No

This is due to climate change don't worry

Its skin pigmentation.. Nothing to worrg about even my dog has the same!!!

This looks like hyperpigmentation. The skin turning color like this is not the problem, but you do need to figure out if what is causing the hyperpigmentation is. Hyperpigmentation on a Shih Tzu is often caused by allergies, (Shih Tzu's are very very prone to having allergies! All of mine have had allergies to several different things.) It could be a food allergy, or your pup could be allergic to something in the environment. I'd ask your vet for guidance.