It is cold right now in parts of the midwestern United States. This has been well-documented. The National Weather Service (NWS)-Twin Cities warned that being stranded in such conditions could be life-threatening. Another tweet from the same office pointed out that temperatures in parts of the Midwest United States will rebound by about 75 degrees F by the weekend, which will bring temperatures into the 30-40 degrees F range. That's perspective folks. Many headlines have latched on to the viral "It's Colder Than Mars in The Midwest" claim. Is this claim true? It depends.
An intrusion of Arctic air is the culprit for the extreme cold conditions. Unless you have been living under a Martian rock, you know that this cold outbreak is related to a split in the Polar Vortex, a swirling cyclonic system above the polar region. When there is a breach, cold air can "spill through the fence" and plunge into the continental United States. My colleague Eric Mack has an excellent discussion in Forbes on Polar Vortex 101. The NWS-Chicago morning forecast discussion captures the magnitude of this cold outbreak:
About as frigid and dangerous of wind chills as can be experienced in northern Illinois and northwest Indiana early this morning with values of -35 to -50 as of 230 a.m...The true Arctic front of this system has lived up to its name, with west-northwest winds gusting 25 to 35 mph early this morning having surged continental polar air in. Temperatures continue to tumble into the -20s and should be for most is not the entire area by 9 a.m. as the peak cold pocket at 925mb of -33C rotates overhead. The cold advection will likely cause the minimum not to be reached until mid-morning. It truly is impressive to have these temperatures with these winds.
By the way, Mars (and other planets) have a Polar Vortex, too, but that is not why it gets so cold on that planet. As Colorado State University Professor Scott Denning often points out, we know that Earth has a Greenhouse Effect because we survive the night. Greenhouse gases and clouds absorbs heat and radiates it back toward the surface providing a temperature range comfortable enough for humans to not require a spacesuit (graphic below). Mars, on the other hand, has a very thin atmosphere, no water bodies, and a barren landscape. All of these factors conspire to present a very interesting temperature profile on the Red Planet.
The Martian atmosphere also includes carbon dioxide, argon, nitrogen, oxygen and traces of water vapor. Carbon dioxide, a greenhouse gas, is the dominant component (~95%), but the atmosphere is very thin compared to Earth. In fact, it is about 100 times thinner than the Earth atmosphere. According to a Space.com article about Mars,
Mars' thin atmosphere and its greater distance from the sun mean that Mars is much colder than Earth. The average temperature is about minus 80 degrees Fahrenheit (minus 60 degrees Celsius), although it can vary from minus 195 F (minus 125 C) near the poles during the winter to as much as a comfortable 70 F (20 C) at midday near the equator.
The thin Martian atmosphere also lacks a significant concentration of methane and water vapor, relatively speaking, to reinforce the Greenhouse Effect. Earth's average temperature, by comparison, is around 57 degrees F.
The temperature on Mars can also plummet rather quickly. The surface pressure on Mars is about 6 millibars. By comparison, Earth's average surface pressure is about 1013 mb. Because Martian pressure is about 1/6 of the Earth's pressure, temperature can drop rapidly. Additionally, the rocky and sandy surfaces of Mars do not retain heat as well as other surfaces. With rather low heat capacity, they release heat rather quickly compared to water. We see this on Earth in deserts too. At night, deserts can actually cool down pretty rapidly for similar reasons. Mars also lacks water. Water has a higher heat capacity than sand and is why ocean water may be quite cold in May while sand is hot. Water regulates temperature, and Mars has no large oceans or seas. Even with all of these factors, the thin Martian atmosphere is the dominant factor controlling its temperature.
Temperatures in the Midwest are quite cold right now. The headline, "It's colder in Chicago than on Mars" is cute, and the type of thing that media organizations love. I suppose it is even technically correct for some snapshot measurements of temperature on Mars. However, Martian temperature certainly varies as a function of where the measurement is taken, what season it is, and the altitude above the surface. Therefore, when I see that headline, I am hoping the article gives the proper context on the Martian temperature being used as a comparison.
Stay warm, Earthlings.
