System Earth 6a

System Earth 6a

Energy balance

Misha Velthuis

m.velthuis@uva.nl

Tue 8 Oct 2024

Content

Energy balance

Electromagnetic radiation

Greenhouse effect

First

Protests

Freezing nuclei?

Tracking Kirk

Winds anyway picking up

We are at 10/25th

Spheres

Next: connecting spheres through time

Carbon cycle

Long term climate variation

Mass extinctions

Anthropogenic perturbation of carbon cycle

Nytrogen cycle

Why so much attention for carbon?

Connected reservoirs

Energy balance

Incoming energy

Outgoing energy

Energy balance and temperature

Electromagnetic radiation

Behaves like a wave

ν = c / λ

ν = frequency

c = speed of light

λ = wavelength

Behaves like a particle

Energy of a photon:

E = h . ν = h . c / λ

h = Planck's constant

Two laws

Wien's law

Stefan-Boltzmann law

Wien's law

\[\lambda_{max} = \frac{2898}{T}\]

T in Kelvins
λ_max in µm

"… the flux of radiation emitted by a blackbody reaches its peak value at a wavelength λ_max which depends inversely on the body's absolute temperature. According to this rule, hotter bodies emit radiation at shorter wavelengths than do colder bodies."

An ideal black body in thermal equilibrium has two main properties:

It is an ideal emitter: at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature.
It is a diffuse emitter: measured per unit area perpendicular to the direction, the energy is radiated isotropically, independent of direction.

Sun = 2898/6000=0.48

Earth = 2898/(273-15)=11.23

"The sun buzzes like a bee, the earth flaps its fins like a whale."

Btw

Stefan-Boltzmann law

\[F=\sigma T^4\]

F = W.m^-2

T = Kelvins

σ = 5.67e^-8 W.m^-2.K^-4

So … let's derive temperature from outgoing EMR?

Greenhouse effect

Basic dynamic

1] Some incoming shortwave radiation is not absorbed by the atmosphere and reaches the surface of the earth.

2] This radiation is absorbed by the surface of the earth and re-emitted at lower wavelengths (because the earth is much cooler than the sun)

3] This longwave radiation is absorbed by the atmosphere and re-emitted in all directions.

4] Some of this re-emitted longwave radiation is absorbed (again) by the surface and re-emitted.

The role of CO2

Initial: in equilibrium

Increasing CO2 concentration disturbs balance

Back in equilibrium

And then: add the Climate feedbacks

Water vapor feedback

"Keeping relative humidity constant"

Ice albedo feedback

Carbon fertilization

Next session

How does carbon move through the spheres?