The Intergovernmental Panel on Climate Change classifies the human influence on our climate as extremely likely to be the main reason of global warming over the last decades. Particularly anthropogenic emissions of carbon dioxide are made responsible for the observed temperature changes, while any natural forcings are almost completely excluded.
However, detailed own calculations with an advanced energy-radiation-balance model indicate that the temperature increase and its variations over the last 140 years can much better be explained by additionally including solar radiative forcing and its amplification by induced cloud cover changes. We present simulations based on different time series of the total solar irradiance and compare them with composed land-ocean-surface temperature measurements of the Northern Hemisphere.
From these simulations we follow that CO2 should not have contributed more than about one
third to global warming over the last century, while solar variations over this period can well
explain two thirds of the increase.