I’m a former climate skeptic turned clean energy entrepreneur. Here’s why.

I’m a clean energy entrepreneur, but I started my career thinking climate change was a big hoax.

I was skeptical into my early 20s. I didn’t think that humans could possibly have the power to alter a geological system as big as Earth single-handedly. And frankly, I didn’t really appreciate some of the people shouting at me that we have to save the planet. Their case seemed to be a moral one rather than a scientific one, and they made me feel guilty for not feeling the same. Some of them were just way too crunchy for my taste. Plus I didn’t like the idea of sacrificing cheap electricity and gas to fight off some distant, uncertain threat that may or may not be real.

Then, thanks to the urging of a few close friends, I actually looked into it. I went to climate science lectures, read peer-reviewed papers, and talked with experts. I took classes on climate science, one taught by a professor who started her career as a skeptic as well, and learned from the experts how the science actually gets done. Hint: It’s done by really nerdy tenured professors, data scientists, and scientific organizations, using a variety of methods including raw data and fancy models — the least political people you can imagine, arguing with each other incessantly to try to parse out the defensible conclusions from the bad ones, and gradually arriving at points of agreement. It’s done by people who have committed their lives to studying physics, biology, geology, chemistry, math, and statistics. These are people who do not have an incentive to be alarmist, and whose careers are on the line if they make an absurd claim that is later proven to be false.

Most importantly, I spent time with people who are on the front lines of climate change. I did a study abroad program in southern Africa, where some of the world’s poorest people live, and stayed in a village where the desert is actually encroaching and threatening their food supply. At conferences, I met people from the far north who are seeing the ice disappear.

I became convinced, as hard as it was to accept. With that much evidence laid out in front of me, I had to change my opinion. I figured, when a physicist tells me something that’s hard to imagine — e.g. that our atoms are made up of 99.99% empty space, or that the light we see from the sun is actually several minutes old — it’s a tough truth to swallow because I can’t see or experience it with my own eyes. But when thousands of scientists tell you something, and when they nearly all agree on a basic concept that has been reproduced across thousands of studies and experiments, they’re probably right.

Same with the basic principles of climate change: when you burn fossil fuels and cut down forests, you release greenhouse gases into the atmosphere, which warms things up rapidly. Warming things up rapidly means the oceans, plants, animals, circulation patterns, and other systems aren’t able to adjust fast enough and they go haywire. Yes, the climate has changed in the past, but never this suddenly and dangerously while humans were around. And yes, that’s bad, because rising sea levels, decreased food production, drying up water sources, and other effects could lead to the forced migration of millions of people (in already politically unstable regions), extinction of millions of species (this is already happening), and unheard-of damage to the economy. These are things that 97% of the scientific community agree on — believe me, I’ve met hundreds of them. Though there is plenty of lively debate over the specifics, the occasional scientist who doesn’t agree with these basic principles is almost inevitably either 1) not an expert on climate or 2) being paid or otherwise incentivized to make spurious claims by an organization that has an interest in sowing doubt about climate change.

So having poked, prodded, and questioned the crap out of these ideas (including really ruffling the feathers of some of the crunchier folks I sat with in college classes), I realized I was wrong. I realized the climate really is changing, it’s because of burning fossil fuels, and we can fix the problem while building a profitable clean energy economy. In addition to a huge threat, it’s an opportunity to build a resilient energy system that is no longer vulnerable to the geopolitics of oil, coal, and gas. So I changed my major to focus on the economics of climate change and clean energy and have been working in the field ever sense.

A few things I’ve learned:

1) This isn’t about sacrifice. We can build an energy economy that supplies the bulk of our needs from clean energy sources, with the right investment and smart policies that support clean energy. If we can unleash American industry on this challenge at scale, we can tackle it profitably. Take it from me: I’ve built three companies in the clean energy space. We’re already making a big dent.

2) This isn’t an issue for hippies. I talk to investors, national security experts, and CEOs of major companies pretty much every week who are genuinely worried about climate change. Even fossil fuel companies are beginning to shift investments over to clean energy technologies.

3) You shouldn’t feel bad for being skeptical. Skepticism is the foundation of good critical thinking. But you also have to be careful where you get your info from. The cigarette industry successfully sowed doubt about its products causing cancer for decades, despite a scientific consensus to the contrary. Be open to changing your opinion.