Can increased atmospheric CO2 levels trigger a runaway greenhouse?
R. M. Ramirez, R. K. Kopparapu, V. Lindner, and J. F. Kasting
Astrobiology (August 2014)
Recent one-dimensional (globally averaged) climate model calculations by Goldblatt et al. (2013) suggest that increased atmospheric CO2 could conceivably trigger a runaway greenhouse on present Earth if CO2 concentrations were approximately 100 times higher than they are today. The new prediction runs contrary to previous calculations by Kasting and Ackerman (1986), which indicated that CO2 increases could not trigger a runaway, even at Venus-like CO2 concentrations. Goldblatt et al. argued that this different behavior is a consequence of updated absorption coefficients for H(2)O that make a runaway more likely. Here, we use a 1-D climate model with similar, up-to-date absorption coefficients, but employ a different methodology, to show that the older result is probably still valid, although our model nearly runs away at ∼12 preindustrial atmospheric levels of CO2 when we use the most alarmist assumptions possible. However, we argue that Earth's real climate is probably stable given more realistic assumptions, although 3-D climate models will be required to verify this result. Potential CO2 increases from fossil fuel burning are somewhat smaller than this, 10-fold or less, but such increases could still cause sufficient warming to make much of the planet uninhabitable by humans.