If 5 degrees is a mass extinction event (I'm just using your numbers here, not positing them as facts of my own), how can you characterize 1-2 degrees (20-40% of your mass extinction event number) as a "small" issue?

As an "engineer" (note: software engineer, not a real engineer), I'd prefer to leave as much wiggle room as we can possibly muster on the spectrum of activities heading us towards "mass extinction event".