We document an observed lower extreme of mid-tropospheric (500mb) temperatures in the Arctic of approximately -45C during the winter season in several datasets. Each dataset shows the coldest air masses in the Arctic reach -45C during the fall months but seldom get much colder even into late winter despite a continued net radiative loss. We demonstrate that mid-tropospheric temperatures are not normally distributed indicating the possibility of a regulatory mechanism at work.

We also provide evidence that Minimum Arctic mid-tropospheric temperatures are regulated by moist convective processes and that minimum 500mb temperatures are controlled to a large extent by high latitude sea surface temperatures. -45C is the expected 500mb temperature in an atmosphere regulated by moist adiabatic ascent from a surface temperature of 1-2 degrees below 0C, the approximate freezing point of seawater. This implies that Arctic air masses are regularly in contact with unfrozen seawater to the south, an easily verified observation.

Climate model simulations of the effects of increased greenhouse gasses hypothesize that high, northern latitude regions should warm at a much faster rate than the globe as a whole; a hypothesis which does not appear to have strong observational support. We discuss the implications of this result for the accelerated Arctic warming hypothesis.