To start, many activists, scientists, and policy-makers have focused on setting climate targets for stopping future warming — that is, how much warmer will Earth have to get (and how much damage will climate change cause along the way) before we finally stop global warming?

To put this in perspective, we have already warmed the planet approximately 1˚C, and the effects are being seen today in our weather patterns, ecosystems, natural resources, and communities worldwide.

That’s not the future, it’s now.

I want to stress that we have already altered Earth’s climate, and this 1˚C warmer world is a significantly changed world — one that is more dangerous to us, with more hazards and systems breakdowns. Even if climate change stopped today (which is sadly impossible), we have already crossed the climate Rubicon; no other people in human history have lived in a world like this one.

In terms of future climate, many climate leaders have suggested we need to put the breaks on climate change before the planet warms 1.5˚C or 2.0˚C — or another half degree or full degree above what we’ve seen so far.

The general thinking is these 1.5 or 2.0˚C targets represent limits of where climate change is still potentially “safe” for humanity, but beyond this point the planet starts to unravel more and more — in ways that could seriously destabilize human societies, ecosystems, natural resources, and global environmental systems.

It is important to note that if we do absolutely nothing more to stop climate change, global warming could exceed this amount. In fact, the latest “business as usual scenario” show the potential to warm the Earth by 3˚C, or maybe more. That’s not just a changed world, that’s a world none of us would recognize.

So these numbers can be helpful. After all, we need to understand the potential dangers of a warming world, and what the ultimate targets for stopping climate change should be.