PHSC midterm 2

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