7.1 A - How and Why Climate has Changed in the Last 10 000 Years

A- How (and why) Climate has Changed in the Last 10 000 Years (since the last ice age)

• Large changes over a short amount of time.
• End of last ice age – 8000BC
• Always fluctuating
• Little ice age 1200-1800
• Rapid temperature change --> 1200 years 5 degrees temp change
• 10000 years fluctuation = short

CAUSES (WHY?) :

Volcanic activity –

Release large amounts of sulphur dioxide (SO₂) haha. This is chem. X) and ash

A layer of these particles act as a ‘cloak’ (like... a protective layer) around the earth

Thus, reducing the amount of solar energy (radiation) (OMG PHYSICS!!) that reaches the Earth’s surface

Orbital Geometry

Orbital characteristics / Orbital Geometry => Milankovitch cycles

1. Shape of earth’s orbit varies from CIRCULAR to ELLIPTICAL to CIRCULAR

every 95 000 years

COLD, glacial periods – circular

WARMer periods – elliptical

2. Tilt of earth’s axis varies -> affects intensity of seasons

from 21.5° to 24.5°

Variation over 40 000 year span

The GREATER the angle, the hotter the summers are and colder the winters are. LARGE VARIATION

The SMALLER the angle, the SMALLER the variation between seasons.

**NOTE: Different sources say earth’s axis varies from 22.5 – 24.5 degrees over 41000 year period**

3. Precession of the earth -> affects timing of seasons (relative to orbital position to the sun)

The earth’s axis precesses (wobbles like a dying spinning top) over the course of 25 000 years

View animations of the milankovitch cycles: http://www.wwnorton.com/college/geo/egeo/flash/18_2.swf

Solar output –

Energy from the sun changes over time

More energy ->high temperature

Less energy -> cooler temperature