LONG TERM: The Earth’s orbit around the sun changes from circular to elliptical and back

over about 100,000 years.• When the Earth is closer to

the sun, temperatures are higher ..when further away, the Earth is cooler.

• Also….

The Earth is tilted on its axis – the angle of tilt changes (41,000 year cycle) – and it also

wobbles about (26,000 year cycle)!• These changes also affect the amount of

sunlight received. • NB These 3 cycles are known as ‘Milankovitch

Cycles’

MEDIUM TERM: Cycles of sunspot activity cause variable solar output

over a few hyndred years

• Sunspots – black areas on surface of sun – areas of greater activity – vary in number – more spots, more energy towards Earth. Changes over periods of a few hundred years may link to cycles of sunspot activity.

This graph suggests that sunspot activity might be a factor in temperature change

(– but be careful – graph only covers a

short period of time)

SHORT TERM: Volcanic eruptions can send ash particles & gases many kms into

the atmosphere – blocking out the sun’s rays. Mount Pinatubo, Philippines, eruption

June 1991, led to a fall in average global

temperatures of 0.5 degree C. However,

the effect is likely to be for a few months or

years only.

• ,

Tambora, Indonesia, 1815 – the biggest known eruption in human

history -• So much ash was shot into the upper atmosphere that

1816 was called ‘the year without a summer’ – crops failed, famine was widespread and 200,000 people died. The effects lasted 5 years.

• (but it did lead to spectacular sunsets, painted by artists like Turner:

Since the 1850s, there has been a rapid rise in temperatures – and human activities are being blamed for this… but that’s the next

instalment!