Somber yet joyful intensity pervades “I Am Greta,” the brilliant documentary by Nathan Grossman that hangs out in the shadows of the last few years of Greta Thunberg’s life. The camera tracks her during her ascent to near sainthood, and instead of proselytizing or over-dramatizing, the approach is one of careful neutral observation. The effect is stunning. We see a teenage girl of precocious intelligence and moral grit keep delivering the same message – my generation (I’m 65) is doing nothing to avert the climate emergency spiraling into disaster for her generation and beyond. It’s a simple message but one that brooks no scientific disagreement, and when expressed so clearly, it’s no wonder Greta has been embraced by the millions and millions around the world terrified about our climate future. Grossman observes how her father devotes himself to her and her message and its delivery; the father-daughter observations are touching and unassuming. Her mother, back in Sweden, is just as much a parent-rock. Scene after scene on trains and in crowds … her fraught yacht trip across the seas to deliver the film’s climactic scene of her unforgettable speech to the United Nations … this is a documentary about purpose and steely determination and clearheaded morality. By eschewing any sermonizing, the filmmaker achieves the seemingly impossible, humanizing Greta at the same time as extolling her message and role. I Am Greta: an incandescent film for our age.