Methodology

NASA's Model

The computer model that generated the results for this graphic is called "ModelE2," and was created by NASA's Goddard Institute for Space Studies (GISS) , which has been a leader in climate projections for a generation. ModelE2 contains something on the order of 500,000 lines of code, and is run on a supercomputer at the NASA Center for Climate Simulation in Greenbelt, Maryland.

Researchers who study the Earth's climate create models to test their assumptions about the causes and trajectory of global warming. Around the world there are 28 or so research groups in more than a dozen countries who have written 61 climate models . Each takes a slightly different approach to the elements of the climate system, such as ice, oceans, or atmospheric chemistry.

A Global Research Project

GISS produced the results shown here in 2012, as part of its contribution to an international climate-science research initiative called the Coupled Model Intercomparison Project Phase Five. Let's just call it "Phase-5."

Phase-5 is designed both to see how well models replicate known climate history and to make projections about where the world’s temperature is headed. Initial results from Phase-5 were used in the 2013 scientific tome published by the Intergovernmental Panel on Climate Change

There are more than 30 different kinds of experiments included in Phase-5 research. These tests address questions like, what would happen to the Earth’s temperature if atmospheric carbon dioxide suddenly quadrupled? Or, what would the world’s climate be like through 2300 if we keep burning fossil fuels at the current rate?

Phase-5 calls for a suite of "historical" experiments. Research groups were asked to see how well they could reproduce what's known about the climate from 1850-2005. They were also asked to estimate how the various climate factors—or "forcings"—contribute to those temperatures. That's why this graphic stops in 2005, even though the GISS observed temperature data is up-to-date. The years 2005-2012 were not a part of the Phase-5 "historical" experiment.