Healthy forests play a crucial role in Earth’s ecosystem as growing trees take up carbon from the atmosphere. NASA satellites and airborne missions study forests to see how carbon moves through ecosystems. Adding in height measurements to more general observations of land cover gives a more complete, three-dimensional portrait of the ecosystem. Scientists need that third dimension to calculate how much carbon is stored in a tree or in a forest. The GLOBE Observer: Trees tool allows citizen scientists to help investigate by using their smartphone to measure tree height. With the tool, observers record tree height by tilting their phone up and down to align the screen with the tree’s top branch and base, and pace off the distance to the tree; the app does the rest to calculate the tree’s height. Tree height measurements could also help scientists working on NASA missions like the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) which use lasers to measure the height of Earth’s surface below them as they orbit our planet. GLOBE measurements can be used to complement tree height measurements from ICESat-2. You can visit to learn more about GLOBE Observer and the Trees tool. For educators, hands on activities (such as how to make a paper clinometer to use alongside the GO app), information about tree science and NASA, and other support materials can be found at Children under the age of 13 should be supervised by an adult when using the app. Always follow guidelines from your local officials, and only participate in GLOBE activities or use the GLOBE Observer app if it is safe to do so.