% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
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100  327k  100  327k    0     0  93034      0  0:00:03  0:00:03 --:--:--  175k
You are running cpanm from the path where your current perl won't install executables to.
Because of that, cpanm --self-upgrade won't upgrade the version of cpanm you're running.

  cpanm path   : -
  Install path : /usr/local/bin

It means you either installed cpanm globally with system perl, or use distro packages such
as rpm or apt-get, and you have to use them again to upgrade cpanm.
!
! Can't write to /Library/Perl/5.10.0 and /usr/local/bin: Installing modules to /Users/arend/perl5
! To turn off this warning, you have to do one of the following:
!   - run me as a root or with --sudo option (to install to /Library/Perl/5.10.0 and /usr/local/bin)
!   - Configure local::lib your existing local::lib in this shell to set PERL_MM_OPT etc.
!   - Install local::lib by running the following commands
!
!         cpanm --local-lib=~/perl5 local::lib && eval $(perl -I ~/perl5/lib/perl5/ -Mlocal::lib)
!