Below are the dates for, among others, Earth Day 2012 and Earth Day 2013.
You can also see on which day the holiday falls and how many days it is until this holiday.

Holiday	Date		Week number	Number of days to go
Earth Day 2012	April 22, 2012	Sunday	17	78
Earth Day 2013	April 22, 2013	Monday	17	443
Earth Day 2014	April 22, 2014	Tuesday	17	808
Earth Day 2015	April 22, 2015	Wednesday	17	1173
Earth Day 2016	April 22, 2016	Friday	16	1539
Earth Day 2017	April 22, 2017	Saturday	16	1904
Earth Day 2018	April 22, 2018	Sunday	17	2269
Earth Day 2019	April 22, 2019	Monday	17	2634
Earth Day 2020	April 22, 2020	Wednesday	17	3000
Earth Day 2021	April 22, 2021	Thursday	16	3365
Earth Day 2022	April 22, 2022	Friday	16	3730

See besides 'Earth Day' even more holidays, click on one of the links below.
2012 Holidays   •   2013 Holidays   •   2014 Holidays   •   2015 Holidays

See also the 2012 Calendar.