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 footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO2-equivalent) per unit of comparison. Such units can be for example tonnes CO2-eq per year, per kilogram of protein for consumption, per kilometer travelled, per piece of clothing and so forth. A product's carbon footprint includes the emissions for the entire life cycle. These run from the production along the supply chain to its final consumption and disposal.
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 2022 were 703 GtC, of which 484±20 GtC from fossil fuels and industry, and 219±60 GtC from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2022, coal 32%, oil 24%, 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.
This is a list of climate change topics.
Kenneth Caldeira is an American atmospheric scientist. His areas of research include ocean acidification, climate effects of trees, intentional climate modification, interactions in the global carbon cycle/climate system, and sustainable energy.
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.
Christopher B. Field is an American scientist and researcher, who has contributed to the field of climate change. The author of more than 200 scientific publications, Field's research emphasizes impacts of climate change, from the molecular to the global scale. His work includes major field experiments on responses of California grassland to multi-factor global change, integrative studies on the global carbon cycle, and assessments of impacts of climate change on agriculture. Field's work with models includes studies on the global distribution of carbon sources and sinks, and studies on environmental consequences of expanding biomass energy.
Steven J. Davis is an earth system scientist in the Department of Earth System Science of the Stanford Doerr School of Sustainability at Stanford University. He is a highly cited researcher and leads the Stanford Sustainable Solutions Lab.
Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
Asmeret Asefaw Berhe is a soil biogeochemist and political ecologist who served as Director of the Office of Science at the US Department of Energy from 2022 to 2024. She is a Professor of Soil Biogeochemistry and the Ted and Jan Falasco Chair in Earth Sciences and Geology in the Department of Life and Environmental Sciences; University of California, Merced. Her research group works to understand how soil helps regulate the Earth's climate.
Whendee Silver is an American ecosystem ecologist and biogeochemist.
Christine Goodale is an ecosystem ecologist and an Associate Professor in the Department of Ecology and Evolutionary Biology at Cornell University. Goodale conducts research that studies the cycling of water, carbon, nitrogen and other nutrients through forest ecosystems.
Jill L. Bubier is a professor emerita of environmental science at Mount Holyoke College (MHC). Her research examines how Northern ecosystems respond to climate change.
Yude Pan is a senior research scientist with the Climate, Fire, and Carbon Cycle Sciences group of the Northern Research Station, USDA Forest Service, and a senior investigator of the Harvard Forest at Harvard University. Her work is in the fields of Ecosystem ecology and Global Change Biology. She studies terrestrial ecosystems and how environmental stressors affect complex interactions within those ecosystems. Much of her research focuses on forest ecosystems and how they relate to the carbon cycle as a whole, as well as forecasting complex effects of land use, climate change and air pollution on forest ecosystems.
Elena Litchman is a professor of aquatic ecology at Michigan State University known for her research on the consequences of global environmental change on phytoplankton.
Sangwon Suh is an American industrial ecologist.
