Ken Fabian

@studiot Those kinds of projects can be huge and the engineering and economics rarely add up. More usually we see water caught and stored within existing water catchments during wet times, uphill of the users, stored over several years, hopefully long enough to get refilled before running out. Existing geography and flows are taken advantage of as much as possible - working with rather than against, and most of the better opportunities have already been taken, for irrigation water mostly; climate change is exacerbating things but the same concerns have been around a long time. We have water diverted from coastwards flowing to inland from Australia's Snowy River Hydro scheme but it works by taking advantage of geography; it was a (relatively) short distance tunneling through mountains to divert the Snowy River, but still a huge engineering project. (Ironically Hydro power output had to be constrained due to too much water - to avoid adding to inland flooding - during our recent and still simmering gas and coal supply shortage/price crisis, despite full dams and wholesale electricity prices going into orbit). Rivers themselves are the preferred means of delivery, with pipes, canals and pumping reserved for short distances and rises. They are expensive. Canals have high loss rates - leakages and evaporation; schemes proposed for Australia (that still get thrown up as a thought bubble) had expected losses too high for the water to reach the intended recipients. The specific example - Kentucky floods, Texas and California droughts? I think (US geography not my strong point) Kentucky floodwater will flow into the Mississippi, so it will get a lot closer to parts of Texas on it's own but still way short. California would need floodwater from somewhere much nearer but geographically that seems harder than for Texas, which doesn't have the mountain ranges.

If water vapor were a big problem then nuclear energy won't help reduce it - I don't see shipping as ripe for conversion except as a hope or perhaps an intention; whilst hydrogen can be burned in an internal combustion engine that won't work with existing diesel engines. Whilst some ships are diesel electric, with propellers driven by electric motors hydrogen ships will need to be fuel cell electric. No major shipping companies will commit to them until supply chains and infrastructure is in place and even then there is a lot of development needed. Making shipping zero emissions is a huge task. Short distance ferries running on battery electric already exist, are reliable and a lot less technically challenging to build and operate. Better batteries will emerge, but how much better is still unknown. I don't know what the best solution to shipping emissions is but I suspect not much will happen until and unless the shipping industry knows in it's bones that they have no choice. Currently they appear to be treating it as optional and making the choice to stick with not doing it. Coal contains some water. A lot more in brown coal. But whilst cars burning Hydrocarbons (the name says there is hydrogen in the fuel) make H2O by chemical reactions coal power plants make lots of it by evaporative cooling (similar to the nuclear plant cooling towers above) at the power plants. Whether atmospheric water is overall warming (greenhouse) or cooling (cloud albedo)? Without it as a GHG - the biggest one - I would expect global temperatures to be much lower, probably below freezing, but that is off the top of my head.

Burning fossil fuels emits water vapor too, in similar amounts for similar energy use. I am not aware of any climate significance for the water vapor from fossil fuels, so not for Hydrogen burning either. I expect that lack of significance is because any immediate atmospheric water vapor content change is very small in proportion to how much is there naturally. And it doesn't accumulate over longer time frames. Any long term change to water vapor content is inextricably tied to and limited by air temperature change, not the "sources", which exist naturally in great abundance. I also don't expect Hydrogen use to be as ubiquitous as the hype suggests; for all the talk the principle uses for hydrogen are still in oil production, not in replacing fossil fuels. That is all supplied by Hydrogen made from fossil fuels, with emissions, not clean energy and electrolysis. Any hydrogen transport economy will require about 3 times the electricity as battery electric, without the ability to piggyback onto existing electricity grids. A bit cynical of me but I think the big energy users like Hydrogen in direct proportion to how long to become a readily available option; commitment to hydrogen over other options is a commitment to delay. Iron smelting and chemical production may be the most important uses but are unlikely to require more hydrogen than oil refining uses now.

Should keep in mind that long term change to atmospheric water vapor content is a feedback induced by change in GHG's - because warmer air holds more water vapor. For each measure of enhanced greenhouse effect from increasing any other GHG's water vapor adds two more measures, so causal attribution of the warming induced is to the other GHG's, not water vapor. This gives estimations of the climate change forcings in play (from IPCC AR6 SPM)-

"More collection, storage and distribution" may be what studiot meant but these encompass a wide variety of engineering options. More efficient use is another "obvious" I suppose. I am interested in what people consider obvious. It sounds like for California there is not a lot of spare water to collect and store and redistribute. I suspect the best sites for dams are already dams or else are valued highly for other reasons/uses - which may present as "politix not permitting", though I doubt it is as simple as mere bureaucratic unreasonableness. The less ideal the site the more it can cost - and in many cases the more uncertain that they will catch enough to fill or avoid storage losses long enough to help much in an extended drought. It can become a rob Peter to pay Paul type of problem. Lake Mead (we get bits of US news mixed with our own) isn't in California but stands as an example; probably it will get times with enough upstream precipitation to fill again and for a time provide a relative abundance of water but it doesn't make a whole of problem, lasting solution. Not even by making it bigger/deeper. A lot of historic water use decisions appear problematic in hindsight; as an Australian I can sympathise - water use permits to farmers (pumping from rivers, which may or may not have flows managed with upstream dams and from artesian basins that were considered effectively infinite) - were handed out freely, in aggregate amounts that often far exceeded what is available. These kinds of historic "right of use" are fiercely defended - a different kind of impediment to "obvious" solutions than just bureaucratic. Of course they cannot pump water that is not there and pumping rights can be limited or suspended but often there is water upstream that never reaches downstream, including by "innovative" practices like flood plain harvesting - diverting and empounding flood water; the assumption was it only takes "excess" water, whilst the reality is downstream flows can be dependent on that flood water (and flood plain ecosystems too). A lot was done before the consequences were understood, without any regulation applying and again, those who did it fiercely defend their "right" to do so (and oppose introduction of regulation) without any responsibility taken for the downsides downstream. It does sound like California agriculture has been overutilising it's limited water sources for a long time and the "right" to do so looks deeply entrenched; the obvious solution of limiting such water use can be hard to apply. Texas, I know less about, but suspect similar issues.

What obvious engineering solution? How is lack of permission the principle impediment?

All the documentation and eyewitness "testimony", from watching the launch to the many amateur radio enthusiasts who - by aiming their receivers at the moon - listened in isn't enough? It didn't make it to the moon but I recall a demo from before the mission of a flag "waver" that was developed to give the flag movement; a bent wire in a sleeve within the top of the flag that turned by a small motor. But I think the actual movement of the actual flag was attributed to static electricity.

In a sense, yes; not pre-existing planetary bodies but ones that coalesced in the early formation of the solar system and underwent differentiation from their own gravity and subsequently got broken up by later collisions. Metallic cores that formed when these proto-planets were hot and molten are where the nickel-iron we find now came from. Surely that was Nickel-Iron, but it has been common to refer to metal meteorites as "Iron". So far as I know meteorite metal is always Ni-Fe and the only pure iron found in meteorites are small crystals and tiny nodules within a nickel-iron matrix (and not independent of it). I have previously done some searches to learn whether pure iron or other relatively pure metals (like nuggets and seams of precious metals) are going to be found in asteroids myself - pure iron being more widely useful than alloys with nickel, although the nickel content is a lot more valuable in metal price terms, probably exceeding any precious metal value. I could not find any references to any metallic meteorite sample that was not nickel-iron, with other metals (eg cobalt, Platinum Group Metals) well mixed (in solution) within them. It appears to be a case of processes that mix them occurring but with an ongoing absence of conceivable processes that can separate them again. (I asked this at https://space.stackexchange.com/questions/27329/can-we-expect-to-find-pure-iron-or-only-nickel-iron-alloys-in-asteroids - and someone answered with a claim to have found a very high, near pure iron content meteorite but he couldn't find any experts who agreed that it was a meteorite and not something with human/terrestrial origins.)

@Markus Hanke Thanks for the reply. I have to admit my level of ignorance has not decreased by much; I will defer to people who know more than me and take it as given that the mass within black holes affecting space-time outside it with gravity isn't a contradiction.

Another question out of ignorance - How does a black hole's gravity influence matter around it if it's mass cannot have a causal effect? Is gravity's effect not causal?

I'd be pleased to be wrong but don't really expect any such loopholes; ignorance allows room for speculation... and makes it more likely I am wrong. A singularity, where the laws of physics break down but that doesn't mean anything could happen; maybe the very opposite - is there anything more inert than what is in a black hole?

Whatever happens on the other side of the event horizon of a black hole there is still mass and gravity interacting with spacetime and matter in the present. I am no physicist but it does seem that out of the things we cannot yet explain within a unified theory of everything gravity is up near or at the top. I would like to think that leaves room for some of those "magic" possibilities - FTL, reactionless drives, anti-gravity - but I remain very doubtful that will be the case.

@mistermack I am still inclined towards boreholes into bedrock as the most widely available inter-seasonal thermal storage for heating buildings. High temperature storage can do other things but probably can't do building heating as cost effectively. It looks even better when large scale, ie district heating rather than one building at a time From what I could find out about the Drake Landing example - and in keeping with my prior understanding - such heat masses need to be "primed" before the heat losses to surrounding rock slow sufficiently to give effective insulation; the first few years a lot more heat went in than came out but once the ground mass had gained enough heat the net flow out got a lot closer to the flow in. They claim Coefficient of Performance of 30 after the system was fully operational, ie 30x more heat than (non-solar) energy requirements, with more recent addition of solar PV to run the electricals. No heat pumps in that example so the storage mass must be hot enough to deliver water at temperatures high enough. Bigger storage mass and lower temperatures would use heat pumps.

There are examples of district heating using seasonal thermal storage using aquifers, tanks and the ground itself, eg like Drake Landing Solar Community in Alberta Canada that has 144 boreholes 34 metres into rock used as a heat store, replenished seasonally by solar collectors on the garages of participating homes during Summer. Not quite all their heating but always over 90%. Not sure what it would take for them to get to 100%. I do think there is a lot of potential for ground source heat pumps for colder climates. Interesting that large buildings with borehole or thermal wall geothermal heating and cooling often have to have a cooling bypass to shed heat rather than pump it all into the thermal mass, because overall they are a heat source; the seasonal differences between taking heat out (Winter) and adding heat in (Summer) being out of balance can make the ground mass too hot (losing system efficiency?) over a few years. Clearly we can use deep ground as inter-seasonal thermal storage and the rate of heat conduction is low enough that the surrounding rock is effectively it's insulation when the scale is large enough. So far as I can tell the up front capital costs are the barrier - despite often being cost effective over the longer term.

I am not sure that pumped hydro could be viable at such small scales, with such small differences in elevation. (I did attempt working out how much energy stored in 1 metric ton of water at 10m elevation and 100% efficiency but got caught by the conversion from joules to kWh (divide by 3.6 x 106 ?) and got about 10 Watt hours but I have serious doubts I did the calculation correctly. Anyone know?). A few thousand tons of water would need stronger construction than the usual rooftop. Wouldn't heated water in an insulated tank do energy storage better on mass required basis? I think pumped hydro will only be viable at large scales where natural geography favours it. Much simpler and cheaper at household level to add batteries. Ours work very reliably. Not sufficient for full heating (in a poorly insulated home in a mild climate) but significantly supplementing wood fired heating; we'd need about 3X current battery to ditch the wood but not much more solar. With respect to our costs it is more expensive than not having grid connected solar and batteries, but not a lot more (with value of blackout backup difficult to assess but a bonus). With power prices surging higher that may even have shifted to less expensive.

Apparently Berlin has one of the biggest district heating systems in the world already in place - a couple of thousand km of pipework, with 3/4 of Berlin homes heated that way. A lot of it is waste heat from other energy use (co-generation) rather than made for the purpose. I suspect the "13 hours" refers to what will be available with expected use, not the time it can hold heat if none of it were being used. Whether heat pumps running from electricity would do it better or not making use of that infrastructure gives a big starting advantage to this kind of thermal storage over building pumped hydro and heating individual homes by other means. It may take an energy crisis or two and time to get significantly more pumped hydro, with reluctance to make those kinds of investments until it is clear it is essential, ie catching up or just in time rather than surging ahead of near future needs.

So many issues, fun in a thought experiment kind of way but for actually moving big blocks of stone... no. If I am getting this right there is a trench that is mercury tight that can be opened up ahead and filled in behind and sealed to be fully mercury tight at every stage, with that excavation/reconstruction being done whilst full (or else mercury ladled out each time - no suction can lift mercury higher than about 760mm). Enough mercury to float the block forward a small way (that still leaves room for the excavation/reconstruction ahead and behind), ladle out the mercury, fill in behind, open up in front, refill, repeat. Wider trench and more mercury for any bends. Fully recover the mercury for re-use without losing significant amounts ... This is supposed to be an easier way to move big blocks of stone?

This would be my preferred method for moving the regular building stones, a method for which there is some archaeological evidence (and some accompanying disagreement). https://www.ling.upenn.edu/~jason2/papers/pyramid.htm These kinds of objects (of unknown purpose) have been found. I'd try wrapping leather straps around to hold it all together - This style was "invented" as a possible solution and tried successfully - but there is no indication of Egyptians having used this type -

Seems like part B of the question is about responsibility for emissions for suppliers of fossil fuels, which arguably includes legal ramifications. Emissions accounting is, quite reasonably (and for practicality) done on a nation by nation basis. Emissions responsibility or culpability isn't so easily compartmentalised geographically except in the sense that climate policy in practice leaves any considerations of culpability to individual nations, which could, if they choose, apply to exports of fossil fuels as well as to the embodied emissions in the goods and commodities traded. Mostly these are being addressed (or proposed to be) via those border adjustment mechanisms, which in practice are about compensating for different climate policies and carbon pricing. As a short term market response, yes. But all else does not remain the same; the longer term response can be increased investment in alternatives, which will also enjoy a relative price advantage. A "never again" response by nations and governments that take the climate issue seriously is likely to push harder for those alternatives irrespective of any immediate crisis management, with rising costs of existing fossil fuel dependence a strong incentive even apart from climate and emissions considerations.

It appears to be a well established legal principle that suppliers of products that cause harm are liable for those harms, irrespective of the benefits of those products - even though courts appear reluctant to rule that way with respect to fossil fuel suppliers and emissions. More usually courts rule on something done at small scales where direct culpability can be assigned - the actions of these people/companies caused these specific harms, without multigenerational, multinational and economy damaging complications - which rulings discourage those same activities by others at much larger scales, before they get too big. Some "duty of care" arguments have succeeded, but courts around the world appear reluctant to grasp this nettle firmly. The arguments that the end user alone bears culpability are widely referred to as "the drug dealers' defense" (along with "but they'll only buy their heroin... coal and oil and gas from someone else"). I think there is culpability at all levels but institutional large scale culpability should trump that of individuals. I suspect that politically it has been advantageous to the opponents of strong action to turn the Environmentalist calls for individual responsibility as the principle response back against their objectives; the general reluctance to adopt personal frugality and belief it makes little difference is used to encourage community reluctance to make demands of institutions.

I note that Australia's government(s) have preferred to view emissions as a fossil fuel consumer responsibility and not a supplier responsibility. Making it an end user responsibility makes Australia's contribution 1.3% whereas if viewed as a supplier responsibility Australia would be 6-8% of global emissions. I don't expect that to change with the new Australian government although they do appear to take the whole issue more seriously than the previous "conservative" government.

There are getting to be less and less unknown unknowns; there was a lot of room for Lord Kelvin to get that wrong but a lot less room now given the progress in science up until now. Knowing more can open up more real opportunities for technology but will also close imaginary ones off.

One data point, yes. But it is 100% of all known data points. That sounds like a very good starting point. I think we (interested scientists) can generate a lot of ideas about what chemical processes can lead to life and will get better at modeling what is possible as well as what is likely.

Some thought has been put into what signatures we might look for - from one side of that question there are efforts like Sara Seager et al to build a comprehensive list of possible volatile compounds. The presence of chemicals that are not in thermodynamic equilibrium - some active process needed to sustain them - seems to be a major criteria, but a lot of chemicals made by life on Earth are unlikely to occur without life. Determining what can or is likely to occur without life is another aspect. What astronomy requires to detect them and how far out is another question. Planets crossing their parent stars visible from Earth and near space will only be a small fraction. https://www.saraseager.com/wp-content/uploads/2020/07/Seager2016.pdf

How much interstellar exploration can a few grams do? What instruments can each carry? How about interstellar data transmissions? Even lots of them strung out as relays - receivers and transmitters and power source along the way needed in that case - I think not. Von Neumann machines look more likely to be successions of complexes of mining, refining, manufacturing machines than machines that can eat asteroid dirt and excrete copies of themselves - I think not. But tech that is thousands and millions of years ahead of us can overcome the obstacles suggests Time somehow erodes the laws of physics to allow magical technologies; we are closing in on a complete theory of everything and it doesn't look like it will support faster than light or time suspension or other magical shortcuts. I see science and tech development as S-curve not exponential or open ended. To the Question - echoing some other comments, vast distances and the limits the laws of physics impose - the difficulties in detection or travel across them - stand out as the most obvious and likely reasons we haven't found any aliens and why aliens have not found us. Any suggestion that we are being deliberately left alone requires evidence they are within range but are avoiding us - we don't have any. I think there is nothing but baseless conjecture to think that; I think not.