evidence: People have long claimed, incorrectly, that the past century's temperature changes are just part of the Earth's natural cycle, rather than the result of human behaviour. [...] We know recent temperature rises weren't caused by the changes in the Sun's natural cycle because the layer of atmosphere nearest the earth is warming, while the layer of atmosphere closest to the Sun - the stratosphere - is cooling. [...] If temperature changes on Earth were being caused by the Sun, we would expect the whole atmosphere to warm (or cool) at the same time.