Some scientists speculate that a severe ice age may have happened at least once over our planet’s history. they call this state an "ice-ball earth", and could have been forced by an imbalance in thermal radiation due to changes in greenhouse gas composition. the idea here is that a small ice age would have the efect of increasing albedo, causing a decrease in temperature, which further increases ice coverage, which in turn increases albedo even further. this process would continue until the surface of the earth is completely covered in ice, and the albedo at this point would be around 0.80. ignoring the greenhouse effect of the atmosphere in this scenario, what would the surface temperature of the earth be, in ◦c?