In its policy statement, the APS declares: "Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes. The evidence is incontrovertible: global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth's physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now."