But the strength of the greenhouse effect depends on the chemical composition of the atmosphere, because the phenomenon is due to the absorption of infra-red radiation by various gases in the air.
To date, no drug has been approved in its leaf form because plants contain a complex composition of compounds with uncertain pharmacologies, metabolisms, side-effect profiles, toxicologies, drug interactions, and no control of relative concentrations.
Mr Freeman finds that, in practice, employment-protection laws appear to have little effect on the overall level (as opposed to the composition) of employment.