© Boardworks Ltd 2009 1 of 32 Climate Change Evidence Climate Change.

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Contents

Teacher’s notes included in the Notes Page

Flash activity (these activities are not editable) Web addresses Printable activity

Extension activity

Icons:

Climate and climate change

The greenhouse effect

Long- and medium-term evidence for past climate change

Short-term evidence for the impact of humans on climate

Climate change sceptics


Key questions: Climate and climate changeClimate and climate change

What is climate?

Where are the world’s main climate zones?

What is climate change?

Whether climate change is a natural process?

By the end of this chapter you should have considered these key themes and questions:


Climate

What is climate?

It is the average atmospheric conditions of a region recorded over at least a 30 year period.

The global climate system is the result of complex links between the atmosphere, the oceans, the ice sheets, the soils and rocks, and living organisms.

Arid & semi-aridTropical

Polar

Warm temperateCold temperate


Climate zones


Is climate change a natural process?

Even a small change to the physical conditions of the ocean, atmosphere or ice caps can result in climate change.

What are the natural forcing agents of climate change?

Climate change is caused by climate forcing agents, a term used to describe causal factors.

The earth’s climate has changed naturally throughout its 4.5 billion year history.

Climate change is any significant change in the expected patterns of average weather for a region or for the whole earth.


Natural causes of climate change


Key questions:

The greenhouse

effectThe greenhouse effect

What are greenhouse gases?

What is the greenhouse effect?

What is the enhanced greenhouse effect?

What are the human causes of the enhanced greenhouse effect?



Greenhouse gases


The greenhouse effect


The enhanced greenhouse effect

What is enhancing the greenhouse effect?

The increase in the natural greenhouse effect is said to be a result of human activities.

It is also known as global warming. The quantities of several greenhouse gases in the atmosphere have increased since the Industrial Revolution and most researchers believe that this is leading to increasing global temperatures.


Causes and effects

Which human activities can you identify? How do they contribute to the enhanced greenhouse effect?


Key questions: Long- and medium-term evidence for past climate change

Long- and medium-term evidence for past climate change

Why is it important to know what climate was like in the past?

What evidence can be used to find out how climate has changed over many thousands or million years?

What evidence can be used to find out how climate has changed in the last few thousand years?



Climate change and the past

Records of past climate change provide a background against which our climate today can be compared.

Because long- and medium-term records show us what the climate was like before the Industrial Revolution, we can see what effect human activities have had in recent times.

Why is it important to know what climate was like in the past?

Using this information it is possible to see if climate change is within a ‘normal’ or ‘natural’ range.


Long-term evidence


What do ice cores tell us?


Medium-term evidence

What medium-term evidence can be used to reconstruct climate?

Historical records: Records of weather conditions include cave paintings, letters and diary entries, scientific writings and early instrumental records.

Tree rings (dendrochronology): The width between tree rings can be used to reconstruct past climate because tree ring growth is affected by moisture and temperature.

Examples include:


Reconstructing past climate


The Little Ice Age was a period starting around 1500 and lasting a few centuries. Global average temperatures fell and glacial expansion took place.

The Little Ice Age

Evidence is in the form of environmental records like ice cores, tree rings and lake sediments. They show that the Little Ice Age consisted of two main cold stages of about a century's length in the seventeenth and nineteenth centuries.

What evidence is there for this period of climate change?

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Key questions: Short-term evidence for the impact of humans on climateShort-term evidence for the

impact of humans on climate

What short-term evidence is there for recent climate change?

How does the evidence show that humans are responsible for the climate change we are experiencing?



Natural or unnatural?

What evidence shows climate change is happening today?

global temperature changes ice cap meltingspecies distribution changes extreme weather

Long- and medium-term evidence shows that climate change has occurred naturally throughout earth’s history.

Short-term evidence suggests that the earth is warming faster than in the past and this is the result of human actions.

Today however, many people argue that climate change is no longer a totally natural process.


Temperature changes

Over the last 150 years global temperatures have risen by about 0.75°C.

The Intergovernmental Panel on Climate Change (IPCC) predict an increase in global temperature of between 1.1°C and 6°C by 2100.

What does the graph show about recent climate change?

Why would the upward trend suggest recent climate change is predominantly caused by human activity?


Glaciers; going, going…

Glaciers are shrinking all over the globe. Negative mass balance trends have been observed in the Alps, Himalayas, Rockies, Andes, Cascades, Greenland and Antarctica.

What does the term mass balance mean?

It is the relationship between accumulation of snow and ice, and ablation (melting and sublimation) of a glacier. A negative balance means that there is more ablation than accumulation and the glacier is getting smaller.


Greenland glacier retreat

Since 1992 in Greenland:

Temperatures are 3–5°C higher

Ice is melting faster than it can accumulate

Glaciers are moving towards the sea more quickly.

Using the image’s scale, estimate how far the glacier has retreated since 1851.


Extreme weather

What trends does this graph show?

As global warming causes sea surface temperatures to rise, it is thought by some that this is causing an increase in hurricane frequency and intensity.

Overall hurricane frequency in the Atlantic has increased since the beginning of the 20th century.


Shifting species

Before 1989 the little egret was very rarely seen in the UK. Rising temperatures have allowed the bird, previously found only in wetlands in southern Europe and Africa, to move northward and expand its range.

The Polygonia comma butterfly is spreading north in the USA at a rate of 10 km per year which indicates that temperatures are increasing.

What effect is temperature change having on species distributions?


Key questions: Climate change sceptics


What opinions do climate change sceptics hold?

What weaknesses are there for different types of climate change data?



Weighing up the evidence

Most people agree that there is undeniable evidence to show the global warming we are experiencing today is above natural levels and is caused by humans enhancing the greenhouse effect.

However, there are some people who are sceptical. They do not agree that human actions fully explain climate change.

What do you think? Do you feel there is overwhelming evidence for anthropogenic climate

change? Or are you a sceptic?


Evidence criticisms


Summary quiz


Glossary

© Boardworks Ltd 2009 1 of 32 Climate Change Evidence Climate Change.

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