In their paper, Projections of Earth’s Technosphere: Scenario Modeling, Worldbuilding, and Overview of Remotely Detectable Technosignatures, authors Jacob Haqq-Misra, George Proktiliotis, and Ravi Kopparapu explore possible trajectories for Earth’s technosphere—its technological impact on the environment—over the next 1,000 years. This research uses a worldbuilding approach common in science fiction to create various “future Earths,” envisioning how humanity’s technological presence might evolve. These scenarios support new strategies in the search for extraterrestrial intelligence (SETI) by identifying potential technosignatures, observable indicators of technology, that might arise if similar civilizations exist elsewhere.

Worldbuilding Earth’s Technosphere and Scenario Modeling

The authors apply techniques from futures studies to develop plausible futures for human civilization. Through scenario modeling, they create ten different models for Earth’s technosphere, each embodying a distinct combination of growth, stability, or decline. These hypothetical worlds help examine what Earth’s technosignatures—observable traits indicating technology—might look like across time. The scenarios broadly fall into four categories:

• Zero-Growth Stability: Models where human technology reaches a stable, sustainable level with minimal growth.
• Collapse and Stability: Scenarios where human civilization declines but finds a new stable state after the collapse.
• Oscillatory Growth and Collapse: Models where civilization alternates between periods of expansion and decline.
• Continued Growth: Models with sustained technological growth, including one ambitious scenario featuring interstellar expansion.

Detecting Technosignatures: Earth’s Possible Future Signals

The study emphasizes nitrogen dioxide (NO₂) emissions as a key technosignature. These emissions can reveal the level of industrial activity, providing a spectral marker that might distinguish various Earth-like civilizations. Analyzing atmospheric changes across different scenarios, the study finds that some future Earths resemble pre-industrial conditions, while others show elevated NO₂ levels. This variety in spectral signatures indicates that technospheres might evolve in unique ways, potentially appearing as transient blips rather than stable markers in time.

For example, in scenarios of collapse and stability, civilization’s technological signature may be minimal, with little change in atmospheric composition. By contrast, continued growth scenarios exhibit clear technosignatures, with detectable industrial emissions and possible markers of interstellar communication or energy use.

Breakdown of Technosphere Scenarios

1. Zero-Growth Stability: These scenarios envision a future Earth that has balanced population growth and technological impact. Here, human society actively prioritizes sustainable practices, resulting in steady technosignatures but no outward expansion.
2. Collapse and Stability: Civilization experiences a major decline, possibly from ecological or social factors, and stabilizes at a lower level. With reduced technological activity, these scenarios exhibit minimal technosignatures, making detection by outside observers challenging.
3. Oscillatory Growth and Collapse: Civilization undergoes cycles of boom and bust, with periods of industrial growth followed by environmental resets. Each collapse reduces the technosphere’s footprint, creating fluctuating technosignatures that would be detectable only intermittently.
4. Continued Growth and Interstellar Ambitions: Only one scenario models rapid, sustained growth, with a future where Earth’s civilization eventually reaches beyond the solar system. This scenario presents unique technosignatures, likely featuring heightened industrial emissions, advanced energy signals, and potential markers of interstellar expansion.

Technosignature Implications for SETI

This study’s future Earth scenarios provide a valuable foundation for the SETI field, highlighting the potential variety of technosignatures. By studying Earth’s hypothetical futures, scientists can better hypothesize what extraterrestrial technospheres might look like and identify both stable and transient technosignatures that could appear across the galaxy. The diversity in scenarios also raises the possibility that short-lived technospheres may be more common than stable ones, suggesting that alien civilizations might similarly pass through periods of detectable technological activity before fading.

Summary

Projections of Earth’s Technosphere offers a forward-looking view into Earth’s potential technological evolutions, providing a unique framework for technosignature detection in SETI research. With ten distinct scenarios, the study explores futures ranging from sustainable zero-growth states to oscillating cycles of expansion and collapse, illustrating a wide range of possible technosignatures. Through analyzing NO₂ as a key indicator, the study enhances our understanding of what signals might reveal advanced civilizations in the cosmos, offering a compelling roadmap for the search for extraterrestrial intelligence.