|Source: The Economist|
The four results seem to clearly indicate a long term increase in global temperature and that there has been an acceleration over the past three decades. There are of course other correlates such as the rise of ocean levels and the melting of glaciers and ice caps that add to the evidence of global warming.
Of course, global warming may have causes other than man's contributions to greenhouse gases and changes in the albido of the land's surface.
Still, the precautionary principle suggests that we should take action now to reduce anthropogenic global warming.