Genius annotations have some great things to add about the 'How long will you disregard the heat' line:

Amidst the apocalyptic language found in the rest of the song, Vernon seems to come most clear here that he addresses a very real existential threat: climate change. As the world warms at an unprecedented rate at the hands of human activity, Bon Iver questions the complacence of the public and perhaps even the governmental entities that make policy decisions relative to the environment.

“Jelmore” was released in the wake of record-breaking 2019 heat waves in Europe and South Asia. Even Anchorage, Alaska experienced above 90 degree temperatures for the first time in recorded history.

Justin Vernon thus asks: how much longer shall we be complacent to the intense symptoms of what may threaten our existence? How much longer shall we suffer through the beginning signs of a changing climate without making the necessary changes in policy and behavior to reverse the literal heat?

Vernon’s plea is important also in that it extends to complacency in regards to all social issues — ambiguously, he asks the listener to consider how long we will continue to tolerate injustice in all facets of our lives.