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Natural forcing driving climate change - Coggle Diagram
Natural forcing driving climate change
Internal
Volcanic eruptions
Very large eruptions release large quantities of ash and sulphur dioxide, which has a colling effect - it is converted to sulphuric acid which forms sulphate aerosols which reflect solar radiation back into space, lowering temperatures
Increase in atm reflects solar radiation away from surface = short term cooling of troposphere
E.g. Mt Pinatubo 1991 = injected 20 million tonnes of sulphur dioxide into the stratosphere - cooled the earth's temperature by 0.5 C for 2 yrs
Tectonics/continental drift
Global distribution and movement of plates
Driven by plate tectonics and sea-floor spreading the global distribution of continents has changed and they have drifted apart to their present-day position
Pangaea - single huge landmass
Presently isolated continents and more landmass at higher latitudes can altar ocean currents
Land in northern hemisphere -> more ice -> albedo -> feedback -> cooling
Ocean currents can carry heat around the earth and plate tectonics can cause the direction of currents to change causing different areas to become warmer and colder
small changes in ocean currents can also have a large effect on global climate
Ocean circulation
Transferring surplus energy from equator to poles
Continental drift modify circulation
5 million years ago when the North and South American continents joined and closed the 'gateway' between the Pacific and Atlantic it intensified the Gulf Stream (carrying water from the Caribbean to the North Atlantic
Precipitation and evaporation increased and the prevailing westerly winds caused more precipitation in the North Atlantic, Europe, and Siberia diluting the salinity of the North Atlantic and Artic oceans
This reduced salinity weakened the downwelling of water in the North Atlantic which as a pump for the whole thermo-haine circulation
Natural greenhouse gases
CO2 fluctuations
Low CO2 = low atmospheric temperatures
High CO2 = higher temperatures (e.g. cretaceous and PETM 55mya)
Removal of CO2 by tectonic/drift
As fold mountains such as Himalayas, Andes and Rockies formed, uplift of these mountains increased rainfall, erosion and chemical weathering by rainfall charged with CO2. This resulted in the removal of large columns of CO2 which then became locked up the carbonate sediments in the oceans
Increased nutrients in the oceans also led to the growth of phytoplankton - which extracted CO2 from the atmosphere for growth - when these died - the CO2 was trapped in deep ocean-sediments
External
Solar output
Positive correlation between sunspot activity and solar energy output
Late 17th Century 'Maunder Minimum' - sever winters due to nearly no sunspots
Milankovitch Cycles
Long-term climatic shifts caused by astronomical events
Eccentricity
Change in elliptical path
Periodicity ~ 100ky
Changes the distance the sun's short wave radiation must travel to the earth
At the maximum eccentricity 30% difference in solar radiation between when earth is closest to the sun (perihelion) and when earth is further from the sun (aphelion)
Ice ages occur when it is at maximum orbital eccentricity
Obliquity (reason for Earth's seasons)
Axis tilt
Periodcity ~ 41 ky
When the tilt is closer to 22 degrees, seasonal differences are reduced and it decreases the difference in radiation received between equatorial and polar areas. i.e. summers are cooler and winters are warmer
Snow and ice accumulating during the winter do not melt during the summer - results in the growth of ice sheets
This has a positive feedback - as increases the albedo - more radiation reflected back and temperatures lower further
Precession (timing of Earth's seasons)
Perihelion of equinox
Periodicity ~ 26ky
The earth 'wobbles' on its axis like a giant spinning top
Changes in the precession affect the intensity of seasons. if perihelion occurs during the northern hemispheres winter, winter will be warmer and summers cooler. Snow and ice accumulating in winter will not melt completely the next summer so ice and snow cover expands - eventually triggering a glacial period
Milankovitch cycles help to explain the episodic nature of glacial and interglacial periods within the present ice age
Where the cycles all reach their maximums - we have inter-glacial (hotter phases) however where these cycles all reach their lowest we have glacials (cold periods)
The Pleistocence ice age was the result of all three cycles operating together