But many implicitly ignore the benefits of fossil fuels. I hear many variations of the comment I originally replied to, i.e., "even if there's no climate change, reducing fossil fuel use is pure win". I think many imagine we could keep roughly the same quality of life with the majority of our power coming from solar panels and wind farms. Smarter environmentalists realise this is not true, but the general public is very confused on the issue, especially as the more rational greens get lumped in with the activist crazies.
(One very important point in to explain Alex's context: many greens (not all, granted) are opposed on moral grounds to nuclear, and even to hydro, which floods valleys and messes with nature. The root of this is the desire to minimise human impact, but "minimising human impact" is ultimately at odds with "maximising human flourishing").
to think that there is zero room to improve our energy pattern and sources compared to what we have now
He doesn't think this. Obviously improved nuclear power, ultimately fusion power, is the real long-term solution. However, hopes that we can significantly improve solar or wind power are doomed to crash into reality -- there's fundamental limits to how much energy you can extract from the wind (https://en.wikipedia.org/wiki/Betz%27s_law) or from photons (https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...). Burning wood and dung works for poor countries that lack infrastructure, but it's more expensive that fossil fuels, and more polluting, even more polluting than coal.