What is the right climate?
Why are we defining ‘dangerous climate change’ with respect to the climate of the 18th century, which was the coldest period in the last millennia, with wicked winters? Why not use a reference point of 2000 or 1970? The IPCC doesn’t provide a convincing explanation for the overall warming between 1750 and 1950; according to climate models, human causes contributed only a very small amount to the global warming to during this period (so presumably this overall warming was caused by natural climate variability). Co-opting the period between 1750 and 1950 into the AGW argument muddies the scientific and the policy waters.
It would make much more sense — from a scientific perspective, from the perspective of adaptation and engineering, and in the public communication of climate change — to refer to warming relative to a more recent reference period. Since the emissions reference periods are between 1990 and 2005, this also adds to the argument of citing a more recent reference period for defining ‘dangerous’.
The argument that human caused warming is already ‘dangerous’ — widely made by politicians, the media and some scientists — flies in the face of scientific evidence reported by the IPCC AR5 and SREX. Extreme weather events were worse earlier in the 20th century, and sea level has been rising for millennia, with recent rates of sea level rise comparable to what was observed in the middle 20th century.
It’s almost as though there’s some sort of political agenda at work.