Keynesian economics is the macroeconomic thought based on the ideas of 20th-century economist John Keynes. Keynesian economists believe that, in the short run, productive activity is influenced by aggregate demand (total spending in the economy), and that aggregate demand does not necessarily equal aggregate supply (the total productive capacity of the economy). Instead, it is influenced by a host of factors and sometimes behaves erratically, affecting production, employment, and inflation.
Richard Heinberg: "The power of fossil fuels fed our collective megalomania. Like people in previous civilizations, we went out on a limb—but modern energy and technology enabled us to go much further than any humans had before. Still, as all civilizations do, ours has reached the point of diminishing returns, of over-reach."