I don't think it's semantics at all. It poisons the debate and allows the do-nothing business-as-usual people to say "But he's talking nonsense about destroying the planet". Which is correct, because that is nonsense.

So is the idea that enough nukes could strip the planet's atmosphere. In theory it's possible, but you should try doing the mathematics; how many nukes would you need? The runaway greenhouse makes much more sense, for heaps of reasons (not the least of them being economics).

I didn't say the nuclear holocaust scenario was easy or likely. It would take a LOT of nuclear warheads launched all at once detonating in a spread out, roughly uniform distribution all over the land mass of Earth. It's more of a "worst case, what if the biggest nightmare of the Cold War happened and every country emptied their silos in expected retaliation" type scenario. It's just to point out that while it would actually take effort to render Earth uninhabitable through nuclear holocaust, it's not entirely impossible.

Also, for the runaway greenhouse effect to occur, we would have to do nothing to stop global warming now. Scientists are already debating whether the damage is done and it's too far along to reverse the process, but we haven't reached the point of no return just yet. If the global average temperature gets too high, at some point the evaporation rate of water will become unbalanced with the precipitation rate. Water vapor is actually a worse greenhouse gas than CO2 so once a critical atmospheric saturation level is reached, you might as well say "bye-bye Earth." Again, it would require a tremendous amount of inaction and a callous "do nothing until it becomes a self evident problem" attitude, but it's still possible for human activity to push the ecosystem beyond the limits of repairing itself.

That is simply not true. Sympatric speciation happens frequently and is a well documented occurrence observed in nature and duplicated in experiments.
Darwins finches would be a good example.
Food sources, body size and type, natural disasters, serve as selection events and wide varieties of coping mechanisms, or lack of, slowly or dramatically influence the development or separation of species.

I have to say, I don't believe that a Venus-style runaway greenhouse is achievable by (unintended) human action. I don't think anyone doing the science is proposing it, either; current models, as far as I understand them, suggest that global temperatures will stabilise several degrees higher than at present. I would guess that the atmospheric temperature necessary for the water-vapour tipover is upwards of 50 Celsius, which is well above the survivable range for humans anyway.

Have you a source for your runaway-greenhouse suggestion?

Other than paying attention in an astronomy lecture one day and in Thermodynamics II another, I don't have anything other than what two university professors in two different disciplines with doctorates and teaching degrees told their two separate classes one day. I'm not saying that guarantees they speak for all scientists everywhere or that they were necessarily right, but seeing as how I spent a semester in each class letting them teach me, I willing to give them benefit of the doubt that they had some idea of what they were talking about. My professor for engineering and the environment also went over it briefly, so I assume he knew what he was talking about as well.

To be fair, they said it would end up being one of two scenarios that are impossible to determine for sure which would happen without observing it after the fact. Either the Earth would get so hot that the seas started evaporating at a greater rate, leading to more saturation in the atmosphere and ever increasing temperatures until the oceans started to boil, or a limit would be reached where the cloud cover due to excess water vapor would begin blocking solar radiation and force Earth into an ice age. The ice age would be reversible and would probably only last 1000-2000 years. A runaway wet greenhouse on the other hand could potentially make the planet inhospitable and would not be reversible. Once the evaporation rate of the oceans reachs a certain level, the effect would become self sustaining. The effect wouldn't be as bad as on Venus until the oceans completely boiled away however.

What questions were the two lecturers responding to, exactly? Because neither of those (nor the engineering/environment prof) sounds as if they were asked a question about the Earth's climate.

And I'd also like to know what the water-vapour tipover point is, please.

It wasn't in response to a question. In the astro lecture it was aside while discussing why the greenhouse effect is necessary but what would happen if it got out of hand, and how human activity was contributing to speeding up the process. In the thermo lecture the professor went on a tangent while discussing dew points and human comfort zones for humidity. Or maybe it was exergy and combustion. I don't remember exactly what segued into it but he started talking about how the Gulf Stream was effected by global warming, what would happen to Northern Europe if it were disrupted, and what scientists theorized might happen if global warming went unchecked.

I actually tried to look up moist greenhouse effect yesterday, but I couldn't find anything about the saturation limit.

OK, thanks; both are talking about an extreme effect which requires a very large (planetary-scale ) influence, not the lesser effects that humans can manage. That's what I figured.

Re the tipover point: Perhaps you should try working it out? IIRC, the various data for water vapour are easily available. I'd be interested to see what the parameters are. I guess the solar irradiation and global albedo would be the place to start?

The influence of humans may be small, but it's still enough to cause disruptions in climate and weather patterns. Over a period of time, the effects of that relatively tiny contribution adds up, which potentially could have dramatic effects on the environment.

As for the tipover point, short of a computer model (which I have neither access to or experience with), anything I calculate by hand would be a rough estimate at best, plus I honestly have the time right now to look up all the numbers and equations and put serious effort into coming up with an answer. I come to the internet to escape from homework, not take on more of it.

So... Junk science "news" with junk science commentary? Brilliant.

"Are we still evolving? Yeah, I would guess so" got mega-LOLZ from me.

"What we should ask is: is our children evolving?"