Embedded Player NPR's Richard Harris reports on new research that both illuminates and further complicates the picture of how the Earth is warming. It's long been thought that forests mitigate the warming effect of the earth, and that as the amount of carbon in the atmosphere grows, more trees will grow. But this built-in braking system on warming may not take place. More trees cause the earth to reflect less solar radiation and absorb more. The findings make calculating future temperatures even more complicated.