Congressional offices track the number of constituents who call or email in support of a bill or an issue. More contacts correlate to more attention. It may seem self-evident to you that climate matters, but elected representatives need to be formally told by many constituents -- and then told again over time.
You can phone during office hours, or phone later to leave a message. If you're more comfortable writing than phoning, you can submit a web email comment instead.
When you call or email, be respectful. Speak your truth, make it simple and concise. Don't stress over what to say.