The scientific community has been investigating the causes of climate change for decades. After thousands of studies, it came to a consensus, where it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times." This consensus is supported by around 200 scientific organizations worldwide, The dominant role in this climate change has been played by the direct emissions of carbon dioxide from the burning of fossil fuels. Indirect CO2 emissions from land use change, and the emissions of methane, nitrous oxide and other greenhouse gases play major supporting roles.
A carbon sink is a natural or artificial process that "removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere". These sinks form an important part of the natural carbon cycle. An overarching term is carbon pool, which is all the places where carbon on Earth can be, i.e. the atmosphere, oceans, soil, plants, and so forth. A carbon sink is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.
Global Warming Potential (GWP) is an index to measure how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been added to the atmosphere. The GWP makes different greenhouse gases comparable with regard to their "effectiveness in causing radiative forcing". It is expressed as a multiple of the radiation that would be absorbed by the same mass of added carbon dioxide, which is taken as a reference gas. Therefore, the GWP has a value of 1 for CO2. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.
Nitrous oxide, commonly known as laughing gas, nitrous, nitro, or nos, is a chemical compound, an oxide of nitrogen with the formula N
2O. At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen.
Trace gases are gases that are present in small amounts within an environment such as a planet's atmosphere. Trace gases in Earth's atmosphere are gases other than nitrogen (78.1%), oxygen (20.9%), and argon (0.934%) which, in combination, make up 99.934% of its atmosphere.
Food miles is the distance food is transported from the time of its making until it reaches the consumer. Food miles are one factor used when testing the environmental impact of food, such as the carbon footprint of the food.
Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide, from burning fossil fuels such as coal, oil, and natural gas, is one of the most important factors in causing climate change. The largest emitters are China followed by the United States. The United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Emissions in the 2010s averaged 56 billion tons a year, higher than any decade before. Total cumulative emissions from 1870 to 2017 were 425±20 GtC from fossil fuels and industry, and 180±60 GtC from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2017, coal 32%, oil 25%, and gas 10%.
The United States produced 5.2 billion metric tons of carbon dioxide equivalent greenhouse gas (GHG) emissions in 2020, the second largest in the world after greenhouse gas emissions by China and among the countries with the highest greenhouse gas emissions per person. In 2019 China is estimated to have emitted 27% of world GHG, followed by the United States with 11%, then India with 6.6%. In total the United States has emitted a quarter of world GHG, more than any other country. Annual emissions are over 15 tons per person and, amongst the top eight emitters, is the highest country by greenhouse gas emissions per person. However, the IEA estimates that the richest decile in the US emits over 55 tonnes of CO2 per capita each year. Because coal-fired power stations are gradually shutting down, in the 2010s emissions from electricity generation fell to second place behind transportation which is now the largest single source. In 2020, 27% of the GHG emissions of the United States were from transportation, 25% from electricity, 24% from industry, 13% from commercial and residential buildings and 11% from agriculture.
The Global Carbon Project (GCP) is an organisation that seeks to quantify global greenhouse gas emissions and their causes. Established in 2001, its projects include global budgets for three dominant greenhouse gases—carbon dioxide, methane, and nitrous oxide —and complementary efforts in urban, regional, cumulative, and negative emissions.
Carbon dioxide removal (CDR) is a process in which carbon dioxide is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in products. This process is also known as carbon removal, greenhouse gas removal or negative emissions. CDR is more and more often integrated into climate policy, as an element of climate change mitigation strategies. Achieving net zero emissions will require first and foremost deep and sustained cuts in emissions, and then—in addition—the use of CDR. In the future, CDR may be able to counterbalance emissions that are technically difficult to eliminate, such as some agricultural and industrial emissions.
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F).
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe, and 28 in terms of its impact over a 100-year timeframe.
Greenhouse gas monitoring is the direct measurement of greenhouse gas emissions and levels. There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments. Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.
Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the largest natural source of atmospheric methane in the world, and are therefore a major area of concern with respect to climate change. Wetlands account for approximately 20–30% of atmospheric methane through emissions from soils and plants, and contribute an approximate average of 161 Tg of methane to the atmosphere per year.
Climate-friendly gardening is a form of gardening that can reduce emissions of greenhouse gases from gardens and encourage the absorption of carbon dioxide by soils and plants in order to aid the reduction of global warming. To be a climate-friendly gardener means considering both what happens in a garden and the materials brought into it as well as the impact they have on land use and climate. It can also include garden features or activities in the garden that help to reduce greenhouse gas emissions through processes not directly related to gardening.
Pete Smith is Professor of Soils and Global change at the University of Aberdeen where he directs the Scottish Climate Change Centre of Expertise, ClimateXChange.
The amount of greenhouse gas emissions from agriculture is significant: The agriculture, forestry and land use sector contribute between 13% and 21% of global greenhouse gas emissions. Emissions come from direct greenhouse gas emissions. and from indirect emissions. With regards to direct emissions, nitrous oxide and methane make up over half of total greenhouse gas emission from agriculture. Indirect emissions on the other hand come from the conversion of non-agricultural land such as forests into agricultural land. Furthermore, there is also fossil fuel consumption for transport and fertilizer production. For example, the manufacture and use of nitrogen fertilizer contributes around 5% of all global greenhouse gas emissions. Livestock farming is a major source of greenhouse gas emissions. At the same time, livestock farming is affected by climate change.
