Geography 1.1.2 Natural Climate Change

How has the global climate changed?

• The global climate conditions of the Earth change over time leading to colder and warmer periods

• The last 2.6 million years are the Quaternary period when there have been 60 cold periods and warmer interglacial periods

• The last ice age ended approximately 25,000 years ago

Greenhouse gases from natural sources  

• Water vapour: Evaporation from the oceans, seas and plants

• Carbon dioxide: Volcanic eruptions, wildfires and respiration

• Methane: Emitted from oceans and soils as part of decomposition, termites also emit methane

• Nitrous oxide: Soils and oceans

Causes of Natural Climate Change

Milankovitch Cycles

• Long term changes to the Earth's orbit and position. This changes how much solar radiation the Earth receives

• The Earth's orbit changes every 100,000 years a more circular orbit leads to cooler periods and an elliptical orbit leads to warmer periods

• The Earth's tilt varies every 40,000 years and the greater the tilt the hotter summers are and colder the winters are

• Every 24,000 years the Earth wobbles on its axis and this can affect the seasonal temperatures

Causes of Natural Climate Change

Volcanic eruptions

• Large scale eruptions lead to vast quantities of ash being ejected into the atmosphere

• Ash in the atmosphere blocks solar radiation leading to a decrease in temperatures

Causes of Natural Climate Change

Sunspot activity

• Increased sunspot activity is linked to higher average temperatures

Causes of Natural Climate Change

Atmospheric dust and asteroids

• Asteroids and meteors entering the Earth's atmosphere may increase the amount of dust which decreases temperatures

• Large asteroid collisions can cause fires which release CO₂ emissions and the dust sent up into the atmosphere can also lead to cooling as dust particles block solar radiation

Causes of Natural Climate Change

Ocean Currents

• Ocean currents affect temperature, warm currents such as the Gulf Stream lead to warmer temperatures. If these currents shift it can lead to changes in climate

Evidence for natural climate change

Ice cores 

• These trap ash, air bubbles and microbes.

  • The air bubbles contain CO₂ providing information about past temperatures

  • Ice cores give information regarding the climate for the last 2.6 million years

Evidence for natural climate change

Preserved pollen

• Allows scientists to know which plants were located where 

  • The climate requirements of those plants can then be used to know what the climate conditions were 

Evidence for natural climate change

Historical sources

• Diaries and art: such as paintings of the Thames river frost fairs

  • These are subjective and so may be inaccurate

Evidence for natural climate change

Tree Rings

• Each ring of the tree shows a year's growth

  • During warmer and wetter years trees grow more and so the rings are larger

  • Fossilised tree remains enable scientists to examine the climate over thousands of years