What are greenhouse gases?
Our climate is changing due to greenhouse gas emissions. Get the low-down on what they are, where they come from and how to help reduce them in our guide to greenhouse gases.
It feels like scientists have been talking about the ‘greenhouse effect’ and greenhouse gases for decades – in fact, they’ve been discussing the issue since the 1820s – but we don’t feel any closer to solving the problems caused by greenhouse gas emissions, mainly global warming.
One issue is that there’s an overwhelming amount of science to get to grips with. So let’s break the topic down into bite-sized chunks, focusing on how the food we eat contributes to climate change.
What are greenhouse gases?
Before we get to greenhouse gases, we need to cover the greenhouse effect. This is when heat and energy from the sun get trapped in the Earth’s atmosphere. Some of this is a natural process, but gases created by human activity are trapping more heat in the atmosphere, raising the temperature and causing global warming or climate change. These gases are therefore known as ‘greenhouse gases’ (GHG).
There are seven greenhouse gases that contribute directly to climate change:
• carbon dioxide (CO2)
• methane (CH4)
• nitrous oxide (N2O)
• hydrofluorocarbons (HFCs)
• perfluorocarbons (PFCs)
• sulphur hexafluoride (SF6)
• nitrogen trifluoride (NF3)
Carbon dioxide makes up the majority of our GHG, which is why so much research is focused on carbon emissions and/or reducing them.
Sometimes you may see greenhouse gases expressed as CO2e, particularly when discussing carbon footprints. This is because a single item or activity can generate multiple GHG, but to keep things simple they are grouped together as a ‘carbon dioxide equivalent’ (the amount of carbon dioxide that would have the same climate-change impact), or CO2e.
Where do they come from?
The most recent figures show transport is responsible for 33% of the UK’s total carbon emissions, including the cars that we drive and lorries transporting goods or materials. The second largest contributor to our CO2 (27%) emissions is the production and consumption of energy, either for heating our homes or via manufacturing.
On a global scale, food production is responsible for 25% of all the GHG produced. This includes the growing, raising and harvesting all the plants, animals and animal products, like cheese, that we eat, plus the processing, transport and storage of that food. Cooking this food uses more energy, and releases more CO2 as a result, while food wastage – throwing away leftovers or perfectly good food that could’ve been eaten – also releases greenhouse gases.
Which foods produce the most GHG?
If you’ve been reading the food news headlines, you’ll know that meat and dairy have by far the biggest impact, responsible for 14.5% of the world’s total GHG emissions every year. This is due to the deforestation involved in clearing land to raise some livestock, the impact of cows and sheep on the environment, and the energy needed to process and transport it all.
Switching to a plant-based diet seems like the best solution, but it isn’t without problems. A 2018 study found global rice farms now produce as much CO2 as the UK, Italy, Spain and Germany combined. Flooding rice fields reduces weed growth but also allows bacteria to break down organic matter, which produces methane. To help reduce methane emissions – and cut down on water use – farmers have been switching between flooding fields and letting them dry out.
However, this increases the amount of nitrous oxide (N2O) released by microbes in the soil: up to 45 times more than in permanently flooded fields. N2O is actually 300 times more damaging than CO2 and also stays in the environment for 100 years longer. To help balance out the release of both GHG, experts say the answer is to keep paddy fields shallowly flooded, but it will take time to teach small-scale farmers these methods.
How you can reduce GHG emissions
Reducing the amount of meat and dairy you eat is one of the most effective ways to cut GHG, while vegetarians and vegans can eat more alternative grains such as quinoa or buckwheat, rather than rice.
If you’re really serious about reducing your contribution to GHG, a controversial 2017 report recommends four ‘simple’ steps:
• switch to a plant-based diet
• avoid travelling by plane
• live car-free
• have one fewer child
If you’ve already got kids, you can’t send one back [sorry…], but teaching them how to reduce their GHG emissions can help create a more sustainable future for you, them, and everyone.
More on sustainability
10 ways to cut your carbon footprint
The facts about food miles
6 pieces of packaging to avoid
10 ways to eat out sustainably
How to reduce food waste
Is a vegan diet better for the environment?
How to compost food at home
Sustainability hub page
Paul Allen is a former BBC environmental editor and a director at Lark. Find him on Twitter @larkingly.