From my understanding, you want to first group the data based on temperature and then add the values of values of 3rd and 4th column based on grouping.
In this case you may use findgroups in order to group the data and to perform operation on grouped data you can use splitapply
You may use below code as example
load('aiub_shc.mat')
G = findgroups(shc12(:,1));
col2sum=splitapply(@sum,shc12(:,2),G);
col3sum=splitapply(@sum,shc12(:,3),G);
col4sum=splitapply(@sum,shc12(:,4),G);
Hope this gives an idea!