Geological evidence suggests that climate change has been occuring throughout the Quaternary period
○ Occurred before humans were on the planet
○ Suggests that long-term climate change is a result of natural causes
Solar output:
● Sun’s output of energy is not constant → changes in short cycles of 11 years/long cycles of 100s of years
○ Periods when solar output is reduced causes Earth’s climate to become cooler in some areas
■ From 1900 – 1940 → solar output slightly increased
■ Over last 50 years → overall solar output has decreased slightly
■ Suggests that solar output is not the cause of climate change
● Intensity of solar energy is recorded using radiometers (since 1978)
Orbital changes:
● Distribution of Sun’s energy on Earth changes due to changes in Earth’s orbit
○ eg/ Earth’s orbit is an ellipse → shape changes every 96000 years
■ Distance between Earth and the Sun changes as Earth orbits
■ Closer to the sun = more energy = Earth is warmer
○ eg/ Earth’s angle of tilt changes due to gravitational pull of the Moon
■ Can exaggerate climates (summers are warmer, winters are colder)
● Changes affect amount of radiation/energy Earth receives
● Could have a significant impact on climate change
○ Despite orbital changes, ice age still only occurs every 30, 000 years
● Orbital changes may be the cause of glacial/interglacial cycles o f the Quaternary period
Volcanic activity:
● Volcanic eruptions can temporarily cause climate change
○ Eruptions eject large quantities of materials into the atmosphere
■ Some of the particles reflect sunlight back out to space
■ Earth’s surface doesn’t receive enough sunlight → temperature is cooler
○ Volcanoes release CO 2 (a greenhouse gas) but not enough to cause warming
● eg/ June 1991 → Mount Pinatubo, Philippines
○ 20 million tonnes of sulphur dioxide was released
○ When SO 2 is mixed with water vapour , it becomes a volcanic aerosol
■ Volcanic aerosols reflect sunlight away → reduced amount of heat entering Earth
Plate tectonics:
● Tectonics cause continents to move which causes volcanoes and mountains to form
● Movements change direction of large ocean currents
○ Carry heat around the Earth
○ Direction of heat carried changes
● Oceans store a large amount of heat
○ eg/ North America and South America → continent joined and cut off ocean current
■ Diverted entire ocean current to the north
■ Makes North Europe warmer
■ Eventually led to ice age
● Increased temperatures allowed more evaporation from the sea
● Water vapour condensed and fell as snow → brought average temperature down
○ Ice covered large areas of the northern hemisphere