a team from burkley. he climbs to the top of these trees to test them for signs of stress. he has been doing this for 20 years. this is my first time. i have a new respect for the itself. >> you can feel the weight of history in the weight of this tree. it's extraordinary to be here. warmer temperatures mean the water. >> a typical tree of this size might use anywhere between fooich and 800 gallons of water in a single summer day. >> reporter: snow pack that provides water is now at a 500 year low. >> the sugar pine seems to be suffering a lot of more at allity that we've seen. another pine as well. the cedar has been going back to a rate that people in the park have never seen before. >> reporter: it was by far the scareyest thing i've done. i've never felt so insignificant. this may be the last time that scientists climb these trees. part of this project is to test the accuracy of the airborne observeatry. >> typically in the past we've missed most of the forest and tried to make an inference from the forest from a few samples. with the advent of image ability, this has e