In the original Figure 1, the x-axis is labelled temperature change relative to ‘today.’ In the new Figures, the x-axis is labelled as temperature change relative to pre-industrial temperatures. The term ‘pre-industrial’ derives from climate scientist’s interest in anthropogenic influences on CO2 levels and they usually assign a date of 1750 as the last time natural CO2 levels were observed. A temperature change of 0 relative to pre-industrial temperatures, existed in 1750. On the newly labelled x-axis, we are ‘today’ at +0.8C.
It would be difficult to imagine economists interested in (or reporting) the effect of climate change on GDP in comparison to the GDP at pre-industrial times, temperatures, and CO2 levels. More likely the economic analyses were performed relative to the GDP of ‘today’ at the time of each publication (e.g. at +0.8C relative to pre-industrial levels in 2014) but calibrated with climate models that expressed results relative to 1750 levels (usually taken at 285ppm). . . .Due to non-linearities and lags in the earth system, a +1C change relative to 1750 has a different impact than a +1C change relative to today’s temperature (already at +0.8C relative to 1750). Presumably, economists calibrate their analyses using available climate model results. . . .Given the shift in labelling of the x-axes, with no adjustments in the position of the data points between the 2009 and current versions of the plots, it is not clear that the author considered the importance of these distinctions so caution in interpreting the relation of the underlying data to published plots is in order.
Given that the studies in Table 1 use different methods, it is striking that the estimates are in broad agreement on a number of points—indeed, the uncertainty analysis displayed in Figure 1 reveals that no estimate is an obvious outlier.
The fitted line in Figure 1 suggests that the turning point in terms of economic benefits occurs at about 1.1 degrees Celsius warming (with a standard deviation of 0.7 degrees Celsius).