Originally published 2017-11-28.
NASA's before-and-after satellite images show, in a single glance, how fast parts of our planet can change: forests burned to ash, lakes shrinking in drought, glaciers retreating and cities spreading into farmland. In 2017 Upworthy turned a selection of these pairs into a short video, including wildfire damage in Canada and drought in Utah. The video is below, followed by what the images really show and how to read them.
Where NASA's before-and-after images come from
The pairs come from NASA's Images of Change collection, an interactive gallery that sets an older image beside a newer one of the same place. Its entries cover floods, wildfires, droughts, volcanic eruptions, melting ice and human changes to the landscape such as dams, mines and new suburbs. Many of the pictures are taken from orbit by Earth-observing satellites; some are photographs from the ground or from aircraft.
The backbone of long-term comparisons is the Landsat programme, run by NASA and the U.S. Geological Survey. Landsat 1 was launched on 23 July 1972, and the series has photographed Earth continuously ever since, making it the longest-running satellite record of the planet's surface. Landsat 8 (2013) and Landsat 9 (2021) carry that record on today, which is why it is possible to compare a place in the 1980s with the same place decades later.
Wildfire: the 2016 Fort McMurray fire
The best-known Canadian fire of that period was the Fort McMurray wildfire in Alberta. It started on 1 May 2016, swept into the town on 3 May and forced about 88,000 people to leave, the largest wildfire evacuation in the province's history. It burned roughly 590,000 hectares, an area similar in size to Prince Edward Island, and destroyed around 2,400 homes and buildings in the town. With estimated costs of about C$9.9 billion, it became the costliest disaster in Canadian history.
From space, a fire like this leaves a dark burn scar across green forest. The scar is visible for years, gradually fading as vegetation grows back, which is exactly the kind of change a before-and-after pair captures well.
Drought: the shrinking of Lake Powell
The drought pairs typically show Lake Powell, the huge reservoir behind Glen Canyon Dam on the Colorado River. Most of it lies in southern Utah, with a smaller part in Arizona. NASA's entry compares the lake in 1984 with 2018, after a drought that began in 2000, and the difference is striking: side canyons that were full of water have turned to pale rock and sandbars.
The decline did not stop there. In April 2022 the lake fell to about 22.9 percent of its capacity, the lowest level since it first filled. Wet years bring partial recoveries, but the long dry period across the American Southwest has kept levels well below full.
How to read a satellite comparison
Before-and-after images are powerful, and also easy to misread. A few habits help:
- Check the dates and the season. A spring and an autumn image can show different vegetation or water simply because of the time of year.
- Look at the scale. A tight crop can make a small change look huge, and a wide view can hide a big one.
- Read the caption. NASA's text explains what changed and why; the picture alone shows only that something changed.
- Separate causes. A fire scar, a drained reservoir and a growing city each have different causes, from weather and climate to water use and planning.
Why these images matter
Satellite pairs give everyone the same view that scientists use: a consistent, repeatable record of the surface. They help fire crews map damage, water managers track reservoirs and researchers measure long-term trends such as glacier retreat and rising temperatures. For the rest of us, they make slow or distant change visible, which is often the first step towards caring about it.
Sources: NASA Science: Images of Change; Wikipedia: Landsat program; Wikipedia: 2016 Fort McMurray wildfire; Wikipedia: Lake Powell. Video: Upworthy.
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