This is likely due to peripheral vasoconstriction. This happens in order for the body to retain heat longer in order to protect the body from hypothermia. The skin would act as an insulator of the organs and water. Also, when this happens, it would allow more of the oxygen to be transported to the oxygen sensitive organs like the brain and the heart.
When fossil fuels are burned, they release large amounts of carbon dioxide, a greenhouse gas, into the air. Greenhouse gases trap heat in our atmosphere, causing global warming.
