The Nenana Ice Classic is a Non-Profit Charitable Gaming Organisation run to provide funds for local charities.
Read about it here:
The object is to guess the date and time the Tanana river ice breaks up. The contest has been running since 1916.
Obviously there are many variables other than global warming that affect the break up - industry up stream, pollution,etc. However, there is no possibility of climate scientists changing the data and so is a true representation of changes in the local environment.
The last few years has seen an increase in the time since beginning of the year for the break up. This year has seen a large drop to 3rd lowest date.
Two plots are shown below. One shows a 2 line fit to the data showing fits from 1916 to 1965 and from 1965 to date.
The second is showing 3 splits that last year showed a possible up-tick from 2005 onwards (now reversed)