The zero-dimensional energy balance model was developed by a Russian and an American-British climatologist. It involves only globally averaged scalar quantities and is characterised by its simplicity. It deals with the heat balance of the Earth's surface: Solar radiation – Earth's emission = Warming of the Earth's surface. Since the concentration c of greenhouse gases (mainly CO₂) in the atmosphere causes part of the emission to be reflected back to Earth—thereby contributing significantly to its warming —this effect is taken into account by introducing an emission factor g < 1 that depends on c. The calculated temperature curve is displayed graphically for three scenarios: temperature increases of 1.5, 2.0, and 3.0 degrees Celsius compared to pre-industrial levels.