Year after year, CO2 emissions reach new record levels – and this is despite the self-commitment of many countries to reduce their greenhouse gas emissions. Many experts now doubt whether it is still possible to effectively combat climate change through emission reductions. Some place their hope in addressing the impending climate catastrophe through other measures: through instruments of climate engineering. These aim either to remove CO2 from the atmosphere and store it safely, or to cool the planet by reducing the amount of sunlight that reaches the Earth's surface. There are already proposals on how this could be technically realized, along with a few pilot projects, but it is clear for all variants: any necessary large-scale manipulation of natural Earth system processes would have enormous impacts on humanity.