Earth and space: weather, climate, and evidence of climate change (grade 12) · lesson

The greenhouse effect

💡 Greenhouse gases absorb heat given off by Earth's surface and send some back down, warming the surface.

Sunlight mostly passes through the air and warms the ground. The warm ground gives off infrared radiation (heat). Greenhouse gases such as carbon dioxide, methane, and water vapor absorb it and send part of it back down.

Nitrogen, oxygen, and argon make up most of the air, but they don't absorb infrared. So they are not greenhouse gases.

Bright snow and ice reflect sunlight. Less snow means darker ground that absorbs more energy, which also warms the surface.

🧠 Let's work it out

For any change, ask: does it keep more energy at the surface or less?
More greenhouse gas or less reflective ice keeps more.
More snow or more reflecting particles keep less.

What do you think comes next?

greenhouse gas: a gas that absorbs heat given off by Earth's surface
infrared: the kind of radiation we feel as heat

🔗 PhET: Greenhouse Effect · PhET Interactive Simulations (free) ↗

Weather versus climate

💡 Weather is conditions now; climate is the average over many years.

A snowy morning, tomorrow's storm, and today's high temperature are weather. A city's average yearly rainfall is climate.

One cold winter in one city can't show a global trend. Climate change is seen in long, worldwide patterns.

🧠 Let's work it out

Check the time span and the area.
Short time or one place → weather.
Long average or global pattern → climate.

What do you think comes next?

climate: the long-term average weather of a place

🔗 Khan Academy: Weather and climate · Khan Academy (free) ↗

Reading climate evidence

💡 Long-term, widespread measurements show how climate is changing and how fast.

Air bubbles trapped in deep ice cores are samples of old air, so they show past carbon dioxide levels.

Rising global sea level and shrinking mountain glaciers worldwide are evidence of warming. Melting land ice adds water, and warmer water expands.

Data tables let you check both the change and the rate of change.

🧠 Let's work it out

CO₂ was 317 ppm in 1960, 354 in 1990, and 414 in 2020.

The first 30 years rose 37 ppm; the next 30 rose 60 ppm.
Same time span, bigger rise, so it is rising faster.
For rates, multiply: 3.5 mm per year × 40 years = 140 mm = 14 cm.

What do you think comes next?

ppm: parts per million, a way to measure a small amount of gas in air

🔗 NASA: Evidence of climate change · NASA ↗

Natural causes of climate change

💡 Slow orbit cycles and big volcanic eruptions can change climate on their own time scales.

Over tens of thousands of years, regular changes in Earth's orbit and tilt change how sunlight is spread over the seasons. These cycles help pace the ice ages.

A large eruption can put sulfur particles high in the air. They reflect sunlight, cooling the surface for a year or two.

🧠 Let's work it out

Match each cause to its time scale.
Orbit cycles act over many thousands of years.
Volcanic particles act for a year or two.
Neither explains a fast rise in CO₂.

What do you think comes next?

From burning fuel to rising seas

💡 Burning fossil fuels adds CO₂, which traps heat, which melts ice and expands seawater.

Burning coal, oil, and gas releases carbon dioxide that was stored underground for millions of years.

More CO₂ traps more heat. Warming melts land ice and makes ocean water expand. Both raise sea level.

🧠 How to think about it

Build the chain cause by cause, and check each link: what does this step cause next? Start with the human activity and end with the final effect.