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Challenges for the Planet

The causes, effects and responses to climate change
Learning objective – to study the causes and effects of climate change and how people have responded to the changes.

Learning outcomes

• To know how and why climate has changed since the last ice age. • To be able to discuss the causes of current climate change on a local and global scale.

• To know the negative effects that climate change is having on the environment and people.

• To be able to explain how people respond to climate change.

How has the world’s climate changed since the last ice age? The graph in Figure 1 shows the trend in the world’s temperature since the end of the last ice age, approximately 10,000 years ago. The temperature since that time has increased by 6°C. Within this general trend, however, there have been a number of fluctuations. After the last ice age the temperature rose rapidly for the following 2,000 years. Between 4,000 and 8,000 years ago there were two warm periods interrupted by a colder spell. Another warm spell happened between the years AD800 and AD1200, which was known as the medieval warm period. There then followed the Little Ice Age where temperatures were below the long-term average for 600 years, ending in the late 1800s. In the past 100 years the temperature has begun to rise steadily, with greater increases since the 1960s. The temperature is projected to increase much more rapidly in the coming years, being 5°C warmer in 2100 than it is now.

7 6 Temperature change (°C) 5 4 3 2 1

Warm periods

Projected temperature change

Cooler periods Rapidly rising temperatures End of last ice age

Medieval warm period

Little Ice Age

0 8000 7000 6000 5000 4000 3000 2000 1000 Years BC

0

1000 2000 3000 Years AD

Figure 1 A graph of the world’s temperature since 8000BC

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Unit 1 Geographical Skills and Challenges

Why has the world’s climate changed since the last ice age? The causes of long-term climate change can be either external, i.e. from space, or internal, from the ocean, land and atmosphere.

External factors

External factors which affect climate change
Solar output

Solar output

World’s climate

Orbital geometry

Internal This is energy that comes from the Sun. The factors energy that comes from the Sun changes over time. Measurements made in the 1980s showed that the total amount of solar energy reaching the Earth has decreased by 0.1 per Surface Change in Tectonic Volcanic activity reflection atmospheric gases activity cent. Although this is not much, if the trend Figure 2 The factors that affect the world’s climate continued for 100 years it could influence global climate. It has been predicted that a 1 per cent change in solar output could make the following year was unusually cold over much of the world with Europe having heavy snowfalls temperature rise or fall by between 0.5 and 1.0°C. It is thought that the activity of sunspots on the and frost throughout the summer; 1816 became known as ‘the year without a summer’. Sun’s surface affects solar output. There was a period of drastically reduced sunspot activity Surface reflection between 1645 and 1715 which might have been a During cooler periods when there is a larger cause of the Little Ice Age. amount of snow and ice on the Earth, global Orbital geometry temperature will drop due to the snow and ice reflecting sunlight back to space. If the planet Orbital characteristics that are responsible for past and possible future climatic changes include: warms up, snow and ice will diminish, and the Earth will continue to get warmer. 1 The shape of the Earth’s orbit around the Sun

varies from nearly circular to elliptical and back to circular again every 95,000 years. Cold, glacial periods have occurred when the Earth’s orbit is circular and warmer periods when it is more elliptical. 2 The tilt of the Earth’s axis varies over time from 21.5° and 24.5°. This variation occurs over a...
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