News about the climate crisis often contains mentions of greenhouse gases and the greenhouse effect. While most find the analogy easy to understand, what exactly are these gases and why do they contribute to global warming?
1. What is the greenhouse effect?
In a greenhouse, sunlight enters and heat is retained. The greenhouse effect describes a similar phenomenon on a planetary scale, but instead of glass in a greenhouse, certain gases are increasingly raising global temperatures.
The Earth’s surface absorbs just under half of the sun’s energy, while the atmosphere absorbs 23% and the rest is reflected back into space. Natural processes ensure that the amount of energy input and output is equal, keeping the temperature of the planet stable.
However, human activity is causing an increase in the emission of so-called greenhouse gases (GHGs) which, unlike other atmospheric gases such as oxygen and nitrogen, are trapped in the atmosphere, unable to escape the planet. This energy returns to the surface, where it is reabsorbed.
As more energy enters the planet than leaves, surface temperatures increase until a new equilibrium is reached.
2. Why is warming up important?
This rise in temperature has long-term adverse effects on the climate and affects a multitude of natural systems. The effects include increases in the frequency and intensity of extreme weather events such as floods, droughts, wildfires and hurricanes, which affect millions of people and cause economic losses in the billions.
“Man-made greenhouse gas emissions endanger human and environmental health”Says Mark Radka, head of the Energy and Climate Division at the United Nations Environment Program (UNEP). “And the impacts will become widespread and more severe without strong climate action.”.
GHG emissions are critical to understanding and addressing the climate crisis: despite an initial drop due to COVID-19, UNEP’s latest emissions gap report shows a recovery and predicts a disastrous rise in global temperature of at least 2, 7 degrees this century unless countries take action. much greater efforts to reduce emissions.
The report found that GHG emissions must be cut in half by 2030 if we are to limit global warming to 1.5°C above pre-industrial levels by the end of the century.
3. What are the main greenhouse gases?
Water vapor is the largest global contributor to the greenhouse effect. However, almost all of the water vapor in the atmosphere comes from natural processes.
Carbon dioxide (CO2), methane and nitrous oxide are the main GHGs to be concerned about. CO2 remains in the atmosphere for up to 1,000 years, methane for about a decade, and nitrous oxide for about 120 years.
Measured over a period of 20 years, methane is 80 times more powerful than CO2 in causing global warming, while nitrous oxide is 280 times more powerful.
4. How does human activity produce these greenhouse gases?
Coal, oil and natural gas continue to supply many parts of the world. Carbon is the main element in these fuels, and when burned to generate electricity, drive transport or provide heat, they produce CO2.
Oil and gas extraction, coal mining and landfills are responsible for 55% of man-made methane emissions. About 32% of man-made methane emissions are attributable to cows, sheep and other ruminants that ferment food in their stomachs. Manure decomposition is another agricultural source of the gas, as is rice cultivation.
Man-made nitrous oxide emissions arise largely from agricultural practices. Bacteria in soil and water naturally convert nitrogen to nitrous oxide, but fertilizer use and runoff increase this process, putting more nitrogen into the environment.
Fluorinated gases such as hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride are non-naturally occurring GHGs. Hydrofluorocarbons are refrigerants used as alternatives to chlorofluorocarbons (CFCs) which, having depleted the ozone layer, were eliminated thanks to the Montreal Protocol. The others have industrial and commercial use.
While fluorinated gases are much less prevalent than other GHGs and do not destroy the ozone layer like CFCs, they are still very powerful. Over a 20-year period, the global warming potential of some fluorinated gases is up to 16,300 times greater than CO2.
5. What can we do to reduce GHG emissions?
Switching to renewable energy, putting a price on carbon and phasing out carbon are important elements in reducing GHG emissions. Ultimately, more stringent emission reduction targets are needed for the long-term preservation of human and environmental health.
“We need to implement strong policies that support stated ambitions,” says Radka. “We cannot continue on the same path and expect better results. Action needed now”.
During COP26, the European Union and the United States launched the Global Methane Pledge, in which more than 100 countries will aim to reduce methane emissions in the fuel, agriculture and waste sectors by 30% by 2030.
Despite the challenges, there are reasons to be positive. From 2010 to 2021, policies were implemented to reduce annual emissions by 11 gigatons by 2030 compared to what would have happened otherwise. People can also join the UN’s #ActNow campaign to get ideas for positive climate action.
By making decisions that are less harmful to the environment, everyone can be part of the solution and influence change. Raising the voice is a way to multiply impact and create change on a much larger scale.
UNEP’s role in GHG reduction
- UNEP outlined its six-sector solution, which can reduce 29 to 32 gigatons of carbon dioxide by 2030 to meet the 1.5°C warming threshold. The six sectors identified are: energy; industry; agriculture and food; forests and land use; transport; and buildings and cities.
- UNEP also maintains an online “Climate Note”, a tool that visualizes the changing state of the climate with reference to 1990.
- Through its other multilateral environmental agreements and reports, UNEP raises awareness and advocates for effective environmental action. UNEP will continue to work closely with its 193 member states and other stakeholders to set the environmental agenda and advocate for a dramatic reduction in GHG emissions.
