No, not Tyra Banks and Riyo Mori, climate models that is.
Modelers don’t purposely err on the conservative side, says Marika Holland of the National Center for Atmospheric Research, but some processes “are just not well understood, and because of that have not been incorporated into climate models.” Holland has published model results on the fate of sea ice and coauthored the recent paper showing that ice is melting faster than models predicted. There are many reasons for the underestimates, she says. For example, models don’t fully capture heat transport between ocean and atmosphere, or faster warming as reflective ice gives way to darker, heat-absorbing waters.
But Rahmstorf says that modelers might unwittingly make models more conservative by applying “one-sided filters”, weeding out models that clearly overestimate the changes seen so far, but hanging onto ones “where everything is too well behaved and stable.”
Scientists are human too. The political and social climate in the US have been harsh to people who overestimate the effects of climate change. So, modeling scenarios that deviate significantly from accepted limits or runaway uncontrollably are discarded. Models are sets of assumptions based on underlying theory. If the theory of a particular sub-process is not clearly understood, then the assumptions become subjective. In a social climate that is waiting to pounce on an overestimate as example of negating the entire global warming phenomenon, assumptions made are conservative. This is not necessarily a bad thing, but it comes at a price! As more observations come in, it does become clear that sometimes, things are happening faster and at greater magnitudes than our model predicted.