4Earth's temperature is determined by the thickness of the ozone layer. When this layer is depleted, more solar ultraviolet radiation reaches Earth, increasing temperatures. The ozone layer has been depleted since the 1960s by human-manufactured gases and since 2014 by extensive lava flows from Bárðarbunga volcano in central Iceland. What Really Causes Global Warming shows that the greenhouse warming theory cannot explain recent climate change. Reducing greenhouse gas emissions would be a total waste of money.