Natural & Enhanced Greenhouse Effect (Edexcel IGCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Natural Climate Change
Changes in the Global Climate
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, during this, there have been 60 cold periods and warmer interglacial periods
The last ice age ended approximately 25,000 years ago
The evidence for these changes comes from:
Ice cores which trap ash, air bubbles and microbes
Preserved pollen
Historical sources such as diaries and art
Tree rings
Causes of Natural Climate Change
Cause | Impact |
|---|---|
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 the summers and the colder winters Every 24,000 years, the Earth wobbles on its axis and this can affect the seasonal temperatures |
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 |
Sunspot activity | Increased sunspot activity is linked to higher average temperatures |
Atmospheric dust | Asteroids and meteors entering the Earth's atmosphere may increase the amount of dust, which decreases temperatures |
Enhanced Greenhouse Effect
The Greenhouse Effect
The greenhouse effect is essential to the survival of life on Earth:
Greenhouse gases in the atmosphere allow short-wave radiation from the sun through to the Earth's surface
This is absorbed by the atmosphere and Earth's surface and re-radiated as long-wave radiation
The greenhouse gases absorb some of the long-wave radiation (which we feel as heat)
They stop it from radiating out into space
This maintains the Earth's average temperature
Without the greenhouse effect, the average temperature would be -18oC
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
The Enhanced Greenhouse Effect
Human activity is increasing the number of greenhouse gases in the atmosphere:
Carbon dioxide (CO2) levels in the atmosphere have increased by more than 100 parts per million (ppm) to 420ppm in 2020
Increased amounts of greenhouse gases have led to the enhanced greenhouse effect:
Less long-wave radiation (heat) can escape the atmosphere
Average global temperatures have increased over 1oC since pre-industrial times
Human Sources of Greenhouse Gases
Greenhouse Gas | Sources from human activity |
|---|---|
Carbon Dioxide (CO2) |
|
Methane (CH4) |
|
Nitrous Oxide (N2O) |
|
Chlorofluorocarbons (CFCs) |
|
Worked Example
Identify which of the following is the result of the enhanced greenhouse effect
(1 Mark)
A | increasing global average temperature due to natural causes |
B | decreasing global average temperature due to human activity |
C | increasing global average temperature due to human activity |
D | decreasing global average temperature due to natural causes |
Answer:
C (1) - The enhanced greenhouse effect causes the average global temperature to increase and is the result of human activity.
Examiner Tips and Tricks
Remember not all scientists agree about the causes of climate change. There are a few scientists who argue that global warming is the result of the Earth's natural climate pattern and not the result of human activities.
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