Large areas of the northern hemisphere’s land mass are covered with peat. As they grow, peatland plants absorb carbon dioxide from the atmosphere and convert it into plant tissue. When they die, they decay quite rapidly at first in the zone above the water table, and start to form peat. Eventually, they become buried so that they are below the water table. Over many thousands of years, peat deposits have built up and may exceed 5-10 m in thickness. The total amount of carbon extracted from the atmosphere and locked up as peat equals about as much carbon (in the form of carbon dioxide and methane) as is currently present in the atmosphere. It is commonly assumed that the peatland carbon store is fairly stable and that the decay of plant material and peat cannot take place below the water table. However, decay does occur below the water table and produces both carbon dioxide and methane. Methane is an important greenhouse gas – that is, it contributes to the enhanced greenhouse effect – and northern peatlands are one of the largest global sources of this gas. We are interested in predicting how much methane enters the atmosphere and how rates of methane loss from peatlands might change over the coming decades. To make such predictions, we need models of peatlands that simulate the production and loss of methane. Rates of methane production and loss from peats depend on physical factors such as peat temperature but also on the composition of the plant community on the peatland, which can change over years to decades. Therefore, our models necessarily became more ambitious to the point where we found we were simulating the growth of peat bogs in our computers. Andy’s film and lecture will consider what we already know about peatland carbon balance processes and their role in climate change together with the challenges faced by developing models of peatland growth.