Evidence that post-industrial global warming is largely caused by man-made CO2  is directly based on straightforward direct measurements of the atmosphere, flow of energy into the land and sea, and measurement of the physical forms (isotopes) of carbon in the biosphere and polar ice. It is further supported by evidence from advanced climate models.
The evidence for the man-made cause of 20th Century climate change is very soundly based on the following direct observations :
  1. The increase in atmospheric CO2   since 1900 correlates very closely with cumulative man-made CO2emissions and can only be explained by the strong predominance of man-made emissions over all other sources.
  2. The carbon isotope 13C is depleted in fossil fuels and plants compared with other natural sources. Decrease in the 13C/12C ratio in the atmosphere, surface water, coralline sponges with annular growth rings, Arctic and Antarctic ice, European and equatorial stalactites etc. all clearly demonstrate that the post-1750 increase in atmospheric CO2 very largely results from burning fossil fuels and forests.
  3. Satellite and surface infrared measurements show that less energy is escaping from the planet  into space at CO2 absorption wavelengths than it did 30 years ago. The brilliant Swedish chemist Svante Arrhenius predicted in 1896 that a doubling of atmospheric CO2  would lead to an eventual rise of 5°C broadly in line with today’s best predictions.
  4. Ocean and surface temperature measurements enable heat fluxes both on land and at sea to be calculated. They show that the planet continues to accumulate heat. The heat accumulation can only be explained by the strong predominance of man-made warming over other possible causes.

In addition a comparison of outputs from a series of different advanced climate models with actual observations indicates that surface temperature patterns, Arctic sea ice, rainfall patterns, Antarctic warming, and  changes in salinity of the subtropical North Atlantic are very likely caused by man-made emissions.