In this paper, an efficient linear time algorithm TACO is proposed for the first time to minimize the worst case clock skew in the presence of on-chip thermal variation. TACO, while tries to minimize the worst case clock skew, also attempts to minimize the clock tree wirelength by building up merging diamonds in a bottom-up manner. As an output, TACO provides balanced merging points and the modified clock routing paths to minimize the worst case clock skew under thermal variation. Experimental results on a set of standard benchmarks show 50-70% skew reduction with less than 0.6% wirelength overhead.