I’ve spent much of my life in oceans. It’s what most underwater photographers do, the serious ones at least. It’s my favorite part of the job. The ocean has always felt like home to me. When I was a kid, I used to splash around at the English seaside and pretend I was Jacques Cousteau. I wanted to explore hidden places and discover fantastic new species. Submarines seemed far more magical than spaceships.

As a teenager, I started scuba diving. Now this was a real eye-opener. Suddenly, all those stunning corals and exotic fishes from my favorite books were there in front of me. I was in their world. I still remember the sensation of taking my first breath underwater. My entire body was tingling with this intense joy, an almost giddy feeling of sheer wonder -- I had found paradise.

Today, paradise is dying.

More specifically, our coral reefs are dying. In 2016 alone, we lost almost 30% of the Great Barrier Reef, the place I dreamed of in my childhood. The problem isn’t limited to one country, region, or even continent. Over the past thirty years, roughly half of the world’s coral has died.

I saw this first-hand while making Chasing Coral, a Netflix Original Documentary that has just been released. It was the most ambitious thing I’ve ever done. For more than three years, our team of divers, scientists, and photographers dedicated ourselves to a single task: documenting the life and death of our world’s coral reefs.

We spent over 650 hours underwater. Sometimes we’d spend months at a single location, watching in somber silence as the seascape changed day by day. Lush coral gardens, rich with color and life, seemed to vanish overnight. The fossilized boneyards they left behind still haunt those of us who swam through them.

But what was killing the reefs? Scientists were baffled for years, until they discovered a devilishly simple answer: the oceans were becoming too hot. Corals are resilient creatures, precisely adapted to their environment. But their environment has changed and it’s killing them.

Some people remain skeptical. Climate change is a tense political issue, and even if one accepts the fact that Earth’s temperatures are affected by human activity, the fluctuations thus far seem quite small. How much of an impact does an increase of a few degrees really make?

Imagine you have a fever. Your normal body temperature is roughly 98.6° F / 36.1° C, but it rises to 100.6° F / 37.1° C. You feel pretty miserable, so you go to the doctor. They give you the usual advice, “Drink plenty of fluids, take an aspirin, get some rest. Let me know if anything changes.” You go home, expecting to feel better soon.

A week later, you’re still feverish. A month later, and there’s still no relief. Your temperature just keeps rising.

How long would you wait to call the doctor?

You wouldn’t wait very long, of course, because you’d be dead if you did. The warning signs would be too obvious to ignore. Your life is precious and so you would do whatever was necessary to save it. We need to be equally protective of our oceans, and our corals in particular—a small rise in temperature can be fatal.

The Paris climate agreement was a huge step in the right direction. Its goal is clear: to limit the rise of global temperatures to a maximum of 3.6°F/2° C above pre-industrial levels, and a target of 2.7°F/1.5° C.

It’s black and white for coral reefs: Paris or bust. If we meet the Paris target, we can save enough coral reefs to enable them to bounce back, if we don’t, we will lose them entirely. It’s that simple. We will lose an ecosystem that provides food, jobs, and protection for about a billion people around the world and supports a quarter of all ocean life.

There is hope for coral reefs. We are leading an initiative called 50 Reefs that has received an outpouring of support from Bloomberg Philanthropies, Paul G. Allen Philanthropies, and the Tiffany & Co. Foundation. Its aim is to catalyze efforts to protect coral reefs globally - rapidly bolstering conservation efforts in key locations that are less vulnerable to climate change. But hope relies on us meeting the Paris target.

I am still haunted by what I saw during the making of Chasing Coral. The beautiful underwater gardens that I remember from my childhood are disappearing. My paradise is dying. The people who have lived off their bounty for centuries are losing their livelihoods and their futures. This is real, this is happening right now, and yet in today’s political climate there are many who refuse to acknowledge this. I challenge any skeptic to watch this film and to remain unconvinced and unmoved.