365 Days of Climate Awareness 2: RCPs

365 Days of Climate Awareness 

2: RCPs

To model the climate as modified by human activities, the first step is to model the human activities. In part 2 we learned about Shared Socioeconomic Pathways, or SSPs, the IPCC's theorized likeliest courses of future social and economic events. In modeling the climate, the social and economic scenarios must be translated into environmental scenarios: hence the RCPs, or Representative Concentration Pathways.

The term "representative" signifies that each emissions scenario used in an IPCC model has been selected from a wider range of possibilities (there is more than one emissions scenario for each SSP). "Concentration" refers to atmospheric gas concentrations being the most fundamental (though far from the only) climate model inputs. (The global atmosphere is assumed to be well-mixed, with uniform composition everywhere. With this (not bad) assumption, total emissions can be converted into global concentrations.) "Pathways" signifies that they are time series.

The historical scenarios--the SSPs--are time series of variables describing the economy, energy use, and population, and changes to each through time. These time series are then plugged into models which produce time series for a wide set of environmental variables: gas emissions (such as, but not limited to, carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)); land use; land cover, and more. These environmental time series are the RCPs.

To summarize: time series of social-economic variables (SSPs) are converted into time series of environmental variables (RCPs), in order to then model climate change. (On a related topic, climate science has nearly as many acronyms as the military.)

Each RCP is named (1.9, 2.6, 4.6, 7.0, 8.5) for the radiative forcing which it produces by 2100, once plugged into the climate model. Radiative forcing is the subject of a future post, but in short, it represents the effect something, like added CO₂, volcanic activity, or increased cloud cover, has on global climate. But for tomorrow's post I'm going to rewind a bit and start where I should have started this series: with the absolute basics, beginning with what the greenhouse effect actually is.

Be well!

(Illustration: IPCC. Continuation of the model plots from #1, showing predicted ocean effects of global warming. First (c) is ocean acidity (pH). The ocean is becoming more acidic as it absorbs CO₂, which dissolves into carbonic acid (weak but still an acid) in water. Second (d) is global (eustatic) sea level rise.)