Global Energy Balance Change (SL IB Geography)

• The Earth's energy budget (EEB) establishes Earth's climate
• When the budget balances, temperatures on the Earth remain mostly constant
• However, the incoming and outgoing energy don’t balance
• The imbalance is partly caused by insolation, as it varies seasonally and with natural changes in the Earth's atmosphere
• Changes in the make-up of the atmosphere alter the amount of energy absorbed and reflected
• Changing factors such as greenhouse gases, water vapour etc., result in small, but significant energy imbalance on Earth
• Other factors include:
  • Distance
  • Seasonal change
  • Latitude
  • Reflectiveness (albedo) 

Factors affecting global insolation

• Distance from the sun
  • Earth's orbit around the Sun is elliptical 
  • Perihelion is when the Earth is closest to the Sun and insolation travels less distance
  • Aphelion is when the Earth is furthest away from the Sun - insolation has to travel further

Elliptical orbit of Earth

• Latitudinal differences
  • Insolation has to pass through more atmosphere in the polar latitudes
  • Insolation is spread over a larger area in the polar regions
  • The Sun is overhead at the Equator and tropical latitudes receive more insolation

Uneven distribution of insolation

• Seasonality and diurnal differences
  • The Earth is permanently tilted in the same direction on its axis
  • This tilt changes which hemisphere is facing the Sun as the Earth orbits throughout the year 
  • This creates the seasons and daylight availability
  • Therefore, differences in the amounts of insolation gained or lost across the globe throughout the year

Seasonality affects global energy

Milankovitch cycles

• Milankovitch cycles describe the effects of changes in the Earth's movements on its climate over thousands of years
• In the 1920s, Milankovitch suggested that variations in eccentricity, tilt, and wobble of the Earth's orbit resulted in cyclic changes in the amount of solar radiation reaching the Earth
• Therefore, orbital changes influenced climatic patterns on Earth

Milankovitch cycles

The shape, tilt and wobble of Earth's movement over thousands of years, affects long-term climate

Sunspots and solar flares 

• Increased sunspot activity and solar flares are linked to higher average temperatures
• Sunspots are areas of intense and complicated magnetic fields that emit solar plasma flares thousands of kilometres above the sun
• The flare quickly rises to temperatures of 20 million °C 
• These bursts of high-energy radiation have the same energy as a few million volcanic eruptions on the Earth 
• Sunspots range from Earth-size 'pimples', to swollen scars halfway across the surface of the Sun
• The Sun goes through 11-year cycles of solar activity

Ejection of solar plasma from the Sun

Photo by NASA on Unsplash

The more 'spots' on the Sun's surface, the higher the Sun's output

Photo by The Adaptive on Unsplash

Cloud cover

• Clouds have higher albedos than the surface below, so more short-wave radiation is reflected back to space
• Cloud cover at the equator reflects insolation – more is reflected having a net cooling effect
• At the same time, clouds help contain the heat that would otherwise be emitted to space, through 'longwave warming,' which has a net warming effect 
  • High, thin clouds, such as cirrus, allow insolation to pass through but absorb some long-wave radiation, warming the Earth’s surface
  • Deep convective clouds, especially cumulonimbus, neither heat nor cool overall 
  • An overcast sky with complete cloud cover of low thick clouds – stratus and stratocumulus, can reflect 80% of insolation and cool the Earth’s surface 

• Global dimming is caused by the increase of pollution in the atmosphere
• Overall decline of 1-2% in insolation per decade since the 1950s
• Between 1960 and 1990, the northern hemisphere saw a reduction of between 4% and 8% in insolation
• Pollution controls in Europe and parts of North America have seen some recovery or global brightening
• China and India have seen further, regional declines
• Southern hemisphere is largely unaffected although increased development is having an impact
• There are two timescales:
  • Short-term natural
  • Long-term anthropogenic

Short-term Natural Global Dimming

Long-term Anthropogenic Global Dimming

• Planetary albedo is the amount of sunlight reflected from Earth's surface
• Fresh snow and ice have the highest albedos, reflecting up to 95% of sunlight
• Ocean surfaces absorb most sunlight, and so have low albedos
• Hot bodies (sun) produce shortwave radiation, whereas, cold bodies (Earth) produce longwave radiation which is easily absorbed by GHGs and clouds

• A feedback loop is a cycle within a system that either increases (positive) or decreases (negative) the effects on that system to achieve equilibrium
• Positive feedback amplifies (enhances) a change and are destabilising 
• Negative feedback 'checks' or dampens change and are stabilising
• Dynamic equilibrium
  
  • A system in a total state of balance is difficult to find, as nature is dynamic (ever changing)
  • Constant short-term adjustments are usually made through negative feedback to maintain balance
  • This process is referred to as 'dynamic equilibrium'.

Simple feedback system

Changes to the processes in a system (disturbances) lead to changes in the system's outputs, which in turn affect the inputs

 Example of a negative feedback loop

Effect of negative feedback through clouds

• Many positive feedback loops contribute to global warming

Examples of positive feedback loops

Effects of positive feedback on ice-cap melt and permafrost thawing