Edit: It has been suggested that my question is a duplicate of What could humans do to render the earth uninhabitable?. That question only asks what would be necessary to make human life impossible. That is much simpler than what I'm asking and every answer is geared only to that limited scope — and are, therefore, unsuitable to answer this question. No amount of time or editing of that other question (unless you change the OP's intent, which is forbidden by SE) will change this state.
I suspect someone read the title to that other question (but not the question itself) and jumped to a conclusion. Nevertheless, vox populii.
The year: 2025
The goal: Kill the Earth
"Kill the Earth" means the Earth is no longer capable of supporting life of any kind. The only possible way for life to grace the planet again is through the reintroduction of life from an outside source or through the same serendipity that brought it about in the first place (if that's even possible on a planet this old).
"Kill the Earth" does NOT mean the orb, sphere, lump-of-dirt-and-molten-metal of the planet is destroyed. That would be "overkill the Earth," and that's not what we're talking about.
Only technology that can be justifiably developed by 2025 may be considered.
The planet's death must be intentional. Unintentional side effects of living life are not allowed. For example, whether you prefer the phrase "climate change" or the phrase "global warming," neither is acceptable as a method of killing the planet. I believe neither apathy1 nor detachment2 meet the mandate of intention.3
However, the reason for the death of the planet is NOT being considered here. In other words, I don't care if it's war or some evil genius. I'm hoping to understand if it's possible, given tech available on or before December 31, 2025, to kill the planet. However, if you just can't stand addressing the question without a premise, assume the nations of the Earth failed to pay Ernst Stavro Blofeld his ransom. Whether you think it can be done with enough nuclear weapons or bubble-gum, you need to justify just what it would take.
The planet must be dead within a month of acting on the intent to destroy the Earth.
I'm using the hard-science tag because I'm not interested in, "well, this might work" answers. Back it up or pack it out.
Question: Is it possible before the end of 2025 to destroy all life on Earth within a 30-day period per the above requirements?
1 The tendency to consume resources and pollute in a thoughtless, even oblivious manner. It isn't that the individual wants to kill the Earth, it's that he/she doesn't care that they're part of the problem. Indeed, they don't even care to discover if they are part of the problem. The entire issue rolls off their back like water on a duck.
2 On the other hand, this is the kind of person who honestly believes they're not killing the planet and would never in a million years agree that they are killing the planet — but see no reason why they shouldn't be allowed to dump chemical waste into a river. After all, it needs to go somewhere, and it costs too much to recycle it. More jobs are to be had if the cost is avoided! Like the job of scraping the barnacles off my new 60' yacht! So such a person deliberately dumps — but isn't actually trying to kill the Earth.
3 The biggest reason for this condition is that almost anything could destroy all life on the planet, like a meteor, but I'm not interested in natural phenomenon, like meteors, or "consequence of living" phenomenon which may or may not kill everything (but likely won't, and hasn't in the last 50 years anyway). I want to know if there's a way to extinguish it. Frankly, I'm not convinced using all the nuclear weapons from the height of the Cold War would do it, which is why I'm asking. Honking cockroaches.