1. Polar bear Ursus maritimus population dynamics under conditions of climate change has become a controversial topic. A survey of expert opinion based on modelled sea-ice data was performed in order to quantify the trends and variance surrounding possible impacts of climate change on polar bear populations. 2. Polar bears have become an iconic species in the communication of climate change. Negative impacts of climatic warming on polar bears have been suggested, but cannot be fully quantified as no Arctic-wide models yet exist to analyse the relationship between polar bear population dynamics and climate change. 3. Ten polar bear experts participated in an expert opinion survey in early 2007, quantifying the trends and variance surrounding possible impacts of climate change on polar bear populations. The experts were provided with maps and time-series of sea-ice extent and duration to 2050, simulated under a mid-range emissions scenario. Expert projections of future polar bear habitat range and population size across the Arctic, and for population size in five regions, were obtained. Experts were asked to define ‘best conservation practice’, and to re-evaluate the total Arctic population projection if this best practice was implemented. 4. Most experts project a substantial decline in polar bear range and population size across the Arctic and in population size across each region. Expert best estimates for total Arctic polar bear population size lie from no change to a 70% decrease by 2050 relative to today; with half the experts projecting at least a 30% decrease. The median best estimates show the Barents Sea, Hudson Bay and the Chukchi Sea populations experiencing the greatest population decline under this scenario. There is much uncertainty both within and between expert responses, especially in little-researched regions such as the Chukchi Sea. 5. Synthesis and applications. Based on projected changes in sea-ice extent, experts suggest that polar bear populations will undergo significant declines by 2050, even implementing best management practices, under the scenario of climatic warming outlined here. The expert survey approach could be applied to a wide range of species for which there is a lack of available data and considerable uncertainty surrounding all aspects of the problem that prevent quantification with more formal modelling approaches.