Impact of arctic ecosystem changes on global climate

Northern Russia is home to extensive taiga and tundra ecosystems, and permafrost terrain, which store large amounts of carbon. We spoke to Professor Peter Kuhry of the CARBO-North project about his work in researching the areas past and current carbon budget, and how its future development can be accurately projected...

Recent research into the impact of future climate change on high-latitude regions has centred primarily on ecosystems’ equilibrium response, such as the migration of the arctic treeline, or the likely new limits of the permafrost zone.

However, the work of the CARBO-North project, an initiative which involved scientists from across northern Europe, Russia and the US, has focused on the transient responses of eco-systems across both spatial and temporal scales.

“CARBO-North looked at how much carbon is stored in the eco-systems of north-eastern European Russia, including both taiga – also known as boreal forest – and tundra areas.

We studied carbon levels in various parts of these ecosystems; in the vegetation _ the phytomass – as well as in the soils, including peat deposits,” says Professor Peter Kuhry, the project’s overall coordinator. Based himself at Stockholm University in Sweden, Professor Kuhry says northern Russia is an area of great ecological importance.

“There is a lot of carbon stored within the trees of the taiga, so its future development is very important – not only in our study area, but across the whole circum-arctic north,” he stresses. “There is also a huge amount of carbon in northern boreal and sub-arctic peatlands.

The depth of these peatlands can be on average between 2 metres in the tundra and 3 metres in the northern taiga, and they contain an enormous amount of carbon, which is also found in frozen peat deposits within permafrost.”

Climate change and permafrost

Not only is northern Russia very important in terms of carbon storage, but it is also expected to be very sensitive to future climate change. With the temperature in our study region predicted to rise by up to 7˚C by the end of this century, natural ecosystems are set to change significantly.

“Permafrost is a very sensitive aspect of these northern systems. The area we looked at is in the transition between nonpermafrost and permafrost, and the permafrost there is actually very warm, close to 0˚C,” explains Professor Kuhry.

However, even the coldest parts of the CARBO-North study area are vulnerable to climate change, Professor Kuhry says. “Our model projections show that the permafrost is going to thaw quickly – in fact this has already started – and by the end of this century most of the permafrost in our study region will be in the process of thawing.

Permafrost does not disappear instantly – it takes time to melt the ice in the ground – but it is clear that most of it is likely to start thawing out over the coming decades,” he continues. “We expect this will have a major impact on the regions eco-systems; the carbon that was previously frozen will gradually become available for much more rapid decomposition.”

The extent of these changes, and the speed at which they are felt, is dependent on a number of factors, including the amount of carbon in the soil and the rate at which temperatures rise. Variability in the surface conditions of permafrost terrain also has an impact on the rate of thawing. “If the surface has only a thin organic layer – maybe there is water at the top or the soil is very moist – then we expect that the thawing will accelerate.

If on the other hand you have a very thick organic layer, for instance in the peat, and this peat is very dry at the surface, then this insulates the permafrost, protecting it from thawing to a certain extent. Under those surfaces thawing can be expected to take place at a slower rate,” says Professor Kuhry.

Most frozen carbon is located in deeper peat deposits, which can provide insights into how the carbon budget has evolved over time. “Fossils are very well preserved in peat deposits, which in general have only partly decomposed plant material. We have looked at plant macrofossils within many peat deposits in the area.

The story is very clear – the permafrost in our study area is actually relatively young, most of it only developed in the late Holocene era, since 3,000 years ago,” outlines Professor Kuhry.

The climate in the area prior to this time, in the early and middle Holocene, was warmer and fossils preserved in lake sediments tell us that the forest was much further north. The peatlands that started to develop under these warmer conditions were not exposed to permafrost conditions. “So, we know that many thousands of years ago, under a warmer climate, there was basically no tundra area – the forest continued all the way up to the Barents coast – and there was no permafrost in the lowlands of our study region. This kind of general picture is very useful in terms of helping scientists predict the evolution of the carbon budget under future global warming,” says Professor Kuhry.

Eco-system models and greenhouse gas measurements

Peatlands play an important role in the regional carbon balance, but until recently eco-system and earth-system models were not very good at capturing peat accumulation. This is an issue the project’s work has helped to address, and the LPJ (Lund-Potsdam-Jena) eco-system model now includes peatlands, while the Hadley Centre’s earth-system model is starting to include peat accumulation in their modelling.

“By including peat deposits you can assess the amount of carbon stored underground more accurately. If you want to know what will happen to carbon in the future you must first have an accurate understanding of current levels,” says Professor Kuhry. The project is also carrying out laboratory analyses of the soil organic matter to assess its potential susceptibility to decay. “So we also have Professor Kuhry. The project is also carrying out laboratory analyses of the soil organic matter to assess its potential susceptibility to decay. “So we also have geochemical indicators of the state of this material,” says Professor Kuhry.

The accuracy of our projections depends to a large degree on a thorough understanding of the current situation. The project has used a variety of methods, including opaque and transparent chambers and eddy correlation towers to assess the carbon budget.

“A transparent box lets solar radiation through and allows plants to photosynthesize. By this method you can measure how carbon dioxide levels are changing when you replace the transparent chamber with an opaque chamber photosynthesis stops, but it measures how much carbon dioxide is coming out from the soil; we can also look at whether methane is coming out of the ground.

One of the project’s most surprising findings, by Ms Maija Repo and colleagues from the University of Eastern Finland in Kuopio, was that certain surfaces in the tundra are major producers of nitrous oxide, a very potent greenhouse gas” explains Professor Kuhry.

These individual chamber and tower measurements can then be up-scaled to the landscape and regional levels, work which holds wider relevance in terms of the global climate.

Treeline migration

“Northern Russia includes the tree line, and a northwards migration will have a significant impact on not only the carbon balance, but also the surface albedo – a measure of how strongly a surface reflects light – of these northern regions,” says Professor Kuhry. “This is because the forest will sequester a lot of carbon dioxide from the atmosphere when it expands northwards.” However, the tree canopies absorb much more incoming solar radiation than the snow-covered tundra vegetation, counteracting the cooling effect by carbon sequestration of the tree-line’s northwards migration.

A complicating factor is that their will likely be a significant timelag between the warming and the northward expansion of the forest. Observations by Professor Martin Wilmking and colleagues from the University of Greifswald (Germany), indicate that there has been very little new tree recruitment in the tundra despite significant climate warming over the last decades.

Policy implications

Professor Kuhry believes it is important to reflect these issues within future global environmental agreements. “Forest carbon sinks are relatively well included in the (post-) Kyoto process. There is much discussion about using forests as a carbon sink, and that is allowed as a mechanism to sequester carbon to counteract human emissions from fossils fuels and so forth. But the peat and permafrost carbon, which are very important in our study area, are not included in the IPCC’s assessment of future greenhouse gas scenarios. This is a very important gap,” he stresses. “We are trying, through field observations, flux measurements and improvements in the eco-system and earth-system models, to provide better data for the representation of peat and permafrost carbon in future greenhouse gas scenarios.” Projections for the CARBO-North study area by the LPJ eco-system model, carried out by Dr. Paul Miler and colleagues from Lund University (Sweden), suggest that there will be a significant loss of carbon from these northern ecosystems over the next decades and centuries.

Peter Kuhry is Professor in Physical Geography at Stockholm University. He obtained his PhD in tropicalpine paleoecology from the University of Amsterdam and has previously worked in Canada and Finland. His current interest is Arctic System Science, with emphasis on the role of permafrost and peatlands in global climate change.

For further information, please visti the CarboNorth website

Published: Friday, 15th October 2010