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Greenhouse gas (GHG) emissions – the atmospheric gases responsible for causing global warming and climatic change – are critical to understanding and addressing the climate crisis. Despite an initial dip in global GHG emissions due to COVID-19, the United Nations Environment Programme’s latest Emissions Gap Report (EGR) expects a strong rebound in 2021, when emissions are expected to be only slightly lower than the record levels of 2019.

While most GHGs are naturally occurring, human activities have also been leading to a problematic increase in the amount of GHG emitted and their concentration in the atmosphere. This increased concentration, in turn, can lead to adverse effects on climate. Effects include increases in the frequency and intensity of extreme weather events – including flooding, droughts, wildfires and hurricanes – that affect millions of people and cause trillions in economic losses.

The Emissions Gap Report found that if we do not halve annual GHG emissions by 2030, it will be very difficult to limit global warming to 1.5°C compared to pre-industrial levels by the end of the century. Based on current unconditional pledges to reduce emissions, the world is on a path to see global warming of 2.7 °C by the end of the century compared to pre-industrial levels.

“Human-caused greenhouse gas emissions endanger human and environmental health,” says Mark Radka, Chief of UNEP’s Energy and Climate Branch. “And the impacts will become more widespread and severed without strong climate action.”

So how exactly do GHG emissions warm the planet and what can we do?

What are the major greenhouse gases?

Carbon dioxide (CO₂), methane and nitrous oxide are the major GHGs. CO₂ stays in the atmosphere for up to 1,000 years, methane for around a decade and nitrous oxide for approximately 120 years. Measured over a 20-year period, methane is 80 times more potent than CO₂ in causing global warming, while nitrous oxide is 280 times more potent.