Last block no, last coin yes.

You say (now) its at risk, but this has always been Bitcoin's design. Take a look at some of the altcoins that people don't care mining anymore, then you can have an educated guess to what will happen.

Fact is Bitcoin miners will greatly diminish, but not disappear. It might go back to what it used to be in the first few years, this time only people that want to do it out of their own pocket. If you think (now) that this is a mistake, you never learned Bitcoin's design.

Since the beginning, Bitcoin (network) doesn't care if 10 or a million miners exist. The blockchain is still safe, and the nodes work and ensure things for everyone. And yes, expect the number of nodes to be higher than the number of miners, when it becomes completely unprofitable to mine in the future.

If you have free electricity, for example because you invested in renewable generation, it would be technically profitable, or perhaps if there is some market for the so called "virgin" coins, which are rapidly diminishing in production.

After 10 years you never saw this coming? What have you been doing? This is NOT a problem, it is doing as intended. Less miners do NOT put Bitcoin at risk, and there is never going to be a complete stop in mining, there is always enthusiasts that don't care.

Now you might remember Cannan's idea of putting asic miners inside household appliances, this is probably something that will be revisited. Canaan simply acted a bit too soon, but Asic miners inside TVs, Wifi routers or even simple heat spreaders will cater to these people, that will want to keep Bitcoin's network running, or the merchants that have already embrace it and are running nodes too.

The hashrate will reduce, but not as much as you think. Because the more efficient asics compensate the situation. However, later it won't be that profitable to manufacture those asics, and much less devote so much money in r&d to improve them as much as with the market in 2016. Even Bitmain will have to reconsider their core business if they want to remain around.

This could take the next halving or two, but it is coming, like it or not. The theory is that at the end Bitcoin transaction fee provide the incentive, i guess so but LN threatens those fees to be negligible anyway so it will be mostly enthusiasts many in from this forum (i expect the large Chinese, etc. miners to leave).

I really doubt LN transactions will fully replace onchain transactions, since onchain transactions will always be viewed as more secure and simple. If Bitcoin in general will be popular enough, mining will be sustained with onchain fees, but in case it won't, we'll have no choice but to introduce inflation.

I think mining activities will continue even if there is a great forest fire. We know that Bitcoin has several large mines, but all of that is electric power which I feel will have very little pollution.
The biggest pollution at this time is still caused by transportation activities. Therefore sometimes it would be wise if we reduce the use of transportation in our daily activities.
For example by moving from gasoline-powered transportation to electricity-powered transportation. All to reduce dirty exhaust emissions. Start with yourself first.

I think mining activities have been greatly reduced since 2018. So this should not be the main issue about the cause of the problem. And besides, why does it have to be Bitcoin? Though not only bitcoin can be mined.
And one more thing, maybe you say that you don't blame BTC for the problem. However, you only underline the carbon footprint of BTC.

When in fact the most basic problem is not this, but more complex. In fact, it was not a forest fire but the burning of the forest by an irresponsible person. For the sake of what? The fire was carried out for the sake of widening their business.

Currently, mining is not profitable in most of the countries except few regions where electricity is cheap and anyway most of the miners have stopped it due to huge loss incurred and I am one of them as we had set up a small mining farm with around 60 GPU but ended up with huge loss which is yet to be recovered. We need some innovative machines for mining as you have described but this is not the reason for climate change.

This was in fact one of the reason why they are discouraged to continue mining business these years, because of the excessive amount of electricity needed for them operate and from my own opinion, requiring mining facilities to have their source of electricity is quite necessary. Especially, to have reserve not specifically to rely all the energy requirements but to help reduce the burning of fossil fuels and carbon by huge electricity companies. In addition, our system could probably adjust in its codes and structures to use different consensus in verifying transactions.

Electric vehicles are only greener than gasoline if your country has the infrastructure to support them with green energy. Charging an electric vehicle from an electricity grid which is in turned powered by burning coal only shifts the emissions from your car to the power station. For electric vehicles to be really beneficial, you need to be buying your electricity from renewable sources or generating it yourself.

Exactly. Think of all the cash being printed and reprinted, all the metal being mined for all the coins to be minted, all the armored vehicles moving it around, all the electricity for all banks, the computers, the servers, the ATMs, and so on. Bitcoin is orders of magnitude less than that.

Because it's easier to just complain than actually do something. Bitcoin is a poor target for their anger, though. As I said above, online porn generates over 30 times as much CO₂ as bitcoin, but no one is rallying against PornHub. Dogs have bigger carbon footprints than SUVs, but no one is suggesting we should make dog ownership illegal.

Indeed, if only renewable energy is a bit more accessible and rampant then we won't have to worry about mining and the bad implications it brings. hopefully the future at the very least bring good news to cryptocurrency mining as it is one of the most potent cryptoccurency earning methods out there.

The means for making mining sustainable are there. Small and large mining facilities can purchase solar, eolian and hydro based energy systems that could save up both on their energy cost and efficiency. The only downside is the initial investment which could maybe ROI faster using that money to buy more equipment.

You cannot just implement a system where the miners who use green energy receive higher rewards or incentives... especially on a decentralised network.