Climate Change banner against puttering cooling tower

Module 1: Climate Change Explained


In this Module, we look at the evidence of climate change, its causes and consequences. 

On Sunday 1st September 2019, Hurricane Dorian made landfall over the Bahamas, then stayed where it was. It was the nation’s strongest hurricane on record. ‘Category 5’ winds of up to 185mph obliterated entire neighbourhoods and triggered a humanitarian crisis. Mia Mottley, the Prime Minister of Barbados, spoke about her thoughts on Hurricane Dorian’s links to the climate crisis. She did not pull her punches:

‘We are on the frontline of the consequences of climate change but we don’t cause it. And the vulnerability that attaches therefore to us is a matter we’re trying to get the international community to deal with consistently.’

Photo: Navy Live

Until now, global changes to the Earth’s climate have occurred slowly, over thousands or millions of years. It is easy to think that the conditions on our planet, so hospitable to life, are stable. But over the past 2.6 million years Earth has undergone dramatic but naturally-occurring 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.

A number of factors have influenced these changes to the climate in times gone by. Temperatures have fluctuated because of variations in the strength of the Sun, the Earth’s orbit, or the amount of naturally-occurring greenhouse gases in the atmosphere.  

But today, by comparison, our climate is changing very quickly. Scientists are now concerned that naturally-occurring changes are being overtaken by rapid global warming caused by human activity. The main causes of concern are carbon gas emissions from burning fossil fuels – coal, oil, petrol, diesel and gas – and the destruction of our forests. Forest absorb carbon gas emissions. But they are either being cut down deliberately, as in the Amazon or lost as a consequence of growing numbers of wildfires. Scientists 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. In the United States, 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

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

Here is the same information about Earth’s long term warming trend in the form of an animated graph.

Credit: NASA’s Earth Observatory

All five temperature records show peaks and valleys in sync with each other. All show rapid warming in the past few decades. All show the past decade has been the warmest. 

This graph shows 2 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 highly 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. 18 of the 19 warmest years all have occurred since 2001, with the exception of 1998. 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.

Read the Carbon Brief assessment for 2019 here.

July 2019 was the hottest month on record

2016 was the hottest year ever recorded


Melting polar ice

Photo: Christine Zenino

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA show Greenland lost an average of 286 billion tons of ice per year between 1993 and 2016. Antarctica lost about 127 billion tons of ice per year during the same time period. The rate of Antarctica ice mass loss has tripled in the last decade.

Scientists don’t believe that the record-breaking temperature recorded in 2016 is a freak occurrence. The Met Office expects future years 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 more and more 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.

Hopes that global CO2 emissions might be nearing a peak were frustrated by evidence that output from fossil fuels and industry grew by around 2.7% in 2018. This is the largest increase in seven years, almost 35.5 billion tonnes of carbon gases.

Source: Carbon Brief

The main way we increase this ‘greenhouse effect’ is through burning fossil fuels – coal, petrol and diesel fuel, oil, and gas. We use these fossil fuels for electric power supply, energy in our manufacturing industries, everyday activities like driving cars, heating buildings, flying. 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 from burning of fossil fuels and 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. 

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 CO2 are found in the Northern hemisphere and the effects of plants and trees on CO2 levels in the spring and summer months.

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

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

Another greenhouse gas, methane, also known as ‘natural gas’ sourced from, for example, North Sea oil wells and fracking, is also released through human activities. There is growing concern 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. And methane is also released from rotting vegetation beneath melting ice on land

What are the impacts 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. . In 1988, the United Nations set up the Intergovernmental Panel on Climate Change, also known as the IPCC. It is the leading international body on climate change. 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.

A dozen years left for 1.5 degrees of global warming 


In October 2108, a new IPCC report warned there is only a dozen years for global warming to be kept to a maximum of 1.5C. Beyond this, even half a degree will significantly worsen the risks of drought, floods, extreme heat and poverty for hundreds of millions of people.

The authors of the landmark report by  the IPCC say urgen say urgent and unprecedented changes are needed to reach the target. Action is still affordable and feasible, they say. It’s clearly up to us all to take the necessary steps. If we do, it may still be possible to meet the Paris agreement pledge to keep temperatures between 1.5C and 2C. 

See summary of report here.

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.

Watch 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’

Human and ecosystem impacts of climate change

  • The health of millions of people could be threatened by increases in malaria, heat exhaustion, water-borne diseases and malnutrition.
  • 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. 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 will disappear.
  • Poorer countries will 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 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. There are already hundreds of ‘dead zones’ across the world’s oceans. The Gulf of Mexico dead zone is 9,000 square miles in size.
  • 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.