A cold state losses its coldest nights

Wyoming's rising minimum temperatures

This updated animation shows the rise of the minimum temperatures across Wyoming's climate stations. The gray lines show all of the records, and each individual record is highlighted in black, one after another. The warmest and coldest station are highlighted for comparison in orange and blue.

The minimum temperatures capture an important aspect of the recent climate changes because they reveal the night-time and winter changes. Solar output or effects that block the Sun's rays, like volcanic activity, influence these temperatures less than the loss of heat from Earth's atmosphere. Like the difference between a cloudy night when clouds help trap heat and a crisp clear night when heat escapes to space, years can also vary as heat loss changes. As the abundance of heat trapping gases, like carbon dioxide, has climbed, the coldest temperature have been risen. The trend is well explained by greenhouse gas theory, but not by other hypotheses about global warming, such as those about the Sun.

Some stations show little change compared to others, but the bulk of the state has seen its low temperatures rise. In graph below, the temperatures are plotted compared to the average for each location rather than the absolute temperature, and we see that the range of temperatures across the whole state has trended upward. Some stations have not warmed as dramatically as others, but we have been lacking cool years at any station - even though some recent years have been the coolest of the past decade. 

Just as we had warm and cold fluctuations in the past, we have them now. They just occur around a new, warmer baseline.