While punctuating a sentence it is important to capitalize the first letter in a sentence. So 'How' is the right way to start the sentence. The given sentence is an exclamatory sentence, wherein the surprise is conveyed through the sentence. We use an exclamation mark to indicate an exclamatory clause or expression in writing. Thus option A is correct. Whereas a question mark is used to denote that what is said is a question. Since the given sentence is an exclamatory sentence and not a question option D is incorrect. A comma is used to indicate the separation of ideas or elements. The given sentence doesn’t contain multiple ideas or elements, therefore, a comma is not necessary. The sentence as the whole functions as an exclamation, therefore we shouldn’t place a comma in front of ‘the climate’ or the verb ‘is’, since it would be illogical. In addition to that, option C doesn’t have an exclamation mark which is unsuitable. Thus options B and C are incorrect.