- Science: Explained
Why does the climate change?
The Earth’s climate has changed naturally for billions of years, but human emissions are rewriting the story.
Scientists know that the Earth’s climate has always changed by itself, even before humans existed.
The climate changed in a pattern for the past 800,000 years. Every 100,000 years, the Earth entered a warm period, called an “interglacial”, lasting 15,000-20,000 years. Between these periods, ice ages called “glacials” dominated.
Changes to the climate that caused these glacials and interglacials in the past can be explained by natural forcings. These are forces that act upon Earth’s climate, causing a change in how energy flows through it e.g., greenhouse gases.
What are some natural forcings?
1. Milankovitch Cycles
Milutin Milankovitch, a mathematician, discovered three “Milankovitch” cycles.
Over the past 800,000 years, these were the dominant causes of climate variability because they affect the amount of solar heat that can reach the Earth’s surface.
Eccentricity occurs every 100,000 years, corresponding with interglacials. Sometimes Earth’s elliptical orbit is more circular, which keeps the Earth at an equal distance from the Sun. When the orbit is more elliptical, Earth’s distance from the Sun changes. When Earth is closer, the climate is warmer.
Obliquity, Earth’s axial tilt, changes between 22.1° to 24.5° every 41,000 years. Larger angles cause warmer summers and colder winters.
Every 19,000 – 24,000 years, Precession impacts seasonal contrasts between the hemispheres and the timing of seasons. The Earth wobbles on its axis due to the gravitational pull of the Sun and moon, changing where the North Pole points.
2. Sunspots
Every 11 years, the Sun gets spots when its magnetic field increases. The temperature is lowered in this area, influencing the amount of solar radiation warming Earth.
3. Changes in Ocean currents
Ocean currents carry heat around the Earth. When the Ocean absorbs more heat from the atmosphere, sea surface temperatures increase, and Ocean circulation patterns change. Different areas become colder or warmer.
Because the Ocean stores a lot of heat, small changes can have massive effects on the global climate. A warmer Ocean can’t absorb as much carbon dioxide (CO2) and will evaporate more water vapour. Both contribute to the greenhouse effect and global warming.
4. Volcanic eruptions
Volcanoes spew out sulphur dioxide and ash, which blocks solar radiation and cools the atmosphere. CO2 released in the eruption eventually overpowers this to increase temperatures, but this is only equivalent to 1% of human emissions.
5. Meteorite and Asteroid impacts
66 million years ago, an asteroid hit the Earth on Mexico’s Yucatán Peninsula. Scientists call this the Chicxulub Impact, and it drove the extinction that killed 60% of all species, including all non-flying dinosaurs.
Lots of sulphur, soot and dust entered the atmosphere, blocking out the Sun. Temperatures plummeted 15°C, causing a 15-year winter.
Some climate change and emissions are unavoidable.
But natural forcings are too gradual or irregular to cause current climate change.
The Intergovernmental Panel on Climate Change (IPCC) states “the observed widespread warming of the atmosphere and Ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past fifty years can be explained without external forcing, and very likely that it is not due to known natural causes alone”.
Just right or too hot?
Greenhouse gases are natural, to an extent.
Some solar radiation passes through the atmosphere, hitting the Earth. Most of this is reflected into space, but some is absorbed by greenhouse gases and re-directed back to Earth.
This keeps Earth just right (Earth is called the “Goldilocks” planet!).
People are emitting too many greenhouse gases, too quickly. Therefore, more heat is trapped in the atmosphere, leading to global warming.
How are people causing climate change?
“External forcings” are things we’re doing that release extra greenhouse gases.
1. Power
We burn fossil fuels like coal, oil and gas to make electricity and heat. This releases carbon dioxide and nitrous oxide to the atmosphere. Half of this electricity powers our buildings.
Globally, only about ¼ of our electricity comes from wind, solar and other renewable sources.
Some people use more power than others: the richest 1% of the global population combined account for more greenhouse gases than the poorest 50%.
2. Food and Manufacturing
To make goods like steel and plastic, fossil fuels are burnt to power factory machines and many other processes. Manufacturing is one of the largest contributors to greenhouse gas emissions worldwide.
Food production emits greenhouse gases at various stages. Livestock and rice farming releases methane, fertilisers release nitrous oxides, and carbon dioxide is released to make packaging and transport the food.
3. Deforestation
In places like the Amazon Rainforest, trees are cut down to make space for farming and houses. From 2003 – 2023, 54.2 million hectares of rainforest was lost there.
When trees are cut down, they release locked up carbon. With fewer trees, less CO2 absorption can take place. Land use changes make up ¼ of greenhouse gas emissions.
4. Transport
Cars, ships and planes all burn fossil fuels such as petrol. This makes up ¼ of global energy-related CO2 emissions. This graph shows our impact on the atmosphere:
Don’t put the blame on natural forcings.
Now we know current climate change is down to us; everyone has a responsibility to reduce their emissions. Have a look and see what you can do!
