You're right to a point. The hotter it gets on average, the faster the less fit die due to various heat related reasons. Once it hits 31c@100% relative humidity

You're right to a point. The hotter it gets on average, the faster the less fit die due to various heat related reasons. Once it hits 31c@100% relative humidity, land mammals die. So it's on a rolling scale up to 31C. At or past, yeah its a binary cliff.