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The high emissions scenario

The high emissions scenario 22 August 2019

Explainer: The high–emissions ‘RCP8.5’ global warming scenario (via CarbonBrief)

By Zeke Hausfather

A sizeable portion of recent studies on future climate impacts have focused on a warming scenario called “RCP8.5”. This high–emissions scenario is frequently referred to as “business as usual”, suggesting that is a likely outcome if society does not make concerted efforts to cut greenhouse gas emissions.

In recent years the emissions scenario used to generate RCP8.5 has come under criticism by a number of researchers for its assumptions around high future emissions and a dramatic expansion of coal use. At the same time, a new set of future scenarios – the Shared Socioeconomic Pathways (SSPs) – has since been released, offering a broader view of what a world without future climate policy might look like.

In this article, Carbon Brief examines how the emissions scenario underlying RCP8.5 was developed and how it has subsequently been used in the academic literature and media. According to the researchers who developed it, RCP8.5 was intended to be a “very high baseline emission scenario” representing the 90th percentile of no–policy baseline scenarios available at the time.

The creators of RCP8.5 had not intended it to represent the most likely “business as usual” outcome, emphasising that “no likelihood or preference is attached” to any of the specific scenarios. Its subsequent use as such represents something of a breakdown in communication between energy systems modellers and the climate modelling community.

While modelling potential worst–case outcomes is important, there is also a need to examine the wider range of no–policy baseline outcomes – the majority of which result in lower future emissions.

Read more via CarbonBrief…