Human Choice, Warming, & Emissions 

More CO2 and other greenhouse gases in the atmosphere equals more warming for our climate. This relationship is straightforward. Less clear is just how much more emissions we will add to our atmosphere and how much warmer things will get. This isn’t a scientific uncertainty. It’s a social, political, and economic uncertainty based on whether we collectively cut our carbon footprints by upholding international agreements, such as the Paris Agreement, and by moving away from fossil fuels, or whether we continue on our high greenhouse gas path by keeping things business as usual.

The Representative Concentration Pathways

To account for emissions uncertainty in climate projections, climate researchers have developed the Representative Concentration Pathways (RCPs). RCPs are added to global climate model simulations to account for a range of human choices, from cutting emissions right away to staying on our high emissions path. RCPs run from RCP 2.6 (low warming) to RCP 8.5 (high warming).

While the RCPs represent a wide range of possible futures, CIRC tends to use just two RCPs that we define in the following way:

  • The Higher Emissions Scenario (RCP 8.5)—simulates our current trajectory of increased greenhouse gas emissions and population growth through the end of the century with nominal policies to reduce emissions. This “business as usual scenario” assumes warming will continue at its current high rate.
  • The Lower Emissions Scenario (RCP 4.5)—simulates a curtailment in greenhouse gas emissions through greenhouse gas mitigation efforts. This scenario assumes warming will continue but will slow from its current rate.

(The numbers in the names, if you’re curious, represent the amount of radiative forcing—trapped energy from the sun as measured by watts per square meter—that can be expected by the end of this century under each scenario.)

  Thinking Deeper:  

the Paris Agreement & RCPs 

The RCPs are meant to represent a range of possible warming under climate change. This range extends outside the temperature goals set by the Paris Agreement, which seeks to hold global mean temperature below 2 degrees Celsius (3.6 degrees Fahrenheit) of warming above preindustrial levels by the year 2100. 


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