Revise GCSE Physics

Question:Why is it difficult for scientists to be sure about Global Warming?

The planet is very big and changes will therefore take a long time to happen.

However this also means that any changes currently under way will take at least as long to correct.

The temperature of the Earth and the composition of the atmosphere are also known to have changed periodically in the past by mechanisms that had nothing to do with Man and therefore any changes may be part of a natural cycle.