Frequently Asked Questions

Background

Methodology

Background

Who prepared this analysis?
The analysis was created via a joint initiative of Climate Interactive and Climate Advisers, based on the simulation model C-ROADS, which was built and tested by Climate Interactive and MIT Sloan.

Does achieving a certain balance year mean that a certain temperature limit will be achieved?
No. Emissions after the balance year help determine 2100 temperature.

What happens with the balance after the balance year?
Emissions are “net negative” after the balance year. That is, the removals exceed the emissions.

The graphs include an assessment of future temperature from the Paris pledges. What is the source and why are there other estimates?
For more on our analysis, consult the Climate Scoreboard. And its FAQs. A team at WRI also wrote about the topic.

What did you assume about carbon dioxide removal approaches in these scenarios?
We included afforestation efforts that are pledged in the national contributions to the Paris Agreement. Additionally, approximately half of the scenarios include carbon dioxide removal (CDR) approaches. When they do, the maximum included is 1 GT/yr of CDR by 2050 and 6 GT/yr by 2100. When we include CDR, the balance year occurs ~3 years earlier from a similar scenario without CDR.

Why do removals decline in the scenarios in which the world reduces emissions?
The net rate of removal is driven by the gap between carbon in the atmosphere and carbon stored in sinks – plants, soils and oceans. Cutting emissions reduces carbon in the atmosphere, so storage into sinks declines, but the sinks continue to release previously stored carbon.

Methodology

How are the balance year and range calculated?
We ran 792 scenarios in the simulation model C-ROADS and picked all of the ones (604) that limited warming to 1.5-1.9°C. We simulated fifteen regions of the world separately, plus carbon dioxide removals (CDR).

Scenarios were varied in several ways regarding whether countries and regions achieve or exceed their Paris pledges, what year emissions peak, and the rate of emissions reduction. For more specifics, consult the Climate Interactive website.

There were two other conditions we met:

  1. Developed countries always reduced emissions at a faster annual rate than developing countries.
  2. Developed countries always began emissions reductions sooner than developing.

How was this model constructed?
C-ROADS was created using System Dynamics, a modeling methodology invented at MIT in the 1950s.

How was the model reviewed?
The C-ROADS model was scientifically reviewed by a panel of outside, independent experts, chaired by Sir Robert Watson (former chair of the IPCC).

How can one learn more about the model behind the analysis?
The model is freely available online for use and review.

It was published in Environmental Modelling and Software as: Sterman, John; Thomas Fiddaman; Travis Franck; Andrew Jones; Stephanie McCauley; Philip Rice; Elizabeth Sawin; Lori Siegel. (2013) Management Flight Simulators to Support Climate Negotiations.

The ~200 page Reference Guide, with all equations, assumptions, parameters, and data sources is available here. A shorter summary is here.

Who uses this model?
Approximately 5,000 people worldwide have downloaded the model.

Some leaders who have used the model include: