In 1958, scientists measured atmospheric CO₂ concentration atop Mauna Loa, Hawaii. The CO₂ concentration was measured at just 316 ppm (parts per million). In May 2013, only 55 years later, the concentration tipped above 400 ppm for the first time. The last time CO₂ concentration levels were this high was 3 million years ago when forests grew in northern Canada, and Homo sapiens were yet to evolve. How has carbon dioxide increased so rapidly?

Greenhouse Gases and Global Warming

Greenhouse gases, despite their negative reputation, are crucial for our survival. Without the natural greenhouse effect, the heat emitted by Earth would pass outwards into space. Earth's surface would have an average temperature of -20 °C, too cold for humans to survive.

The natural greenhouse effect works as follows. Some infrared radiation from the sun passes through the Earth's atmosphere. Greenhouse gas molecules absorb most of it and re-emit in all directions - much like a greenhouse for growing plants. This warms the Earth's surface and lower atmosphere – keeping the heat in like an insulating blanket and the Earth at an optimum temperature. When there is an increase in the atmospheric concentrations of greenhouse gases, this leads to a rise in the warming effect and, ultimately, the phenomenon that is global warming.

Types of Greenhouse Gases

The contribution of a gas to the greenhouse effect, or global warming, depends on its heat absorption, its heat re-emission and the amount present in the atmosphere.

The gases that contribute most to Earth's greenhouse effect are:

• Water vapour (H₂O)

• Carbon dioxide (CO₂)

• Nitrous oxide (N₂O)

• Methane (CH₄)

• Ozone (O₃)

Anthropogenic Impact on Climate Change

Since the Industrial Revolution began in the 18th century, anthropogenic activities have caused an increase in atmospheric greenhouse gases – primarily carbon dioxide. This leads to an enhanced greenhouse effect or global warming:

Increased greenhouse gas concentrations

↓

More heat is absorbed and re-emitted within the atmosphere

↓

Earth's surface and atmosphere become warmer

Higher temperatures alter Earth's physical systems, causing climate change.

Human Impact on Climate Change: Cause and Effects

We've learned that anthropogenic activities release greenhouse gases, contributing to climate change.

Sources of Greenhouse Gas Emissions

The vast majority of greenhouse gas emissions stem from burning fossil fuels. The remainder comes from deforestation, land use change, and cement production.

• Burning Fossil Fuels: Fossil fuels are non-renewable, carbon-rich deposits. When burned, they release energy - but also carbon dioxide and other greenhouse gases. This enhances Earth's natural greenhouse effect, increasing temperatures and causing climate change.

• Deforestation: The act of cutting down trees is known as deforestation. Forests are carbon stores. When they are cut down, the carbon is released as greenhouse gases, which enhances the greenhouse effect.

• Land Use Change: Any anthropogenic modification of the landscape is classed as land use change. Often, land use change concerns agricultural and urban expansion, which emit greenhouse gases and various pollutants, affecting the local and global climate.

• Cement Production: An astonishing 8% of global anthropogenic carbon emissions stem from cement production. Half of these emissions are generated by the chemical process itself – carbon dioxide is produced when calcium carbonate is heated. Other emissions stem from burning fossil fuels to power this production process.

  Over 900g of carbon dioxide is emitted for every kilogram of cement produced.

The majority of greenhouse gas emissions originate from four economic sectors.

Climate Models vs Weather Forecasts

Weather forecasts present a detailed picture of expected weather in the near future.

Climate models indicate regions likely to experience a change in the long term.

Climate science is a complicated field. It's difficult to predict how atmospheric greenhouse gas concentrations can change in the future, so scientists can never be sure about climate change. Many factors can influence the climate, and there are countless uncertainties due to a lack of data.

Despite this, climate models can help scientists make predictions. They alter variables and equations in the climate model to see how the climate will change according to a scenario.

These models show how the decisions and behaviours of today can influence the climate of the future.

Positive Human Impact on Climate Change

It's not all doom and gloom in the future. Understanding how our decisions and behaviours affect the climate has helped the world to make meaningful changes. Some of the positive changes that are happening or current agreements that will have a positive change on climate change are:

• One hundred and ninety-seven countries have signed the Paris Agreement, the first legally binding global climate agreement. Legislation like the Paris Agreement tracks countries' progress and holds them accountable, encouraging them to make important policy changes to reduce greenhouse gas emissions.

• Over 100 countries have pledged carbon neutrality by 2050. Carbon neutrality is also known as net-zero, which means that all greenhouse gas emissions must be balanced with their removal or elimination.

• Electric vehicles are becoming cheaper and more efficient. Many countries have proposed plans to phase out fossil-fuel-powered cars. Phasing out these vehicles limits the emissions of greenhouse gases and other harmful pollutants.

• Millions of people around the world have shifted towards a plant-based diet. Plant-based protein sources emit up to 90% fewer greenhouse gases than meat.

• Renewable energy resources are becoming commonplace. Electricity from these resources is free from greenhouse gas emissions and is derived from natural, sustainable sources that can be replenished faster than consumed.

^{1. British Geological Society, The greenhouse effect, 2022}

^{2. Che Project, Main sources of carbon dioxide emissions, 2017}

^{3. Christina Nunez, Fossil fuels, explained, National Geographic, 2019}

^{4. Climate.Gov, Climate Models, 2022}

^{5. Diego Arguedas Ortiz, Ten simple ways to act on climate change, BBC Future, 2018}

^{6. Earl J. Richie, Exactly How Much Has the Earth Warmed? And Does It Matter?, Forbes, 2018}

^{7. EURACTIV, Denmark calls for EU plan to phase out diesel and petrol cars, 2019}

^{8. European Commission, Climate Action, 2022}

^{9.Good Food Institute, Environmental benefits of plant-based meat products, 2022}

^{10. Grace McGregor, How You Can Have a Positive Impact on the Climate Change Emergency, Brigham Young University, 2020}

^{11. IPCC, Climate Change 2014: Mitigation of Climate Change, 2014}

^{12. Liana Minassian, Why the Global Rise in Vegan and Plant-Based Eating is No Fad (30x Increase in US Vegans + Other Astounding Vegan Stats), Food Revolution Network, 2022}

^{13. Madeleine Stone, 5 possible climate futures—from the optimistic to the strange, National Geographic, 2021}

^{14. Maeve Campbell, Which country is the world leader in renewable energy in 2021?, EuroNews, 2021}

^{15. Maimunah Mohd Sharif, Cities: a 'cause of and solution to' climate change, UN News, 2019}

^{16. Meteorological Office, Effects of climate change, 2022}

^{17. Nicola Jones, How the World Passed a Carbon Threshold and Why It Matters, Yale Environment 360, 2017}

^{18. UN News, The race to zero emissions, and why the world depends on it, 2020}