Climate Change Reasons for climate change divide into 2 main causes; natural and human Natural Reason Human Reasons Variation in insolation Enhanced Greenhouse Astronomical Changes Effect Volcanic Eruptions Plate Tectonics Changes in Ocean Currents

Variations in Insolation Evidence suggests that the amount of heat energy from the Sun is not always the same, but that there are cycles of increased solar energy – sunspots Astronomical Changes The 95,000 year stretch The earth’s orbit changes from circular to elliptical and back again, when it is elliptical some areas will be nearer the sun than they were and some further away, so some will be hotter, others colder.

2. The 42,000 year tilt The tilt of the earth’s axis changes from 21.5 to 24.5 degrees and back again – the greater the angle of tilt, the greater the area receiving the Sun overhead The 21,000 year wobble The axis also wobbles, meaning that some areas get more insolation at some times than others. When all these 3 are giving thier lowest insolation at the same time, that is when the Earth is most likely to have major glacial periods.

Volcanic Eruptions Large volcanic eruptions cause extra dust particles in the atmosphere which absorb more solar radiation, lowering temperatures. When many eruptions occur over a short time, this can significantly lower temperatures. Krakatoa (1883) Mt St Helens (1980) Mt Pinatubo (1991)

Plate Tectonics Continents have had different climates in the past because they have been in different latitudes due to continental drift. Changes in Ocean Currents Changes in the pattern and strenght of ocena currents may lead to changes in the distribution of heat around the planet. A short term example might be El Nino which happens every couple of years.

Task Think of the different types of human activity that takes place. What activities might cause changes in climate?