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.
“The climate emergency demands action from all of us. We need to get to net zero greenhouse gas emissions by 2050 and everyone has a role to play,”
said Niklas Hagelberg, UNEP’s Climate Change Coordinator.
Coal, oil and natural gas continue to power many parts of the world. Carbon is the main element in these fuels, and when they’re burned to generate electricity, power transportation or provide heat, they produce CO2, a colourless, odourless gas. Oil and gas extraction, coal mining and waste landfills account for 55 per cent of human-caused methane emissions. Approximately 32 per cent of human-caused 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. Human-caused nitrous oxide emissions largely arise from agriculture practices. Bacteria in soil and water naturally convert nitrogen into nitrous oxide, but fertilizer use and run-off add to this process by putting more nitrogen into the environment.  What are the other greenhouse gases? 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 depleted the ozone layer and were phased out thanks to the Montreal Protocol. The other gases have industrial and commercial uses. While fluorinated gases are far less prevalent than other GHGs and do not deplete the ozone layer like CFCs, they are still very powerful. Over a 20-year period, the various fluorinated gases’ global warming potential ranges from 460–16,300 times greater than that of CO2. Water vapour is the most abundant GHG in the atmosphere and is the biggest overall contributor to the greenhouse effect. However, almost all the water vapour in the atmosphere comes from natural processes. Human emissions are very small and thus relatively less impactful. What is the greenhouse effect? The Earth’s surface absorbs about 48 per cent of incoming solar energy, while the atmosphere absorbs 23 per cent. The rest is reflected back into space. Natural processes ensure that the amount of incoming and outgoing energy are equal, keeping the planet’s temperature stable, However, GHGs, unlike other atmospheric gases such as oxygen and nitrogen, are opaque to outgoing infrared radiation. As the concentration of GHGs in the atmosphere increases due to human-caused emissions, energy radiated from the surface becomes trapped in the atmosphere, unable to escape the planet. This energy returns to the surface, where it is reabsorbed. Since more energy enters than exits the planet, surface temperatures increase until a new balance is achieved. This temperature increase has long-term climate impacts and affects myriad natural systems.
What can we do to reduce GHG emissions? Shifting to renewable energy, putting a price on carbon and phasing out coal are all important elements in reducing GHG emissions. Ultimately, stronger nationally determined contributions are needed to accelerate this reduction to preserve long-term human and environmental health. “We need to implement strong policies that back the raised ambitions,” says Radka. “We cannot continue down the same path and expect better results. Action is needed now.” During COP26, the European Union and the United States launched the Global Methane Pledge, which will see over 100 countries aim to reduce 30 per cent of methane emissions in the fuel, agriculture and waste sectors by 2030. UNEP has outlined its six-sector solution, which can reduce 29–32 gigatons of carbon dioxide by 2030 to meet the 1.5°C warming limit. UNEP also maintains an online “Climate Note,” a tool that visualizes the changing state of the climate with a baseline of 1990. Despite the challenges, there is reason to be positive. From 2010 to 2021, policies were put in place which will lower annual emissions by 11 gigatons by 2030 compared to what would have otherwise happened. 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 drastic reduction in GHG emissions. Beyond these movements, individuals can also join the UN’s #ActNow campaign for ideas to take climate-positive actions. By making choices that have less harmful effects on 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 bigger scale. UNEP is at the front in support of the Paris Agreement goal of keeping the global temperature rise well below 2°C, and aiming - to be safe - for 1.5°C, compared to pre-industrial levels. To do this, UNEP has developed a Six-Sector Solution, a roadmap to reducing emissions across sectors in line with the Paris Agreement commitments and in pursuit of climate stability. The six sectors identified are: Energy; Industry; Agriculture & Food; Forests & Land Use; Transport; and Buildings & Cities. Global warming describes the current rise in the average temperature of Earth’s air and oceans. Global warming is often described as the most recent example of climate change. Earth’s climate has changed many times. Our planet has gone through multiple ice ages, in which ice sheets and glaciers covered large portions of the Earth. It has also gone through warm periods when temperatures were higher than they are today. Past changes in Earth’s temperature happened very slowly, over hundreds of thousands of years. However, the recent warming trend is happening much faster than it ever has. Natural cycles of warming and cooling are not enough to explain the amount of warming we have experienced in such a short time—only human activities can account for it. Scientists worry that the climate is changing faster than some living things can adapt to it. In 1988, the World Meteorological Organization and the United Nations Environment Programme established a committee of climatologists, meteorologists, geographers, and other scientists from around the world. This Intergovernmental Panel on Climate Change (IPCC) includes thousands of scientists who review the most up-to-date research available related to global warming and climate change. The IPCC evaluates the risk of climate change caused by human activities. According to the IPCC’s most recent report (in 2007), Earth’s average surface temperatures have risen about 0.74 degrees Celsius (1.33 degrees Fahrenheit) during the past 100 years. The increase is greater in northern latitudes. The IPCC also found that land regions are warming faster than oceans. The IPCC states that most of the temperature increase since the mid-20th century is likely due to human activities. The Greenhouse Effect Human activities contribute to global warming by increasing the greenhouse effect. The greenhouse effect happens when certain gases—known as greenhouse gases—collect in Earth’s atmosphere. These gases, which occur naturally in the atmosphere, include carbon dioxide, methane, nitrogen oxide, and fluorinated gases sometimes known as chlorofluorocarbons (CFCs). Greenhouse gases let the sun’s light shine onto the Earth’s surface, but they trap the heat that reflects back up into the atmosphere. In this way, they act like the insulating glass walls of a greenhouse. The greenhouse effect keeps Earth’s climate comfortable. Without it, surface temperatures would be cooler by about 33 degrees Celsius (60 degrees Fahrenheit), and many life forms would freeze. Since the Industrial Revolution in the late 1700s and early 1800s, people have been releasing large quantities of greenhouse gases into the atmosphere. That amount has skyrocketed in the past century. Greenhouse gas emissions increased 70 percent between 1970 and 2004. Emissions of carbon dioxide, the most important greenhouse gas, rose by about 80 percent during that time. The amount of carbon dioxide in the atmosphere today far exceeds the natural range seen over the last 650,000 years. Most of the carbon dioxide that people put into the atmosphere comes from burning fossil fuels such as oil, coal, and natural gas. Cars, trucks, trains, and planes all burn fossil fuels. Many electric power plants also burn fossil fuels. Another way people release carbon dioxide into the atmosphere is by cutting down forests. This happens for two reasons. Decaying plant material, including trees, releases tons of carbon dioxide into the atmosphere. Living trees absorb carbon dioxide. By diminishing the number of trees to absorb carbon dioxide, the gas remains in the atmosphere. Most methane in the atmosphere comes from livestock farming, landfills, and fossil fuel production such as coal mining and natural gas processing. Nitrous oxide comes from agricultural technology and fossil fuel burning. Fluorinated gases include chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons. These greenhouse gases are used in aerosol cans and refrigeration. All of these human activities add greenhouse gases to the atmosphere, trapping more heat than usual and contributing to global warming.Effects of Global Warming Even slight rises in average global temperatures can have huge effects. Perhaps the biggest, most obvious effect is that glaciers and ice caps melt faster than usual. The meltwater drains into the oceans, causing sea levels to rise and oceans to become less salty. Ice sheets and glaciers advance and retreat naturally. As Earth’s temperature has changed, the ice sheets have grown and shrunk, and sea levels have fallen and risen. Ancient corals found on land in Florida, Bermuda, and the Bahamas show that the sea level must have been five to six meters (16-20 feet) higher 130,000 years ago than it is today. Earth doesn’t need to become oven-hot to melt the glaciers. Northern summers were just three to five degrees Celsius (five to nine degrees Fahrenheit) warmer during the time of those ancient fossils than they are today. However, the speed at which global warming is taking place is unprecedented. The effects are unknown. Glaciers and ice caps cover about 10 percent of the world’s landmass today. They hold about 75 percent of the world’s fresh water. If all of this ice melted, sea levels would rise by about 70 meters (230 feet). The IPCC reported that the global sea level rose about 1.8 millimeters (0.07 inches) per year from 1961 to 1993, and 3.1 millimeters (0.12 inches) per year since 1993. Rising sea levels could flood coastal communities, displacing millions of people in areas such as Bangladesh, the Netherlands, and the U.S. state of Florida. Forced migration would impact not only those areas, but the regions to which the “climate refugees” flee. Millions more people in countries like Bolivia, Peru, and India depend on glacial meltwater for drinking, irrigation, and hydroelectric power. Rapid loss of these glaciers would devastate those countries. Glacial melt has already raised the global sea level slightly. However, scientists are discovering ways the sea level could increase even faster. For example, the melting of the Chacaltaya Glacier in Bolivia has exposed dark rocks beneath it. The rocks absorb heat from the sun, speeding up the melting process.Many scientists use the term “climate change” instead of “global warming.” This is because greenhouse gas emissions affect more than just temperature. Another effect involves changes in precipitation like rain and snow. Patterns in precipitation may change or become more extreme. Over the course of the 20th century, precipitation increased in eastern parts of North and South America, northern Europe, and northern and central Asia. However, it has decreased in parts of Africa, the Mediterranean, and parts of southern Asia. Future Changes Nobody can look into a crystal ball and predict the future with certainty. However, scientists can make estimates about future population growth, greenhouse gas emissions, and other factors that affect climate. They can enter those estimates into computer models to find out the most likely effects of global warming. The IPCC predicts that greenhouse gas emissions will continue to increase over the next few decades. As a result, they predict the average global temperature will increase by about 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade. Even if we reduce greenhouse gas and aerosol emissions to their 2000 levels, we can still expect a warming of about 0.1 degree Celsius (0.18 degrees Fahrenheit) per decade. The panel also predicts global warming will contribute to some serious changes in water supplies around the world. By the middle of the 21st century, the IPCC predicts, river runoff and water availability will most likely increase at high latitudes and in some tropical areas. However, many dry regions in the mid-latitudes and tropics will experience a decrease in water resources. As a result, millions of people may be exposed to water shortages. Water shortages decrease the amount of water available for drinking, electricity, and hygiene. Shortages also reduce water used for irrigation. Agricultural output would slow and food prices would climb. Consistent years of drought in the Great Plains of the United States and Canada would have this effect. IPCC data also suggest that the frequency of heat waves and extreme precipitation will increase. Weather patterns such as storms and tropical cyclones will become more intense. Storms themselves may be stronger, more frequent, and longer-lasting. They would be followed by stronger storm surges, the immediate rise in sea level following storms. Storm surges are particularly damaging to coastal areas because their effects (flooding, erosion, damage to buildings and crops) are lasting. What We Can Do Reducing our greenhouse gas emissions is a critical step in slowing the global warming trend. Many governments around the world are working toward this goal. The biggest effort so far has been the Kyoto Protocol, which was adopted in 1997 and went into effect in 2005. By the end of 2009, 187 countries had signed and ratified the agreement. Under the protocol, 37 industrialized countries and the European Union have committed to reducing their greenhouse gas emissions. There are several ways that governments, industries, and individuals can reduce greenhouse gases. We can improve energy efficiency in homes and businesses. We can improve the fuel efficiency of cars and other vehicles. We can also support development of alternative energy sources, such as solar power and biofuels, that don’t involve burning fossil fuels. Some scientists are working to capture carbon dioxide and store it underground, rather than let it go into the atmosphere. This process is called carbon sequestration. Trees and other plants absorb carbon dioxide as they grow. Protecting existing forests and planting new ones can help balance greenhouse gases in the atmosphere.Changes in farming practices could also reduce greenhouse gas emissions. For example, farms use large amounts of nitrogen-based fertilizers, which increase nitrogen oxide emissions from the soil. Reducing the use of these fertilizers would reduce the amount of this greenhouse gas in the atmosphere. The way farmers handle animal manure can also have an effect on global warming. When manure is stored as liquid or slurry in ponds or tanks, it releases methane. When it dries as a solid, however, it does not. Reducing greenhouse gas emissions is vitally important. However, the global temperature has already changed and will most likely continue to change for years to come. The IPCC suggests that people explore ways to adapt to global warming as well as try to slow or stop it. Some of the suggestions for adapting include:
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What are the different gasses that contribute to the greenhouse effect how strongly do they impact in the atmosphere?
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