The Arctic region is where numerical climate models generally predict the largest warming under the influence of increased greenhouse gas concentrations. It is also the area where discrepancies between predictions are greatest. Arctic processes seem to be crucial for maintaining the oceanic meridional overturning circulation (MOC), and some models suggest that global warming might freshen the Arctic Ocean and peripheral seas to the extent that this circulation collapses. Should that happen, parts of the North Atlantic region might cool rather than warm over the next 100 years. So, what are the global consequences of natural or human-induced changes in the Arctic climate system? Is the Arctic climate system really as sensitive to enhanced greenhouse gas concentrations as climate models suggest?