1. What is the greenhouse effect?
In a greenhouse, sunlight penetrates and heat is retained. The greenhouse effect describes a similar phenomenon on a planetary scale, but instead of the glass of a greenhouse, certain gases are causing global temperatures to rise more and more.
The Earth’s surface absorbs just under half of solar energy, while the atmosphere absorbs 23% and the rest is reflected back into space. Natural processes ensure that the amount of energy entering and exiting is equal, keeping the temperature of the planet stable.
However, human activity leads to an increase in the emissions of so-called greenhouse gases (GHG) which, unlike other atmospheric gases such as oxygen and nitrogen, find themselves trapped in the atmosphere, unable to escape from the planet. This energy returns to the surface, where it is reabsorbed.
Because more energy enters than comes out of the planet, surface temperatures rise until a new equilibrium is reached.
2. Why is warming important?
This increase in temperature has long-term adverse effects on the climate and affects a myriad of natural systems. The effects include the increasing frequency and intensity of extreme weather events – including floods, droughts, forest fires and hurricanes – that affect millions of people and cause billions in economic losses.
“Human-made greenhouse gas emissions endanger human and environmental health,” said Mark Radka, Chief of the Energy and Climate Branch of the United Nations Environment Program (UNEP) . “And the impacts will become more widespread and more severe without strong climate action. “
GHG emissions are key to understanding and dealing with the climate crisis: Despite an initial drop due to COVID-19, UNEP’s latest emissions gap report shows a rebound and predicts a catastrophic rise in global temperature d ‘at least 2.7 degrees this century, unless countries put much more effort into reducing emissions.
The report found that GHG emissions must be halved 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 main 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 worry about. CO2 stays in the atmosphere for up to 1,000 years, methane for about a decade, and nitrous oxide for about 120 years.
Measured over a 20-year period, methane is 80 times more powerful than CO2 in 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 power many parts of the world. Carbon is the backbone of these fuels, and when burned to generate electricity, power transportation, or provide heat, they produce CO2.
Oil and gas extraction, coal mining and waste landfills account for 55% of human-made methane emissions. About 32% of human-made methane emissions are attributable to cows, sheep and other ruminants that ferment food in their stomachs. Another agricultural source of gas is decomposing manure, as is rice cultivation.
Human-caused nitrous oxide emissions come largely from agricultural practices. Bacteria in soil and water naturally convert nitrogen to nitrous oxide, but fertilizer use and runoff add to this process by releasing more nitrogen into the environment.
Fluorinated gases – such as hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride – are GHGs that do not occur naturally. Hydrofluorocarbons are refrigerants used as alternatives to chlorofluorocarbons (CFCs) which, having depleted the ozone layer, have been gradually phased out thanks to the Montreal Protocol. The others have industrial and commercial uses.
While fluorinated gases are much less common than other GHGs and do not deplete the ozone layer like CFCs, they are still very potent. Over a 20-year period, the global warming potential of some fluorinated gases is up to 16,300 times that of CO2.
5. What can we do to reduce GHG emissions?
Switching to renewables, carbon pricing and phasing out coal are all important elements in reducing GHG emissions. Ultimately, stricter emission reduction targets are needed to preserve long-term human and environmental health.
“We need to implement strong policies that support high ambitions,” says Radka. “We cannot continue on the same path and expect better results. We must act now. “
At COP26, the European Union and the United States launched the Global Methane Pledge, which will see more than 100 countries aim to reduce methane emissions by 30% in the fuel, agriculture and waste sectors. by 2030.
Despite the challenges, there is reason to be positive. From 2010 to 2021, policies were in place to reduce annual emissions by 11 gigatonnes by 2030 compared to what would otherwise have happened. Individuals can also join the UN’s #ActNow campaign to find ideas for taking positive climate action.
By making choices that are less harmful to the environment, everyone can be part of the solution and influence change. Speaking up is one way to multiply impact and create change on a much larger scale.