Although grass dominates most agricultural systems in the North Atlantic region (NAR), barley is the most important cereal and is used for animal feed and food and drink products. Recent changes in climate have resulted in warmer conditions across the NAR which have major implications for crop production. In this paper, we investigate the thermal requirement of barley in the region and use the results to examine the effects on barley cultivation of recent trends in temperature and rainfall at 11 regional meteorological sites. At these sites, between 1975 and 2015, we found significant warming trends for several months of the cropping season and significant trends for increases in the cropping season degree days (CSDD). In recent years, at sites above about 60oN, this has resulted in an increased proportion of years when the estimated minimum thermal requirement for barley has been met. However, annual variations in CSDD are large and years still occur at these sites where this is insufficient. While warming could potentially allow an earlier start and later end to the cropping season, it is likely that high rainfall at maritime sites, and low rainfall at continental sites, will limit the ability of growers to benefit from this. Warming is considered to have been a major factor in the large expansion of the area of barley cultivated in Iceland since the 1990s.