Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and large oil and gas companies. Human-caused emissions 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 (GHGs). Emissions in the 2010s averaged 56 billion tons a year, higher than any decade 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.

At current emission rates averaging six and a half tonnes per person per year, before 2030 temperatures may have increased by an average of 1.5 °C (2.7 °F) over pre-industrial levels, which is the limit for the G7 countries and aspirational limit of the Paris Agreement.

Carbon accounting (or greenhouse gas accounting) is a framework of methods to measure and track how much greenhouse gas (GHG) an organization emits.

A related concept, which is popular in the media is carbon footprint which is defined as a "certain amount of gaseous emissions that are relevant to climate change and associated with human production or consumption activities".