S4.14.8 Chapter 8

Responding to climate change

Leila’s village gets less reliable rain, and her town needs more power. What can people do about the causes of climate change, and about its effects?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

A Nothing: the change has already started, so nothing we do now can matter.
You picked A. Read on. At the end, the chapter comes back to your guess.
B Only the countries that burn the most fuel can do anything, so villages can do nothing.
You picked B. Read on. At the end, the chapter comes back to your guess.
C Two things: cut greenhouse gas emissions to slow the change, and adapt to the changes that will come anyway.
You picked C. Read on. At the end, the chapter comes back to your guess.
D Planting a few trees would be enough to stop it.
You picked D. Read on. At the end, the chapter comes back to your guess.

By the end you can

Compare ways to cut greenhouse gas emissions
Explain how people adapt, such as by storing water and growing new crops

The last chapter showed that the Earth has warmed and that people are the cause. What can be done? There are two kinds of response. Mitigation means cutting the greenhouse gases that people put into the air, to slow the warming. Adaptation means changing how we live, so that we are safer from the changes that are coming.

Both are needed. Cutting emissions makes the changes smaller. Adapting protects people from the changes that cannot now be avoided. The more we cut, the less we need to adapt to.

Start with the causes. Carbon dioxide stays in the air for centuries, so the warming depends on the total that people add. Scientists say that the Earth stops warming roughly when the net emissions of carbon dioxide fall to zero. Net means what is put into the air, less what is taken out again, by plants for example. This goal is called net zero.

To cut emissions, we first need to know where they come from. The world’s greenhouse gas emissions are shared across several kinds of activity.

Where the world’s greenhouse gas emissions come from, in 2019, rounded. Energy supply means making electricity and heat, and getting coal, oil and gas out of the ground, with their leaks. Buildings counts only the fuel burned in them. The shares add up to a little over 100 % because of rounding.

The biggest share is from energy supply, and most of that is making electricity and heat. So cleaner electricity is the biggest single change. Burning coal, oil and gas gives out carbon dioxide. Wind, sun, water and nuclear power give out almost none while they run. Making the equipment does use energy, so the whole life of each source gives out a little.

Greenhouse gas for each kWh of electricity, over the whole life of the source. Water power gives about 24 and nuclear power about 12. The values are rounded, from the IPCC.

Worked example

A home uses 3 000 kWh of electricity in a year. How many kg of carbon dioxide are released if the electricity comes from coal, at 820 g for each kWh? How many if it comes from wind, at 11 g for each kWh?

There are 1 000 g in 1 kg. So kg = kWh × g for each kWh ÷ 1 000.
Coal: 3 000 × 820 ÷ 1 000 = 2 460 kg.
Wind: 3 000 × 11 ÷ 1 000 = 33 kg.

Answer: coal 2 460 kg, wind 33 kg

Each way of making power has limits. The sun and wind come and go, so they need a way to store energy or a back up. Dams for water power flood land and move people. Nuclear power leaves waste that must be kept safe for a very long time, and its plants are costly. The best mix depends on the place, whether it is sunny, windy or has rivers.

The second way is to use less energy for the same job. This is energy efficiency. A 10 W LED lamp gives about as much light as an old 60 W filament lamp. Insulation keeps houses warm or cool with less energy. A good stove burns less fuel to cook the same food.

Worked example

An old lamp of 60 W is on for 5 hours each day through a year of 365 days. How much energy does it use in kWh? An LED of 10 W gives the same light. How many kWh does the LED save?

Convert watts to kilowatts: 60 W is 0.06 kW. The energy is power × hours.
The old lamp: 0.06 kW × 5 h × 365 = 109.5 kWh.
The LED: 0.01 kW × 5 h × 365 = 18.25 kWh.
The saving is 109.5 − 18.25 = 91.25 kWh.

Answer: 109.5 kWh, saving 91.25 kWh

Two lamps that give about the same light. The LED uses about one sixth of the power.

The other ways are more varied. In transport, walking and cycling give out nothing. Buses, trains and electric vehicles charged from clean power give out much less carbon dioxide for each person. In farming and on land, stopping the clearing of forests keeps carbon out of the air. Planting new forests takes it in. Better feeding of cattle, and draining rice fields now and then, cut methane. Wasting less food also helps, because about a tenth of emissions come from food that is thrown away.

Methane deserves special mention. It lasts only about a dozen years in the air. So cutting it slows warming fast. People can mend leaks from gas pipes and mines. They can catch the gas from rubbish tips. Some factories can also catch carbon dioxide from their chimneys and store it deep underground. This is called carbon capture. It is still done on a small scale.

Cleaner cooking links back to the chapter on air pollution. A stove with a chimney takes the smoke out of homes. So does a cleaner fuel, such as biogas, gas or electricity. They also use less wood. This is better for health, and it cuts emissions as well.

Now adaptation. Even if emissions fall fast, some warming and some changes are already coming. People can get ready. The right choices depend on the risk in each place.

Some risks, and some responses to them. The best response depends on the place.

Storing water is an old and sound idea. Rain from a roof can run into a tank. Ponds and small dams can hold rain for the dry months, and wells can be recharged by letting rain soak in. A tank turns a short wet season into a store for a long dry one. Remember that 1 mm of rain on 1 m² is 1 litre.

Worked example

A flat roof of 30 m² collects 30 mm of rain into a tank. A family of 5 uses 20 litres each every day, for drinking, cooking and washing. For how many days does the water last?

1 mm on 1 m² is 1 litre, so the roof gives 30 × 30 = 900 litres.
The family uses 5 × 20 = 100 litres a day.
The water lasts 900 ÷ 100 = 9 days.
So the tank lasts for 9 days.

Answer: 9 days

The water from the roof of the worked example, in a tank.

Farmers can grow other crops. Millet, sorghum and cassava need less water than many crops. Seeds that ripen in a shorter season, or that stand floods, are another choice. Farmers can also change the planting dates. They can spread the risk with more than one crop. A covering of straw or leaves keeps water in the soil.

On the coast, mangrove trees and reefs break the waves. Sea walls and raised houses keep the water out, and a family can move to higher ground. Storm warnings by radio and phone, with shelters that people know, have saved many lives in tropical storms. In hot places, shade trees, light coloured roofs and rest in the heat of the day protect health.

Governments, towns and families all have a part. In 2015 almost all the world’s countries made an agreement. They would try to hold the warming well below 2 °C above the late 1800s level, and aim for 1.5 °C. The places that have added least to the problem often face the most risk, so help in paying for adaptation matters.

Try it

How much water could your roof collect?

You need: a tape measure, or a stick of known length, or your own steps, a rain gauge reading from the earlier chapter, or a figure from the radio, paper and a pencil.

Be safe: Never climb on a roof to measure it. Measure from the ground. Keep stored water covered, so that mosquitoes cannot breed in it, and a child cannot fall in.

From the ground, measure the length and width of a roof. Walk along the wall below it. Do not walk on the roof. Do not climb on a roof.
Work out the area in m²: length × width, for the part that rain falls on, seen from above.
Take a rain figure in mm, from your rain gauge for one rainy day, or from a local figure for a month.
Multiply the area by the rain in mm. That is the water in litres that falls on the roof.

What you will see: A modest roof gives a lot of water from even one good rain. Rain tanks make this water available when the rain has stopped. You can compare the litres with what the family uses in a day.

If you cannot try it, this is what happens.

A wrong idea many people have

The Earth has already started to warm, so nothing we do now can matter.

Why it feels right: If some change cannot be undone, it seems there is no point in trying to change what is left.

The test that breaks it: Warming depends on the total amount of carbon dioxide put into the air. Each tonne less means a little less warming. The difference between a warming of 1.5 °C and one of 3 °C is a large difference in harm.

What is true: Every cut helps, and the sooner the better. Mitigation limits how much worse things get, and adaptation protects people from what is coming.

A wrong idea many people have

Planting trees is enough to solve climate change.

Why it feels right: Trees take in carbon dioxide, so it seems that planting enough of them would clear the air.

The test that breaks it: Trees do take in carbon dioxide, and it is very useful to protect forests and plant new ones. But burning fossil fuels puts far more into the air each year than new trees could take in. And a forest that burns or is cut down gives its carbon back.

What is true: Forests help, but cutting the burning of coal, oil and gas is needed as well. No single action is enough.

A wrong idea many people have

Wind and solar power give out no greenhouse gas at all.

Why it feels right: Nothing burns while the wind turns the blades or the sun shines on a panel.

The test that breaks it: Making steel, glass and panels, and building and moving the equipment, uses energy. Over its whole life, wind gives out about 11 g of carbon dioxide for each kWh and solar about 48 g. Coal gives out about 820 g.

What is true: Wind and solar give out very little compared with coal and gas, but not nothing.

Key words

mitigation: cutting greenhouse gas emissions, to slow the warming.
adaptation: changing how we live, to be safer from the changes that are coming.
net zero: the point where the carbon dioxide put into the air equals what is taken out.
energy efficiency: doing the same job with less energy.

Back to your guess

The answer is C: Two things: cut greenhouse gas emissions to slow the change, and adapt to the changes that will come anyway.

There are two kinds of response, and both are needed. Cutting emissions slows the warming. Adapting protects people from the changes that cannot now be avoided. Every tenth of a degree of warming that is avoided makes things easier to live with.

Keep it

Copy this into your exercise book.

Mitigation cuts emissions: clean power, less waste, better farming. Adaptation protects people: store water, new crops, coastal defences, warnings. Both are needed.

Draw: Two boxes side by side. One is titled mitigation, with three ways to cut emissions. One is titled adaptation, with three ways to cope.