ABSTRACT
Climatic trends are inadequately established and it is not certain whether human activity will counter or reinforce natural changes. Human activities are raising natural levels; indeed they probably account for over 90 per cent of what there is in the atmosphere. The main anthropogenic sources are oil refining, woodpulp production, the combustion of hydrocarbons, and breakdown of sewage. If warming is happening, countermeasures should reduce difficulties, but not prevent environmental change because effective and long-active greenhouse gases have already been released into the atmosphere. The cutting of forests and pollution of oceans has probably cut the rate at which atmospheric gases that are responsible for global warming are rendered inactive by photosynthetic lock-up or deposition as carbonates. Temperate zone plants are generally less well adapted to withstand Ultraviolet (UV)-B than many tropical species: that might counter relatively greater benefits from global warming in higher latitudes.
