The primary grades are a wonderful time for foundational work on climate change, Noah. Fortunately, Next Gen Science Standards give us a guide for age-appropriate learning goals for each level. I have pulled out all of the goals related to climate change, and categorized them by grade level, K-12. See link below for Climate Change & NGSS. As you'll see, the focus in the primary grades is on developing a basic understanding of nature, and how one thing can have an impact on another; for example, a change in habitat affects those who live there. As with every grade, it's important that children know that there are many ways we can help protect nature. For more ideas, visit the Start Learning page on Kids Against Climate Change.

Noah, have you explored Project WILD or Project Learning Tree? Both programs' curricula and educator training sessions offer a variety of activities and resources to introduce foundational climate concepts like habitat to elementary students. The new Project WILD curriculum guide published this year has given a lot of attention to teaching climate change.
Kids in lower elementary are pretty concrete thinkers, and climate change is too abstract and overwhelming for them, so in our field trips and summer camps, we focus on exploring, experiencing and connecting with the plants and animals in local ecosystems and being helpful (coastline cleanups, recycling and composting, etc.). A colleague and I follow the principle of "no tragedy before 4th grade" so we focus on things like understanding butterfly life cycles, how plants grow, how sea turtles migrate, etc. and encouraging a love of, interest in, and sense of responsibility for nature. Understanding life cycles, habitats or interdependence will go a long way to bringing home the significance of climate change and human impacts when they are introduced in, say, 5th grade.