The Intergovernmental Panel on Climate Change (IPCC) sums up the research to say “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (man made) greenhouse gas concentrations”.
Ice core records that go back 420 000 years show that carbon dioxide levels in the atmosphere varied between 180 and 280 parts per million (ppm) mainly due to glacial cycles. However, since the Industrial revolution, concentrations of greenhouse gases in the atmosphere have increased dramatically. Human activities such as burning fossil fuels, land clearing and agricultural practices have increased carbon dioxide by more than a third (to around 380 ppm), nitrous oxide levels by about 17 percent and methane concentrations have more than doubled. According to research, the current rate of increase in carbon dioxide is unlikely to have been experienced at least in the last 20,000 years.