Ken Fabian

Seems like a tipping point on relative costs has been crossed. The economics of renewables has never been better and that has to be the case for massive growth of it to be possible as a policy. Not so much deep, long planning as taking advantage of the extraordinary cost reductions for RE; even one decade earlier and the IRA would not have been possible. I think carbon pricing can only work if there are available alternatives for energy companies to invest in that are approaching cost parity - which is only recently the case for RE for much of the world and is more difficult for a nation with extreme winters like Canada to take advantage of. More long connectors to the USA to take advantage of cheap solar out of season? More wind and hydro? More nuclear? But sticking with fossil fuels is not a good option.

I'll wait until one happens where I am - 2030 looks good for here. The last time I was where a full eclipse happened (suburban Sydney) the hush that descended was a surprise - most people headed inside (to watch on TV?) and the traffic mostly stopped. It seemed like some people were spooked (and fearful for children) as much as they were interested and the park we headed to was nearly empty, only one person with a telescope. Didn't have the gear ourselves to view directly - but did the pinhole thing and saw the impression. Mostly we observed the effects, like the sharpening shadows as it became a crescent, saw stars and watching/listening to birds, some doing their morning calls as the light came back.

I think the vulnerability of airships to bad weather is their greatest weakness and that isn't different by using hydrogen - there are uses for them but they are limited. I am still a bit surprised there haven't been serious efforts to use hydrogen by improving ways to do so safely; I am sure it could be done a lot safer than a century ago. And most zeppelins back then never caught fire. Dramatic examples of things going wrong don't necessarily mean they are very likely or cannot be avoided

@CharonY That is interesting and shows I don't know as much as I would like to. Thanks. Some green light gets used by photosynthesis yet a whole lot of green light goes unused by Earth's dominant plants or it would be absorbed, not reflected nor pass through leaves so much; I am still inclined to think the biochemistries that can do photosynthesis well could be limited and stronger green light won't necessarily lead to plants that use more green light more effectively.

A different opinion here. I expect that the light from other stars will still have a lot of energy across the whole visible spectrum, that eg Blue stars don't make only blue nor have a pronounced lack of red light in the spectrum and Chlorophyll a and b would work just fine. Despite the amount of energy available to Earth plants between Red and Blue they have not evolved photosynthesis that utilises Green effectively, despite the great abundance of green light - the limitations may be in the kinds of photosynthesis chemistry that work and the other, non chlorophyll sorts of photosynthesis (some not doing CO2 to O2) are less effective. Maybe plants elsewhere will manage with Red and Blue photosynthesis (and look green like here) because those kinds of photosynthesis are easier for biochemistry to achieve.

@Carrock Seems to me we would try for Near Earth Objects (NEO's) by preference. Atiras asteroids are inside Earth's orbit around the sun without crossing it, Atens are inside but do cross it, Apollos are outside and cross it and Amors are outside and don't. They seem likely to have recurring "windows" where lowest delta-v will be possible. I wouldn't start with the Asteroid Belt. I've suggested C-type (carbonaceous) asteroids by choice, for the water content (for reaction mass) however in general those are more likely to be found further out in the solar system and the Near Earth ones more likely to be S-type (stony). All probably contain nickel-iron but whether they contain carbonaceous or others suitable for extracting fuel/reaction mass is not clear. But the fact that carbonaceous meteorites are common suggest that carbonaceous asteroids could amongst those NEO"s. And if going further afield then there are Mars' moons, which appear to be carbonaceous. Any potential target would deserve some survey sampling.

@Phi for All There may be imaginary "better" uses in space - never any shortage of those - but the only advanced industrialized economy that actually has high demand and high value uses for PGM's and can pay for them, the only one at all - is Earth's. The 'but we can use in space' is sort of right; most of what any proposed asteroid mining operation produces will be for use in space, as essential to being able to deliver resources of high value to Earth - like fuel for the rockets. There is no independent space economy only outposts of Earth's economy. Sure, if my proposed test case worked it could deliver small amounts of usable asteroid materials eg water, raw nickel-iron, carbonaceous material to NEO there could be demand for them from whatever space stations there are. But what are those space stations doing that makes a profit? I've asked this before but no-one can answer without getting all imaginary. Taxpayer funded space stations that make no profits using such materials may reduce their costs doing that, but the overall totality still relies on Earth subsidy, just a bit less direct. I don't think any projects in space can achieve self perpetuating growth unless the economics work. What are those activities in orbit that pay their own way with enough left over to support future growth? Subsidy until it works isn't good enough; we need a lot better than that to commit the levels of investment needed. Without a way to deliver tangible returns to Earth investors it is just dreaming.

@GeeKay the alleged values don't mean much and any mining attempts, if ever, are likely to start small and probably continue to have a lot of very high costs to recover before achieving profitability - and not much affect the market price. I am amongst the more pessimistic commenters when it comes to space but the resources in asteroids are real - notably Platinum Group Metals mixed in nickel-iron at 10's of parts per million (going by meteorite samples). Even the nickel-iron, raw and unrefined would be considered valuable here on Earth, just for the nickel content. Most things in space have no potential to make money but asteroid minerals are a real "prize" of enormous potential monetary value, so I think the interest will always be there. Yes, the differences in velocities are huge; most of any asteroid mining/refining operation would be making enough fuel/reaction mass for the rockets, which must have exceptional durability and long working life. That is probably the first test that needs to be passed - a rocket that can do a round trip between asteroid and LEO exclusively with "fuel" (and other consumables) produced out of asteroid resources. And do it over and over reliably with absolute minimum of ongoing supply from Earth. Probably not an M-type. We need to know what those rockets will run on and know if a target asteroid has it. Off the top of my head I would target C-type; going by carbonaceous meteorites they contain the target mineral - nickel-iron with PGM's mixed in - as nodules and grains within a softer carbonaceous material that also contains significant amounts of water. Can solar electric arc-jets use simple water for reaction mass? H2 + O2 chemical rockets present serious problems, including very large tanks as well as, ultimately, inadequate performance. I think things get harder if any rocket uses requires more exotic fuels, eg the Keck Institute of Space Studies proposal to capture a small asteroid and return in to near Earth space with a solar electric rocket using (if I recall) xenon for reaction mass. Seems very unlikely to find a source of xenon in an asteroid. Hydrazine is used with arc-jets and it seems possible (with water and a source of Nitrogen and equipment) to manufacture it, but water, even if less ideal, presents a simpler challenge to produce and store and use.

Close planting - more like 1 per m2 rather than 5 - is common practice for forest regen projects here in Australia, and I expect worldwide. It mimics the mass germination and growth from broken canopy in natural forests. Attrition is of course part of that; you end up with a very few mature trees. The pre-colonization mature forest where I am (if I am recalling correctly) was around 6 to 12 trees per hectare. Big trees. The regrowth forest present now is in between - maybe near a hundred trees per hectare after much higher numbers of (naturally germinated) seedlings and saplings. Had the original land clearing intention been followed through the regrowth would have been prevented as far as possible and over time the soil seed bank would deplete - and planting becomes the only way. But natural regrowth favours some species over others; there is no expectation that what will regrow will have all the same species in similar proportions. And some species never really recover, including some of the most prized timber species, that were mostly gone before the land clearing and haven't and won't ever recover. The glib cutting trees down promotes new trees, more than before defense of widespread exploitation of old growth forests was and is a half truth; we get lots of smaller trees dominated by a few species and the ecosystem is different to the original.

I'm not sure we know how any typical forest planted now will be faring in 200 to 300 years; do we choose which species to grow based on what the climate is now or what we expect it to be? Sounds like a concept with benefits to farmed and gardened forests but not necessarily useful at very large scale. There are good reasons to have forests and natural ecosystems but emissions mitigation isn't one of them. I think it is more appropriate to think of the CO2 reforestation sequesters as counting towards reductions in land use emissions rather than to justify ongoing fossil fuel burning. The impacts on emissions of mass forest plantings are going to be complex but ultimately they'll be finite and won't exceed what was emitted from prior deforestation; this kind of forest cultivation might take down the Carbon faster but it will reach peak biomass faster and stop being a carbon sink sooner. I don't think we can depend on sustained, non-reversible increases in global biomass to make a significant difference to the climate problem. If it doesn't reduce fossil fuel burning it isn't fixing the climate problem. And in my view it is a travesty to plant forests in order to protect fossil fuels from global warming.

To be serious about zero emissions we need these kinds of mechanisms in place in the world's major trading economies. Preferably pricing at rates like we really mean it, that ramp up predictably over time, like we mean it and without rafts of exemptions and exceptions, like we really mean it. But anything tariff related gets bent by geo-political concerns and I fear that anti-China sentiment will be used expressly to impede global growth of RE and EV's, in ongoing efforts to save fossil fuels from global warming.

If you want to make arguments to support these assertions you are welcome, but stating them doesn't make them true. In my experience pretty much only staunch doubt, deny, delay opponents of addressing global warming seem chronically unable to update what they are sure they know about climate science or climate policy or options for doing something, like renewable energy. Around 3/4 of all new electricity generation being added around the world is now solar and wind, on their merits, as commercial decisions - not out of deep commitment to zero emissions (although the possibility of emissions accountability emerging in the future does figure into investment decisions) but because of this - .

Sure, with fictional propulsion systems the impediments don't look so overwhelming. Reality is not so easy. Not that I would expect chemical propellants to be the favored choice apart from the initial launch - I would be looking at solar electric/arc-jets using asteroid water for reaction mass (or something like), ie something with barest minimum of consumables sourced from Earth. Whilst examples of electric arc-jets do exist that is not the same as large scale, long lasting versions with proven extreme reliability suitable for such a job; every part of such a mining project would be bespoke.

I have no fear of corporate tyranny in space because space lacks opportunities for profitable enterprise. It is only in fiction that there are opportunities that are worth the effort. Space companies milking the taxpayer funded agencies is a depressingly ordinary kind of bad behavior. Unless there is something I am missing, something big, it looks like if we take away the taxpayer funding there is no self funding commercial opportunity in space exploration or any space activities that don't directly service Earth customers. I don't count transporting astronauts to and from the ISS - or the ISS itself - as self funding. No space tourism venture comes close to recovering costs, let alone makes a profit. If anyone can point to anything we do in space apart from ground sensing and communications satellite services that earns income from Earth customers and can be self funding I'd be interested. Asteroid mining, in potential, is the best I can see and even that appears to be far short of viable. For unashamedly taxpayer funded ambitions in space I think meteor defense is as good as it gets - far reaching enough to support ongoing space R&D with big ambitions, with multi-nation participation, that might end up opening up and spinning off something commercially self funding, but will be worthwhile even if doesn't.

I expect the rate of success for self made wealth from initial poverty is very low compared to those starting from even modest (well short of "wealthy") inheritances - or just with families that can afford to be loan guarantors. "Just try hard and you will succeed" works much better for those with existing resources to draw upon - including being able to try again if not succeeding first time around more readily too.