U.S. Republican Jeb Bush said on Wednesday that the Earth’s climate is changing but that scientific research does not clearly show how much of the change is due to humans and how much is from natural causes. While President Barack Obama and many scientists believe humans are largely to blame for climate change, Bush said the degree of human responsibility is uncertain. The former Florida governor challenged Obama’s determination earlier in the day that climate change is now a threat to U.S. national security. --Reuters, 21 May 2015
