A decade ago, Johan Rockström identified the limits to Earth's life support systems. From chemical pollution to climate change, we're veering into the danger zone - so why is he (cautiously) optimistic about the future?

Humanity’s life-support system, as seen from space JSC/NASA

HUMANITY can only thrive if our planet is hospitable to us, but what are the limits to its stability? That was the question posed by Johan Rockström in 2009 in the first scientific assessment of the limits to safe living for humans on Earth. He and 28 co-authors called them the planetary boundaries. They warned that if we exceed any of those nine boundaries, we risk destabilising Earth’s life-support systems and plunging the planet into chaos. The good news, they said, is that staying inside them provided a “safe operating space” for humanity. The bad news is that we have already exceeded four of them.

The boundaries have drawn plenty of criticism, so does Rockström still stand by the findings? Is he more or less pessimistic about where we are headed? And where do Harley-Davidsons fit in?

Fred Pearce: What is the bottom line for Earth and human civilisation?

Johan Rockström: For the past 10,000 years, our planet has been in a uniquely stable state, a warm interglacial era with largely unchanging climate and ecosystems that we call the Holocene. It is the era during which human civilisation has developed, from hunter-gatherers to digital technology. It is all we know.

But humanity is now driving changes like global warming and species extinctions. These threaten to push us beyond the thresholds of the life-support systems that have sustained the Holocene.

The changes could be abrupt and irreversible. We don’t know where things may end up. If the Holocene is our desired reference point – the stable planet we …