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Module 1: What Is Climate Change? A Comprehensive Guide To The Whats And The Whys.

Are you right at the beginning of your relationship with climate change? Then start from a firm foundation. In this module, you'll clarify what climate change is, understand what's causing it and review the evidence for how much the Earth's climate is changing. You'll get an introduction to the Greenhouse effect and the difference between global warming and climate change. By the end of this module, you'll have a solid base for the next steps ahead - deciding what you truly want for your future and what steps you need to take to get there.

What You’ll Learn In This Module

You’ll start by learning some climate change fundamentals:

What is Climate Change?

Climate change is a change in the earth’s usual pattern of weather, plus any related changes in its land surfaces, ice sheets and oceans.

It includes average rainfall, the amount of cloud, humidity, pressure, wind…

It also includes how often extreme events occur, such as heat waves.

Climate change is a shift in these ‘usual’, average, conditions.

In the past, our climates took hundreds or even thousands of years to change. But climate change today is occurring at a much, much faster rate.

Scientists have been studying and predicting future climate change for the last 40 years.

They have used:

  • Satellite measurements since the 1970s;
  • Thermometer readings since the 1850s;
  • Natural indications from tree rings, corals, stalagmites and stalactites covering thousands of years;
  • Air samples trapped in the polar ice cores covering hundreds of thousands of years;  
  • And ocean sediments covering millions of years.

All of this evidence shows that the temperature of the earth has followed an upward trend, especially since the 1950s.

The temperature of the earth is now about 1.2 degrees centigrade warmer than it was in the 1800s.

This might not sound like much. When you’re outside, you probably can’t detect the difference, for example, between 20 and 21 degrees centigrade.

But when this is just the average increase, which affects the entire planet, it can have very relevant consequences.

Recently, and for the first time, you can start to see the impact of climate change yourself.

Examples include more frequent and violent storms, greater floods, extreme heat waves, forest fires and sea-level rise.

What is the difference between global warming and climate change?

Global warming refers to a rise in the average global temperature as a result of human activities.

Climate change refers to this increase plus other changes in the earth’s usual pattern of weather and any related changes in its land surfaces, ice sheets and oceans.

In other words, although the terms are often used interchangeably, global warming is only one dimension of climate change.

What is causing the Earth’s climate to change?

Scientists have shown that the climate is changing due to one simple fact: The world is getting hotter because of a high and increasing level of greenhouse gases in the atmosphere – a direct result of human activity.

Since the industrial revolution, mankind has been burning fossil fuels such as coal, oil and gas.

We use them for just about everything we do.

For example, to power energy generation, to heat our homes, to make things in our factories and to power our cars, trains, planes and ships to travel and transport things around the world.

These actions produce greenhouse gases, such as Carbon Dioxide (CO2), as a waste product.

These gases are released into the atmosphere, where they collect over time.

They act like a blanket, trapping heat radiation from the earth’s surface and keeping the earth warmer than it otherwise would have been, causing global warming.

Before we started to burn coal, the amount of Carbon Dioxide in the atmosphere was around 280 parts per million. Now it’s over 400 parts per million.

Why does more Carbon Dioxide in the air lead to climate change?

Carbon Dioxide leads to global climate change through what is now called ‘the greenhouse effect’.

Back in 1856, Eunice Newton Foote, an American scientist, inventor, and women’s rights campaigner ran experiments showing that changes in Carbon Dioxide in the atmosphere could affect the Earth’s temperature.

Later in 1859, John Tyndall, a prominent Irish physicist, made the same discovery.

Certain gases, called greenhouse gases, have the effect of trapping the sun’s heat, rather like a blanket, or the glass in a greenhouse.

Light from the sun flows into the earth’s atmosphere. This solar radiation warms up the surface of the earth.

Part of that heat is then radiated back towards space, but certain gases in the atmosphere prevent it from fully leaking out.

Instead, the heat lingers in the atmosphere longer, and the earth’s environment holds more heat, rather than it just bouncing back into space. 

How the global temperature rises

We need this effect to a point. Without an atmosphere with a greenhouse effect, the surface of the Earth would be too cold (about 30°C cooler).

But mankind has been releasing enormous amounts of greenhouse gases into the atmosphere, by burning fossil fuels (coal, oil and gas), cutting down forests (which release carbon when they decompose or are burned) and farming livestock (which produce another greenhouse gas – methane).

As a result, the amount of these gases in the atmosphere is much higher than ever before and the earth is heating up too much.

What evidence is there for climate change? How much is Earth’s climate changing right now?

Evidence of global climate change today is huge.

1. Top of the list, the amount of greenhouse gases in the atmosphere is increasing.

At over 400 parts per million, the level of Carbon Dioxide in the atmosphere is the highest it’s ever been.

Take a look at the graph below from NASA’s website.

The level of Carbon Dioxide in the Earth’s Atmosphere (in parts per million), Image from NASA’s website

It compares the levels of atmospheric Carbon Dioxide for thousands and thousands of years. These were collected from samples of atmosphere stored in ice cores.

The graph shows that despite many ups and downs, the level of Carbon Dioxide was always below 300 parts per million until the 1950s. Now it stands far above that level.

In other words, over at least the last 800,000 years, the concentration of carbon dioxide in the atmosphere has never been as high as it is now.

At the same time, greenhouse gas emissions continue to increase as humans continue to burn fossil fuels.

2. Temperatures are rising.

There has been a rise in the Earth’s average surface temperature by 2.1 degrees Fahrenheit or 1.18 degrees Celsius since the late 1800s.

Using thermometer readings covering the entire planet, scientists have reconstructed global temperatures back to about 1850.

Global average temperature change, image from the Climate Change Committee, UK

Take a look at the chart above from the Climate Change Committee in the UK.

One line represents one year, with the blue colours showing cold years and the red lines showing hot years.

Starting in 1860, until the 1920s we see many cold years.

Moving to the right on the chart and forward through time up to the present day, the stripes get redder and darker.

This means that the planet is warming up.

Most of the global increase in temperatures has taken place in the past 40 years and especially in the last 7 years.

The period 2011 to 2020 was the warmest decade ever recorded.

The years 2016 and 2020 were the warmest ever measured on earth.

The globe is warming at an increasing rate. The average temperature rise is currently 0.2 degrees Celsius per decade.

These warmer temperatures are being experienced everywhere. In every country, and over the oceans as well.

If we add more greenhouse gases to the atmosphere it will continue to warm up. Scientists say that they are certain of this.

3. There are many more extreme weather events.

Our weather is changing significantly.

A warmer planet is changing the global climate, resulting in more frequent record high temperatures, and more intense and frequent heat waves.

These are drying out the soil, resulting in more frequent and worse droughts and wildfires.

A warmer earth means that more moisture evaporates off the oceans into the air and more moisture in the air results in more rainfall.

Episodes of intense rain, flooding, tropic storms and hurricanes have been increasing.

4. The evidence for climate change also extends far beyond the weather.

Oceans are warming up alongside the temperature rise in the global climate.

  • The top 100 meters of the ocean have warmed more than 0.6 degrees Fahrenheit, or 0.33 degrees Celsius in the last 50 years.

Ice sheets and glaciers are melting and there is less snow.

  • The polar ice sheets in Greenland and the Antarctic are shrinking, while the Antarctic was expected to expand.
  • NASA estimates that Greenland lost an average of 279 billion tons of ice each year between 1993 and 2019. It’s now losing ice 5 times faster than 25 years ago.
  • Antarctica lost about 148 billion tons of ice each year between 1993 and 2019. It’s now losing ice at a rate 3 times faster than 25 years ago.
  • Sea ice in the arctic ocean has been melting in summer more than it refreezes in winter.
  • Glaciers are also melting the world over, including in the highest mountain ranges such as the Alps, Himalayas, Andes and Rockies.
  • Records show that less snow has been falling in Spring over the last 50 years and the snow that does fall is melting earlier.

Sea levels are rising.

  • Sea levels were stable for several thousand years. But in the last century, global sea levels have risen 8 inches or 20 centimetres. The sea level increases have been higher for some individual developing countries.
  • The rate of increase in the last 20 years was nearly twice that in the previous century.
  • The current rate of increase is doubling every year.

The ocean is becoming more acidic.

  • The surface waters of the ocean have become 30% more acidic since the beginning of the industrial revolution.
  • This is because the ocean has absorbed 20-30% of the greenhouse gas emissions released by human activity into the atmosphere.

What do these changes in the climate system mean for you? Get clear on the Consequences of Climate Change.