Frequently asked questions

About the Site About Climate Change About the Model Using the Site Questions from Investigating the Model

What is C-Learn?

C-Learn is the 3-region version of the scientifically reviewed, policymaker oriented C-ROADS model, which allows users to explore how changes in fossil fuel emissions, deforestation, and afforestation will affect atmospheric carbon dioxide levels, global temperature, sea level rise, cumulative emissions, and emissions per capita.

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Who should use C-Learn?

C-Learn was created for all users, from children and teachers to researchers and policymakers.

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Who created C-Learn?

C-Learn was built by Climate Interactive, Ventana Systems, and MIT Sloan School of Management's System Dynamics Group, building off of Dr. Tom Fiddaman's (of Ventana Systems) PHD dissertation at MIT. For more information, see

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Does it cost anything to use it?

There is no cost associated with using C-Learn. In fact, we actively encourage you to share your findings and we hope that you may use the graphs and tables from the site in presentations and projects. For additional resources and more information on Climate Interactive's open-source efforts, please visit .

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What is the purpose of the site?

This site serves two purposes. First, we hope that you will use this software to investigate various emissions scenarios to see what it will take to reach set targets and that you can share these results in your presentations. Second, we hope to inspire other organizations and individuals to develop their own interfaces and uses for the scientifically-rigorous equations in the simulation. For more on our motivations, see

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What is global warming?

According to the EPA Climate Change Basic Information, "Global warming is an average increase in the temperature of the atmosphere near the Earth's surface and in the troposphere, which can contribute to changes in global climate patterns. Global warming can occur from a variety of causes, both natural and human induced. In common usage, "global warming" often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities."

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How dire is the problem?

According to the IPCC, over the last century, average global temperature has increased by 1.2 to 1.4 degrees Farenheit, and over the next century, estimates put the temperature increase at 3 to 7 degrees (Source: IPCC Climate Change 2007: The Physical Science Basis)

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What are CO2 emission levels currently?

About 390 parts per million. On average the level of CO2 in the atmosphere has been rising at around 2 parts per million per year (see:

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What are the results of sea-level rise?

Large-scale flooding in low-lying countries like Bangladesh could reap disastrous consequences in forms such as economic disaster and home relocation. The IPCC has concluded that the impacts are "virtually certain to be overwhelmingly negative" ( IPCC, 2007).

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What are different ways for countries to reduce emissions?

Many measures to curtail emissions are initiatives begun by individuals. For more information on these measures, check out the following sites: and Governmental measures to reduce emissions include taxation on carbon dioxide emissions, incentives for "green" companies, and investment in innovative technologies that reduce carbon dioxide emissions. A more detailed CBO analysis is available at:

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How can I find out more?

Check out the following sites, if you're looking for more information on climate change:

Environmental Protection Agency FAQ
This site answers several elementary questions about climate change, emissions, and their effects.

NOAA National Climate Change Overview
The US National Oceanic and Atmospheric Administration (NOAA) National Climate Data Center provides data, reports, and images covering many aspects of climate change.

NOAA Global Warming FAQ
Provides a general overview of climate change data and issues

NOAA Climate Change Education
Here you can find educational materials to aid teachers and others learning about climate change.

Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change (IPCC), established under UN auspices, is a broad-based international panel of leading experts, and conducts scientific assessments on the causes and consequences of climate change.

RealClimate, "climate science from climate scientists" provides commentary on current issues in climate change science and policy by climatologists and other scientists. They work to separate what is science from what is advocacy and misinformation.

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How was the model made?

The model was made using a methodology known as system dynamics, which helps create simulation models and analyze system evolution for complex systems involving feedback loops.

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What is the scientific basis of the assumptions in the C-Learn model?

As explained in the C-ROADS technical review, "The simulation model is based on biogeophysical and integrated assessment literature and includes representations of the carbon cycle, other GHGs, radiative forcing, global mean surface temperature, and sea level change." The report continues, "The core carbon cycle and climate sector of the model is based on Dr. Tom Fiddaman's 1997 MIT dissertation. The model structure draws heavily from Goudrian and Ketner and Oeschger and Siegenthaler, et al. The sea level rise sector is based on Rahmstorf. In the current version of the simulation, temperature feedbacks to the carbon cycle are not included." For the entire report, check the following link:

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What data is used?

Also in the C-ROADS technical review, "The model uses historical data through the most recent available figures, for values such as country-level GDP and population, CO2 emissions from fossil fuels and from changes in land use. Scenarios for the future including Business As Usual CO2 emissions projections are calibrated to the IPCC SRES scenarios with the World Energy Outlook growth allocations between regions."

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Why are there so many graphs, and what do they show?

The graphs on the home page show the basic information regarding the emissions projections, carbon dioxide concentration increase, and global temperature increase over the 21st century resulting from the input changes made by the user. More specific graphs displaying emissions, atmospheric GHG concentration, temperature increase, and sea level increase can be accessed by clicking on the menu items provided.

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Are there limitations in what inputs we may use?

Variable Minimum input value Maximum input value
Stop Growth Year 2010 2100
Reduction Start Year 2010 2100
% Annual Reduction 0 10

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Are we allowed to copy the graphs from the site?

Yes. By right-clicking the graphs and selecting "copy image", you can copy the graphs and distribute them to any papers/projects/presentations you would like. The data for generating graphs using your own graphing software are also available under the data menu.

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Does deforestation and afforestation really have that small a difference?

Based on the model, the difference they make is fairly minor. There is a limit to how many forests can be created and how long they take to sequester carbon dioxide from the atmosphere.

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Why is there an awkward jump/change in the otherwise smooth graphs?

The policy changes only begin to take place from the "start year". However, the graphs begin in 2000. Consequently, the graphs will always have a sudden change, resulting from the policy decision, whenever it starts.

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