Since the 1950s, research stations on the Antarctic Peninsula have recorded some of the largest increases in near-surface air temperature in the Southern Hemisphere(1). This warming has contributed to the regional retreat of glaciers(2), disintegration of floating ice shelves(3) and a 'greening' through the expansion in range of various flora(4). Several interlinked processes have been suggested as contributing to the warming, including stratospheric ozone depletion(5), local sea-ice loss(6), an increase in westerly winds(5,7), and changes in the strength and location of low-high-latitude atmospheric teleconnections(8,9). Here we use a stacked temperature record to show an absence of regional warming since the late 1990s. The annual mean temperature has decreased at a statistically significant rate, with the most rapid cooling during the Austral summer. Temperatures have decreased as a consequence of a greater frequency of cold, east-to-southeasterly winds, resulting from more cyclonic conditions in the northern Weddell Sea associated with a strengthening mid-latitude jet. These circulation changes have also increased the advection of sea ice towards the east coast of the peninsula, amplifying their effects. Our findings cover only 1% of the Antarctic continent and emphasize that decadal temperature changes in this region are not primarily associated with the drivers of global temperature change but, rather, reflect the extreme natural internal variability of the regional atmospheric circulation.