Causes of Climate Change

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  • Created by: keeels
  • Created on: 09-05-14 11:29
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  • Causes of Climate change
    • Some causes in climate change are caused by changes in how the sun's energy is received, trapped and distributed around the Earth, e.g when more energy is received, the Earth will get hotter. When less energy is received, the Earth will get cooler
    • Milankovitch Cycles
      • Eccentricity
        • The path of the Earth's orbit around the Sun changes from an almost perfect circle to an ellipse and back again about every 96,000 years
        • This changes the distance from the sun to the Earth, and so the amount of energy the Earth receives from the sun (at different times of the year)
        • The Earth's orbit is elliptical right now - it's closest to the sun in January and furthest away in July
      • Obliquity
        • The Earth is tilted at an angle as it orbits the sun, called it's axis (currently 23.5)
        • This changes between 21.8 and 24.4 over a cycle of about 41,000 years
        • The change in tilt changes the amount of energy that different latitudes receive, changing global climate
        • When the tilt is greater (24.4) areas that receive lots of energy, such as the tropics, will be larger. Other climate regions, such as temperate zones beyond the tropics will be smaller
      • Precession
        • The axis of the Earth also wobbles like a spinning top on a cycle of about 22,000 years
        • Because Earth is closest to the Sun in January, winter in the northern hemisphere is mild and summer is cool
        • The wobble of the axis means this gradually changes - the seasons will eventually swap over
        • When this happens, the Earth will still be closest to the Sun in January, but this will be now be summer in the northern hemisphere. The Earth will still be furthest away from the sun in July, but this will now be winter in the northern hemisphere
        • So in the northern hemisphere, winter would then be colder because it would be at the time when the Earth is further from the sun, and the summer would be hotter, because it's at the time when the Earth is closer to the Sun.
    • Variations in solar output
      • The Sun's output of energy isn't constant
      • Sunspots are darker areas on the sun that increase solar energy output
      • They're thought to increase and decrease in number in an 11 year cycle - though there's variation within this cycle
      • E.g a period of cooling in the late 17th century called the little ice age is thought to have coincided with a period when sunspot activity was low
    • Meteor impacts
      • The impact of a meteor (up to 10m across) or an asteroid (larger than 10m across) forms a large crater and can throw up huge amounts of material into the sea
      • This can result in a lot of sunlight (energy) being blocked out for months or even years, changing the climate.
      • E.g the mass extinction of the dinosaurs is widely thought to have been caused by the climate change brought about by a massive asteroid impact
    • Volcanic eruptions
      • Major volcanic eruptions also eject large quantities of material into the atmosphere
      • This can also block out sunlight (energy) which changes climate
      • E.g the eruption of mount Tambora in 1815 is thought to have lowered global temperature by about 0.5
    • Human activity
      • Enhanced greenhouse gas emissions
        • Greenhouse gases include CO2, Methane, ozone and water vapour
        • The greenhouse effect is where greenhouse gases absorb outgoing energy , so less is lost to space. It;s essential for keeping the planet warm
        • But too much greenhouse gas in the atmosphere means too much energy is trapped and the planet warms up
        • CO2 is released into the atmosphere when fossil fuels like coal, oil, natural gas and patrol are burnt e.g in power stations or in cars
        • since the start of the industrial revolution in the mid 19th century levels of atmospheric CO2 have increased from 280ppm to 380ppm. The level had been broadly stable for the previous 10,000 years
        • The increase in CO2 has been caused the increase in temperature over the same period because of the enhanced greenhouse effect
      • Destruction of natural CO2 sinks
        • CO2 sinks store CO2, keeping it out of the atmosphere - so it's not contributing to the greenhouse effect
        • The biggest sinks are the oceans - CO2 dissolves in sea water and gets moved to the deep oceans by natural cuurents
        • Another big sink is plants - plants take in CO2 and convert it into organic matter using photosynthesis. It is also stored in the soil as dead organic matter
        • CO2 is released into the atmosphere when trees are burnt by forest fires or to make way for agriculture
        • It was thought that a lot of greenhouse emissions from humans could be stored in CO2 sinks. It's now thought they won't be able to keep pace with increasing emissions, so more CO2 will go directly into the atmosphere


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