In aggregate, higher - cost active options lead to returns about 1 % lower on average (because the strategies cost about 1 % more), while also generating
a substantially wider range of outcomes — relative to the market performance.
But given that carbon dioxide levels were now
substantially higher than anything in the past two millions
of years, in either glacials or interglacials, it had become abundantly clear that the greenhouse effect was something we needed to take extremely seriously: even if the precise future increase in temperature was still an unknown quantity, with a fairly
wide error -
range, models indicated that for a doubling
of carbon dioxide from pre-industrial levels, a rise
of three degrees celsius as a global average was the most likely
outcome.