Earth’s Climate System (part 1) climate system electromagenetic spectrum Earth’s radiation budget albedo greenhouse effect

Earth’s climate system climate driven by “solar energy” climate operates to distribute solar energy across surface Can ask: Q1. What is “solar energy”? Q2. How does solar energy interact with planet?

What is solar energy? -- electromagnetic radiation (light) both a particle (photon) and wave photons can have different energies (wavelengths) high energies = shorter wavelengths low energies = longer wavelengths

Electromagnetic spectrum: describes what light of different wavelengths is called

How does solar energy interact with planet? -- some is stopped by atmosphere, some is not -- depends on wavelength atmosphere “transparent” for visible light, less so for other wavelengths

Consider the transparency of Earth’s atmosphere to light of (1) short wavelengths (2) medium wavelengths (3) long wavelengths

Short wavelengths a.k.a. “shortwave radiation” transparency in Earth’s atmosphere: very low (shortwaves almost completely blocked) If not blocked, life as we know it wouldn’t exist on Earth -- cell damage! UV & Ozone layer

Medium wavelengths a.k.a. “visible light” transparency in Earth’s atmosphere: mostly high (visible light mostly gets through, except when cloudy) If not transparent, life as we know it wouldn’t exist on Earth --too cold!

Long wavelengths a.k.a. “longwave radiation” transparency in Earth’s atmosphere: somewhat transparent (some longwaves get through, but not all) If not somewhat transparent, life as we know it wouldn’t exist on Earth -- too hot or cold! (Greenhouse Effect)

Radiation budget describes inflow & outflow of solar energy “budget” because energy is conserved energy in =energy used for warming + energy radiated back to space -- most of the “energy in” is visible light -- energy radiated towards space is visible light & IR light

Energy used for warming: -- absorbed by atmosphere -- absorbed by Earth’s surface Energy radiated back to space: -- reflected or scattered off of clouds or surface ~70% of incoming ~30% of incoming

Energy in

If sun overhead, get more photons concentrated in a smaller area... more energy in

Earth’s spin axis is inclined, so we get seasons

Albedo --the brightness of a surface can be quantified: 0% albedo 100% albedo --darkest surface--brightest surface --all light absorbed--all light reflected none reflected none absorbed Energy out is controlled by albedo

energy in =energy used for warming + energy radiated back to space % energy radiated back to space = albedo % energy used for warming = (100 - albedo)

the amount of light absorbed depends on the incident angle of sunlight Low incident angle High incident angle Albedo of water listed as 5-10%… these diagrams imply not always true

Energy radiated back to space: -- reflected or scattered off of clouds or surface ~30% of incoming If ~30% of incoming solar energy is reflected back to space, what does this say about the overall average albedo of Earth?

~30% overall average

Can have temperature- albedo feedback

Can we have have temperature- albedo feedback if the initial change is climate warming? warming

Can have temperature- vegetation- albedo feedback

Energy used for warming: -- absorbed by atmosphere -- absorbed by Earth’s surface ~70% of incoming Visible light that is absorbed does two things: (1) it raises the temperature directly (2) it is converted into lower energy (infrared) light

But recall that atmosphere is not completely transparent to IR light…...this means that the IR light can’t be radiated back to space easily...so it becomes trapped This leads to the Greenhouse Effect

Greenhouse Effect Visible light from the sun passes through the atmosphere and warms the surface. Heat radiated from the surface (infrared or IR light) travels back out into space but is absorbed or deflected back to the surface by certain gas molecules.

Greenhouse Effect... Trapped IR light warms the atmosphere, which warms the surface. Temperature goes up gradually.

Greenhouse effect.

Energy out

Main point of this is that ~95-96% of the IR light radiated from the surface is trapped in the atmosphere --warming it & the Earth’s surface Confusing! X

Only some gases contribute to the Greenhouse Effect. N 2 and O 2 (the main constituents of our atmosphere) are not greenhouse gases. H 2 O, CFCs (chloroflourocarbons), CH 4, CO 2 are “greenhouse gases” and absorb IR light. SO 2 is not a greenhouse gas. It combines with water to form H 2 SO 4 (sulfuric acid) droplets. These droplets reflect incoming solar light back into space, resulting in planetary cooling.

Greenhouse gases. H 2 O is ubiquitous; we can’t control the amount of it in the atmosphere. CH 4 is a fermentation product. Large amounts could be released from ocean (ice) deposits if the ocean warms. CFCs are largely man-made. International agreements in the 1970s limited their use, because of their harm to the ozone layer.

Greenhouse gases. CO 2 is released by volcanoes. CO 2 is produced by burning petroleum products and by burning trees. This can be controlled.

Is the greenhouse effect all bad? No! It makes life as we know it possible on Earth. Earth gets about 31 o C of greenhouse warming. T average = 15 o C now, with Greenhouse Effect. T average = o C = -16 o C, without Greenhouse Effect.

Venus Earth Mars avg. temp. 460 o C 15 o C -55 o C greenhouse 285 o C 31 o C 5 o C warming avg. temp. 175 o C -16 o C -60 o C with no greenhouse Climates on three planets Too cold Just right

Venus Earth Mars greenhouse 285 o C 31 o C 5 o C warming atmosphere 96% CO 2 77% N 2 95% CO 2 composition 3.5% N 2 21% O 2 2.7% N % CO % H 2 O Climates on three planets OK with

10000 ppm = 1% so 370 ppm = 0.037% CO 2 abundance is rising in our atmosphere

CH 4 abundance is also rising 1725 ppb = ppm = %

Can have temperature- H 2 O vapor feedback possibly also with CO 2 and CH 4