Final answer:
Australia's 2020 wildfires spread primarily due to extreme weather conditions influenced by climate change, compounded by the susceptibility of fragmented forests to fire, which increased due to human land-use activities.
Step-by-step explanation:
The spread of Australia's bushfires, like the catastrophic 2020 wildfires, was due to extreme weather conditions intensified by climate change, rather than by ocean currents, volcanic activity, or intentional human actions (though anthropogenic factors cannot be entirely dismissed as they play a role in the broader context of climate change). Factors that influence bushfire spread include vegetation, topography, meteorological conditions, and area-specific conditions such as the availability of ignition sources like lightning strikes. Additionally, human activities have fragmented forests, making them more susceptible to fire spread due to increased edges that are drier and accumulate more combustible materials. Aboriginal fire management historically maintained stable vegetation patterns through skilful burning in patches, showing an in-depth understanding of controlled fire use in land management.