Essay
Suggest why the Earth’s climate naturally varies
- Module
- Climate Change
- Institution
- OCR
Suggest why the Earth’s climate naturally varies [6].
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CLIMATE CHANGESuggest why the Earth’s climate naturally varies [6]
Natural forcings, which induce change in the climate system may be external or internal. External
forcings include shit in Earth’s orbit, axial tilt, precession of the equinoxes & also fluctuations in solar
output. These forces control the distribution of solar radiation on the planet’s surface. Internal forcings
also play an important role in global climate change & these include volcanic eruptions, continental
drift, changes in ocean circulation & fluctuations in atmospheric CO2. The concentration of GHG
which traps solar radiation in the atmosphere is a natural occurrence. There’s a relationship between
atmospheric CO2 levels & average global temps. Periods of icehouse Earth, such as the past 3
million years, correspond with low levels of CO2 in the atmosphere which reduce natural greenhouse
effect. Milankovitch cycles also influence the Earth’s climate. It consists of obliquity which is the tilt of
Earth’s axis. Earth’s axial tilt varies from 22-24.5° and when tilt is close to 22°, seasonal temperature
differences are reduced & thus summers are cooler & winters are warmer which means snow
accumulated during winter doesn't melt in summer so glaciers & ice sheets expand. The eccentricity
of orbit varies from near circular to elliptical. With maximum eccentricity, differences in solar radiation
receipt of around 30% occur between perihelion (when Earth is closest to Sun = more insolation) &
aphelion (when Earth is farthest from Sun). Precision of equinoxes is when the Earth rotates on its
axis, so that the point in the Earth's orbit when it’s closest to the Sun (perihelion) changes over time &
this affects the intensity of seasons. If perihelion occurs during the northern hemisphere's winter,
winters will be warmer & summers cooler. Snow & ice accumulating in winter will not melt so snow
cover expands, eventually triggering a glacial period. Volcanic eruptions also influence climate as
eruptions pump huge amounts of volcanic ash & sulphur dioxide which has a cooling effect. The
aerosols can be moved around by winds & cause significant cooling worldwide. E.g Mount Pinatubo
eruption in Philippines which cooled Earth's climate by 1.3°C
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