Global warming will cause northern peatlands to absorb more carbon and slow climate change over the coming decades, new research suggests. Rising temperatures will lengthen the growing season in northern latitudes, which allows plants growing in northern peatlands to absorb more carbon from the atmosphere through photosynthesis. Once these plants die, the acidic and waterlogged conditions of peatland environments slow the decomposition process. Carbon in the plants gets locked in the ground and the plant remains form peat, instead of carbon being released back into the atmosphere. About half of peat is carbon.
In environments such as forests, carbon from dead plants is released back into the atmosphere faster. This makes peatlands vital “carbon sinks,” currently storing more carbon than all of the world’s vegetation.
However, the research shows that peatlands will store even more carbon in the future than was previously believed. The study estimates that by 2100 peatlands have absorbed 5% more carbon than during the preceding thousand years.
Climate change may create effects which slow warming
This effect – a so-called “negative feedback” where climate change causes effects which slow further climate change – will increase over the coming decades but will decline after 2100 if warming continues, according to an international team of 70 scientists.
University researcher Minna Väliranta and Professor Atte Korhola from the University of Helsinki participated in the study. Väliranta and her colleagues sent Finnish peat samples to the lead researchers of the study at the University of Exeter and took part in analysing and interpreting the samples.
“This study gives us completely new knowledge of how northern peatlands will benefit from climate change when it comes to absorbing carbon,” Väliranta says.
“However, the models have their uncertainties. For example, in this study the classification of different types of peatlands was fairly simple, and the study doesn't account for possible future changes in peatland types or areas covered by bogs,” Väliranta notes.
“In addition, predicting how general humidity conditions will change is much more difficult than estimating future temperatures, while the nutrient regimes might also change, which affect carbon balance,” Atte Korhola adds.
Finland has particular expertise in peatland research as a third of the country's land mass is covered by peatlands.
Tropical peatlands will store less carbon
The initial increase in carbon storage in the northern peatlands will eventually be offset by reduced storage in tropical peatlands in places like Borneo and the Amazon region. In tropical areas, higher temperatures will not boost plant growth, as the circumstances there are already optimal for peat plants. Instead, decomposition will speed up releasing more carbon back into the air. Even though most peatlands are located in high latitudes in places such as Siberia, Canada, and Finland, eventually release of carbon in tropical peatlands will surpass the increased carbon uptake in the north.
The researchers looked at a range of estimates for future warming – from an average warming of between 1°C and 3.7°C by 2100. Modeled future projections under all scenarios suggest that the present-day global sink in peatlands will increase slightly until about 2100 but will decline thereafter.
The research team used a new global data set of peatland carbon accumulation rates over the last millennium.
The paper, published in the journal Nature Climate Change, is entitled: “Latitudinal limits to the predicted increase of the peatland carbon sink with warming.”