Soils store huge amounts of carbon, warming can release it


One of the biggest carbon reservoirs in the world is also one of the least glamorous: the dirt under our feet.

Soil around the world probably contains more than 2,000 billion tonnes of stored carbon, scientists estimate. This is at least three times more than what floats in the Earth’s atmosphere.

Is he going to stay there is a big question.

Recent research suggests that climate change may play an increasing role. As the world warms and gets wetter, some scientists believe more carbon can come out of the ground and move through the atmosphere. This could accelerate the pace of climate change.

Like other natural carbon reservoirs (forests, wetlands and oceans), soil has the potential to absorb carbon from the air or to release its own carbon into the atmosphere, depending on environmental conditions.

Major disturbances, such as clearing land for agriculture, can release huge volumes of stored soil carbon. At least a study, published in 2017, suggests that agriculture has released an estimated 133 billion tonnes of soil carbon over the past 12,000 years. About half of these losses have probably occurred in the last few centuries alone.

Scientists increasingly believe that climate change is also a threat.

Recent research indicates that warming causes faster carbon loss in some soils. Scientists believe that as temperatures rise, some microbes in the soil become more active. These microbes eat away organic matter and release carbon in the process.

Now a new study suggests that a more humid climate may also accelerate this process.

Posted this week in Nature, the study examines long-term records of the Ganges-Brahmaputra River basin in India dating back almost 20,000 years. During the wettest periods in the region’s history, he argues, the rate of soil carbon turnover increased.

This suggests that more carbon was going into the atmosphere instead of staying locked in the ground.

To conduct their analysis, the researchers, led by Christopher Hein of the Virginia Institute of Marine Science, collected samples of ancient sediment mined from the earth. They performed carbon dating analyzes to determine the age of the carbon inside the sediments and whether the age of the carbon has changed at different times in history.

Older carbon, over a period of time, would suggest that carbon remains stored in the soil for longer periods. A younger carbon suggests that it is “turning over” at a faster rate. Older carbon is released into the atmosphere, while younger carbon sources, from falling leaves or dying organisms, for example, replace it.

In climate projections, the future of precipitation is a thorny issue. Models generally suggest that some parts of the world will get drier and others wetter. And in some cases it can be both – some places may see an increase in both extreme droughts and extreme rainfall, alternating over time.

Plus, the new study looks at just one location spanning thousands of years. It is not necessarily clear that other regions will behave in the same way or that the same location will react in the same way today.

But it can be a red flag, something scientists need to start looking at more seriously. If the study is on track, it could point to another potential climate feedback, where climate change causes natural landscapes to emit more carbon into the atmosphere, thereby contributing to even more climate change.

At the same time, it is increasingly clear that warming can also be a problem for soil carbon.

One of the oldest climate experiments in the world, a 26 year study in a Massachusetts forest, tested plots of soil to find out how they responded to higher temperatures. Plots heated to 5 degrees Celsius appeared to lose carbon in phases: a sudden release, followed by temporary stabilization, followed by another release, and so on.

Researchers believe this gradual response likely reflects the way microbial communities move and adapt to environmental changes. The heated plots lost about 17% of the carbon in their top layers of the soil, although it should be noted that they were subjected to fairly extreme levels of warming.

Another long term study, conducted over two decades in a Colorado prairie, also suggested that warming is having some effect. In warmer plots, where soil temperatures were typically about 1 ° C higher than unheated plots, carbon decreased in one soil layer.

Other shorter-term studies have also indicated that warming has an effect. On the other hand, a 20 years experience on the arctic tundra found no change in soil carbon stores.

So there is still debate about the exact effects of climate change on soil carbon, where those effects may be strongest, and how much warming – or precipitation – it takes to make a difference.

In general, natural climate feedbacks present a major uncertainty regarding future climate change. Scientists are asking similar questions about how the world’s forests or oceans can respond to continued warming and how much carbon they will absorb versus how much they will emit into the atmosphere.

Understanding these responses better can help scientists make more accurate projections of climate change. And soil, as unglamorous as it is, could become a growing part of the puzzle, with billions of tons of carbon at stake.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of energy and environmental news essential to www.eenews.net.

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