1. The last warm period, the Medieval warm period, wasn't as hot as it is today, it was also not as widespread, the polar bears' habitat wasn't nearly as affected. It also happened little under 1000 years ago, so I don't understand the why your comment directed at young Earth creationist.

2. The problem is not that it's a warm period, it's that it's an unnaturally warm period with temperatures rising at alarming rates never before seen. If it were similar to the medieval warm period it wouldn't be as big of a problem.

3. That's not true. Solar energy has been making leaps and bounds since governments and businesses started pumping money into its R&D due to the Paris Agreement. It went from a stagnant technology to have a breakthrough almost every single day. It's constantly getting more efficient and much cheaper. Almost 90% of the power generated in Europe in 2016 came from renewable resources (factoring in Solar and Wind power)

a) Yes, reducing the Earth's population would solve Global Warming, but there are certainly easier ways to solve the issue than to try and stop people from having unprotected sex, or to punish them for having more than a certain amount of children. It would be naive at best, despotic at worst.

b) It's irrelevant if an individual buys eco-friendly stuff, it's a systemic issue, many times the products billed as eco-friendly are built and delivered is not very "eco-friendly" at all. Not (necessarily) because of bad intentions, but because sometimes there are no other ways but the old ways. Hence why the focus should be on finding alternative energy sources that could replace the old ways for everyone, rather than on commodified items like the Tesla.