The 'Repeat Photography' project by the US Ground Survey is the simplest way to keep track of the effects that climate change has had on the Earth. The collection of pictures often places images of the same location side-by-side, photographed decades apart.
A prevailing pattern in all the photos show that once-frozen glaciers and iced caps have since melted and turned into grass-laden landscapes. The basic tool of repeat photography is the most inexpensive way of tracking climate change and you don't have to be a scientist to understand the worrying messages that these images portray.
For context, the Glacier National Park in Montana was covered by 150 glaciers in the 19th century. Today, only 25 remain. Apart from the ice that vanishes, local wildlife that is not suited for warmer climates is also dramatically affected.