Permafrost has been the topic of recent greenhouse gas and climate change concerns because it contains vast reservoirs of ancient carbon. Many people worry about what will happen as the ice in the soil melts, and the ocean temperatures rise because the process may release enormous quantities of methane into the atmosphere. In the quest to either justify this unease or prove it wrong, a team of University of Rochester researchers studied methane emissions from a period in Earth’s history akin to the warming of Earth today.
What they found was that old carbon reservoirs are unlikely to cause massive greenhouse gas release and that the focus regarding fighting climate change should be directed at human activities, not natural feedbacks. A small amount of methane that is released from natural stores, such as melting permafrost, due to climate change reaches the atmosphere. The research has been published in Science.
Graduate student Michael Dyonisius, in the lab of Vasilii Petrenko, professor of Earth and environmental sciences, who were both involved in the study said:
One of our take-home points is that we need to be more concerned about the anthropogenic emissions—those originating from human activities—than the natural feedbacks.
Permafrost is soil that has been frozen for at least a year, even throughout the summer. When the environmental conditions are icy, decomposing carbon-based organic matter (from dying plants or animals) freezes and becomes trapped rather than being emitted into the atmosphere. When the ice melts, the carbon is released and remains trapped in the waterlogged soil. The low-oxygen conditions created are an ideal environment for microbes who happily consume the carbon and consequently produce methane.
Methane hydrates are the carbon stores of the ocean. They come from marine sediments trapped within cages of water molecules along the deep continental margins due to low temperatures and high pressures. When ocean temperatures rise, the conditions change, causing the hydrates (cages of water molecules) to destabilize, break apart, and release methane.
Petrenko explains:
If even a fraction of that destabilizes rapidly and that methane is transferred to the atmosphere, we would have a huge greenhouse impact because methane is such a potent greenhouse gas. The concern really has to do with releasing a truly massive amount of carbon from these stocks into the atmosphere as the climate continues to warm.
To determine how much methane might be released to the atmosphere from ancient carbon deposits as the world gets warmer, the team drilled and collected ice cores from Taylor Glacier in Antarctica. Within these samples of ice were tiny air bubbles with small quantities of ancient air trapped inside. The team then used a melting chamber to extract the old air from the bubbles so they could analyze its chemical composition and see what the atmosphere looked like on Earth for the past 15,000 years.
Dyonisius said:
The time period is a partial analog to today when Earth went from a cold state to a warmer state. But during the last deglaciation, the change was natural. Now the change is driven by human activity, and we’re going from a warm state to an even warmer state.
What they found was that the ancient emissions consist of a small reservoir of carbon-14 isotope of methane. Thus, Dyonisius concluded:
The likelihood of these old carbon reservoirs destabilizing and creating large positive warming feedback in the present day is also low.
Furthermore, much of the methane from permafrost and methane hydrates likely won’t make it to the atmosphere to affect climate change. In the case of permafrost, if it’s deep enough in the soil, it may be oxidized by bacteria that eat the methane. Similarly, the methane released from methane hydrates deep in the ocean will mostly be dissolved and oxidized by ocean microbes on the way up and never make it to the surface.
Petrenko explains:
It seems like whatever natural buffers are in place are ensuring there’s not much methane that gets released. Our data shows we don’t need to be as concerned about large methane releases from large carbon reservoirs in response to future warming; we should be more concerned about methane released from human activities.
The findings of this research don’t mean we shouldn’t be concerned with methane gas emissions. It is only showing that natural stores appear to play a less significant role in accelerating global warming.
