Create a Curves layer just above the picture layer. Steepen the curve to create lots of contrast in the cloud. On the curve layer mask, use a black brush to exclude everything but the RED clouds from the effect. Consider selectively steepening just the Red curve by itself, as well.
If that's not enough, do the same with a Hue Saturation layer until the clouds are Red In Color.
There are other ways of course, and numerous elaborations on my basic technique such as luminosity masks, different blending modes, etc. But transparency film or even Mama Nature don't usually do that unassisted, your input is required.
When you're done, sell it to a millionaire. Pictures like that don't bother them and Peter knows that all too well. Also Peter now shoots digital.
Oh, photograph made all in computer??? - why? Since the image is 3:1 and shot in Australia perhaps he used 617 and shot was perhaps captured years ago? Regardless would make sense to capture as optimum as can in field rather than try to make a photograph exclusive in computer??? Else how print large to high quality?
ND grad + polarizer + Fuji Velvia ISO 50, then enhanced in computer. Not mere applying an arbitrary S-curve, but to do so by fine tuning it, and also color enhancements (including local such) per say like a painter would to enhance and make colors stand out so to create an enhanced rendering of the experience per the feelings when captured...
Peter Lik rocks in my opinion, my favorite living landscape photographer