Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide (CO2), 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 fuelling 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.
Carbon dioxide (CO2) is the main greenhouse gas resulting from human activities. It accounts for more than half of warming. Methane (CH4) emissions have almost the same short-term impact. Nitrous oxide (N2O) and fluorinated gases (F-gases) play a lesser role in comparison. Emissions of carbon dioxide, methane and nitrous oxide in 2023 were all higher than ever before.
Electricity generation, heat and transport are major emitters; overall energy is responsible for around 73% of emissions. Deforestation and other changes in land use also emit carbon dioxide and methane. The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil fuel industry. The largest agricultural methane source is livestock. Agricultural soils emit nitrous oxide partly due to fertilizers. Similarly, fluorinated gases from refrigerants play an outsized role in total human emissions.
The greenhouse effect occurs when greenhouse gases in a planet’s atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source as in the case of Jupiter, or from its host star as in the case of the Earth. In the case of Earth, the Sun emits shortwave radiation (sunlight) that passes through greenhouse gases to heat the Earth’s surface. In response, the Earth’s surface emits longwave radiation that is mostly absorbed by greenhouse gases. The absorption of longwave radiation prevents it from reaching space, reducing the rate at which the Earth can cool off.
Without the greenhouse effect, the Earth’s average surface temperature would be about −18 °C (−0.4 °F), which is less than Earth’s 20th century average of about 14 °C (57 °F), or a more recent average of about 15 °C (59 °F). In addition to naturally present greenhouse gases, burning of fossil fuels has increased amounts of carbon dioxide and methane in the atmosphere. As a result, global warming of about 1.2 °C (2.2 °F) has occurred since the Industrial Revolution, with the global average surface temperature increasing at a rate of 0.18 °C (0.32 °F) per decade since 1981.
Starting about 1750, industrial activity powered by fossil fuels began to significantly increase the concentration of carbon dioxide and other greenhouse gases. Emissions have grown rapidly since about 1950 with ongoing expansions in global population and economic activity following World War II. As of 2021, measured atmospheric concentrations of carbon dioxide were almost 50% higher than pre-industrial levels.
The main sources of greenhouse gases due to human activity (also called carbon sources) are:
- Burning fossil fuels: Burning oil, coal and gas is estimated to have emitted 37.4 billion tonnes of CO2eq in 2023. The largest single source is coal-fired power stations, with 20% of greenhouse gases (GHG) as of 2021.
- Land use change (mainly deforestation in the tropics) accounts for about a quarter of total anthropogenic GHG emissions.
- Livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, human-made lake, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.
- Use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
- Agricultural soils emit nitrous oxide (N2O) partly due to application of fertilizers.
- The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Cattle (raised for both beef and milk, as well as for inedible outputs like manure and draft power) are the animal species responsible for the most emissions, representing about 65% of the livestock sector’s emissions.
Australian Study
Climate change is upon us and one of the major factors contributing towards its expansion is the greenhouse effect. Greenhouse gas emissions are known to have an adverse impact on our Ozone layer and also for its heat-trapping effect, and this is further exacerbated by anthropogenic emissions.
However, a new study conducted in Australia has exhibited that switching food choices and making rudimentary food and drink swaps could have a longing impact on the environment, and the greenhouse gas effect from groceries can be reduced by 26%. Scientists from The George Institute for Global Health and Imperial College London’s School of Public Health performed an in-depth analysis of the environmental effects of a country’s food purchasing behaviours. They analysed comprehensive data on greenhouse gas emissions and sales for numerous products in Australian supermarkets, reflecting the typical Western diet found in many nations.
Further, the research also highlighted that if major dietary changes are employed such as opting for a vegetarian meal instead of frozen meats would enhance the impact of reducing GHG (Greenhouse gas) emissions by 71 percent. The researchers are advocating for on-pack food labelling of GHG emissions so that consumers are able to exercise an informed choice.
Dr. Allison Gaines, the lead author, and epidemiologist who conducted the analysis for The George Institute and Imperial College London’s School of Public Health, stated, “Dietary habits need to change significantly if we are to meet global emissions targets, particularly in high-income countries like Australia, the UK, and US. Consumers are willing to make more sustainable food choices, but lack reliable information to identify the more environmentally-friendly options.”
“Incorporating sustainability targets in national food policies could directly contribute towards reaching global environmental goals, without burdening consumers” Dr. Pareskevi SeferidiSchool of Public Health, Imperial College London “The results of our study show the potential to significantly reduce our environmental impact by switching like-for-like products,” said Dr Gaines.
Based on this research, The George Institute has developed a free app called ecoSwitch, currently available only in Australia. This app allows shoppers to use their phones to scan a product’s barcode and check its emissions. Professor Neal said, “EcoSwitch is a much-needed first step, but our vision is for mandatory display of a single, standardised sustainability rating system, on all supermarket products.”
Agricultural activities produce emissions of three greenhouse gases: carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). Each of these gases has a distinct impact on climate change. Agricultural emissions of greenhouse gases stem from complex natural processes that are challenging to measure, unlike the more straightforward emissions from burning fossil fuels.
Methane (CH4) primarily originates from livestock digestion (known as enteric fermentation) and the management of livestock manure. It is the largest contributor to agricultural greenhouse gas emissions. The second largest contributor is nitrous oxide, which predominantly results from the application of agricultural fertilizers to soils and from manure management.
Carbon dioxide emissions arise from the heightened decomposition of plant matter in soils and the conversion of lands to agricultural uses. However, these emissions are partially counterbalanced by the augmented storage of plant matter in cropland soils.
In 2021, carbon dioxide emissions made up about 7.2 percent of agricultural greenhouse gas emissions not related to energy. The primary source of these emissions in agriculture is the disturbance of soil organic matter, acting as a repository or “sink” for emissions. Soil tillage, which involves turning over and preparing soil for cultivation, speeds up the decomposition of organic matter by microbial activity. This process leads to higher carbon dioxide emissions as microbes respire more.
To decrease emissions from soil management and boost carbon dioxide storage in agricultural soils, interventions are necessary to minimise soil disturbances and enhance soil organic matter levels. One commonly adopted method for increasing soil organic matter involves cultivating a “cover crop” to shield the soil between planting seasons and subsequently incorporating the plant material into the soil. Additionally, reducing soil disturbance through alterations or elimination of conventional tillage practices has been advocated.
The formation of nitrous oxide is closely linked to fertilizer application practices, making it crucial to prevent nitrogen fertilizer overuse or mistimed application. Various strategies can be employed to achieve this objective.
One approach involves distributing fertilizer in multiple smaller applications throughout the growing season instead of applying a single large dose at the beginning. Another strategy entails leveraging advancements in drone-based remote sensing technology to assess nitrogen levels in soils accurately. This allows for targeted fertilizer applications in areas where the need is highest, thus optimising nitrogen use efficiency and reducing nitrous oxide emissions.
The decomposition of manure, a significant source of methane emissions, can be curbed through the utilisation of anaerobic digesters. These devices actively promote methane production from manure decomposition and subsequently capture the generated biogas, comprising methane and other gases. The captured biogas can then be utilised onsite or sold offsite as an energy source, thereby reducing methane emissions from manure management while simultaneously harnessing renewable energy.
As we move forward, the need to mitigate the impacts of climate change becomes imperative. Opting for eco-friendly measures is no longer an option, as the rate at which we are implementing mitigation measures may prevent us from reaching our goal of returning to pre-industrial climate levels. The maximum temperature increase threshold set by the 2015 Paris Agreement has also been surpassed in recent times, which is another cause for concern. Therefore, such research serves as an important tool for us to mitigate the climate crisis looming over our heads.
