If you're still looking for ways that you can do your part to stop climate change but you've already cut all the carbon emissions you possibly can, check out the National Phenology Network. They use data collected from lilacs (and other plants) around the country to determine global patterns in climate, by recording when plants at different latitudes go thorugh different cycles of blooming. Send in your request for lilacs and then report when your plants go through different phenological events.

(Thanks to Tammy for the link!)