Have you not heard, "climate change is happening," spoken as a version of "duh?"
Now I know, and perhaps you know, that the Arctic sea ice summer extent declined sharply, glaciers melted back, mosquitoes live at higher altitude than in previous generations, animal and plant species have moved, and global temperature measurement has revealed major changes, including accumulation of heat in the oceans.
Mouthful of examples there, yet only a bite.
So, yes, climate change is happening, all the time 24/7, or 365/24/7.
But can we assume that your listener already has seen the evidence, and agrees with your conclusion? If your listener turns around in their air-conditioned office, orders lunch, and gazes at a pretty park across the street, in that moment does he or she see any sign that climate change, indeed, "is happening?" Unlikely.
Does your listener understand that the price of ingredients in the lunch was affected by global supply, in turn affected by climate? Or the hours of use of air-conditioning? Or the plant species in the park? Or the odds of severe weather? Also unlikely.
For many humans, "is happening" refers to a present moment of personal awareness; "It's happening, baby."
I'm leaning towards another phrase with the word "happens," and say,
Climate change happens.
Crop failure happens. Floods happen. Refugees happen.
We have moments when we notice.
In looking ahead, or planting ahead, let's be real about what has happened to date, and take into account both shifted conditions of heat, moisture, insects, etcetera and a shifted level of uncertainty.
In short, planning for uncertainty, as well as new certainty.