Secular stagnation is where economic growth is persistently negligible or very low. The first notable economist to talk about secular stagnation was Alvin Hansen, who argued in the late 1930s that economic growth in the US was low and would remain low due to declining population growth and declining technological innovation. The post-war baby and technological booms meant that people largely forgot about Hansen's theory. However, in the light of low economic growth and near-zero real interests which have persisted since 2008, Larry Summers and others have revived the secular stagnation hypothesis - click here and here. In the video below, Oxford's Kevin O'Rourke gives a lecture to the British Academy entitled "Economic Impossibilities For Our Grandchildren?" which addresses the secular stagnation hypothesis and prescribes various policies to address it. A working paper version of his lecture is available here.
The Berkeley Earth Project , an independent study of global warming, has found that the earth has become a degree warmer over the past half century. However, the statistical uncertainty surrounding pre-1920 estimates makes it very hard to say much about long-term trends - click here for graph . This is one of my concerns with the global warming debate - we simply don't have trustworthy long-run data which looks at temperature changes over the last millennium (or two). My second concern with the global warming debate is that it is very hard to prove any sort of casual link between global warming and human activity. The scientists may be able to show correlation between global warming and our production of carbon dioxides etc., but correlation is not causation. My third concern with the debate is that those who are sceptical or agnostic are stereotyped as flat-earthers or intellectually-challenged crackpots. This only stifles debate and the progress of science itself.