In this episode, we breathe and feel our human connection to the short carbon cycle. Long-sequestered carbon stores from deep underground -- as oil reservoirs or within frozen permafrost -- are brought to the surface by human activity, and then converted into greenhouse gases. These gases, like CO2 and methane (CH4), float into Earth's atmosphere, circulate, and trap heat -- causing the planet to warm. We have thrown the carbon cycle out of balance.

topics and purpose: how humans participate with the carbon cycle, and how to enact systemic change for a climate-positive future

terms defined: short carbon cycle, long carbon cycle

notes: Join the climate movement and get involved with political mobilization by working or volunteering with organizations like 350.org and Protect Our Winters.

In episode four we learn about carbon stored within woolly mammoth bones and ancient plants, long held within the walls of the the Cold Regions Research and Engineering Laboratory's permafrost tunnel located near Fairbanks, Alaska.

Forty thousand years ago permafrost trapped microbes, rock, and sediment when water froze around it all. The ground ice also captured ancient plants and mammal bones, making carbon stores visually apparent as permafrost oxidizes or thaws. These processes also have an odor.

topics and purpose: What all is in permafrost and emerges as it thaws?

terms defined: the Pleistocene Ice Age, organic matter

notes: Learn more about the Army Corps of Engineers' Permafrost Tunnel Research Facility in Fox, Alaska here. A previous version of this episode suggested that the tunnel was excavated to act as a protective underground enclave in the event of foreign occupation during the Cold War; this has been revised for accuracy. It was actually excavated in the 1960s as an experiment to test whether the tunnel could act as a bunker for military weapons systems.

In episode three of Ice and Fire, we hear about a microbial reawakening of microscopic life that was frozen into permafrost, often for thousands of years. These small life forms spring back when permafrost thaws. Though individually tiny, microbial communities -- composed of bacteria, fungi, and archaea -- have substantial impact to Earth, including the greenhouse gases they emit when they metabolize and perform cellular respiration.

topics and purpose: the significance of microbes to the atmosphere and global warming as permafrost thaws

terms defined: microbes and microbial communities

notes: Check out Dr. Romanowicz's website to read more about microbes and their significance to permafrost thaw. Learn more about the Permafrost Pathways Program, part of the Woodwell Climate Research Center, here.