1. 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

2. 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.

3. 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.

4. 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)

5. 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.

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