ch 11 temperature record and climate forcing

ocean science lecture 05/20

radiative forcing

the change in energy trapped in the atmosphere caused by a change in the amount of radiation absorbed vs. emitted

radiative forcing can be

positive (warming) or negative (cooling)

main sources of radiative forcing

greenhouse gases

solar intensity

volcanic activity

anthropogenic aerosols

what effects does volcanoes have on climate depending on the timescale

long term (millions of years): warming

short term (years): cooling

silicate weathering cycle

volcanoes are a source of CO2 to the atmosphere over millions of years

weathering consumes atmospheric CO@ (cooling by

reaction with silicate rocks

Metamorphism releases CO2 to the atmosphere (warming) through

volcanoes

volcanoes short term (years) : cooling

• Increases albedo

▪ Importance depends on location and plume composition

Composition of Volcanic Plumes

- 1% nitrogen

- 80% water vapor

- 12% carbon dioxide

- 7% sulfur dioxide (SO2)

- lots of ash!

Sulfur dioxide gas (SO2) from volcanoes creates sulfate aerosols that cause what

cooling

sulfate aerosols

small droplets produced act to scatter incoming sunlight (important effect for climate)

aerosol

a fine particle or tiny liquid droplet suspended in air

what do Sulfate aerosols temporarily do

raise the albedo by lowering absorption of sunlight

big tropical volcanoes can affect global climate

true

Most sulfate aerosols injected into the troposphere (lower atmosphere) last how long before being rained out

a few weeks

Aerosols injected into the stratosphere can last for ____ and winds in the stratosphere go from equator towards poles

several years

A typical major volcanic eruption will eject a plume ___ into stratosphere

20-30km

Sulfate aerosols injected at higher latitude do not spread globally

true

Sulfate aerosols injected into the stratosphere near the equator are spread globally very efficiently by stratospheric circulation

true

what kid of volcanoes ONLY cause a GLOBAl effect on climate

large tropical volcanoes

what do Major volcanoes do

inject SO2-containing plumes into the stratosphere, where sulfate aerosols can last for several years

Sulfate aerosols from major tropical volcanoes are spread globally by

prevailing stratospheric circulation

Anthropogenic aerosols

aerosols (fine particles/tiny liquid droplets suspended in air) derived from industrial activities

Anthropogenic aerosols are generally emitted into

troposphere (effect is short lived but its being continually emitted)

type of “anthropogenic aerosol”

Sulfate aerosols from coal combustion

Black Carbon (BC, or “Soot”)

• results from incomplete combustion of fossil fuels, biofuels and biomass

• relatively short-lived in the atmosphere, so emission regulations would have an immediate effect on radiative forcing and warming

primary sources of BC

emissions from diesel engines, wood burning and forest fires

Suspended BC

absorbs sunlight and warms surrounding atmosphere (which can also affects cloud formation)

Deposited BC

decreases albedo, especially in snow and ice covered regions (e.g., glacier melting in Himalayas)

BC radiative forcing (warming)

is equivalent to 1/3 of that associated with total atmospheric concentration of CO2

Direct effect of anthropogenic aerosols

• aerosols affect albedo

▪ Light colored aerosols (e.g., sulfate aerosols) cool by scattering light and increasing albedo

▪ Dark colored aerosols (e.g., soot) warm by absorbing light and lowering albedo (especially deposited on snow/ice)

Indirect effect of anthropogenic aerosols

• aerosols promote cloud formation

▪ Cooling or warming depending on type of clouds (high clouds = warming, low thick clouds = cooling)

Historical anthropogenic aerosol forcing is likely to be

cooling