Week 13 · 2-4 The Atmosphere and the Role of Science in Its Sustainability (A): global warming and the greenhouse effect, ways to reduce emissions, air pollutants (carbon monoxide, sulphur and nitrogen oxides), formation of acid rain · 3 lessons
1
Greenhouse gases and global warming
Integrated Science Sec 1 Term 1, Unit 2: pp. 98–102
GoalExplain the greenhouse effect and global warming, and name the gases and the effects.
New words
global warming · the continuing rise in the temperature of the air near Earth’s surfacefossil fuels · coal, oil and natural gasgreenhouse gas · a gas such as CO₂ or methane that holds part of Earth’s heat in the airinfrared radiation · the long-wave heat radiation sent out by the warm surface
Explanation
Global warming is the continuing rise in the temperature of the air near Earth’s surface. It follows from burning fossil fuels (coal, oil and gas), which release greenhouse gases: carbon dioxide CO₂, methane CH₄, nitrous oxide N₂O, chlorofluorocarbons (CFCs) and water vapour. Sunlight, which has a short wavelength, passes through the air; the surface absorbs it and sends it back as long-wave thermal (infrared) radiation; greenhouse gases keep part of it in, like a blanket. This natural effect is needed: without it Earth’s surface would average about −18 °C instead of about 15 °C (extra). The problem is the extra gases added by people. The glass-house comparison is only a picture. Effects: ice at the poles melts and breaks off, which risks coastal flooding; polar species lose habitat; biodiversity falls and the balance of ecosystems is disturbed; extreme events such as hurricanes, floods and droughts become more likely. Global warming is not the same as ozone depletion, and weather is not climate: one hot day does not show a trend.
sunlight passes in→surface absorbs it and sends out infrared→greenhouse gases hold part of it→lower air is warmer
Worked examples
Read the invented CO₂ series (not real data): 400, 404, 408, 413, 417, 421 ppm over six years. The rise is 421 − 400 = 21 ppm, about 4 ppm each year. A steady rise like this, caused by burning fuels, strengthens the blanket.
Sort the sources. Burning coal in a power station, a bus engine and gas for heating release CO₂. A growing forest takes CO₂ in by photosynthesis. So power stations and buses add gas, while forests remove some.
Is this statement right? “It was cold today, so global warming is false.” No. Weather is the conditions on one day; climate is the pattern over many years, so one cold day cannot cancel a long-term rise.
Class activity
Blanket diagram on paper. Draw the Sun, a thick arrow of sunlight reaching the ground, a thinner wavy arrow of infrared going up, a layer of greenhouse gases, and a smaller arrow going back down. Label each part. Then write two sentences: why the natural effect is needed, and why extra gas changes the balance. Do not use jars or thermometers.
Practice
1
Name three greenhouse gases.
For example: carbon dioxide, methane and nitrous oxide (also CFCs and water vapour).
2
What does the surface send back after absorbing sunlight?
Long-wave thermal (infrared) radiation.
3
Is the natural greenhouse effect harmful? Explain.
No, it is needed to keep Earth warm enough for life; the extra gases are the problem.
4
Give two effects of global warming.
For example: polar ice melts, which risks coastal flooding; more extreme weather such as floods and droughts.
