PHSC final review

Why ¼ factor for solar radiation flux in one layer model

S is the insolation that hits the Earth at any given moment, but the Earth is spherical and so as radiation hits one given spot its spread over ¼ of the Earths surface; earth a sphere account of per time per area units

Atmosphere emits both upwards and downwards in one layer model

The reason it emits both upward and downward is that the Stefan-Boltzmann law tells us how much energy a blackbody will radiate per area per time. A layer of atmosphere has area that can emit both on its top and on its bottom.

Negative feedback

regulatory process caused by perturbation of system that functions to return system to stable state

Positive feedback

intensification of deviation, as perturbation only sets into motion more reactions that push system further from stable state

Ice-Albedo Feedback

It describes how changes in ice cover affect the planet's temperature. Ice and snow have a high albedo, meaning they reflect a significant amount of incoming solar radiation back into space. This self-reinforcing climate process can in rising temperatures melt white ice and snow (high albedo), exposing darker ocean or land (low albedo) underneath. These darker surfaces absorb more solar heat, causing further warming and melting, creating a cycle that accelerates polar warming and sea ice loss. Or cause snow ball earth with high albedo.

Water-Vapor feedback

The fact that water vapor is a strong greenhouse gas means that the more water vapor you have in the atmosphere, the stronger the greenhouse effect, and the more greenhouse warming you get.

Water vapor increases strongly to increase in temp

The temperature doesn’t have to increase by very much in order to cause the saturation water vapor pressure to increase by a lot, which then increases moisture, increasing heat retention, warmer air holds more moisture

Cirrus

high wispy clouds that can precede storms but do not lead to precipitation themselves

Stratus

low clouds that form at a constant layer and stretch for large horizontal distances and can be associated with light rain

Cumulus

low levels, look like cotton balls, are not associated with rain, and often (but not always) come in 1D or 2D patterns

alto-

prefix to mean high (altocumulus, high cumulus)

nimbus

rainstorm fixutre

circostratus

cirrus/ stratus mix

cirrcocumulus

cirrus and cumulus

cumulonibus

rainstorm cumulus

altocumulus

high culumulus

altostratus

high stratus

nimbostratus

rainy stratus

stratocumulus

stratus and culumulus

fog

very low

Shortwave cloud radiative effect

effect of clouds on shortwave radiation at the top of the atmosphere = upward shortwave radiation at the top of the atmosphere when there are no clear

clouds - the upward shortwave radiation at the top of the atmosphere when there are clouds

Cloud albedo

clouds bright and reflect shortwave light, whiteness means they reflect most waves. The tropical convective clouds (deep cumulus and cumulonimbus clouds), which extend to high in the atmosphere. Low clouds (decks of stratus) off the coast of Peru and at high latitudes. These low clouds cover much more of the planet than high tropical clouds. The shortwave cloud radiative effect is much larger over ocean than land because the albedo of ocean is much lower than that of land.

Longwave cloud radiative effect

clouds have strong greenhouse effect, that the longwave cloud radiative effect is positive in all normal situations. radiative effect is that it tends to be larger for high clouds than for low clouds. The reason is that the atmosphere gets colder as you go higher up. No clear disinction between land and ocean as in short waves, still concentrated around tropics

In the global mean, the longwave cloud radiative effect is

+30 W m ́2, bc radiation coming from cloud less than that coming from surface, meaning less radiation lost in space when there is cloud

The net cloud radiative effect

Sum of the shortwave and longwave cloud radiative effects

global mean, the net cloud radiative effect

-20 W m ́2, so clouds have a net cooling effect on the climate.

The main places where clouds have a positive net cloud radiative effect

ice sheets and deserts, both of which have high surface albedos so the shortwave cloud radiative effect is small.

In most places clouds have a cooling effect

especially over oceans. The large stratus deck off the coast of Peru really stands out.

Clouds are the largest source of uncertainty in forecasts of climate.

Clouds are very hard to model in Global Climate Models because they are small relative to the size of the typical model grid, which has a horizontal dimension of about 100 km. Since small changes in clouds cause huge changes in the radative balance and clouds are hard to model

GCM

Global Climate Models (GCMs) are the main tool we use to forecast the climate. Solve the partial differential equations for fluid flow (fluid moving around, which carries heat with it) and radiative transfer for the atmosphere and ocean on a planet like Earth, typically used by specifying some change in greenhouse forcing and seeing how the climate responds

How GCM’s work

break the atmosphere and ocean up into little boxes called gridboxes such that each model variable, like temperature, pressure, and humidity only has values at these boxes. Versions of the equations are then developed that relate the values of variables on each gridbox to each other and can step them forward in time.

What type of computers are GCMs run on

Supercomputers

Why clouds are difficult for GCM

They are comparatively much smaller and more sensitive to smaller things than the GCM can account for, so cloud like variables are put in place instead of clouds based on observation and theory

climate sensitivity

the change in global-mean surface temperature

due to some radiative forcing. It is often quantified as ∆T2x

∆T2x

GCM as climate senstivity models

Not completely independent from one another so we might not expect the GCM climate sensitivity estimates to reflect the full possible range of climate sensitivity, could do all possible simulations but still wont reflect real world

Paleoclimate record to estime climate sensitivity

While we have good records for these factors there may be other influencing factors we cant account for

Different estimations of climate sensitivity

The first thing to notice from the figure is that we can’t constrain the climate sensitivity very well!

Cost-Benefit Analysis

C = C0e^λT

The larger the discount rate

the bigger the future cost

Discount rate

λ

low discount rate

the cost is lower than benefit

e

water vapor pressure,

water vapor pressure

es

saturation vapor pressure, max amount of water vapor in the air

Wet Bulb Temp

is the measure of the lowest temperature that can be reached by evaporating water into the air, ability of the surrounding air to absorb moisture. It is an important concept in determining relative humidity and is often used in weather forecasting and tells how temp feels to people

Global warming as a threat multiplier

intensifying already intense climate, leading to resource stressors that can impact national conflicts

How many calories humans need

2000 C

calorie

The amount of heat needed to raise 1g of water 1c

Extinction

when all members of a species die out do that species no longer exist, origination often counter balances

Mass extinction

when origination is less than extinction rate, 75% or more of all species die out over a few million years

How many mass exctinctions

5 left mark in geological record and though causes unknown linked to climactic events, currently could argue that extinction underway due to human impact on climate

weather

short term conditions in atmosphere, highly variable on timescale and locality

Climate

long-term average of weather condtions

E (exa)

10^18

P (peta)

10^15

T (tera)

10^12

G (giga)

10^9

M (mega)

10^6

k (kilo)

10³

h (hecto)

10²

da (deka)

10^1

d (deci)

10^-1

c (centi)

10^-2

m (mili)

10^-3

u (micro)

10^-6

n (nano)

10^-9

p (pico)

10^-12

f (femto)

10^-15

a (atto)

10^-18

Th earth has warmed how much roughly over past few hundred years

1.2 C

Why cant we look back at past climatic events?

Because despite fluctuations that have had the earth colder and warmer, the current rise of temperature is unprecedented and makes it difficult

Photosynthesis

6CO2 6H2O ---> C6H12O6 6O2

aerobic respirations

C6H12O6 6O2 ---> 6CO2 6H2O

Where tree bark comes froms

Carbon atoms are the bulk of trees, bulk of the plant mass of any plant is carbom

CO2 in atmopshere during glacial periods

170 and 280 ppm

CO2 before industrial rev

480 ppm

Current CO2

410 ppm

Electromagnetic radiation

suns energy that reaches Earth through waves of light, propagating oscillation in electrical magnetic fields, everything has electromagnetic radiation but type depends of temperature and properties

Speed of wavelength

C= λ (wavelength) ν (frequency)

visible light

very small part of possible wavelegnths (400-750nm), suns emissions are mostly visible or near infrared

Ultraviolet

shorter wavelength/more energy than visible light

Infrared

longer wavelength/less energy than visible light, usually refered to as longwave radiation, it is the type of wavelength the Earth emits

Sun’s luminosity

Is not having impact on global warming, though the Sun is heating up slowly it is on a timescale that has no impact on human civilization

Insolation at Earths distance from the sun

S0 = L/4πd2, W m^-2

L

Suns luminosity in W

d

distance from the sun in m

Current insolation of Earth

S0=1361 W m -²

eccentricity

is the ovalness of the planets orbit, now that it is at 0.0167 this leads to an insolation difference of 7% larger when Earth is closer to the sun in January than when furthest in July

Obliquity (tilt)

currently 23.5 degrees, cause for seasons as when a given hemisphere is pointed toward the sun it is summer when it is pointed away it is in winter, w/o tilt no seasons

Solsitces

when the tilt is directly at/away from the sun

Equinox

when the tilt is between being directly at/away from the sun

Solar Zenith Angle

Angle that the sun is from vertical at given location, S= S0cosθz, depends on latitude and declination

Solar Zenith Angle

Zenith Angle = latitude - declination

declination for winter solstice

-23.5

declination for summer solstice

23.5

Albedo

ratio of reflected light to incoming light — Earth is about 0.3. Things such as ice have higher albedo than ocean leading to ice-albedo feedback, albedo depends on wavelength of light

Blackbody Radiation

perfect emitters and absorbers of electromagnetic radiation

Plank function

function by which blackbodies emit wavelengths, hotter bodies emit more radiation and have peak emission at shorter wavelengths

Wien’s displacement law

The decrease in the wavelength of peak emission (λm) as a function of temperature

λmT = b

b = 2897 μm K.