Which sources would provide the most relevant and credible evidence in this excerpt from a speech?
The Earth's Giant Sewer

Global warming is the rise in the earth’s surface temperature that has been happening since the mid-1900s.(Physiologist, scientists, Historians) believe that greenhouse gases are to blame. A study conducted by(Caltech University, The boys scouts of America,The youth empowerment Fund) showed that greenhouse gases trap heat in the earth’s atmosphere. The heat warms the air and eventually, the oceans and the ground.