| I would say we are largely past the second threshold too (that the warming is human caused). The last IPCC report had as the first statement in the summary for policymakers (from WG1 - the physical science group) A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred. The previous report (from 2013) only said (and much further in) Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system. The equivalent statement from AR4 (2007) was The understanding of anthropogenic warming and cooling influences on climate has improved since the TAR, leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming, ... You could argue there is more of a question about what to do about it (e.g. try and mitigate climate change or just pay for the damanges). There is pretty good evidence at this point that mitigating the change through reducing CO2 emissions is a lot cheaper and comes with a host of other benefits (energy security, improved public health), but I can see wherer there might be arguments to have about this. |