Problems like climate change and food insecurity are not technological problems at this point. They are political problems. The job board you want is the board that organizes people to demand political change.
As the target audience for a job board like this, the question I am starting with isn't "how can tech solve climate change?", it's "how can I apply my tech skills to a problem like climate change?".
That's true by definition. As political systems are very sensitive to technology, doing tech work can be a very effective form of activism.
Excellent and simple analysis. I should also add housing (in most parts of the world ) to the list.