Apparently one of the numbers used by Tol (2009) to estimate the Economic Effects of Climate Change is incorrect. Chris Hope’s 2006 study actually predicted a -0.9 % change in GDP for a 2.5oC rise in temperature (since 2009) not 0.9 (as used in Tol 2009). I’ve done a quick test and as far as I can tell this reduces the temperature at which the % change in GDP will become negative, from 2.2oC to about 2oC (see Figure below – dashed line is my new estimate). I should acknowledge that it’s a Saturday morning, so I have done this quickly and rather crudely, so may have made a mistake.
This error/typo in Tol (2009), presumably, also changes the year in which we would start to see the economic effects of climate change becoming negative. Based on the same assumptions as Matt Ridley seems to use, I get that this would happen in about 2065, rather than 2080. To be clear, I think this is heavily over-interpreting the work of Richard Tol anyway, but given that Matt Ridley has based his article on Richard Tol’s paper, and given that his paper has an acknowledged error (certainly Chris Hope has confirmed the error, as has Richard Tol I believe) this would seem to be an easy error to acknowledge and fix. If you want to read more about other issues with Matt Ridley’s article, I recommend articles by Chris Hope himself and by Bob Ward.