“If we can amplify her message and get more people involved and listening to what she's saying, then we're doing some good,” Paul Scott, the executive director of One Atmosphere, the group financing the painting, told US broadcaster CNN.
The work is going up on a wall near Union Square in the city centre and is expected to be completed by Tuesday.
“They're struck by the image and want to learn more .If they take the time to learn more about what she's trying to share, that I think has an impact on most people. Makes them want to help.”
The image is the work of Andrés Petreselli, who has already painted a mural of the zany stand-up comic Robin Williams in the city.
Petreselli said Thunberg was setting an example to the entire world. “We're pretty much at the beginning of our extinction, so if we don't do anything right now, it's going to be too late,” he told CNN.
Thunberg's image has already been featured on walls in Bristol, England and Edmonton, Canada.
The activist is currently in North Carolina on the US East Coast, and recently put out a request for help to get her back across the Atlantic to Europe, after next month's UN Climate Summit was shifted from Chile to Spain.