Landsat Study Reveals Greening Across North America's Arctic
An extensive analysis of Landsat images by NASA scientists reveals that the North American Arctic is getting greener amidst climate change. Analyzing 29 years worth of satellite images (1984-2012), the research team found nearly one-third of land cover has been changing to resemble landscapes in warmer ecosystems, NASA Goddard Space Flight Center's Kate Ramsayer highlights in a news report.
NASA Goddard's researchers analyzed 87,000 Landsat images, concluding that higher temperatures have resulted in longer growing seasons and changed soils in Canada's northern coastal zone and tundra in Labrador, Quebec and Western Alaska. Grassland tundra has been changing to scrubland and shrubs are growing to be bigger and denser.
Operated jointly by NASA and the U.S. Geological Survey (USGS), the Landsat Program "provides the longest continuous space-based record of Earth's land vegetation in existence," Ramsayer explains. The study was the first to map an entire continent yet provide detail at human scale.
A finer grained view of climate warming impacts in the North American Arctic
Spanning an area of more than 4 million square miles, the Landsat images revealed that vegetation increased in 30 percent of the area . Vegetation decreased in just 3 percent.
The study, research team member Jeffrey Masek elaborated: "...shows the climate impact on vegetation in the high latitudes. Temperatures are warming faster in the Arctic than elsewhere, which has led to longer seasons for plants to grow in and changes to the soils. Scientists have observed grassy tundras changing to shrub lands, and shrubs growing bigger and denser – changes that could have impacts on regional water, energy and carbon cycles."
Overall, the research team found that vegetation had increased in 29.4 percent of the area, in shrub lands and sparsely vegetated areas in particular. They did note variations: forests had greened in Canada but tended to decline in Alaska, for example.
Landsat satellites remotely sense visible and near-infrared light reflected by vegetation. Computer programs log each individual pixel of images over time, enabling researchers to determine changes in plant life and cover. The technology incorporated in Landsat satellites offer finer grained data than others, such as that from the Advanced Very High Resolution Radiometer (AVHRR), Ramsayer points out.
The ¨Big Picture¨ in greater detail
"We can see more detail with Landsat, and we can see the trend more reliably," NASA Goddard remote sensing scientist Junchang Ju said. The higher resolution images and better calibrated data from Landsat enable the researchers to zoom in on changes in vegetation, data that has been made available to other researchers.
"The resolution with Landsat is drastically improved, it lets you look at the local effects of things like topography, such as in areas where you might have small woodlands or open areas," Masek added. "You can do detailed studies of how climate impacts vary with geography."
The additions the study makes to previous studies that used AVHRR sensor data increases the certainty of how climate, vegetation and habitats are changing. Having completed the larger map, the researchers are moving on to examine changes in localized areas to determine the factors that may be driving the ecosystems changes.
"One of the big questions is, 'Will forest biomes migrate with warming climate?' There hasn’t been much evidence of it to date," Masek explained. "But we can zoom in and see if it’s changing."
The NASA Goddard research team's study is available online in the April 2016 edition of Remote Sensing and the Environment.
*Image credits: NASA-USGS Landsat Program; NASA Goddard Space Flight Center