First off, I absolutely hate the diamond industry. So I by no means am saying natural diamonds are better than lab grown ones.

That said, the article does have some point. Based on a quick look online, diamonds actually require a lot of energy to form. The range seems to be between 300 and 2000 kWH per carat. Here's just one site:

A modern larger multistone cubic HPHT press will use 75–150 kWh per rough ct., which would end up around 350–700 kWh per successful polished ct.

[A CVD producer] told me [it used] around 60–120 kWh per rough ct. and 1,000–1,700 kWh per polished ct. There is more unused rough from CVD since they are cube shape, which is why those ratios are higher.

According to the EIA the average monthly household power usage is 900 kWH.

That means a one carat diamond can likely require more power than your entire house uses in one month.

Coal power plants in the US operate art an avg of 33% efficiency. Therefore, your one carat of diamond requires at least 3000 kWH of coal.

1 kWH requires 1.14 pounds of coal. So then your one carat consumes 3,420 pound of coal.

I'm no expert, but I imagine that is a lot of emissions for one diamond. Plus, none of that accounts for unregulated countries which could make any of those numbers so much worse.

Once again, I'm all for lab diamonds. There's still a point to be made that they require massive amounts of energy and that we can do better to make sure that energy is clean. Renewable power is the best way to make diamonds for sure.