A team from MIT recently published the results of a modeling exercise in which they ran multiple 21st century climate change scenarios through the state-of-the-art MIT Integrated Global Systems Model (IGSM) in order to compare projected outcomes. These scenarios derive from three respected sources: the IPCC Special Report on Emissions Scenarios (SRES); the US Climate Change Science Program (CCSP); and a set of Shell corporate climate scenarios. Drawing on these, scientists assembled a dozen different climate scenarios reflecting different emissions profiles, biogeochemical process models, public policies (including aggressive mitigation), and other critical assumptions. The results of subsequent test runs are unnerving:
"The broader implication of these scenarios is that all see substantial continued increases in temperature that would create serious environmental concerns. If we rule out the highest [impact scenario] as unthinkable and the lowest ... as possibly unachievable we arrive at a scenario-dependent temperature increase ranging from about 2.5 to 4.5 degrees [C] compared to present. Such increases will require considerable adaptation of many human systems and will leave some aspects of the earth's environment irreversibly changed." (p. 529)
In other words, regardless of the precise trajectory climate change follows, emissions mitigation will not be sufficient to prevent serious harm to people and the planet. This is the basis on which a growing number of observers (myself included) advocate for climate intervention. Geoengineering, in combination with sustained and robust emissions cuts, represents the only viable path to avert potentially catastrophic climate change. Without it, the future looks increasingly bleak.