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On bone-dry land, severely affected by drought, two women search for their daily water supply.


1. What is the greenhouse effect?

A greenhouse lets sunlight in and heat is kept inside. The greenhouse effect describes a similar phenomenon on a planetary scale but, instead of the glass of a greenhouse,  certain gases are increasingly raising global temperatures.

The surface of the Earth absorbs just under half of the sun’s energy, while the atmosphere absorbs 23 per cent, and the rest is reflected back into space. Natural processes ensure that the amount of incoming and outgoing energy is equal, keeping the planet’s temperature stable.

Human activity is increasing the emissions of so-called greenhouse gas (GHGs), which unlike other atmospheric gases like oxygen and nitrogen, become trapped in the atmosphere and are unable to escape the planet. This energy is then absorbed back to the surface.

The planet receives more energy than it expends, so surface temperatures rise until a new balance can be achieved. 

On bone-dry land, severely affected by drought, two women search for their daily water supply.

© Apratim Pal

Two women seek water on a dry, bone-dry landscape that has been severely affected by drought.

2. Why does warming matter?

The temperature rise has long-term and adverse effects on the climate and a multitude of natural systems. 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.

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

GHG emissions are essential to understanding and addressing the climate crises: despite a dip in the initial levels, COVID-19The latest UNEP report Emissions Gap ReportThe rebound is evident, and the global temperature rise of at minimum 2.7 degrees Celsius this century is predicted if countries do not make greater efforts in reducing their emissions.

The report found that GHG emissions need to be halved by 2030, if we are to limit global warming to 1.5°C compared to pre-industrial levels by the end of the century.

Carbon dioxide levels continue at record levels, despite the economic slowdown caused by the COVID-19 pandemic.

Unsplash/Johannes Plenio

Despite the economic slowdown resulting from the COVID-19 pandemic, carbon dioxide levels remain at record levels.

3. What are the main greenhouse gases?

The greenhouse effect is mainly caused by water vapour. However, almost all of the water vapour in our atmosphere is produced by natural processes.

Major GHGs to watch out for are carbon dioxide (CO2) methane, nitrous oxide and methane. The atmosphere can hold CO2 for up to 1,000 years, methane around a decade and nitrous oxide approximately 120 years.

Over a 20-year time period, methane is 80x stronger than CO2 in causing global heating. Nitrous oxide, however, is 280x stronger.

4. How does human activity cause these greenhouse gases to form?

Many parts of the globe still rely on coal, oil, or natural gas for power. Carbon is the main element in these fuels and, when they’re burned to generate electricity, power transportation, or provide heat, they produce CO2.

55 percent of methane emitted by humans is caused by oil and gas mining, coal mining, and other waste sources. Cows, sheep, and all other ruminants that ferment food are responsible for around 32 percent of human-caused Methane emissions. Manure decomposition and rice cultivation are other agricultural sources of the gas. 

Most of the human-caused nitrogen oxide emissions are due to agricultural practices. Although soil and water naturally contain bacteria that convert nitrogen to nitrous oxide, fertilizer use and runoff can increase this process by adding more nitrogen to the environment.

Fluorinated gases – such as hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride – are GHGs that do not occur naturally. Hydrofluorocarbons were used as refrigerants to replace chlorofluorocarbons. CFCs have been eliminated due to their effect on the ozone layer. Other refrigerants have industrial and commercial applications.

Although fluorinated gases are not as common as other GHGs and don’t deplete ozone like CFCs they are still very powerful. Some fluorinated gas’ global warming potential is up to 16,300x greater than that of carbon dioxide over a 20-year span.

Wind farms generate electricity and reduce reliance on coal-powered energy.


Wind farms produce electricity and reduce dependence on coal-powered energy.

5. What can be done to reduce GHG emissions

GHG emissions can be reduced by a variety of factors, including shifting to renewable energy, putting an end to carbon, and phasing-out coal. For the long-term preservation of human and environmental health, it is necessary to set higher emission reduction targets.

“We need to implement strong policies that back the raised ambitions,” says Mr. Radka. “We cannot continue down the same path and expect better results. Action is needed now.”

The Global Methane Pledge was jointly launched by the United States of America and the European Union during COP26. This pledge will see over 100 countries commit to reducing methane emissions in fuel, agriculture, and other waste sectors by 2030.

Despite the challenges there is reason for optimism. From 2010 to 2021, policies were put in place  to lower annual emissions by 11 gigatons by 2030 compared to what would have otherwise happened. Individuals can also join the UN’s #ActNow campaign for ideas to take climate-positive actions.

Everyone can make choices that have less negative effects on the environment and be part of the solution. You can multiply your impact and make a bigger impact by speaking up.


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