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