Greenhouse gas emissions
The link between CO2 emissions and rising temperature is very robust. Scientists have known since the early 1800s that gases in the atmosphere trap heat. The first calculations to show the link between changes in CO2 levels and changes in the earth’s temperature were made over a hundred years ago. Global CO2 emissions resulting from human activity have increased by over 600% since 1950. As a result, the concentration of CO2 in the air is around 400 parts per million by volume (ppm) and rising, compared to about 280ppm in pre-industrial times.
Agriculture, industry and waste disposal all lead to further greenhouse gas emissions (such as methane and nitrous oxide). While other forms of air pollution (such as sulphates and nitrates) have partially offset this greenhouse warming to date, human activity is having a strong overall warming effect. After looking at a variety of factors, natural and human, the Intergovernmental Panel on Climate Change concluded there is a 90% probability that human-related greenhouse gas increases have caused most of the observed increase in global average temperature since the mid-20th century.