Greenhouse gases and climate change

Last time

Before we start: last time, in Biodiversity, habitat loss, deforestation and conservation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

A blanket round the Earth

Without any atmosphere, Earth would be a frozen planet. A natural blanket of gases keeps it warm enough for life. But we have been making the blanket thicker. Today: the greenhouse effect, the gases involved, and what a warmer planet does to living things.

The greenhouse effect

The Sun's energy reaches Earth as light and heats the surface. The warm surface gives out infrared radiation. Greenhouse gases in the atmosphere absorb some of it. They then radiate it in all directions, including back to Earth. This keeps the planet warmer than it would be.

Greenhouse gases

The main greenhouse gases are carbon dioxide, methane and water vapour. Carbon dioxide comes from burning fossil fuels, and from deforestation, which removes trees that absorb it. Methane comes from cattle digesting food, rice fields, landfill sites and decaying waste.

The enhanced greenhouse effect

Human activities have increased the concentrations of greenhouse gases in the atmosphere. More gas absorbs more infrared, so more heat is trapped near the Earth's surface. The result is global warming: a rise in the average temperature of the Earth, and so climate change.

Effects on the climate

Ice caps and glaciers melt, and the oceans expand as they warm, so sea levels rise. Low-lying coastal land floods, and weather becomes more extreme: heatwaves, droughts and storms. Rainfall patterns change, so some areas become drier and others wetter.

Effects on living things

Habitats change, and species that cannot move or adapt fast enough may become extinct. Species move towards the poles, or up mountains, to stay cool. Their food webs are disrupted. Crop yields can fall in areas hit by drought, and disease-carrying insects may spread to new regions.

What can be done

Burn less fossil fuel by using renewable energy, such as wind, solar and hydroelectric power. Plant trees and stop deforestation, to take carbon dioxide out of the air. Reduce waste in landfill, and use energy more efficiently, to cut emissions of both gases.

Evidence

Carbon dioxide is measured in the air and in bubbles trapped in ancient ice. It has risen sharply since industry began. Average global temperatures are measured at thousands of stations, and they have been climbing for decades. Glaciers are shrinking and the ice at the poles is melting, which fits the pattern.

A common confusion

The ozone layer protects us from harmful ultraviolet light. Damage to it is a separate problem. Global warming is caused by greenhouse gases absorbing infrared, not by holes in the ozone layer. Keep the two ideas apart, and you avoid a mark-losing mistake.

Why numbers rise together

Carbon dioxide and temperature both rise over the same period, which suggests a link. Correlation alone is not proof, but the greenhouse effect gives a mechanism, so scientists accept the link. In an answer, describe the pattern first, then explain it using the greenhouse effect.