Eating organic is all the rage these days - but could it actually help save the planet from climate devastation? As the reality of global climate change continues to sink in - scientists - activists - and lawmakers all across the world are working to find new ways to fight back against greenhouse gas emissions before it's too late. Thom's guest for tonight's Conversations With Great Minds - Tom Newmark - is one such person. A former corporate attorney turned organic farmer - Tom is now at the forefront of the movement to use agriculture to fight global warming. He is the co-founder of the new non-profit the Carbon Underground as well as the co-owner of Finca Luena Nueva - an organic farm in Costa Rica. Tom is also the co-founder of Sacred Seeds - a trustee of the American Botanical Council.

Global warming is real - and possibly even worse than we've been told. Could it lead to the destruction of human civilization within just a few decades? For tonight's Conversations With Great Minds - I'm joined by Guy McPherson -Professor Emeritus of Natural Resources - Ecology - and Evolutionary Biology at the University Arizona. Guy is one of America's most influential experts on global warming - and writes about a variety of climate change-related issues for the Arctic News and his own website - Nature Bats Last. In the field of climate science - Guy is best known for his assertion that runaway global warming is already on a path to cause the extinction of the human race - an idea he has written about in his book - "Going Dark."

Could encouraging more private investments in solar power and other forms of clean energy help make renewable forms of energy more popular in America - and lead to the downfall of dirty fossil fuels? That and more in our Conversations with Great Minds with Billy Parish. Billy is the co-founder and president of Mosaic - a solar power investment platform. In 2002 - Billy dropped out of Yale University to help found the Energy Action Coalition - which quickly grew into the largest youth advocacy organization in the world working on the climate change crisis. He's been honored by Rolling Stone magazine as a "Climate Hero," and by the Utne Reader as one of the "50 Visionaries Who Are Changing Your World." Billy is also the co-author of the book, "Making Good: Finding Meaning, Money and Community in a Changing World."

During his first presidential campaign - then Senator Barack Obama said that people would look back on his time in office and say that that was the "moment when the rise of the oceans began to slow and our planet began to heal" But has he really lived up to his own high standard on climate policy? I'll ask Dr. Michael Dorsey in tonight's Conversations with Great Minds. Dr. Michael Dorsey is currently the Interim Director of the Energy and Environment Program at the Joint Center for Political and Economic studies - where he works to combine the study of climate policy with the study of social justice issues. Before taking this position - Dr. Dorsey taught environmental studies at Wesleyan University and Darthmouth University. He was also a member of Barack Obama's energy and environment campaign team in 2008 and is on the Environmental Protection Agency's national advisory committee.

Shane Bauer, Joshua Fattal and Sarah Shourd - A Sliver of Light: Three Americans Imprisoned in Iran, all join Thom. It was a story that captivated the world: Three Americans hikers captured by Iran - and thrown into solitary confinement for over a year.

For tonight's Conversation With Great Minds - I'm joined by one of the country's foremost experts on nuclear security and nuclear nonproliferation. As the president of the global security organization the Ploughshares Fund - Jospeh Cirincione is on the frontline of the fight to prevent the spread of dangerous nuclear weapons. He is also a member of Secretary of State John Kerry's International Security Advisory Board and the Council on Foreign Relations. Before taking his position at the Ploughshares Fund in 2008 - Joseph worked on nonproliferation issues for the U.S. House of Representatives - Center for American Progress - and the Carnegie Center for International Peace. He is the author of a number of books on nuclear weapons policy - including his latest -"Nuclear Nightmares: Securing the World Before It Is Too Late" - a fascinating - and often sobering - look at the reality of modern day nuclear destruction.

Professor Anthony Townsend, Smart Cities: Big Data, Civic Hackers, and the Quest for a New Utopia joins Thom Hartmann. If you think the world is crowded now - then watch out. By 2030 - 6 out of 10 people on earth will live in an urban area. Will technology help keep things under control?

Joining Thom for tonight's Conversations with Great Minds are Evan Weber - Co-Founder of USClimate Plan - and Angela Anderson - Director of the Climate and Energy Program with the Union of Concerned Scientists. While the East Coast is digging out from the latest massive Winter Storm - the West Coast is dealing with a devastating drought. How much more severe weather does America need before lawmakers in Washington get serious about fighting climate change?

For many Americans - success means money and money means success. That's why even after the biggest financial crisis since the Great Depression - a job at a top-notch investment bank still holds allure for many young Americans starting their professional lives. But is working on Wall Street really worth it? For tonight's Conversations With Great Minds - I'm joined by someone who lived the life of a Wall Street millionaire and left it all behind. Sam Polk spent most of his 20's working as a trader for high-powered Wall Street investment firms - but at 30 he decided to leave the world of finance for good. Since then - he has become a successful nonprofit entrepreneur and has written about his time on Wall Street for The New York Times and Forbes Magazine.

Congressman Keith Ellison(D-MN, 5th District) / Author of the new book, My Country 'Tis of Thee: My Faith, My Family, Our Future joins Thom Hartmann.