Editor's note: This is the latest in a series of stories about how climate changed and is changing our world -- spiritually, physically -- as a result. Find more climate change coverage here.

Researchers like Harvard professor Dr. David Keith have to ask some hard questions if they are going to learn anything about a topic as difficult and complicated as climate change. Learning to ask those questions and seek answers is what Dr. John Shepherd, retired physics professor at the University of Wisconsin-River Falls, spent his 31-year career teaching students to do.

“”In the hard sciences, the STEM subjects, our current knowledge is based on hundreds and even thousands of years of study,” Shepherd said. “Some of the knowledge has been shown to be wrong, but not much, and a lot falls into the area of being approximate with the approximations getting better with further study.”

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The challenge is that professors must make decisions about what to teach and what to leave out, Shepherd said. These decisions can be influenced by the need for students to write grant proposals for research projects which must provide topics that interest the grant providers.

Shepherd said one of the things scientists researching climate change need to be concerned about is “unintended consequences.” For example, human beings release large amounts of greenhouse gasses into the atmosphere and they trap the energy from the sun, causing temperatures to rise.

“Subtle changes in ocean temperatures can cause changes in currents which then can cause massive changes in the climate on the land surrounding the ocean,” Shepherd said. “It appears that the Gulf Stream, which is part of the Atlantic circulation and keeps England at a moderate temperature, is slowing down and stopping. So projects like a proposal to block sunlight with aerosols or other things could backfire.”