Why?

Evolution provides the answer to why things are the way they are. If you never learn evolution then you'll never know the answer to the question of why.

Humans are mammals. Mammals are endothermic (they generate heat). Heat is needed to sustain the chemical reactions for life. Up to 90 percent of the metabolic energy used in mammals is used to generate heat.

Lizards are ectothermic. They get most of their heat from their environment. They bask in the sun in the morning to warm up. Lizards also lose excess heat to their environment. Raymond Cowles demonstrated in the 1930s that a lizard can not wear a fur coat because it would interfere with their heat exchanging capabilities with their environment. A fur coat can not keep a lizard warm because they can’t get warm in the first place with a coat on. Since mammals produce their own heat they use hair to insulate themselves from heat loss.

A lizard uses 10 times less energy than a mammal of the same size. A lizard eats 10 times less food than a mammal of the same size.

The prevalent conditions on Earth for the past 40 million years have been cold and the period is referred to as "Ice House" conditions. The Polar caps first formed 40 million years ago.

Mammals have proliferated during the past 40 million years and now have a ubiquitous presence on Earth today. The Cenozoic is known as "the Age of Mammals", because of their rapid evolution to fill niches that were vacated during the KT mass extinction.

The endothermic capabilities of mammals make them the perfect inhabitants of cold Earth. As the Earth warms up mammals will need to evolve into new forms to cope with the increasing heat. If the heating is too rapid then species will not have time to evolve and will become extinct. Anthropogenic (human) activities are accelerating the change in climate and the effect is known as Anthropogenic Global Warming.

The climate has always changed on Earth but the rate of change has never been affected by a species to the extent that humans have. If the polar caps melt then the 40 million year “Ice House” will come to an end. This would be an entirely artificial climate produced by humans. We are destroying the habitability of Earth for mammals.