Climate change

Not quite - climate change is the result of global warming. Global warming refers to how much the Earth's surface temperature is rising, and it is the effect of this warming on average weather conditions that is known as climate change.

While weather is what happens in a certain place at a certain time - such as whether it's snowing or raining in London one day, climate is the average weather a place experiences - such as how many snowy or rainy days are likely to occur in London in any given year.

Climate change alters these established patterns, leading to consequences: more frequent droughts and heatwaves, more devastating hurricanes, and more intense rainfall, to name a few. As well as causing more extreme weather events, climate change can also alter the timing of the seasons, disrupting the lives of plants and animals.

Dr Joeri Rogelj, Director of Research at the Grantham Institute, Imperial College London, says, 'Global warming and climate change have both occurred throughout Earth's history. But it's the speed at which the world is currently warming, and how fast the climate is changing, that is so concerning.'

The surface temperature of the planet has increased around 0.08°C per decade since 1880. However, the average rate of increase between 1981-2019 has been more than twice that rate. These changes are unquestionably the result of human actions.

Find out more about climate change and why it matters.

Your carbon footprint is how much carbon is released into the atmosphere as a result of your everyday activities. Carbon emissions - in the form of carbon dioxide and methane - are what cause global warming and climate change.

Unless you drive a car that runs on petrol or diesel, you might not think that you emit any carbon. But if you get your energy from a supplier that doesn't use renewable sources, you will be creating carbon emissions every time you turn on the lights or your TV. The vast majority of homes in the UK are also heated using gas-fired boilers or have gas stoves for cooking, which release carbon dioxide.

Your food choices also impact your personal carbon footprint. For example, if you buy fruit that has been shipped from overseas, the carbon emitted on that journey will add to your footprint. Similarly, if you travel by flying or driving, you will contribute more carbon emissions than if you ride a bike or use public transport.

The USA has one of the highest average carbon footprints in the world, at a rate of about 16 tonnes of carbon released per person per year in 2019. In the same year, the figure for the UK was nearly 5.5 tonnes per person, with the global average sitting at around 4.7 tonnes. To avoid global temperatures rising by much more than 1.5°C, carbon emissions, and therefore carbon footprints, need to drop to zero by 2050.

Carbon footprints don't only apply to people - they can be calculated for companies, events, places and products. Alyssa Gilbert, Director of Policy and Translation at the Grantham Institute, Imperial College London, says, 'While we can all do more to reduce our own carbon footprint, we should also put pressure on companies and those in power that have an even bigger capacity to make changes and reduce carbon emissions.'

A variety of organisations have created carbon footprint calculators to help you estimate your personal impact on the planet. Check out this useful list of calculators.

Explore ways you can help the planet, including reducing your carbon footprint.

Carbon dioxide (CO₂) is a greenhouse gas. This means that it causes an effect like the glass in a greenhouse, trapping heat and warming up the inside. This effect is important: without the CO₂ that naturally exists in the atmosphere, Earth might be too cold to support human life. However, the atmosphere is very sensitive to changing levels of CO₂. Even though this gas makes up less than 0.1% of the atmosphere, it can have a huge effect on how much heat the planet's surface retains.

When energy from the Sun reaches the top of our atmosphere, most of it passes through to Earth's surface, where it is absorbed. Some of this energy is re-emitted, heading back towards space. At this stage, it interacts with molecules of CO₂ in a way that prevents some of it from escaping Earth's atmosphere. The trapped heat energy leads to increased average global surface air temperatures.

One reason carbon dioxide has such a big impact on global temperatures is that hotter air can hold more water vapour. Water vapour is itself a greenhouse gas, which further enhances the greenhouse effect.

While the presence of carbon dioxide in Earth's atmosphere is natural, the rising levels since the Industrial Revolution in the 1800s are due to human activities, primarily the burning of fossil fuels such as coal and oil.

Carbon dioxide (CO₂) comes from both natural sources (including volcanoes, the breath of animals and plant decay) and human sources (primarily the burning of fossils fuels like coal, oil and natural gas to generate energy). Human activities have been the main cause of rising carbon dioxide levels in our atmosphere since the 1800s.

The amount of carbon dioxide in the atmosphere is determined by the carbon cycle - a system of 'sources' and 'sinks' of the gas that add and remove it, respectively. One part of the cycle involves rocks, starting with volcanoes, which belch CO₂. This is countered by 'weathering', a process where atmospheric CO₂ mixes with rainwater to make an acid that reacts with rocks, locking the CO₂ away.

The emergence of life on our planet added a new layer to the carbon cycle. As plants grow, they take CO₂ out of the atmosphere, and when they die, it is released again. Animals that consume the plants also store the CO₂ for a while, before they too die and decompose.

Some dead plants don't decompose and instead become layers of coal, oil and other organic-rich sediments such as peat. Eventually, these layers would naturally burn or be recycled through volcanoes, returning the CO₂ to the atmosphere over many thousands (if not millions) of years.

However, humans have been digging up these layers and burning them at a rate the planet has never seen before, releasing vast amounts of CO₂ in a geological blink of an eye. Estimates show that by burning these fossil fuels, humans have essentially taken millions of years of carbon uptake by plants and returned it to the atmosphere in less than 300 years.

Natural sinks of carbon are unable to keep up with this rate of change. This causes CO₂ to build up in the atmosphere, which rose from a concentration of around 280 parts per million (ppm) in 1750 to more than 415ppm in 2021.

A person, company or country is carbon neutral if they balance the carbon dioxide they release into the atmosphere through their everyday activities with the amount they absorb or remove from the atmosphere. This is also called net zero carbon emissions or net zero carbon, because overall no carbon dioxide is added to the atmosphere.

The definition of net zero emissions is sometimes expanded to include other gases such as methane, nitrous oxide and hydrofluorocarbons. This is sometimes referred to as net zero greenhouse gas emissions or simply net zero. These other gases contribute about 24% of global greenhouse gas emissions and carbon dioxide the remaining 76%.

There are two main ways to achieve net zero: reducing emissions and removing carbon dioxide from the atmosphere, through technologies that actively take in carbon dioxide or by enhancing natural removal methods - by planting trees, for example. These methods can be used in combination.

Net zero greenhouse gas emissions are seen as key targets for reaching the Paris Agreement goal of keeping the rise in global temperature well below 2°C and preferably below 1.5°C above pre-industrial levels. Many countries have pledged to reach net zero emissions by 2050, including the UK, which has enshrined in law a target to slash greenhouse gas emissions by 78% by 2035 compared to 1990 levels.

The UK's plan for reaching net zero includes increasing energy efficiency, using more renewable energy to produce electricity for heating and transport, and making use of hydrogen to replace fossil fuels.

Carbon capture and storage is a process that prevents carbon dioxide from entering the atmosphere when it is emitted from sources such as coal-fired power plants. A related term is carbon dioxide removal, which refers to methods for taking carbon dioxide back out of the atmosphere, either by using technologies or enhancing natural processes - by expanding forests and wetlands, for example.

Both carbon capture and storage and carbon dioxide removal often involve a step that locks away the carbon dioxide for a long time, making sure it can't re-enter the atmosphere. This is called carbon sequestration. The carbon dioxide can be 'stored' by being used in products like building materials, or it can be pumped underground where it reacts with certain kinds of rocks, locking it inside.

Alyssa Gilbert, Director of Policy and Translation at the Grantham Institute, Imperial College London, says, 'Many countries are working to reduce their carbon emissions, and these reductions are the central pillar to tackling climate change. But there are some areas where reducing emissions is particularly difficult - in some types of heavy industry, for example. This means we will need to remove some carbon dioxide from the atmosphere to limit climate change. However, many carbon removal technologies and methods are not well developed yet. The slower we reduce our emissions, the more we will need to rely on these methods that may not be available to pick up the slack.'

Methane is a more powerful greenhouse gas than carbon dioxide, but there is far less of it in the atmosphere and it does not stay there as long. Methane is more than 25 times as potent as carbon dioxide at trapping heat in the atmosphere over the course of a century, but it has an 'atmospheric lifetime' of around 12 years, whereas carbon dioxide molecules hang around for hundreds of years.

This means that if humans stopped adding any methane to the atmosphere tomorrow, within several decades all trace of the extra methane and its climate influence would be gone, whereas the same is not true for carbon dioxide. However, methane is still an important greenhouse gas because there are many human-caused sources of it. Methane today is responsible for about 0.5°C of total warming.

Methane is released during the extraction and transport of fossil fuels including coal, oil and natural gas. It is also released by rice fields, the decay of food waste in rubbish dumps, and even cows - meaning the rise in beef consumption worldwide has increased methane emissions.

There are also natural sources of methane that are being released faster due to global warming itself. These include the melting of permafrost, the layer of previously permanently frozen ice within soil in polar and sub-polar regions. These methane emissions could in turn accelerate warming, leading to the release of more methane, and so on.

Dr Joeri Rogelj, Director of Research at the Grantham Institute, Imperial College London, says, 'Methane does not persist for long in the atmosphere but is nevertheless a powerful greenhouse gas. If we make rapid cuts to methane emissions now, together with efforts to drastically reduce our carbon dioxide emissions, it will ensure that we limit global warming as much as possible.'

At the COP26 climate summit, more than 90 nations agreed to cut their methane emissions by 30% by 2030 compared to 2020.

By many definitions, nuclear energy is not renewable. But in terms of climate change, nuclear energy production does not release greenhouse gases, so it is a low-carbon fuel.

Renewable energy refers to energy from sources that are constantly replenished - like the water for hydroelectric dams that is topped up by the rain, or the sunlight that reappears every day for solar panels. Because nuclear power uses up radioactive fuel, it is not renewable in the same way.

Nuclear energy, however, is the second-largest source of low-carbon electricity in the world behind hydropower. Some researchers say it is essential for helping countries including the UK reach targets of producing all their energy without releasing greenhouse gases. This is because there is not yet enough renewable energy capacity to provide for all our electricity needs. Renewable power is also intermittent - for instance, wind turbines don't produce power when the wind doesn't blow (although large batteries to store this energy are improving all the time).

Nuclear energy is not without its issues. Most notably, it produces radioactive waste that must be transported safely to long-term storage, where it will not be disturbed for tens of thousands of years until the material is no longer a danger to human health or the environment. These challenges are ongoing.

Climate change warms the ocean, causing knock-on effects such as thermal expansion - which leads to a rise in sea level - and changes in ocean currents. The melting of ice both on land and in the sea also affects the ocean, causing more sea-level rise and reducing the salinity of the ocean, respectively. Greater concentrations of carbon dioxide in the atmosphere also mean that more of it dissolves in the ocean, leading to acidification.

Each of these changes affect marine wildlife. Warming ocean temperatures can lead to coral bleaching - the sudden die-off of large parts of coral reefs - as well as cause animals such as fish to seek cooler waters, shifting their habitats north. This can have a knock-on impact on human communities that rely on those fish for food.

Why is ocean acidification a problem?

Acidification can weaken sea animals' shells and external skeletons. This includes coral exoskeletons - a further reason coral reefs are under threat worldwide.

What happens when sea ice and glaciers melt?

When ice on land - ice sheets and glaciers - melts, it adds water volume to the ocean. This increases sea levels globally, which can inundate low-lying land and important coastal environments such as mangrove forests and wetlands.

When sea ice melts, it doesn't add volume to the ocean, but it does add freshwater, locally decreasing the saltiness of the sea. Saltiness and temperature are the drivers of ocean currents that move heat and nutrients around the world. Melting sea ice and rising temperatures can disrupt these currents, not only affecting wildlife that depends on them but also, potentially, local climates.

For example, the UK is comparatively mild because of the heat brought by an ocean current from the Gulf of Mexico. Melting Arctic sea ice is weakening this current, meaning the UK could face more extreme weather as a result of climate change.

The algae found on sea ice is also essential to many species in the Arctic. In the long term, the loss of sea ice will likely have cascading effects within the food web and impact the coastal ecosystem resources on which Indigenous Peoples rely.

Sea ice decline is also linked to a loss of genetic diversity in polar bears, putting these animals at an increased risk of extinction.

Climate justice recognises that climate change will not affect everyone in the same way, and that this will lead to inequalities between places, people and even generations. It moves climate change conversations beyond the science and the physical impacts, to questions of politics and ethics, such as who should bear responsibility for paying for the damage caused by climate change, or how much developed countries should help the developing world increase their energy use in a sustainable way.

The impacts of climate change are likely to be felt most by those communities that contributed least to the problem, such as developing countries, indigenous peoples and future generations. For example, a study published in 2021 found that children born today across the globe will on average face seven times more scorching heatwaves, 2.6 times more droughts, 2.8 times as many river floods, almost three times as many crop failures, and twice the number of wildfires during their lives than their grandparents.

In recent years, various actions to increase awareness or tackle these issues have arisen. For example, in 2019 The Hague Court of Appeal ordered the Dutch government to reduce the country's greenhouse gas emissions by at least 25% by the end of 2020 compared to 1990. This placed the Netherlands under a legal obligation to take measures to protect its citizens from the consequences of climate change.

Movements like Fridays for Future and Extinction Rebellion have also gained in popularity as people use their voices to call for climate justice.