The desire to understand space and reach beyond the limits of Earth's atmosphere has provided us with the ideal platform to study our planet and combat our most pressing challenge: climate change.
May 15th, 2021, marks this year's International Astronomy Day, when scientists and amateur space-enthusiasts alike will celebrate our massive advances in the study of the cosmos.
As this day of celebration approaches, it is also important to note that space technology and its advancement have also allowed humanity to look the other way. Scientists are now routinely using space-based equipment to stare back at our own planet. A perfect example of this is the use of the International Space Station (ISS) to study Earth¹.
Orbiting 250 miles above our planet's surface the ISS hosts a multitude of Earth-observing technology mounted upon its exterior.
Amongst these devices are the cameras and assorted tools that sit on the edge of the Japanese Experiment Module (JEM). Meanwhile, miniature satellites weighing between 1 and 10 kilograms called CubeSats² are regularly deployed from the airlocks of the ISS and sent to conduct observations from low-Earth orbit.
Perhaps the most' low-tech' — albeit no less important — example of Earth observations occurring aboard the ISS are the images captured from the station's observation windows by its rotating team of 11 or so astronauts.
Thus far, these pioneering men and women have been able to capture around 4 million images of Earth from space, in the process, creating one of the longest-running records of how Earth is changing over time. Not only have these images been used to address climate change, but they have also helped in tackling disaster relief efforts during events like hurricanes and wildfires.
The ISS isn't just an observation deck, however. The space station also functions as an in-orbit laboratory where Earth science experiments can be carried out.
All of this means that the ISS has become a vital platform in the understanding of our planet, and in particular, its climate. This allows researchers not just to monitor the climate and understand how it is changing but also permits us to prepare for future changes.
If you don't have a good understanding of how things might change, you are in a very poor position to be able to handle it when they do. Weather reflects the conditions of the atmosphere over a short period of time, and climate is how the atmosphere 'behaves' over decades, hundreds of years, or even geological time spans.
William Stefanov, Manager, Exploration Science Office, Johnson Space Center, NASA
This means that in order to properly understand the climate, it is vital to track the long-term influences over it. This makes the two decades it has spent in orbit make the ISS ideal for such a lengthy mission.
Twenty Years of Monitoring Earth's Climate
The length of the ISS's service is matched by the fact that on its regular trips around the Earth it passes over around 90% of Earth's human population. Additionally, as the ISS has a 52⁰ orbital inclination means that from the station it is possible to see the Sun both rise and set 16 times each day in locations across the globe.
"That orbit allows the space station to pass over different spots of Earth at different times of day or night and collect data," continues Stefanov. "It is a fundamentally different data set than most other remote sensing instruments collect on free-flying satellites."
Amongst these pieces of remote-sensing tech are the internationally operated devices ECOSTRESS, GEDI, DESIS, TSIS-1, HISUI, and OCO-3, all mounted on the ISS exterior and all collecting climate data. This results in an impressive and constantly updating data set, which is revolutionizing environmental science.
The primary mission of OCO-3 ( The Orbiting Carbon Observatory 3)³ is of particular importance in understanding and potentially combating climate change. The sensor uses the reflection of sunlight through the atmosphere to monitor atmospheric carbon dioxide and how it changes.
The device has a high enough sensitivity to spot changes as minuscule as a single part per million.
Most gases like ozone, carbon monoxide, or water vapor double or triple in atmospheric concentration when they are polluted, so it is pretty easy to detect. But for carbon dioxide, it is uniquely difficult to see the changes.
Annmarie Eldering, OCO-3 Project researcher, Jet Propulsion Lab, NASA
Measuring even these tiny changes in CO2 could be vital in answering long-standing questions surrounding this greenhouse gas which plays a major role in global warming. And the goal of the OCO-3 nicely links up to the goals of some of the other devices it shares the ISS exterior with.
"The OCO-3 team wants to understand plants and their role in the carbon cycle. It turns out our space station neighbor ECOSTRESS is looking at how plants respond to stress. And then there is GEDI, which is looking at how much plant material is on the ground," adds Eldering. "Scientists who are thinking about plants and their role in the carbon cycle are super excited. We have heard lots of discussion about how we can use all the data together to better understand plants."
In conjugation, these projects could lead scientists to a better understanding of the role both plants and the ocean play in the storage of anthropogenic — human-produced — carbon dioxide, and why this quality varies from year to year.
This is something that is not just being studied on the exterior of the ISS, it is also being tested in experiments held in the station's interior.
Investigating Life's Role in Carbon Storage and Removal
Within the ISS is a Photobioreactor (PBR) built by Airbus, which takes part of the carbon dioxide extracted by the station's life support system and converts it to oxygen and biomass³. This could help us better understand how microalgae can be better used to convert carbon dioxide into more useful substances.
Microalgae isn't the only organism aboard the ISS that is being investigated for its carbon-processing properties. The Kuwait-operated experiment Combating Climate Change Through Carbon Dioxide Consuming Escherichia coli (E. coli C5)⁴ is attempting to understand the effects of microgravity on a strain of E. Coli that has been specifically engineered to consume carbon dioxide.
In both cases, this ability in both organisms could help mitigate climate change by reducing atmospheric carbon dioxide, but the teams behind these separate research projects are also looking at the potential to produce biofuels and organic carbon food sources, something that could also have a positive environmental impact.
The ISS is also monitoring organisms that benefit from climate change here on Earth by tracking outbreaks of Harmful Algae Blooms with the Hyperspectral Imager for the Coastal Ocean (HICO) instrument⁵. These organisms can be harmful to marine life as they both deplete oxygen in aquatic ecosystems and drive up water temperature.
Monitoring Earth's climate also involves other elements for which the ISS is well-equipped such as energy flowing to Earth from the Sun, monitoring ozone, and tracking lightning.
"Monitoring the energy that flows into, within, and out of the system underpins our ability to understand how the climate system works, recognize that it is changing, and identify those mechanisms responsible for climate change," says University of Colorado Boulder professor Peter Pilewskie, principal investigator with TSIE, an experiment that tracks energy received from the Sun.
The experiments conducted at the ISS that involve the monitoring of Earth's climate are almost to numerous to list. In addition to those listed above, there are more set to begin in the next few years.
For example, Pilewskie will be involved in the operation Climate Absolute Radiance and Refractivity Observatory Pathfinder (CLARREO), a solar spectrometer that will monitor Earth's climate by measuring the amount of sunlight reflected by the Earth and the Moon.
It is humanity's desire to explore space and reach beyond the limits of our atmosphere that could be the determining factor in our most pressing and urgent battle; the fight against climate change. That means, on International Astronomy Day, we should also celebrate instruments trained not on the stars, but those that reflect back upon our own home that will be vital in the coming years.
As Pilewskie concludes, "Climate change presents what is perhaps humankind's greatest environmental challenge."
1. ISS 20, NASA, [https://www.nasa.gov/mission_pages/station/expeditions/index.html]
2. Technology CubeSats, ESA, [http://www.esa.int/Enabling_Support/Space_Engineering_Technology/Technology_CubeSats]