Scientific evidence shows that the Arctic Boreal Zone (ABZ) is changing more rapidly than any other part of the planet. Satellites play a critical role in monitoring change in this largely remote and inhospitable region. A recent article in Reviews of Geophysics examined the strengths and limitations of the current suite of observations from satellites. Here, three of the lead authors give an overview of what has been learned from satellite observations to date and what additional data and approaches are needed to improve predictions of future environmental change.
What comprises the Arctic Boreal Zone and why is it important to observe?
The Arctic Boreal Zone (ABZ) is the region that lies north of approximately 50°N and includes the boreal, sub-Arctic, and Arctic climate zones.
There are complex and often poorly understood interactions between the cryosphere, biosphere, hydrosphere, and atmosphere of the ABZ, which currently limit our ability to predict future ABZ changes in a globally warmer world.
While we often think of high latitudes as being sparsely populated, they are actually home to over 10 million people.
These residents are directly impacted by changes in wildfire frequency, the composition of ecosystems, the stability of local infrastructure, and much more.
Additionally, ABZ changes may have profound negative impacts for humans far beyond the ABZ, such as by exacerbating global warming through the release of vast amounts of carbon stored in frozen soils and raising sea levels via melting of land ice, especially on Greenland.
What insights have observations from satellites given into the changes in the Arctic Boreal Zone?
Prior to the advent of satellites, we had only a limited view of the vast ABZ, with little understanding of how it was changing.
The images from the early satellites launched in the 1960s were often grainy by today’s standards, but they demonstrated the primary advantage of satellite data: unprecedented spatial coverage, obtainable repeatedly over the course of a year.
In the decades that followed, improvements in satellite technology allowed for the documentation of profound changes in the ABZ cryosphere, biosphere, hydrosphere, and atmosphere. Satellites have been able to measure variables such as surface temperature, sea ice extent and thickness, snow cover extent and seasonality, ocean color, wildfires, and ice sheet mass, all of which are indicators of change. For example, the multi-decade record of sea ice coverage shown in this animation would not have been possible without satellites.
The changing annual Arctic sea ice minimum from 1979 to 2018. Credit: NASA Scientific Visualization Studio https://svs.gsfc.nasa.gov/4686
What are some of the strengths and weaknesses of these satellite data?
Observations of the ABZ taken from the surface, aircraft, Unmanned Aerial System (UAS), balloon, and boat are sparse and expensive to collect in the often inaccessible and inhospitable environment.
While these suborbital data have been invaluable, they lack the far more complete, repeat spatial coverage that Earth-observing satellites uniquely provide, which has transformed our ability to observe large-scale changes.
Each satellite instrument has its own strengths and weaknesses; for instance, instruments measuring visible data have the strength of obtaining images that are readily understood but the weakness of having surface information hidden in the presence of cloud cover. Meanwhile, measurements that require sunlight can be difficult to interpret because they’re only available during part of the year in the ABZ.
However, even with the range of environmental variables that can be measured from satellites, the current observational suite is insufficient to understand many of the complex interactions of the Earth system that are unique to the ABZ.
What new approaches, data or models might enable a more accurate prediction of future changes?
More accurate predictions will be enabled by a combination of improved models, new satellite instruments, and an improved data network.
To simulate the complex interactions taking place within the ABZ, Earth system models are needed that incorporate such aspects as ice sheet dynamics, biogeochemical cycles, permafrost thaw, vegetation change, and wetland dynamics, as well as the atmosphere and oceans.
Many of these processes are crudely represented or altogether missing in current climate models.
In our review, we recommend continuation of the capabilities of the currently operating instruments, to extend the long-term records, and augmentation of these records with data from new instruments, such as lidars that provide their own light source, an advantage in the often low-light conditions of the ABZ.
Among the observational needs that our review ranked as being most important are those associated with gaining a process-based and large-scale understanding of the ABZ carbon cycle and hydrologic cycle (which includes sea level rise) as they have the potential to affect a large portion of Earth’s population via economic loss, displacement, etc. For example, these carbon cycle observational priorities include atmospheric concentrations of methane and carbon dioxide and also the factors that are necessary to infer their emission source strengths, such as from wetlands, permafrost, and wildfires.
At the same time, a well-developed and more comprehensive ABZ observing network would provide data for a more thorough evaluation of Earth system model performance and identification of areas where further developments are needed. We need data collected from a wide variety of satellite instruments, as well as instruments based on aircraft and on the ground. Our review makes recommendations for an interdisciplinary and stepwise approach to develop a comprehensive ABZ observing network (ABZ-ON).
Another important thing to note is that modelers often rely on more than one satellite dataset to thoroughly understand processes, which means that having contemporaneous observations of certain parameters is critical. Space agencies need to consider a system-based observing approach in the future.