Changes in the energy balance due to external forces

What are ‘external forcings’?

Processes both outside and within the atmosphere that can force changes in climate

What is ‘climate forcing’?

Any mechanism that alters the global energy balance and ‘forces’ the climate to change in response.

External forcings

Solar radiation

Changes in albedo

Global brightening/

dimming

Volcanic

Solar Radiation - MilankovicTotal solar radiation reaching the Earth varies due to the Earth’s orbit. This was a theory developed by a man called Milankovic

Milancovic argued that the surface temperature of the Earth changes due to variations in the Earth’s orbit and axis tilt.

Solar radiation – sunspot activityThe amount of solar radiation emitted by the sun varies as a result of sunspots.

They are dark spots that appear on the sun caused by intense magnetic storms.

Decreases of 0.2% of solar energy occur during the week long passage of large sunspots.

Changes in albedoWhat does ‘albedo’ mean?The Earth’s albedo is the proportion of solar energy reflected from the Earth back into space.

Low albedo (dark objects)

Greater the amount of solar

radiation the Earth will absorb

High albedoThe more solar radiation the

Earth will reflect

Albedo examples

Areas suffering

desertification

Less vegetation – more sand

and soil

Albedo increased

from 14% to 35%

Areas suffering

deforestation

Less vegetation –

more soil

Albedo increased by as much as

20%

Arctic loss of sea ice

Replaced by ocean water

Albedo shifts from high to

low

Global brightening/dimming

Global brightening – an increasing amount of sunlight reaching the Earth’s surface caused by an intensification of solar radiation

Global dimming – a worldwide decline of the intensity of the sunlight reaching the Earth’s surface, caused by particulate air pollution and natural events, for example volcanic ash

NOTE:Like other areas of this topic…..This is an area of ongoing research and debate.

Volcanic Volcanic activity can alter global climate

Major eruptions eject ash, sulphur dioxide, water vapour and carbon dioxide into the stratosphere which are then distributed by winds.

In 1991 Mt Pinatubo in the Philippines ejected 17 million tonnes. This reduced the amount of sunlight received at the Earth’s surface

This led to temporary temperature falls