That will give you the minimum value for each year. The OP wanted just the overall minimum. If he doesn't need the y/m of the minimum, then he could use 

use List::Util qw( min max );

my $min = min map { min values %{$Year{$_}} } keys %Year;
my $max = max map { max values %{$Year{$_}} } keys %Year;

[download]

Update: Fixed s/values/keys/ as per reply.

In reply to Re^3: min and max in a hash of hash by ikegami
in thread min and max in a hash of hash by nagalenoj

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