high school Climate Change

Climate Change

Climate is the average state of the atmosphere over 30 years or more, and since industrialization fossil-fuel use has raised CO₂ and global mean temperature by about 1.1°C. Greenhouse gases absorb and re-emit infrared from the surface, keeping Earth warm; without them the average would fall to about -18°C. Natural factors such as Milankovitch cycles exist but act over tens of thousands of years, so the rapid warming of recent decades is explained by human greenhouse-gas growth. Change the year and watch CO₂ concentration and temperature anomaly.

Earth is warming

🌡️ What is climate change?

①Climate: 30+ year average atmospheric state (different from weather!)

②Since the Industrial Revolution: fossil fuel use → CO₂ rises sharply → Earth warms

③Global average temperature ~1.1°C above pre-industrial (2020 · CO₂ ≈ 415 ppm)

CO₂ concentration and temperature change

Year2020

💡 Key observations

①CO₂ and temperature rise together (correlated)

②Sharp rise after 1950 — industrialization and fossil fuel surge

③Projection: without mitigation, 2100 could exceed +3.5°C

Greenhouse effect

Greenhouse effect principle

solar radiation → surface heating → IR emission → greenhouse gases absorb and re-emit → temperature maintained

without greenhouse gases, Earth's average would be ~-18°C (now ~15°C)

Main greenhouse gases

Types of greenhouse gases

CO₂ (carbon dioxide)

fossil fuel burning, deforestation

largest contributor

CH₄ (methane)

livestock/agriculture, wetlands, natural gas

~25× greenhouse effect of CO₂

N₂O (nitrous oxide)

fertilizers, industrial processes

~300× CO₂

CFCs

refrigerants, also damage ozone layer

~thousands× CO₂

Milankovitch cycles (natural climate change)

Milankovitch cycles

eccentricity (100 ka) + axial tilt (41 ka) + precession (26 ka)

the distribution of solar energy Earth receives changes cyclically → ice ages / interglacials

🔬 Natural vs anthropogenic climate change

①Natural: Milankovitch cycles, volcanic eruptions, solar activity (thousands–tens of thousands of years)

②Anthropogenic: greenhouse emissions, deforestation, urbanization (decades–centuries)

③Current rapid warming cannot be explained by natural variability alone → anthropogenic cause

Worked Examples and Exam Practice

Example 1

If there were no greenhouse gases in the atmosphere, about what would Earth's average temperature be? (currently about 15°C)

Greenhouse gases absorb and re-emit the infrared the surface gives off, warming the surface.

Without them, that warming is lost and the average temperature falls to about -18°C.

▸ About -18°C

The greenhouse effect itself is a natural process essential for life; the problem is the part humans have intensified.

Example 2

Why can recent decades of rapid warming not be explained by Milankovitch cycles?

Milankovitch cycles act very slowly, over tens of thousands to hundreds of thousands of years.

The recent rise happened within decades and matches the surge in CO₂, so it is attributed to human causes.

▸ Different time scales: Milankovitch over tens of thousands of years, the recent rise over decades (anthropogenic)

Natural factors (Milankovitch, volcanoes, the Sun) and human factors (greenhouse gases) are distinguished by their time scales.

exam-style

Which statement about climate change and the greenhouse effect is correct?

①Climate means the day-to-day state of the atmosphere

②CO₂ contributes most to warming because it is emitted in large amounts

③The greenhouse effect is an artificial phenomenon created by humans

④The eccentricity cycle of Milankovitch is about 26,000 years

⑤Without greenhouse gases, Earth would be warmer than now

▸ ② CO₂ contributes most to warming because it is emitted in large amounts

Methane and nitrous oxide are stronger per molecule, but CO₂, emitted in far greater amounts, contributes the most to overall warming.

Climate is a 30-year-plus average (①), the greenhouse effect is natural (③), the eccentricity cycle is about 100,000 years (④), and without greenhouse gases Earth would cool to about -18°C (⑤).

Summary

Climate change core

fossil fuels → CO₂ ↑ → enhanced greenhouse effect → global warming

natural (Milankovitch) and anthropogenic (greenhouse gases) factors combine

🎯 Exam Points

①Greenhouse effect: absorb/re-emit IR → maintains Earth temperature (a natural phenomenon)

②Main GHGs: CO₂, CH₄, N₂O, CFCs — CO₂ contributes most by quantity

③Milankovitch: eccentricity (100 ka) + tilt (41 ka) + precession (26 ka)

④Warming impacts: sea-level rise, extreme weather, ecosystem changes

⑤Without greenhouse effect, Earth would be ~-18°C (currently ~15°C)

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