Because ice is always changing -- melting, shifting, expanding, cracking -- any route that's made up of ice is difficult to assign a grade to. And because ice can change from year to year, an ice climbing route may have a different grade than it did in previous years. Because of this, ice climbing grades focus mainly on the steepness of the climb and the technical ability required to make the ascent.
In the U.S., there are three grading systems used to measure climbing on three different types of ice: water ice (WI), alpine ice (AI) and mixed ice (M).
Water ice (WI) is ice that's seasonal, or that disappears during the warmer months of the year. The scale for water ice ranges from WI1 (not very steep) to WI7 (vertical or overhanging, and very dangerous).
Alpine (AI) ice is permanent ice, like the ice usually found in high altitudes or glaciers. The scale for alpine ice is the same as the scale for water ice, except the prefixes are different (AI1-AI7 instead of W1-W7). The major difference between the two is the type of ice being graded.
Mixed ice (M) refers to routes that may contain ice, but are also partly rock. The mixed climbing scale is very closely tied to the Yosemite Decimal System (YDS). While the mixed climbing scale ranges from M1 to M13, each grade is described relative to a YDS rating. So, for instance, M1 is similar to a YDS rating of 5.5. Because mixed ice climbs are also partly rock, they can be rated using the International French Adjectival System (IFAS).
If ice climbing is a little too cool for your tastes, or if climbing in high altitudes gives you the shivers, why not try something a little closer to the ground? In the next section we'll discuss the grading systems for bouldering -- a climbing style for adventurers who may be a bit more grounded.