Why Do Climate Scientists use 15°C for Current GMST?
There's a conspiracy theory floating around the blogosphere and social media that argues (oddly) that climate scientists manufactured global warming by artificially lowering global temperatures. The "thinking" goes like this. Back in 1896, Svante Arrhenius calculated global mean surface temperature (GMST) to be 15°C. Following this, other scientists confirmed this value for later years. For instance, Hansen is reported to have claimed that value in 1981. The first IPCC report is claimed to confirm it again in 1990. In some incarnations of this conspiracy theory use other sources using 15°C, but the concept is the same. Then, after the so-called "pause" began in 1998, scientists needed another way to manufacture global warming, so they lowered GMST to 14°C so that they could increase it again. If that sounds confusing to you, it should. It doesn't make any sense. But let's unpack what's actually going on. Arrhenius' Calculation in 1896 Svante Arr...