In 2015, the Paris Agreement was signed, creating voluntary benchmarks for countries to meet in order to stay well below two degrees of warming, or RCP 2.6.
Well, in the early 2010s, a set of emissions scenarios called RCPs ranging from very stringent climate policy to no climate policy at all was developed to represent what warming could look like by 2100.
So in the case of RCP 8.5, this means that humans would have emitted enough greenhouse gases into the atmosphere to add an additional 8.5 watts per meter squared of solar radiation to the climate by 2100.