Freezing Degree Days

"Freezing Degree Days" (FDD) are defined as the temperature below freezing. Here FDD use 0°C as the freezing point like the Polar Science Center. Other institutions use -1.8°C as the freezing point.

1. Day: average Temp: -3°C
2. Day: average Temp: -5°C
3. Day: average Temp: -7°C
Total: 15°C

ERA40 is a reanalysis data set from ECMWF that has been applied to calculate daily mean temperatures (2m) for the period from 1958 to 2002.

Data source: Danish Meteorological Institute:

Orginal project by Andrew Slater:

This graph shows Freezing Degree days over the whole freezing season. The sea ice thickness can be estimated based on the following formula (Lebedev 1938): 
Thickness (cm) = 1.33 * FDD (°C)0.58

It is important to note that the calculated thickness using this formula only accounts for the freezing of sea water and not ice growth from snowfall, freezing rain or ridging. By using 0°C as the freezing point the formula matches measured ice thickness better.

More info at:

When the graph goes up the year was colder than the 1958 - 2002 mean temperature. When the graph goes down the year was warmer. 
Individual Years. 
 Individual Years anomaly.