Theories about causes of climate changes

This theory suggests when there are large volcanic eruptions the ash and sulphur dioxide it emits spread around the stratosphere and blocks some sunlight from reaching the Earth, reflecting it back into space. This cools the planet and lowers the average temperature.

Tambora, Indonesia (1815):

• Biggest eruption in human history
• Temperature was so cold in 1816 it was called the year without summer
• So much sun was blocked, crops failed and 200,000 people died
• The effects lasted 4-5 years (usually only lasts 2)

Lots of sun spots = lots of solar energy fired towards the Earth

Less sun spots = Less solar energy fired towards the Earth

The sun has an 11 year cycle, from almost no sunspots to hundreds

Cool periods such as the Little Ice Age and warms periods such as the Medieval warm period have been caused by changes in sunspot activity.

Sunspots can vary the Earth's climate by 1-2 degrees

Orbital changes affect the amount of sunlight on the Earth's surface and where it falls. On a timescale of thousands of years, the changes could start an ice age or stop one. The cycles are called Milankovitch cycles.

3 ways the Earth's orbit change:

• The Earth's orbit is sometimes circular, sometimes oval
• The Earth's axis tilts, sometimes it is upright, sometimes it's side
• The Earth's axis wobbles like a spinning top about to fall over

These cause cold periods 5-6 degrees colder than today and warm periods 2-3 degrees warmer than today.

It takes 100,000 years for the orbit to change from circular to oval and back

It takes 41,000 years for the axis to tilt, straighten and back

It takes 26,000 years for the axis to wobble, straighten and wobble again.