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How Do Satellites Help Us Track Climate Change?

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Following the publication of the 2021 United Nations climate report, Secretary-General António Guterres warned that the findings were “a code red for humanity.” With rising ocean temperatures accounting for 91% of global warming seen to date, rates of sea ice melt in the Arctic are an important indicator of overall climate change. The satellite age has provided humans with a crucial tool for monitoring climate conditions because of the frequency and precision with which space-based instruments can measure changes in sea ice, giving us a near-constant picture of Arctic waters since 1979. The ensuing decades have, however, demonstrated that satellite imaging is not a panacea for climate research. Key issues – including practical concerns about space junk and political uncertainty about data sharing - remain unresolved.

Satellites observe sea ice coverage through thermal microwave radiation. Microwaves radiate from the entirety of the Earth’s surface, but different substances emit different wavelengths. Satellites equipped with microwave radiometers and imagers can create a digital picture of Earth’s surface indicating what’s land, what’s water, and what’s ice to track the surface area of ice sheets illustrating regions of expanding or retrenching ice coverage. This type of sensing is very durable even in the harsh polar environment since analytical models can account for snow, rain, and fog.

A more challenging issue has been measuring the thickness of sea ice. This is an important metric because warming ocean waters thin out ice sheets or lead to calving icebergs; the subsequent melting ice is the largest contributor to sea level rise. In 1992, American and European space agencies began equipping satellites with altimetry instruments, which emit radio pulses or laser beams to earth. By measuring the amount of time it takes the signal to return to the satellite, analysts can calculate the difference in height between the ocean surface and the sea ice surface, or the thickness of the ice sheet.

Radar and laser altimetry aren’t substitutes but operate in tandem to create an accurate depiction of sea ice melt. The former can observe larger ice areas at a time, enabling frequent observations of glaciers or ice sheets. The latter uses a very focused, narrow beam that only observes small ice patches, but can deliver more precise data. Scientists use lasers to gather information on particularly concerning areas of ice melt, or for swaths of ice with difficult or uneven terrain. The complementary abilities of radar and laser altimetry mean that these devices are most effective when used in concert. For example, a 2021 study by Susan L. Ustin and Elizabeth M. Middleton outlines the 2020 project undertaken by the European Space Agency’s CryoSat-2 (radar) and NASA’s ICESat-2 (laser) satellites to synchronize their Arctic overpasses, collectively delivering simultaneous radar and laser observations. These overlapping orbits allow analysts to track changes in ice flows, flooding, snow melt, and snow water content on a daily basis.

Current development efforts suggest that forthcoming missions will focus on higher-resolution imaging to gain a clearer picture of localized sea ice conditions. For example, Ustin and Middleton also point to the American and Indian space agencies jointly developing the NASA-ISRO Synthetic Aperture Radar (NISAR), a satellite equipped with imaging tools that capture 25-100 square meters of ice surface as an individual pixel. Given that most satellites currently in orbit image sea ice at around 1 square kilometer per pixel, this development is a major advancement. The NISAR data will be used to help the ecological community understand nuanced changes in Earth’s carbon uptake by tracking sources and sinks of carbon.

Despite the value space-based instruments provide for climate monitoring, policymakers have yet to address two key issues. First, climate-monitoring satellites contribute to the proliferation of objects in Earth’s immediate orbit. Dozens of states operate satellites for research, communications, and intelligence. Adding new climate satellites will increase the risk of collisions that create clouds of space junk. Second, increased attention to melting sea ice contributes to questions of access to satellite data, with climate watchdogs and scientific communities lobbying for access to government-collected data.

Increased attention to on-orbit servicing, assembly, and manufacturing (OSAM) could address the issue of satellite proliferation by allowing for hardware and software updates to be added to satellites in orbit rather than launching replacement satellites. OSAM has sustainability applications across space technologies, but the Science & Technology Policy Institute has already outlined plans to retrofit existing satellites with imagery payloads that would allow them to take on climate monitoring functions. These OSAM upgrades will save an estimated $20 million over a 5-year payload life, increasing state incentives to expand sea ice monitoring programs.

Addressing data access issues require organizational rather than technological change. There is a growing global trend of satellite-operators making their climate data publicly-accessible. Satellite data is invaluable to researchers working on climate-related issues, offering a global picture of warming trends. But the cost of launching an imaging satellite – which can range from tens of millions to the hundreds of millions of dollars – means these tools are out of reach for much of the scientific community, leaving these researchers reliant on government open access or declassification policies. In the private sector, organizations such as Data for Climate Action have created coalitions of top industry leaders willing to contribute their proprietary data on climate conditions for free access. Similar trends have emerged in the public sector. The EU, for example, adopted a full, free, and open data policy in 2013, mandating that all member states open up government-collected data on climate change and other issues.

Within the U.S. government, the National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), Department of Defense, and U.S. Geological Survey all own satellites in orbit that collect climate data, with the Department of Energy and Federal Aviation Administration providing analytical support. All of NOAA’s data on sea ice and select NASA forecasting is publicly-accessible. But despite President Barack Obama’s Climate Data Initiative, aimed at making federally-collected data accessible, other agencies have yet to release their sea ice forecasting. The Department of Defense, for example, relies on satellite-collected data to inform geopolitical risk analysis and strategy planning, keeping even innocuous data points like sea ice coverage behind classification barriers. Especially as new innovations increase the number and quality of sea ice observations and as climate science takes on new urgency, U.S. agencies that withhold data may find themselves facing increasingly hostile resistance from scientific organizations and climate watchdogs. The satellite age and ensuing sea ice monitoring advancements have given government researchers unprecedented insight into localized and global contributors to rising temperatures. But just as climate change is a problem with a centuries-long horizon, so too must climate monitoring be equipped for longevity. Technological advances such as OSAM capabilities and organizational changes embracing a more nuanced classification process to give researchers access to non-sensitive satellite data are concrete steps towards improving global climate resiliency.


About the Author: 

Kathryn Urban is a current graduate student in the School of International Service’s Global Governance, Politics, and Security program. Her research interests include Arctic securitization and the strategic logic of drone warfare.