And 1) is both true empirically (climate models are failing to accurately predict climate) and openly acknowledged to be true by, among others, the IPCC. Openly in AR3, relegated to selected paragraphs deep in the document in AR5, but there nonetheless.
2) is still an open question -- or rather, there are definitely feedback that mute the severity, but it is also claimed that there are positive feedbacks and it is not yet clear which one wins. CO_2 alone would produce between 1 and 1.5 C of warming by 600 ppm (some 0.5 of which we have already realized). Hansen believed (and probably still believes) that water vapor feedback would at least double, more likely triple it to between 3 and 5 C. Empirical evidence has gradually forced nearly all of the climate science community to cut back their "best estimates" (based on a statistically meaningless mean of the predictions of the broken climate models, see 1) above) of total climate sensitivity to roughly 2.7 C in AR5 and it is currently in free fall in the literature, increasingly constrained by the lack of tropospheric warming, "the hiatus" (as it is named and discussed in AR5) and Bayes theorem. Currently the argument is whether or not it will end up as high as 2.3C, with papers appearing arguing that it will end up being in more or less neutral net feedback territory -- 1 to 1.5 C -- and others covering the range of 1.7 to 2.3 C. Since basically this is a scientific crap shoot and has been from the 1980s on (partly because we are still learning about clouds, partly because the "physics" that the models supposedly are based on begins by averaging phenomena in a nonlinear Navier-Stokes equation from its Kolmogorov scale of around 1 mm to the cell size of around 100 km -- with adjustable parameters galore -- as if it does not matter) so you pays your money, you places your bet. Net negative feedback hasn't even been ruled out by the data, and the longer the hiatus continues the more likely it is that the feedback is indeed net negative.
4-6) are what they are. Sea level rise is almost invariably given as the primary cause of catastrophic damage, yet it has also proven to be the one place where there is absolutely no sign of catastrophe. SLR rates have changed little for 140 years. It is also remarkably difficult to predict the rates at which land ice will melt, given the problems with 1) and 2) -- Hansen (as the primary author of the entire claim for future catastrophe) goes on TED Talks and with a straight face says that he expects 5 meters of SLR. Any other sane climate scientist I've talked to is now talking about anywhere from 30 cm to as much as a meter. The data itself suggests that we'd be unlucky to make as much as 30 cm by 2100. Public media are full of egregious claims of ongoing disaster (melting Himalayan glaciers, increasing tornado or hurricane damage) often and sadly backed by public figures in the scientific community that should no better as there is no evidence of any of the above). This quite correctly reduces the credibility of the other claims of these individuals -- if one went back and looked at the predictions that Hansen in particular has made in fully public view ex officio as head of GISS and how badly they've failed, it would be difficult to see how he has any credibility left. Beyond that, many -- although not all -- of the claims for damage due to "climate change" (something that happens all of the time naturally and hence is impossible to attribute or refute) are marginal results that are not statistically significant. And estimates for the damage resulting or likely to result from climate change often fail to take into account benefits accruing from climate change or the simple fact that nature has already accommodated the change given the smear of temperatures and climate ranges available between the equator and the poles.
All of this greatly complicates the discussion of costs and benefits. Not everything about global warming is bad. Indeed, the global warming that has been ongoing since the end of the Little Ice Age has been almost entirely beneficial. If SLR and climate sensitivity are admitted to be at best poorly informed guesses based on models that are in terrible agreement with the data (e.g. HADCRUT4) from 1850 to the present everywhere but the reference period (training set for the model, which does not count), as is clearly visible in figure 9.8a of AR5 it is by no means clear that "the science is settled" -- whatever that means when the "settled science" is based entirely on trying to solve what is arguably the most difficult computational problem ever attempted by humans with completely inadequate methodology and tools -- or what the most prudent course of action is for humans to take in the meantime.
Given the enormity of the investment required to do anything at all significant about CO_2 concentration -- where all of the measures taken by all of the world over the last 20 years, in spite of their enormous price tag, have done almost nothing -- the most prudent course is probably to wait and see before dumping another half-trillion or trillion dollars into the well without even the prospect of the investment impacting the overall rate of CO_2 increase globally -- while continuing to invest heavily on the keystone technologies that might actually eventually have a cost-effective impact. Solar power, for example, cannot form the basis of an actual global civilization as things now stand. It is barely cost-effective in ideal locations as a means of eking out fossil fuel derived power that is still required to bridge the substantial temporal gaps when the sun goes behind clouds, when it is night time, when it is winter and the sun is tipped to too great an angle for efficient generation. We have no cost-effective technology yet for storing solar power under any circumstances so that it could provide 24 hour power at global civilization rates in the middle of Death Valley or the Sahara. We have no way of transporting electricity generated in Arizona to Maine, or the Sahara to Finland -- current power transmission technology is limited to around 300 miles, and to get even to 3000 would require nearly linear scaling of e.g. high voltage transmission line dimensions, with a highly nonlinear scaling of their cost (that is, they would have to transmit power at order of ten million volts, instead of order (less than) one million, and air just isn't that good an insulator, especially when it is damp or electrically charged itself). Wind is even more problematic as even places with comparatively reliable wind can have windless weeks as easily as days. Nuclear is the only viable non-Carbon source of power, and as of this moment it has to be the primary electrical generation means eked out by alternatives as no alternative generation mechanism is capable of functioning as a primary. And many of the same people who oppose coal based electricity oppose nuclear just as vehemently.
In the comparatively rich West it is all too easy to forget that roughly 2/3 of the world's population is unbelievably energy poor. 1/3 of the world's population is just plain old poor -- living basically not even in the 19th century or early 20th century but in the 17th century. All global poverty, at its root, is energy poverty. With enough, cheap enough, electricity one can create clean water, plenty of food, jobs, air conditioning and heating, safe and comfortable houses, the means to cook food and light homes after dark that don't involve burning dried animal dung in a tiny hut while exposed to disease-bearing parasites that fly in through the smoke one is breathing. China and India, with a huge fraction of their populations who are in precisely this category, have sensibly enough chosen to mostly ignore the claims of possible future catastrophe because to do nothing to provide energy for these people right now is an ongoing catastrophe that the world blinds its eyes to while worrying about 2100 and CO_2.
Maybe CO_2 will cause a global ecological and economic catastrophe. Maybe not -- the evidence is so far not at all clear or universal that it will do either one. In assessing the risks, however, one has to fairly balance out the costs of measures that everyone knows will do nothing to ameliorate the CO_2 level likely in 2100 (and are enormously expensive now) against the benefits that could be derived from the same level of investment trying to, say, ameliorate global poverty, global ignorance, and global disease right now. Half a trillion dollars, wisely spent, could probably come damn close to solving these problems over 20 years. In 20 years, we might also actually have accumulated enough actual evidence (as opposed to the "projected on the basis of dysfunctional General Circulation Models" not-really-evidence-at-all kind of evidence that is actively pushed at the moment) to have a much better idea of how the climate really functions. We might have fixed the models by then so that they come a lot closer to agreeing with the data. Money currently and wisely being invested in breakthrough research and technologies -- high density energy storage, lower costs photovoltaics, low hanging fruit like LFTR -- as well as longer shots such as high-temperature high-current superconductors capable of carrying energy the 10,000 miles necessary to provide Finland with electricity generated in the Sahara in winter, Maine with energy generated in Texas in the winter, or fusion (the universal solution to all of the world's energy woes if and when it works) might have time to mature.
That's the really silly thing. Solar technology is a no-brainer -- once costs drop to where one can amortize the investment over 10 years or less. At that point one doesn't have to "encourage" its adoption, one has to stand back and let the free market work. In some parts of the US, solar has marginally reached that (for corporate level investments) although for individual homeowners the amortization is still too long, more like 20 years. The latter is too long (and too close to the expected lifetime of the cells) to be a truly comfortable investment, but costs are dropping, the amortization along with it, and at some point new construction will often come with a solar roof not because it is mandated or "green", but because owning a house with most of its lifetime energy costs rolled into the mortgage at a discount relative to over-the-counter energy prices is an appealing prospect. At that point solar will rise to displace/eke out maybe 30% of our energy needs, perhaps even as much as 50% if people synchronize manufacturing energy demand to the daytime in sunshiny states. That will, of course, still not suffice to keep CO_2 levels from increasing (if the Bern model is correct) -- only the replacement of coal burning plants with nuclear power can do that, and if that were done solar itself would once again be a hammer looking for a nail, at least for a century or three.
Solar on top of mature base technologies is even more of a no-brainer -- if somebody perfects e.g. zinc oxide batteries or any of the other potential ultra-high-energy-density batteries people are working on (perhaps with breakthrough nanoscale techonology) tomorrow, that is a game changer. The global warming crisis would truly be over, because solar would become a viable replacement even for nuclear, and if one achieves enough energy density (e.g. anything within a factor of 2 or 3 relative to gasoline or fuel oil), one could ship electricity to Maine by charging a train-sized battery during the day in West Texas and running the charged batteries up to Maine overnight to deliver the next day's electrical power, then running it back the next day to be recharged once again. But until that happens solar will not be the basis of any real solution to the CAGW/CACC problem.
So far, I haven't heard one single solution proposed that makes sense and is capable of actually solving the problem, with the obvious exception of the adoption of global nuclear power for as long as our nuclear fuel resources hold out. Climate aside, the human species needs to solve the problem of generating power for the indefinite term in order to build a steady state civilization without the extremes of energy wealth and energy poverty clearly visible to anyone who doesn't have their head stuck in a mansion today. If that problem is solved, climate issues become moot. Until it is solved, measures being taken are simply transferring your money into the carefully selected pockets of those who make the loudest claims for greenness and have the right friends, who -- paradoxically enough -- turn out to predominantly be precisely those energy companies that everybody excoriates as being the cause of all evil. Who makes the most money out of the global warming crisis? Oil companies. Coal companies. Power companies. None of those companies suffer losses due to the "crisis" -- most of them are profitable at record levels because of the crisis.
Something to think about.
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