BIOLOGY · Stage 9 · Chapter 12: The Carbon Cycle and Climate Change
Biology 12.3 Historical impacts of climate change — Sea Levels and Extreme Weather — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 6 parts Lesson 3 of 6
Lesson summary
12.3 Historical impacts of climate change — Sea Levels and Extreme Weather — Alhussan International Academy — Biology (Stages 7–9) notes: Describe how past and recent climate change has affected sea level, weather events and human societies.Evidence — scientists study carbon diox…
- Glaciation
- Theories for cold periods
- Global warming events
- Causes of rise
- Floating ice
- Present rise
Section 1 of 6Climate change in ancient history
- Evidence
- scientists study carbon dioxide levels and other evidence for climate change millions of years ago and in recent history.
- A fossil shark's tooth from Europe is evidence that tropical sharks once swam in countries that are now very cold and dry.
- Glaciation
- at times the Earth's surface was very cold and covered in ice and snow, and huge frozen rivers of ice called glaciers carved out valleys.
- Most countries were covered in ice at some time in Earth's history.
- During the last glacial period sea level was about 120 m lower and Britain was joined to Europe by land.
- Theories for cold periods
- huge volcanic eruptions filling the air with ash, giant meteorite strikes throwing up dust, changes in Earth's orbit and changes in the activity of the Sun.
- Global warming events
- the climate has changed from ice ages to tropical forests and desert heat.
- Evidence shows that warming events are always linked to increases in greenhouse gases such as carbon dioxide, for example from massive volcanic eruptions.
Section 2 of 6Climate change in recent history
- Scope
- almost every country produces greenhouse gases, and every country is affected by global warming.
- Flooding
- global warming is linked to more torrential rain and severe flooding.
- In 2010 massive flooding in Pakistan killed at least 2000 people and affected the lives of 20 million others.
- Drought
- some regions have extreme heat and a lack of rain.
- Over the last 30 years Africa has become hotter and drier, crops have failed and lakes have dried up, so many people cannot grow enough to eat.
- Droughts in Australia led to huge bush fires that threatened species such as koala bears.
- Extreme weather
- hurricanes, tornados, blizzards, heavy rain and very high temperatures are becoming more common.
- Major named storms rose from 89 in 1900-1910 to 127 in 1950-1960 and 170 in 2000-2010.
- Hurricanes rose from 45 to 72 to 94 over the same periods.
Section 3 of 6Climate and sea level
- Causes of rise
- ice on land melts and flows into the ocean, and seawater expands as it warms (thermal expansion).
- (glaciers and the Greenland and Antarctic ice sheets)
- ice on land melts and flows into the ocean, and seawater expands as it warms (thermal expansion).
- Floating ice
- melting sea ice that is already floating does not raise sea level much, like melting ice cubes in a full glass.
- Present rise
- mean sea level has risen about 21-24 cm since 1880, and the rate is now increasing.
- Wider effects
- rising sea level increases coastal erosion and changes ocean currents.
- This affects the movement of the tiny organisms that support all ocean food chains.
Section 4 of 6Effects of rising sea level
- Low-lying coasts and islands, such as the Maldives, Bangladesh and parts of the Nile delta, flood more often.
- Salt water enters rivers and groundwater, harming drinking supplies and farmland.
- Coastal erosion increases and damages homes and ports.
- People may be forced to move and become climate refugees.
Section 5 of 6Climate and past societies
- Medieval Warm Period (about 900 to 1300 CE)
- Europe had good harvests and Vikings settled in Greenland.
- Little Ice Age (about 1300 to 1850)
- cooler weather brought failed harvests, famine and frozen rivers such as the Thames in London.
- Droughts
- long droughts have been linked to the decline of some ancient civilisations.
- Lesson
- societies are sensitive to climate.
Section 6 of 6Comparing past and present
| Feature | Natural past changes | Present changes |
|---|---|---|
| Main cause | Orbit, volcanoes, solar changes | Greenhouse gases from human activity |
| Speed | Over thousands of years | Over decades |
| Population affected | Small, mobile groups could move | Billions, many in coastal cities |
- Adaptation
- sea walls, restoring mangroves and wetlands that absorb storm waves, raising buildings and better warning systems.
- Mitigation
- cutting emissions reduces the long-term risk.
Last updated: