetry-asymmetrystructures of the patterns and interpret its causes.

(i) Plot the vertical profile of climatological atmospheric air-temperature for summer and winter at following locations. (1) at x=180e,y=0; (2) at x=80e, y=40s; (3) at x=300e, y=40n; Make a short note on the profiles.