- Global emissions of greenhouse gases are steadily rising. Most of these emissions come from the energy sector, followed by agriculture, industrial processes, waste and land use change.
- Carbon dioxide makes the largest contribution to the enhanced greenhouse effect, followed by methane and nitrous oxide. Carbon dioxide is mostly produced by the burning of fossil fuels.
- Synthetic gases such as hydrofluorocarbons used in air conditioning and refrigeration, are produced in small amounts but have a large global warming effect.
- The world has set up organisations and agreements to support decreasing emissions. Many countries are working to achieve emission reduction targets in various ways and an increasing number of private sector organisations are taking action to reduce their emissions.
Types of emissions
The levels of some greenhouse gases in the atmosphere are being affected by human activities. This is enhancing the greenhouse effect and causing warming.
The main gases are:
- carbon dioxide (CO2)
- methane (CH4)
- nitrous oxide (N2O)
- synthetic gases (sulfur hexafluoride [SF6], hydrofluorocarbons [HFCs] and perfluorocarbons [PFCs]).
Greenhouse gases are sometimes measured in terms of their ‘carbon dioxide equivalent’ (CO2-e). CO2-e is used to compare the emissions from various greenhouse gases, based on how well they trap heat in the atmosphere. This is called their ‘global warming potential’.
For example, the global warming potential for methane over 100 years is 28. This means that the warming generated by 1 million metric tons of methane is equivalent to 28 million metric tons of carbon dioxide.
Carbon dioxide is produced by burning of coal, natural gas, oil, wood, solid waste, and also by some chemical reactions. Carbon dioxide is removed from the atmosphere when it is absorbed by plants, soils and oceans.
As a result of burning fossil fuels and land clearing, carbon dioxide is being added to the atmosphere faster than plants, soils and oceans can remove it. This is causing an enhanced greenhouse effect and the acidification of our oceans.
Methane has a high impact on the enhanced greenhouse effect because it has 28 times the global warming potential of carbon dioxide. Methane has been responsible for around 23% of warming since 1750.
Methane is emitted during the production and transport of coal, natural gas and oil. Methane is also produced by livestock and other agricultural processes, and by the decay of organic waste in landfills.
Nitrous oxide has 265 times the global warming potential of carbon dioxide. Nitrous oxide is released when fertilisers are applied to soils. It also comes from the burning of fossil fuels and solid waste, as well as decomposing animal manure.
Synthetic gases are emitted from a variety of industrial processes. They are produced in very small quantities, but they have a very strong greenhouse effect. Thus, they are sometimes called ‘high global warming potential gases’.
SF6 has 23,500 times the global warming potential of carbon dioxide. There are different types of HFCs and PFCs, and these have up to 12,400 times the global warming potential of carbon dioxide.
Trends in global emissions
Greenhouse gas production by humans has increased steadily since the Industrial Revolution in about 1750. The increase has sped up in recent decades. Global emissions have risen by approximately 42%, from 32.7 gigatonnes (Gt) of carbon dioxide equivalent (CO2-e) in 1990 to 48.9 Gt CO2-e in 2018.
Energy, namely the use of fossil fuels for power generation and transport, contributed on average 74% of annual global emissions over that period. Agriculture contributed 14%. Industrial processes and product use, waste and land use change and forestry each contributed around 4% of annual global emissions.
Over 1990-2018, on average, 73% of emissions are in the form of carbon dioxide, 19% methane, 7% N2O and 1% synthetic gases.
Source: Climate Watch, 2020.
What the world is doing to reduce emissions
There are international organisations and agreements in place to try to reduce emissions and limit climate change.
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 to conduct objective scientific assessments on the causes, state and impacts of climate change. World renowned experts from across the globe donate their time to support the work of the IPCC.
In 1992, the United Nations Framework Convention on Climate Change (UNFCCC) was adopted as a framework for international cooperation to combat climate change.
In 1997, the third UNFCCC Conference adopted the Kyoto Protocol, the world’s first agreement to reduce greenhouse gas emissions. The Protocol binds more-developed countries to emission reduction targets. Overall, the targets add up to a 5% reduction of emissions compared with 1990 levels by 2012, and at least 18% below 1990 levels by 2020.
The Kyoto Protocol was followed by the Paris Agreement, adopted by 196 countries in 2015. The Agreement commits almost all countries to undertake efforts to address climate change and adapt to its effects. The overall goal is to limit global average temperature warming to well below 2°C, and preferably to 1.5°C, compared with pre-industrial levels.
What countries are doing to reduce emissions
Many countries have set national targets to reduce emissions. Strategies that different countries are using to reduce emissions include:
- investing in or subsidising renewable energy sources
- closing down power stations run with fossil fuels
- setting industry limits on emissions
- expanding electric car sales and use
- reducing land clearing and deforestation
- establishing carbon trading schemes to help industry reduce emissions.
In 2017, Mission 2020, a new global carbon emissions reduction strategy, was launched by political and business leaders to increase the urgency of climate change action. It has identified milestones to be achieved in 6 sectors – energy, infrastructure, transport, land, industry and finance.
Some leaders and scientists estimate that reducing emissions will not be enough to limit climate change. They believe we also need to reduce the existing levels of greenhouse gases in the atmosphere, such as by planting new forests or using new technologies to remove carbon dioxide from the air.
Greenhouse gas emissions – Our World in Data
Three years to safeguard our climate – Nature 2017
Urgent climate action to protect our oceans – UNFCCC 2021
Global strategy to rapidly reduce emissions – Mission 2020
Climate solutions – Union of Concerned Scientists