Unit 6. Climate Change
Climate Change Over the Last 5 Million Years
Earth’s climate has shifted between ice ages (cold periods) and interglacials (warm periods).
The most recent ice age ended about 11,700 years ago.
Natural causes include orbital changes, volcanic activity, and solar radiation.
How Scientists Study Past Climate Change
Ocean Sediments: Layers of mud and shells show past ocean temperatures.
Radiometric Dating: Uses radioactive decay to find ages of rocks and fossils.
Ice Cores: Trapped air bubbles reveal past CO₂ levels and temperatures.
Tree Rings: Wide rings = warm/wet years; narrow rings = cold/dry years.
Factors Influencing Climate Change
Solar Radiation
The Sun’s energy warms Earth.
More solar energy = warmer Earth; less = cooler Earth.
Small changes can affect climate over long times.
Volcanic Eruptions
Ash and dust block sunlight → Earth cools for a few years.
Volcanoes also release CO₂ → warms Earth in the long term.
Example: Mount Pinatubo (1991) cooled Earth for 2–3 years.
Orbital Variations (Milankovitch Cycles)
Earth’s orbit and tilt change slowly over thousands of years.
More tilt = hotter summers, colder winters.
Orbit changes can trigger ice ages or warmer periods.
Global Warming vs. Climate Change
Global Warming: The rise in Earth’s average temperature caused mainly by human activities
(burning fossil fuels, deforestation).
Climate Change: A broader term that includes global warming and other changes like
shifting rainfall, stronger storms, and melting ice.
In short: Global warming is one part of climate change.
Impacts of Climate Change
Floods
Heavier rainfall and rising sea levels cause more flooding.
Damages homes, roads, and farmland.
Droughts
Longer dry periods reduce water supplies.
Affects farming and drinking water.
Heatwaves
Extremely hot weather lasting days or weeks.
Dangerous for health, especially for the elderly and children.
Wildfires
Hot, dry conditions make forests catch fire more easily.
Destroys habitats and releases more CO₂.
Crop Yields
Some crops grow less well due to heat, drought, or floods.
Food shortages may occur in some regions.
Pests
Warmer climates allow pests and diseases to spread to new areas.
This harms crops and livestock.
Revision Table
Term
Meaning
Global warming Rise in Earth’s average temperature
Climate change All long-term changes in climate (warming, rainfall, storms, etc.)
Floods
More rainfall and rising seas → damage
Droughts
Long dry periods → less water
Heatwaves
Very hot weather → health risks
Wildfires
Hot/dry conditions → forest fires
Crop yields
Farming affected by climate changes
Pests
Spread of insects/diseases harming crops
Why Today’s Climate Change Is Not Natural
Much faster than past natural changes.
CO₂ and methane levels are the highest in hundreds of thousands of years.
Matches human activities: burning fossil fuels, deforestation, farming.
Natural factors alone cannot explain today’s rapid warming.
Greenhouse Gases
Trap heat in Earth’s atmosphere like a blanket.
Carbon dioxide (CO₂): from burning fossil fuels and deforestation; long-lasting.
Methane (CH₄): from livestock, rice paddies, landfills; stronger heat trap but shorter-lived.
Too many greenhouse gases → Earth overheats.
International Agreements
Kyoto Protocol (1997): first treaty with binding targets for developed countries to cut
emissions.
Paris Agreement (2015): nearly all countries; aim to keep warming below 2°C, ideally 1.5°C;
each country sets its own climate plan (NDCs).
Can Global Warming Be Stopped?
Cannot be stopped instantly, but can be slowed and stabilized.
Goal: become carbon neutral (net zero) → balance emissions with absorption.
Strategies to Cut Emissions
Use renewable energy (solar, wind, hydro).
Improve energy efficiency.
Switch to electric transport and public transit.
Sustainable farming, reduce food waste.
Protect and expand forests.
Everyday actions: save energy, recycle, eat less meat.