Today, permafrost soils are prevalent in Canada and Siberia. Locally, it is also possible to find patches in the Scandinavian mountains. However, if you are searching for signs of past permafrost, it is possible to find traces of its existence as far south as France.
Since present-day permafrost stores a lot of carbon per unit area compared to unfrozen soil, it is not particularly strange that the overall assumption has been that the larger area of permafrost also meant greater carbon storage. Perhaps in sufficient amounts to explain how there could be less carbon in the atmosphere at that time. But simple solutions are not always correct.
”We arrived at the conclusion that the total amount of soil carbon is larger today, despite the decrease in permafrost area. Simply put, it means that the permafrost cannot have contributed to the net increase of carbon dioxide in the atmosphere”, says Amelie Lindgren, PhD student at the Department of Physical Geography. Together with Peter Kuhry, professor in Physical Geography and Gustaf Hugelius, Senior Lecturer, they have worked with the study Extensive loss of past permafrost carbon but a net accumulation into present-day soils published in Nature.
Rising levels of atmospheric carbon dioxide continues to be a hot topic, both in society and among researchers. At timescales of hundreds of thousands of years, the concentrations of carbon dioxide has never been higher than they are now: 400 ppm, which means parts per million.
“We generally talk about a drastic increase since the industrial revolution, when the concentration fluctuated around 280 ppm. However, it has been lower in the past. By the end of the last ice age, the concentration of carbon dioxide was as low as 180 ppm. Over the course of thousands of years, it increased as the world grew warmer.
The question is where these carbon emissions originated from after the ice age, long before the start of the industrial revolution.
“Interestingly enough, researchers aren’t entirely sure where these additions of carbon came from”, says Amelie Lindgren.
Looking at evidence from atmospheric chemistry, researchers have tried to find a carbon sink on land, which gradually released its carbon as the world grew warmer. This pattern is an excellent fit for thawing permafrost, but these new results show that the carbon storage in permafrost was in fact lower back then than it is now if the same area is compared. The study concluded this by reconstructing different permafrost environments and their carbon storage from empirical studies.
“However, this does not mean the permafrost has not mattered at all. That we have greater amounts of carbon in our soils today does not exclude that we, at some point in time, might have lost ice age carbon that became available for release as the permafrost thawed. This very carbon could still be a good candidate to explain the land emissions we see over a certain period.”
Today, much of our emissions to the atmosphere are compensated by an uptake of carbon by vegetation and increased soil storage, but at times in the past, the soils have sometimes released carbon.
“These new results also provide yet another hint that the increasing levels of carbon dioxide prior to the industrial revolution might have come from the oceans. Today, the oceans act as a vital buffer by taking up carbon dioxide from the atmosphere, but just as the soils, the oceans have released carbon in the past, possibly in large amounts.”
Foremost, it is the climate models that need this type of information to better predict how the carbon cycle might react to future warming and anthropogenic emissions of carbon dioxide.
“The fact is, that to reliably project the future, we must also know about the past. How the carbon has moved between atmosphere, land and ocean in the past hopefully gives us better opportunities to understand what awaits us the coming century. With this new piece of research, we are one step closer to solving the climate puzzle,” says Amelie Lindgren.
The article “Extensive loss of past permafrost carbon but a net accumulation into present-day soils”, is published in Nature.
