Gazing at the Andromeda Galaxy through binoculars with my science teacher dad is one of my earliest memories. And the more I learned about science, the better it got. Who wouldn’t want to know why the sky is blue, that polar bears have black skin and translucent fur, and how tiny amounts of heat-trapping gases in our atmosphere serve as the thermostat for the planet?

Despite my fascination with the universe and this planet, I still thought of human-caused climate change as a distant, far-off issue, something that only really matters to David Suzuki or those polar bears. It wasn’t until I was looking for an extra credit to round out my astronomy and physics degree at the University of Toronto and I ended up in a class on climate science that my perspective abruptly changed. That’s when I learned it’s not the planet that’s most at risk, it’s us; and the window of time to prevent serious consequences is closing fast.

I switched fields and headed to grad school at the University of Illinois at Urbana-Champaign to study climate science. For the past 20 years, I’ve been working with cities, states and federal agencies to figure out how to prepare for the impacts of a changing climate. And I don’t just study climate change—I also talk about it. A lot. In classes I teach in person at Texas Tech University and online around the world. On Twitter and Instagram and Reddit AMAs. To farmers and oil-and-gas executives and congressional staffers. On local news and the Today Show, I’ll talk anywhere and to anyone.

But the more I talk about it, the more pushback I get. I’m accused of lying and peddling “UN-derived satanic deception” and a multitude of other sins when I’m upfront about what the data tells us: Climate is changing, and humans are responsible. “Global warming is a freaky genocidal doomsday cult,” one man tweeted at me the other day. “You lie for money,” another posted on Facebook, “and change the data.” I’ve been called a loony, a fraud, a clown and a libtard.

Here’s how I handle the tough conversations.

Read the full essay here.