Predicting future climate change is one of the biggest scientific and societal challenges facing humankind. Whist carbon emissions from human activities are the main determinant of future climate change, the response of the earth system is also extremely important. Earth system processes provide 'feedbacks' to climate change, either reinforcing upward trends in greenhouse gas concentrations and temperature (positive feedbacks) or sometimes dampening them (negative feedbacks). A crucial feedback loop is formed by the terrestrial global carbon cycle and the climate. As carbon dioxide concentrations in the atmosphere and temperature rise, carbon fixation by plants increases due to the CO2 fertilisation effect and the lengthening of the growing season at high latitudes (this is a negative feedback). But at the same time, increasing temperatures lead to increased decomposition of the carbon stored in soils and this results in more carbon dioxide being released back to the atmosphere (this is a positive feedback).

The balance of these competing processes is especially important for peatlands because they are very large carbon stores. Northern Hemisphere peatlands hold about the same amount of carbon that is stored in all the world's living vegetation including forests, so determining the response of this large carbon store to future climate change is especially critical. One hypothesis is that warming will increase decomposition rates in peatland soils to such an extent that large amounts of carbon will be released in the future. However, the vast majority of peatlands are in relatively cold and wet areas and evidence from past changes in accumulation rates suggest that for these regions, warming may lead to increased productivity that more than compensates for any increase in decay rates, leading to increased carbon sequestration overall. Furthermore, in the northernmost areas of the Arctic, there is potential for further lateral expansion of peatlands, increasing the total area over which peat accumulates. We intend to answer the question of whether changes in accumulation in Arctic peatlands plus the increased spread of peatlands in cold regions will lead to an overall increase in their carbon storage capacity.

Our approach will be to use a novel combination of data from the fossil record stored in peatlands together with satellite data to test a global model that simulates changes in both carbon accumulation rates and the extent of peatland vegetation over Arctic regions. If we can demonstrate that the model performs well in simulations of past changes, we can then confidently use it to make projections of future changes in response to warming for several hundred years into the future. We know that fluctuations in Arctic climate over the past 1000 years should have been sufficient to drive changes in peat accumulation rates and lateral spread, so we are focusing our analyses on this period. In particular, we know there were increases in temperature over the last 150-200 years and especially over the last 30-40 years. If our hypothesis that increased temperature leads to increasing accumulation and spread of Arctic peatlands is correct, we expect to see the evidence for this in the fossil record of peat accumulation and spread, and also in satellite data of vegetation change. Our previous work and our new pilot studies show that we can reconstruct accumulation rate changes and also that our proposed remote sensing techniques can detect peatland vegetation increases since the mid-1980s, so we are confident in our methodology. The model will provide estimates of northern peatland carbon storage change for different climate change scenarios over the next century and longer term to the year 2300. If we can show that there is a potential increase or even no change in carbon storage in Arctic peatlands, it will radically change our perception of the role of the Arctic terrestrial carbon store in mediating climate change.

Potential Impact:
The results of the proposed project will provide an answer to the question of whether Arctic peatlands are accumulating carbon faster now than they were under previously colder climate conditions and provide projections of the likely change in carbon storage under future warmer climates. If we demonstrate that this is the case, we will radically change our understanding of the role of Arctic ecosystems in mediating global warming and provide evidence for a new ecosystem service of these unique and valuable habitats. Even if our hypotheses are not correct, the results of our project will be valuable in providing further information on the overall role of Arctic peatlands in the carbon cycle.

Therefore, our research has potential benefits for:

- The education sector and the wider public;

A deeper understanding of the possible effects of climate change on high latitude ecosystems is something that we need to communicate to the wider public and especially to educators so they can have a comprehensive picture of the likely changes in Arctic ecosystems and transmit it to their students, who will make the society of the future. A better understanding of the complexities of the response of the Arctic to climate change will allow the public to make better future choices and change their behaviour in order to mitigate climate change.

- The Inuit or First Nation populations in Canada and the Sami people in Finland/Russia.

The project will provide these populations with information on how the ecosystems they live in will respond to climatic changes. People who live near the study sites and that have traditionally lived in close proximity to these ecosystems will benefit by having access to a wide range of information on the value of their land in terms of carbon budgets, how their land is involved in the global carbon cycle and how their ecosystem is responding to climate change. This will allow them to make better choices of how they relate to their environment and adapt to the changes in the ecosystems.

- Policy makers and land managers involved in national and international carbon budgeting and management of international peatland resources for both carbon management and biodiversity conservation purposes.

The outcomes of the project have implications for peatland management and carbon dynamics throughout the northern hemisphere, especially in assessing future impacts of climate on peatland distribution and functioning, including the development of carbon management policy and peatland management practice. National and international policy and peatland management and adaptation need to be informed by accurate assessments of the likely trajectory of peatland carbon under warming, especially now that wetland carbon sequestration and emissions can be included in national greenhouse gas inventories as recommended by the Intergovernmental Panel on Climate Change (IPCC) Guidelines (IPCC, 2014).

In particular, we identify the International Union for the conservation of Nature (IUCN), UK Environment Agency, Environment and Climate Change Canada and the Environment DG of the European Commission as potential beneficiaries. These policy makers and/or peatland managers will benefit from a more comprehensive picture of the role of Arctic peatlands. The output of the project will be important for these environmental agencies that currently are unaware that Arctic ecosystems may respond in unexpected ways to climate change. This will allow a better management of this natural resource.

IPCC, 2014. 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories: Wetlands, in: Hiraishi, T., Krug, T., Tanabe, K., Srivastava, N., Baasansuren, J., Fukuda, M. and Troxler, T.G. (eds) (Ed.), Switzerland.