After making your way through trees for the first half of the hike, the trail will open up a bit and get steeper.

“We always knew that the path to net zero would get steeper over time, and that’s reflective of the fact that we haven’t done a great job of reducing emissions to date,” said Kate Larsen, a partner at Rhodium Group.

Cliffs become increasingly unstable as they get steeper and less supported at the base, Young said.

For now, the credit curve only seems likely to get steeper, in particular because companies have issued a lot of risky long-dated debt.

The rails also change in height based on how each of the three heads are used: shallow on the 3-4 and progressively taller as the swings get steeper on the 5-6 and 7-8 models.