Munich Re and United Nations. The graph shows a ratio of global weather-related disaster losses to global GDP expressed in 2011 dollars and calculated at market exchange rates. For a peer reviewed analysis which goes into some depth on this subject, see this Munich Re-funded study:
E. Neumayer and F. Barthel. 2011. Normalizing Economic Loss from Natural Disasters: A Global Analysis, Global Environmental Change, 21:13-24 (here in PDF).
They conclude: "there is no evidence so far that climate change has increased the normalized economic loss from natural disasters."