To test whether we would see a flip coming, Gauthier Hulot of Denis Diderot University in Paris, France, and colleagues ran computer simulations of Earth's magnetic dynamo based on a range of plausible values for inputs such as the viscosity, electrical and thermal conductivity of the outer core, and the temperature difference across it. (newscientist.com)
Rough estimates indicated that under the most optimistic scenarios, corresponding to the lowest plausible value for the Planck scale, black holes could be produced at the rate of one per second. (scientificamerican.com)
This suggests to me that it should be easy to get a lower than 2.1 ECS version with plausible values. (planet3.org)