the global energy assessment forthcoming has estimated that the required share of zero carbon energy in would need to be about per cent in order for the target of staying below a c increase from preindustrial levels to be achieved with a probability of at least per cent only the most ambitious technologyoptimistic scenarios achieve such a high share as illustrated by a literature review of renewable energy scenarios hamrin hummel and canapa the most technologyoptimistic of the iea scenarios iea etp tech plus barely reaches this level the others include the eu world energy technology outlook wetoh scenario with c constraint and the greenpeace revolution scenario assumptions in these scenarios are heroic indeed requiring unprecedented technological progress international cooperation and transfers