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.

During the period of human civilization, changes to the Earth’s climate have occurred slowly, so 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, our climate is changing very quickly. Scientists have identified 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. Forests 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. This creates a vicious cycle of detrimental impacts and  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.

This graph from NASA shows how rapidly greenhouse gas emissions have risen since industrialisation.

Evidence | Facts – Climate Change- Vital Signs of the Planet (

Evidence | Facts – Climate Change: Vital Signs of the Planet (

What is the evidence for climate change?

As early as 2014 it was possible to say that ‘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.

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 visualisation 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.

SVS: Global Temperature Anomalies from 1880 to 2021 (

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.

A World of Agreement: Temperatures Are Rising – Climate Change: Vital Signs of the Planet (

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

  1. Since 1880, the global average surface temperature has risen about 1.0 – 1.1 degree centigrade. This 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 have all 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 and on 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 Climate Brief assessment for 2021 here. State of the climate: How the world warmed in 2021 – Carbon Brief

2021 was the 45th consecutive year (since 1977) with global temperatures rising above the 20th-century average.

2016 was the hottest year on record and Scientists don’t believe that this is a freak occurrence. The Met Office expects future years to be even hotter, and the ten hottest years on record have all been in the twenty-first century. Top 10 Warmest Years on Record | Climate Central

Melting polar ice

 The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA showGreenland had an average 268 billion metric tonnes a year between 2002 and 2020, while Antarctica lost 149 billion metric tonnes per year. The rate of Antarctica ice mass loss has tripled in the last decade.

This can be seen here

Annual Arctic Sea Ice Minimum 1979-2021 with Area Graph – YouTube

And here,

Antarctic Ice Mass Loss 2002-2020 – YouTube

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.

Although the rate of increase has slowed from 1.1% a year for the decade from 2010 – 2020, down from 2.5% a year between 2000 and 2010, output from fossil fuels and industry still grew by around 1.0% in 2022; almost 36.6 billion tonnes of carbon gases.

Analysis: Global CO2 emissions from fossil fuels hit record high in 2022 – 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, or 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.

Greenhouse Gas Emissions by TypeAs 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. The world’s largest concentrations of methane are in frozen soil in the arctic and the more this soil thaws and ice retreats the more will be released.

What are the impacts of climate change?

The effects of climate change impact differently across countries and regions of the world.Although it is the Global North that produces the majority of CO2 emissions (see NASA visualisation above), it is the Global South whose ecology and climate is most profoundly affected. 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. Since 1988, 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 six key findings in its latest report published in 2022.(3)

1.    Climate impacts are already more widespread and severe than expected.

Withering droughts, extreme heat and record floods already threaten food security and livelihoods for millions of people. Since 2008, devastating floods and storms have forced more than 20 million people from their homes each year. Since 1961, crop productivity growth in Africa has shrunk by a third due to climate change. 

Today, half the global population faces water insecurity at least one month per year. Wildfires are scorching larger areas than ever before in many regions, leading to irreversible changes to the landscape, so, for many, climate catastrophe is not ‘coming’, it is already here.

2. We are locked into even worse impacts from climate change in the near-term.

Current emissions trends will make some very significant climate impacts unavoidable through 2040. The IPCC estimates that in the next decade alone, climate change will drive 32-132 million more people into extreme poverty. Global warming will jeopardise food security, as well as increase the incidence of heat-related mortality, heart disease and mental health challenges. This will also displace many people, exacerbating a climate refugee crisis.


A recent study published in Nature Sustainability shows that on the current trajectory of global heating, unless urgent action is taken now, 2 billion people will be living in areas with an annual average temperature of 29C by 2030, including almost half the population of India. This is outside the climate niche of 13 -25C that human societies need to thrive.

3. Risks will escalate quickly with higher temperatures, often causing irreversible impacts of climate change.

Every tenth of a degree of additional warming will escalate threats to people, species and ecosystems. Overshooting 1.5 degrees C increases the probability of high-impact events, such as mass forest dieback, which would turn critical carbon sinks into carbon sources.

The IPCC projects that these risks will compound one another as multiple hazards occur at the same time and in the same regions.

4. Inequity, conflict and development challenges heighten vulnerability to climate risks.  

As of now, 3.3 billion-3.6 billion people live in countries highly vulnerable to climate impacts, with global hotspots concentrated in Small Island Developing States, the Arctic, South Asia, Central and South America, and much of sub-Saharan Africa.

5. Adaptation is crucial. Feasible solutions already exist, but more support must reach vulnerable communities.

The IPCC estimates that adaptation needs will reach $127 billion and $295 billion per year for developing countries by 2030 and 2050, respectively. Existing adaptation options can reduce climate risks if they’re sufficiently funded and implemented more quickly. The 2022 IPCC report proposes three key measures; 

  • Social programs that improve equity and justice, like reconfiguring social protection programs (such as cash transfers, public works programs and social safety nets) to include adaptation while improving access to clean water, sanitation and healthcare.
  • Ecosystem-based adaptation like integrating trees into farms, increasing crop diversity and planting trees in pastures, and
  • New technologies and infrastructure coupling nature-based solutions with engineered options and access to better technologies, such as more resilient crop varieties, improved livestock breeding, or solar and wind power.

6. Some impacts of climate change are already too severe to adapt to. We need action now to address losses and damages.

With the 1.1 degrees C of global warming the world is already experiencing, some highly vulnerable people and ecosystems are beginning to reach the limits of what they can adapt to.

In some regions, these limits are “soft” — effective adaptation measures exist, but political, economic and social challenges hinder implementation, such as limited access to finance.

 But in others, people and ecosystems already face or are fast approaching “hard” limits to adaptation, where climate impacts are so severe that no existing adaptation measures can effectively prevent losses and damages. For instance, some coastal communities in the tropics have lost entire coral reef ecosystems that once helped sustain their food security and livelihoods. Others have had to abandon low-lying neighbourhoods and cultural sites as sea levels rise.

The agreement at COP27 in November 2022 to set up a Loss and Damage facility is a breakthrough, but funding will have to be negotiated and agreed by COP 28.

2030 deadline for 1.5 degrees of global warming

Climate Change Kills Me Banner


The science is unequivocal: Climate change endangers the well-being of people and the planet. Delayed action risks triggering impacts of climate change so catastrophic our world will become unrecognisable.

The next few years offer a narrow window to realise a sustainable, livable future for all. Changing course will require immediate, ambitious and concerted efforts to slash emissions, build resilience, conserve ecosystems, and dramatically increase finance for adaptation and addressing loss and damage.

See summary of IPCC 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. This film was from 2017, but it’s disturbingly accurate in its predictions.

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.

Reference and links to further reading