Introduction: Sinkholes (02:10)

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In 2014, a helicopter crew discovers a crater over 80 feet wide and 180 feet deep in Siberia; more craters have since been discovered. Scientists from around the world work to better understand the northern hemisphere's permafrost.

Yamal Peninsula, Siberia (06:28)

The peninsula is located above the Arctic Circle. Scientists investigate a massive crater and find a raised rim, debris field, and high levels of methane; the crater likely resulted from a natural explosion. More craters are discovered and scientists notice a climate connection.

Kotzebue, Alaska (05:37)

A pilot notices bubbling water at Esieh Lake. Scientists discover that the lake emits over 10 tons of methane gas every day. A diver locates a hole in the lake floor and sonar radar reveals that it is 50 feet deep.

Permafrost (07:22)

Permafrost can extend a mile beneath the Earth's surface. Rising temperatures causes permafrost in some regions to thaw, resulting in a "drunken forest" near Fox, Alaska and warming ice cellars and retreating coastlines in Utqiagvik. Scientists expect 30 to 70% near-surface permafrost loss within the next century.

Fox Permafrost Tunnel (02:57)

Permafrost contains vast amounts of organic matter and carbon. Experts work to understand how much and how quickly carbon will enter the atmosphere.

Greenhouse Gases (05:59)

Susan Natali examines permafrost samples. As permafrost thaws, it releases carbon and methane. Experts discuss rising levels of greenhouse gases, warming temperatures, and carbon budgets. Carbon lasts for centuries in our atmosphere; methane lasts for about 12 years but is more potent.

Positive Feedback Cycle (04:48)

Other lakes in the permafrost region are releasing methane. Permafrost thaw is creating vast numbers of new lakes across the Arctic. Experts discuss greenhouse gas emissions, fossil carbon, and fossil methane reservoirs.

Fossil Methane (06:50)

A network of geological fault lines covers the territory near Esieh Lake; the lake sits above 500 feet of still-frozen permafrost. Nick Hasson scans the permafrost and lake floor with Very Low Frequency and discovers a thaw chimney. Experts discuss methane seeps and climate change.

Batagaika Megaslump (07:54)

Clearing trees exposed the permafrost to the sun, causing it to thaw and the ground to sink, exposing more permafrost. Experts discuss the permafrost region's tipping point and irreversible damage near Utqiagvik. Houses and roads are sinking and some towns have had to relocate.

Arctic Changes (01:41)

Arctic inhabitants are adapting to the changing environment. Scientists strive to better understand our climate future. The Big Thaw could affect everyone on Earth; lowering emissions is important.

Credits: Arctic Sinkholes (01:12)

Credits: Arctic Sinkholes