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Module 1: Climate Change Explained


It is easy to think that the world we live in is unchanging and that conditions on our planet, so hospitable to life, are stable. But over the past 2.6 million years Earth has undergone extreme changes. There have been ice ages and phases of relatively warm temperatures. At times, Britain has had a climate hot enough for animals like hippos and rhinos to live here and cold enough for giant woolly mammoths.Flood-Polaroid3

A number of factors have caused these dramatic changes to the climate. Temperatures have fluctuated because of variations in the strength of the sun, the Earth’s orbit, or the amount of greenhouse gases in the atmosphere. However, until now, global changes have occurred slowly, over thousands or millions of years.

Today, by comparison, our climate is changing very quickly. Scientists are now concerned that naturally-occurring changes are being overtaken by a rapid global warming caused by human activity. They believe this has serious implications for the stability of the planet’s climate and this in turn will have a dramatic effect on the lives of us all.

What is the evidence for climate change?

‘Climate scientists agree: climate change is happening here and now. Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening. This agreement is documented not by a single study but by a converging stream of evidence over the past two decades from surveys of scientists, content analyses of peer reviewed studies and public statements issued by virtually every membership organisation of experts in this field’

Report by the American Association for the Advancement of Science, 2014

When scientists talk about global climate change, one of the most important trends that they look at is the average temperature of the Earth. NASA (The National Aeronautics and Space Administration) conducts scientific research into Earth as well as the solar system and universe. It uses many thousands of temperature measurements each day taken across the globe, on land and at sea. These measurements from around the world show a clear, long- term, global warming trend.

Below is a visualization NASA have created to illustrate this. It shows the temperature changes from 1880, when modern record-keeping began, to 2015. Orange colours represent temperatures that are warmer than average, and blues represent temperatures cooler than average.

Watch the video.

Earth’s Long-Term Warming Trend, 1880-2015

Below is the same information about Earth’s long term warming trend in the form of a graph.


This graph shows 3 key pieces of information:

  1. Since 1880, the global average surface temperature has risen about 1.0 degree centigrade. 1.0 degree may not sound like a lot but it’s unusual in our planet’s recent history. Earth’s climate record is preserved in tree rings, ice cores, and coral reefs. It shows that the global average temperature is stable over long periods of time. Small changes in temperature correspond to enormous changes in the environment. For example, towards the end of the last ice age, average temperatures were only 5 degrees cooler than today.(1)
  2. 15 of the 16 warmest years on record have occurred in this century. If you look again at the graph, you can see that the global temperature starts to rise much more steeply towards the end of the 20th century through to now. Experts warn that the record-breaking temperatures of this century show the pace of global warming is speeding up and driving the world’s climate into uncharted territory.
  3. 2015 was the hottest year ever recorded. Read the NASA press release here and how it was reported on the BBC website and Guardian newspaper.

ASA, NOAA Analyses Reveal Record-Shattering Global Warm Temperatures in 2015

Climate change: 2015 ‘shattered’ global temperature record by wide margin

Record hot 2015 gave us a glimpse at the future of global warming

An exceptionally hot year, 2015 shattered records, but will just be the norm in 15 years’ time

Scientists don’t believe that the record-breaking temperature recorded in 2015 is a freak occurrence. The Met Office expects 2016 to be even hotter. This means the global temperature records will have been broken for three years running, indicating a very worrying trend. (2)

What is causing climate change?

Evidence for climate change abounds, from the top of the atmosphere to the depth of the oceans. Scientists and engineers from around the world have meticulously collected this evidence, using satellites and networks of weather balloons, observing and measuring changes in location and behaviours of species and functioning of ecosystems. Taken together, this evidence tells an unambiguous story: the planet is warming, and over the half century, this warming has been driven primarily by human activity.

U.S Global Change Research Program, Third National Climate Assessment, May 2014 – Overview and Report Findings, p.7

Climate change refers to the broader set of changes that are happening as a consequence of global warming. These include changes to the weather patterns, oceans, ice and snow, and ecosystems. The cause of global warming is the increase in heat-trapping gases in the atmosphere. These heat-trapping gases are called ‘greenhouse gases’. They exist naturally in the atmosphere, where they help keep the Earth warm enough for plants, animals and human beings to live. But we are adding extra greenhouse gases to the atmosphere and this has been happening dramatically since the Industrial Revolution. These extra gases are causing the Earth to get warmer.

The main way we increase this ‘greenhouse effect’ is through burning fossil fuels like coal, oil, and gas. We use these fossil fuels for energy in our manufacturing industries and to do everyday activities like driving cars, heating buildings, making electricity. Burning these fossil fuels causes even more greenhouse gases to build up in the atmosphere. These in turn cause the Earth to trap extra heat, causing the planet to get warmer.


As you can see from the chart, at the moment, carbon dioxide (CO2) is the principal heat trapping greenhouse gas. Most man-made emissions of carbon dioxide are through the burning of fossil fuels, as well as through cutting down carbon-absorbing forests. Trees and plants absorb carbon dioxide and release oxygen so play an important role in lowering greenhouse gas emissions.

This animation uses narration and illustrations to explain the Earth’s carbon cycle and how it is connected to climate change. Watch the video.

The Carbon Cycle

Since the Industrial Revolution began in 1750, CO2 levels have risen by more than 30%. The concentration of CO2 in the atmosphere is now higher than at any time in at least 800,000 years.

Click on the play button to see NASA’s visualisation of how carbon dioxide travels around the globe. Notice how the highest concentrations of COare found in the Northern hemisphere and the effects of plants and trees on CO2 levels in the spring and summer months.

NASA | A Year in the Life of Earth’s CO2 

Other greenhouse gases such as methane and nitrous oxide are also released through human activities, but at the moment the amount is small compared with carbon dioxide. However many scientists are getting more concerned about the role of methane in global warming. According to recent research by US scientist, Dr Robert Howarth, methane is a hundred times more powerful as a heat-trapping gas, although it stays in the atmosphere for a shorter period of time compared to carbon dioxide. Domestic livestock, like cattle, produce large amounts of methane as part of their natural digestive process. It’s also generated from industry, landfill sites and significant amounts from the gas industry, particularly from shale gas fracking.

What is the impact of climate change?

The effects of climate change impact differently across countries and regions of the world. There are also effects that are measurable now and those that are predicted in the near and distant future.

To begin with we can look at the effects that have already been measured by scientific studies around the world. The Intergovernmental Panel on Climate Change, also known as the IPCC, is the leading international body on climate change. It was set up by the United Nations in 1988. Since then, the IPCC has been reviewing and assessing scientific, technical and socio-economic information worldwide relevant to the understanding of climate change.

Here is a summary of some key findings in its 5th report published in 2014.(3) 

  1. Climate change is happening. ‘The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen’.
  1. ‘Human influence on the climate system is clear and recent….emissions of greenhouse gases are the highest in history’.
  1. ‘Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease’.
  1. Much of recent warming has been in the ocean. ‘The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation’. This means warmer, expanding oceans which cause stronger storms, rising sea levels and eroding coastlines.
  1. The oceans are becoming more acidic and will continue to do so through absorbing so much extra carbon. This is already affecting marine life and its effects will become increasingly severe‘.
  1. ‘Heat waves will occur more often and last longer’ … Extreme rainfall and flooding events will become more intense and frequent in many regions. ‘The ocean will continue to warm and acidify, and global mean sea level to rise’.
  1. ‘Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.’
  1. Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped.

The conclusions of this report are alarming but the effects of climate change are probably far worse than outlined. To begin with, the IPCC takes a very cautious approach when publishing its conclusions.(4) In addition, the scientific information in the 2014 report was all published before March 2013. Since then we know we have had two record-shattering hottest years ever in 2014 and 2015.

How will climate change affect us?

It is hard to accurately predict the actual scale of the potential impacts of climate change on humans but the following scenarios are likely.

The frequency of extreme weather events will continue to rise bringing increased deaths from floods, storms, heat waves and droughts. It will also mean potential food and freshwater shortages. Global conflicts over diminishing resources could increase.

Scientists forecast more rainfall overall, although inland areas, during hot summers, will be at increasing risk of droughts. More flooding is expected from storms and rising sea levels making it particularly dangerous for people living near the coast or low lying areas including major cities like New York, Mumbai, Shanghai, London. Some islands may disappear.

Poorer countries will probably suffer the most because they are least equipped to deal with rapid change and are often more dependent on agriculture which is vulnerable to extreme weather events.

Plants are experiencing earlier flowering and fruiting times and there are changes in the territories (or ranges) occupied by animals. Plant and animal extinctions are predicted as habitats change faster than species can adapt.

The health of millions of people could be threatened by increases in malaria, water-borne diseases and malnutrition.

The on-going process of acidification of the oceans as they absorb more CO2 will increasingly endanger marine life and fragile eco systems like coral reefs. This could ultimately make the oceans a dead zone.

Climate change could cause the largest refugee crisis the world has seen and the mass migration of people suffering the worst effects of drought, food shortages, floods etc.

Meanwhile, our planet must carry on supplying us – and all living things – with air, water, food and safe places to live. If we don’t act now, climate change will rapidly alter the lands and waters we all depend upon for survival, leaving us and future generations in a very different world.

Click on the video below to hear Professor Kevin Anderson discuss a wide range of issues relating to climate change and its social implications. He is the Deputy Director of the Tyndall Centre on Climate Change and a leading UK scientist.

Professor Kevin Anderson ‘Impacts of Climate Change’

Reference and links to further reading

  1. How is Today’s Warming Different from the Past?
  3. IPCC 2014 Report

Click here to test your understanding