"The crucial scientific question for policy isn't whether the climate is changing. That is a settled matter: The climate has always changed and always will. Geological and historical records show the occurrence of major climate shifts, sometimes over only a few decades. We know, for instance, that during the 20th century the Earth's global average surface temperature rose 1.4 degrees Fahrenheit.
Nor is the crucial question whether humans are influencing the climate. That is no hoax: There is little doubt in the scientific community that continually growing amounts of greenhouse gases in the atmosphere, due largely to carbon-dioxide emissions from the conventional use of fossil fuels, are influencing the climate. There is also little doubt that the carbon dioxide will persist in the atmosphere for several centuries. The impact today of human activity appears to be comparable to the intrinsic, natural variability of the climate system itself...
Society's choices in the years ahead will necessarily be based on uncertain knowledge of future climates. That uncertainty need not be an excuse for inaction."
Much better than I expected of the WSJ. If it consistently took this line instead of buying into absurd conspiracy theories or claiming snow in January means climate change is a hoax, our national discourse would be much healthier, on both sides.
> Dr. Koonin was undersecretary for science in the Energy Department during President Barack Obama's first term and is currently director of the Center for Urban Science and Progress at New York University. His previous positions include professor of theoretical physics and provost at Caltech, as well as chief scientist of BP, BP.LN +0.42% where his work focused on renewable and low-carbon energy technologies.
> We are very far from the knowledge needed to make good climate policy
Complete and total horseshit. Even if you'd only assume that the scientists are 90% right any good actuaries will tell you that you should spend about 90% on measures that back up what they've put forward.
Hacker News, I expected something better than this in the #2 spot.
Edit: Alright, here we go with the downvotes for calling out bullshit regarding climate change on Hacker News. Well, it's not like I expected any better. Next I expect a replies either trying to argue random points about how there were forests in Greenland in the middle ages or some pretensions about being open-minded. While still barely having a grasp of a periphery of relevant facts.
But that's OK, the warriors having upvoted this to the top immediately know best. Or at least as well as Murdoch, publisher of the WSJ who has recently installed a prime minister in Australia who called climate change 'crap' and has abolished a carbon tax a minute fraction of those found in the rest of the OECD.
I would take the opinions of an industry expert with a large pinch of salt on the subject of negative externalities of the industry they are involved in, no matter what the industry.
I am sick to the back teeth of "the sky is falling!" rhetoric.
I refuse to live in mortal fear for the future of humanity.
The climate will change, big deal, we'll adapt -- the range of habitats humans inhabit far exceeds the variation in climate that individual habitats will experience.
On the list of things to worry about climate change should be way down. But wow, you're so vocal -- because you feel that it is an existential threat. Newsflash, it ain't.
Homelessness is a bigger problem. Ditto poverty and starvation. I _welcome_ the push back against the drumbeats and rhetoric and hope climate change disappears off the political agenda entirely. Some hope.
It is a bit of an existentialist threat. It's one of the possible answers to the Fermi paradox. Why haven't we met anyone? Because they boiled themselves to bits before they could interstellar space. Which, inherently, requires huge amounts of energy, possibly enough to change climates.
I can't think of things more fundamental to existence or non-existence in this universe than it being the wrong temperature.
Your reaction to this is exactly what is wrong with the discussion: I can stomach the person who talks down climate science because they fear for their job at the oil refinery or whatever, but when someone so viciously responds to someone simply saying that the common narrative about climate science is oversold (a simple truth that anyone with any rational sense understands), it is disturbing. It is when it is far past a rational scientific winnowing to an understanding, but instead has become religion.
Wage your religious battle and set up the caricatures of anyone who might disagree, but you sway no one.
> climate science is oversold (a simple truth that anyone with any rational sense understands)
Now replace 'climate science' with astrology on the one hand or astronomy on the other and you might understand why what you're saying is not at all helpful.
That said, if he's bringing something new to the table, then I will lend him three ears. But first the strawman of whether climate science is settled (it won't ever be, just like statistical mechanics won't ever be 'settled', whatever that means), followed by plain wrongness and inaccuracies and only some minor salient points... while calling for what he's calling for is completely out of whack with not only what the IPCC but so many others have determined.
No religion here, mate. And no, I don't think that climate change per se will be the extinction of the human race. If nothing else, we might still have the sulphur dim-the-sun kill switch. And yes, climate science is complicated and, yes, nuclear energy everything. Religion? Please...
I'm surprised by the finest possible resolution quoted, a 60 mile grid. It corresponds to about 55,000 cells covering earth (times maybe 100 altitude bands). That's not a large amount of memory.
I assume the limitation is that all those cells have to be simulated in small time slices for 100 years, and the necessary time slice would scale inversely with the grid size, so computation is O(n^3) on the inverse size of the grid.
Can someone comment on what kind of computer it would take to halve the size of the grid?
Simulations are typically done in one day time-steps or less.
The thing is, there is a lot of physics going on in each cell, and in some respects reducing the cell size makes things more problematic rather than less. For example, the effects of a supercell thunderstorm can dominate the atmosphere over tens of kilometers. With a 100 km (60 mile) scale you can plausibly average over those effects within a cell, as you can reasonably claim that most such "local" phenomena will be happening well away from cell boundaries.
So as you reduce the cell size, you start having to think about the internal details of local disturbances that you were previously averaging away and hoping to catch in your overall parameterizations, and the model complexity goes up tremendously, likely without becoming a whole lot more accurate.
Even at these large scales the amount of physics that goes on within a single cell is huge, and getting all the heat and mass balances right is fantastically difficult, which is where a lot of the computational power goes.
So it isn't really a question of halving the grid size while keeping the physics the same, because you are going to have to substantially revise your model to accommodate the new scale. I'm sure this work is ongoing, but it's extremely complex and difficult.
What sort of physics calculations can you do within a cell? I would have expected the data structure for a cell to contain a handful of scalar parameters (e.g. temperature, pressure, humidity, velocity vector) related by a few scalar equations - a negligible amount of computation. It sounds like there's quite a few orders of magnitude more stuff going on within a cell than I would have expected. What am I missing?
Steve Koonin is an incredibly smart guy with a huge amount of experience in climate and energy issues, and is saying things in this article that any competent computational physicist who has looked into climate modelling believes.
You'll see basically similar concerns raised. If you're seriously wedded to the idea that consensus is important to the science, you should dig up the independent opinions of a few other computational physicists (not climate scientists, who are not computational physicists). Having done so, you might find that there is a consensus amongst computational physicists that climate models are problematic in ways that make them questionable guides to policy, although most of us will also say that we should be concerned about the amount of garbage we are dumping into the atmosphere (and there are reasons to want to get off fossil fuels that go beyond the climate change argument.)
Denialists have poisoned the public discourse on climate change, but Warmists have unfortunately responded by digging in their heels in a particularly anti-scientific way. I hope Koonin's piece will help bring the scientific discussion back to fundamentals, and perhaps decouple the policy discussion from models a bit.
For example: we know that carbon taxes work pretty well in reducing CO2 emissions (http://www.theglobeandmail.com/globe-debate/the-insidious-tr...) and we know that carbon taxes can be used to reduce corporate and income taxes. So anyone who is opposed to carbon taxes is necessarily in favour of higher corporate and income taxes.
This is a policy discussion that can and should be had independently of any detailed climate model results, and I invite everyone who is in favour of higher corporate and income taxes to chime in here in support of their position, and explain why those taxes are so much better than the carbon taxes that could partially replace them.
And can you please stop with the 'Warmist' label? It's stupid, about as much as 'denialist' is narrow for the veritable zoo of opinions - educated or uneducated - that's sprung up in the public discourse.
I've also read your post and 1-2 W/m2 does sound like very little. However, and I quote from Wikipedia:
> Of the ~340 W/m2 of solar radiation received by the Earth, an average of ~77 W/m2 is reflected back to space by clouds and the atmosphere, and ~23 W/m2 is reflected by the surface albedo, leaving about 240 W/m2 of solar energy input to the Earth's energy budget.
That's a change of 0.5%. Doesn't sound like much, does it, but at 273 K that corresponds to about 1.5 degrees already. At the upper end of that and 300 K it's 2.5 degrees. Sure, it's simplistic and it's how to keep it quite that straightforward, but to see that number and be ignorant enough of the context to trivialise it and call it not a big deal is pretty disingenuous. Sure, a 2.5 K (or something like it) rise isn't going to bring the downfall of civilisation per se. But there's more to it than that. And, mind you, 2.5 K is at the lower end of IPCC projections, so there's evidently a lot more ground to cover than the simplistic numbers mentioned here.
>Sure, a 2.5 K (or something like it) rise isn't going to bring the downfall of civilisation per se.
well, it did it for Roman Empire - the Mediterranean climate became unsuitable for grain production while Europe north of Alps became drier and comfortable.
Height of the Caliphates ( at 969)
http://en.wikipedia.org/wiki/Islamic_Golden_Age
coincides with the height of the temperature during middle ages. The caliphates were result of conquest by Arabs from Arabian Peninsula and the caliphates folded back with temperature dropping as the Little Ice Age was coming.
Add to that Vikings (http://en.wikipedia.org/wiki/Viking_Age) whose reach was maximized during about the same time as Caliphates as North Atlantic was more comfortable for sailing in the small open drakars. They reached Greenland and established colony there (which disappeared with Little Ice Age). Vikings are the "Normans" as in Normandy - and we know the key role they played in the history of Western Europe. Vikings founded the Kievana Rus which because of their leadership was pretty strong expanding and aggressive state for hundreds of years, almost until Mongols. Thus the warmth of 1000+ years ago and resulting Vikings outreach were defining factors in shaping the foundation of Western Europe and Russia as we know it.
Getting back to our days - one can only speculate how political landscape of USA for example would change in the next decades when growing corn in Iowa and cattle in Texas would become economically impossible.
The percentages don't change as the sun's output increases.
273K is slightly below freezing. ~290K is closer to the average earth temperature.
Look up black body radiation. http://en.wikipedia.org/wiki/Thermal_radiation
Radiation is T^4. If incoming energy increases by x temperature increase by x^(1/4). (1.001)^(1/4) = 1.00025. So 1.00025 * 290K = 290.0725K.
PS: This is of course a ridiculously simplified model but a 2.5k rise would take an increase of around ((290+2.5)/290) ^4 - 1 = 3.5%. The sun is no where near that unstable.
I didn't say the sun was - this calculation is past the point of radiation and already in Watt being received by Earth. And I'm pretty sure those Watt are linearly (edit: or at least somewhat like it, given enough time) related to temperature.
Edit: parent had a good point (which may or may not have been edited out) about how radiation from the sun - Black body radiation - is power to the fourth away from translating into temperature. Which, though, I don't think is too relevant here.
Sorry, had a bad edit. I am going to skip out on this discussion, but I really suggest you do some reading on Thermodynamics. It's complex and most people really mess up when talking about it.
If by that you mean that the outbound radiation of Earth will increase to provide negative feedback due to black-body radiation, then that's absolutely right. T^4 in fact, like you said. But if the greenhouse gas levels are coming up 50% higher than they ever were just a few hundred years ago... anyway, I shan't talk about it any more. It is too complex to do justice here.
Who is trivializing anything? This is what is so bizarre about these discussions, and why I use the term "Warmist": because it identifies a nearly religious zeal on the part of some non-scientists who insist that anyone who does anything other than repeat the mantra "the science is settled; we must implement every imaginable solution except nuclear power" is somehow "trivializing" the issue.
I'm clearly on the record as being concerned about climate change and strongly in favour of implementing social policies (including carbon taxes) that will a) reduce GHG emissions and b) protect the most vulnerable, but because I don't quack like precisely the right kind of duck I'm routinely accused of somehow trivializing something, or being the enemy (this is not the first time I've had this kind of discussion, obviously). This is what you see from rival religions, not from scientists. I was involved in the 17 keV neutrino controversy, so I'm no stranger to scientific disagreement, and it simply doesn't have this strange dynamic.
If anyone is trivializing anything, it is Warmists trivializing physics. For example, why anyone would go from a 0.5% change in energy budget to a 0.5% change in absolute temperature is beyond me. Heating and temperature in the atmosphere are connected by complex and non-linear factors, which is one of the reasons we need to do modelling in the first place. Even in the simplest case of a black body the non-linear Stephan-Bolzmann law applies, not Newton's law of cooling (which is linear, but irrelevant to this case.)
So the argument you're making is not even wrong: it simply doesn't speak to the question of what the plausible effect of climate change on the Earth in general and humanity in particular will be.
This kind of argument just feeds the Denialist trolls who are doing so much damage to this discourse, because they will pick up on your errors and cry "hoax!" and other such nonsense rather than "honest, innocent and naive mistake", which in fairness what I think your error most likely is.
Finally, as I said above, I've had this kind of discussion before and it's never ended well, so I'm going to stop here and let you have the last word. Enjoy!
You aren't having a discussion. You are arrogantly dismissing discussion and proclaiming yourself not just right, but beyond reproach, while strawmanning your opposition.
No I didn't. I said that it's something like that from a 30,000 view. I even put being happy about a +/- 50% difference without a problem.
But if I put 1 energy into object x, at the simplest I'll get something about 1 temperature more if that object is in a vacuum, given enough time. Sure, it's never as simple as that, but that's all I was saying, plus/minus several dozen percent, from a bird's eye view. And greenhouse gases don't just trap incoming energy, but also serve to suppress black body radiation... and are 50% higher now than they were some centuries ago. So, point being, do I agree with you that black body radiation is the ultimate end to climate change? Absolutely. But I've just got to look over at Venus and the Sun to see how that dynamic plays out elsewhere and it's much hotter than 300 K.
>it identifies a nearly religious zeal on the part of some non-scientists who insist that anyone who does anything other than repeat the mantra "the science is settled; we must implement every imaginable solution except nuclear power"
Is not a response to what was said. It is a response to a fantasy opponent that was made up.
I agree that global warming attracts religious types. As a result, it is generally hard to have a serious conversation about it. HN has a better ratio of science vs religion, luckily.
Based on my experience, the debate about Global Warming is is mostly polemical.
In my opinion, a debate about measurable natural phenomena should be scientific - where a single verifiable fact trumps all previous consensus and conjecture.
This hits home for me. Although I suspect I probably fall into the "warmist" camp from your perspective and would support steep carbon taxes even without offsetting cuts in corporate/income taxes, I'm plenty comfortable with the statement that even the better climate models have at best a rough correspondence with reality: they're just a sketch to help us get closer to understanding how things really work. I'm pretty sure most climate scientists agree with that as well, FWIW.
But swapping all corporate taxes for a carbon tax? That really is a no brainer, and most policy experts not in the pay of the fossil fuel industry would leap at it. I don't know why we don't see it happen. Maybe because the American political system does not reward risk taking, even if it can substantially improve economic outcomes.
I am not a computational physicist but I had the privilege of being lectured to by one who worked on multiple environmental models. The key takeaway was that the models aren't truly predictive, they had to do a substantial amount of tweaking to get the model to line with historic in sample data but could never expand the model to out sample data.
A larger point that was raised by a different lecturer is that solar output has increased drastically over the last 100 years and that the global warming trends we see correlate perfectly with this increase in output. He actually believed that the industrial revolution lining up with this increase in solar output was entirely coincidental.
So to confound the issue further, we may not be responsible for global warming but our production of greenhouse gasses undoubtedly has an impact on our environment/climate that seems unlikely to be positive.
In a nutshell, CO2 is near enough on the path to increasing by 50% and it's pretty important for the greenhouse effect. Solar variation over millenia is, peak-to-peak, 0.1%.
That lambda value in the equation under Figure 2 is their 'fudge factor'. How do you quantify that value when we only have one complex system with multiple inputs to study?
Do you know much about the models they use? It all seems kind of silly to me because as I understand it they use neither monte-carlo simulation nor stochastic calculus. The models don't spit out anything about probabilities. They only describe the one outcome your starting assumptions produce. It's a glorified excel spreadsheet.
It's kind of like that. In three ways that I can think of. The models are run hundreds or thousands of times across different countries. The climate, modelled on a day by day basis, is effectively random for any particular instant. And the input variables, where they do change even minutely, act like seeds in a random number generator. It's not so much a glorified Excel spreadsheet as it is having thousands of Excel spreadsheets, each dependent on the one before and a slightly different scenario that's different for every set of these Excel sheets.
And yes, they even mention the 15 year hiatus - they don't sweep this under the rug like so many have taken to believing they do. In fact, it's mentioned throughout the AR5. In fact, you can get a sense of them being just eager to tackle it in substantial detail - it's wonderful.
Solar forcing as an explanation for AGW has been tested and rejected by the scientific consensus. The scientific consensus could certainly be wrong, but it's a huge red flag if anyone implies that it hasn't been given serious consideration by mainstream climate science, that it has been swept under the rug, etc, because that couldn't be further from the truth.
Pages 188-193 summarize why the scientific consensus believes what it does:
I just did a back of the envelope calculation. A change of 0.5 W/m^2 would yield (in equilibrium) an increase of 0.4 degrees C based on basic heat transfer. I see them dismissing the significance of solar irradiance but no where do I see them explain their methodology for determining the relationship of solar irradiance to temperature. 1% of 1300 W/m^2 is still a significant amount of extra energy that the planet needs to dissipate.
Also, while the lead author of that paper is a physicist, looking at his published history he seems firmly biased into the realm of particulate/aerosol driven climate impacts. It would be against his academic interests to publish a paper that at all discounts his historic work.
If you have any knowledge of papers that try to quantify and link solar irradiance changes to global climate change I'd be interested in reading over their methodology. I just didn't see that in here (correct me if I'm wrong).
Yeah, they don't discuss methodology in the summaries, and it's a PITA to chase down their references. It looks slightly easier in AR5 so I'll switch to that one.
First of all, did you multiply by the geometric and albedo factors (0.25 and 0.7 respectively)? Because 0.5W/m^2 * 0.25 * 0.7 is 0.9W/m^2 which is within the range given in 5AR in the context of this energy-balance comparison (made in units of radiative forcing):
Effective RF due to all anthropogenic effects: 1.1-3.3W/m^2
Effective RF due to greenhouse gasses: 2.54-3.12W/m^2
Effective RF due to non-CO2 GHGs: 0.43-0.53 W/m^2
RF due to Solar Forcing: 0.05-0.10W/m^2
These numbers indirectly answer your question (solar forcing is estimated to only be accountable for a fraction of the ~1ºC warming we have seen thus far) but I'm afraid that the detailed methodology is buried in a completely different section of the report (probably because it involves models of steady-state equilibrium between energy reservoirs now). I don't have the time to dig it up today and I'm not a subject expert, I am just loath to let people get away with the "scientists haven't considered..." type arguments when they're so blatantly wrong.
I was with you until "Cap-and-trade is a sound market-based solution". It's goofy market cargo-culting of something that isn't a market. If you want a policy intervention to burn less coal, end policies that are de-facto mandates to burn coal. If you want a policy intervention to build more nuclear plants, end policies that are a de-facto ban on nuclear power plants (and switch to policies that are a mandate to build nuclear power plants, unless you have some actual plan to move from a mandate-driven energy infrastructure to a free-market one). You can't expect policies to lower co2 emissions in general in the face of policies that mandate emissions in the specific because the specific always beats the general.
I don't know why this comment deserves down-votes.
As far as I know, Cap-and-trade has essentially failed as a policy to reduce carbon emissions and has stimulated a wide variety of dubious speculative enterprises. It is entirely plausible that policies to encourage or discourage the use of different energy types should be as direct as possible - it neither makes that paying for someone else to save resources would work nor has it been proven in practice.
Nothing is a market until you make it a market. All markets are artificial: they require the government to recognize and legitimate property rights in a particular good and therefore allow the market in that good to be governed by the rule of law.
I was a promoter of cap-and-trade for a long time, but the data, which I cited in my original post, suggest that straight carbon taxes work better. They are simpler to implement and demonstrably effective, and allow the reduction of income taxes and corporate taxes.
Am I correct in assuming you are in favour of higher income taxes and corporate taxes? This seems odd to me: I think it makes more sense to tax things we don't want (dumping gigatonnes of garbage into the atmosphere) and lower taxes on things we do want (people making oodles of money.)
The claim that you can't expect emissions reductions from carbon taxes is simply false, on the data. I believe in the data. Why should I believe an unsubstantiated claim to the contrary?
Yep. If you read closely, he's not taking an extreme position at all (he actually reaffirms CC and AGW), but he knows that this opinion wouldn't get him any recognition (or $$) on its own so he loaded it up with a linkbaity, unrepresentative title and hook that are guaranteed to get him attention by virtue of being politically "useful." He's trying to get the best of both worlds:
* Maintain standing in the scientific community by presenting a very reasonable, even understated argument that is impossible to refute
* Win political glory, perhaps even funding, by deliberately making himself easy to "misrepresent"
We have to figure out a way to punish people for this kind of bait-and-switch.
"Settled" is not a word you can use when describing any science. Medicine is not settled, nor is physics or computer science. But we can still glean useful insights from the evidence and experiments we have done. While it's wrong to claim climate science is settled, I can't recall any credible figure who said that it was. So to me this seems like a bit of a straw man.
"Climate Science Is Not Settled" is an irresponsible title IMO when the main points of contention in public discourse are whether anthropogenic climate change is even real or not, and action vs. inaction.
It's a good article and I'm happy to see it (assuming the information is accurate). But deniers will point to the title to argue that the whole things is a hoax and that we should do nothing.
I'm sure the phenomenon of "Warmists" is a real thing too, and something to watch out for. But it's incredibly hard to talk about the subtle points presented in this article when so many people refuse to believe that anything is happening at all. It's like trying to debate foreign policy with someone who thinks that 9/11 was an inside job.
I always thought that when people used the word "settled" in connection to climate change they were referring to the question of whether humans have influenced climate. Even though this article dismisses that question as "yeah there's little doubt about that", this is precisely what plenty of people have been arguing is not the case. So this article seems a lot like moving the goal posts to me.
Obviously climate science as a whole isn't "settled", any more than any other science is "settled".
Yeah I agree. The article was actually good and calls out very reasonable criticisms against current climate science. However the headline makes it seem the debate on whether humans influence the climate isn't settled.
One thing that the author points out is that the impact by humans is relatively small (compared to natural sourcing), and that natural variation is both vast and frequent.
I was hoping to find something about acidification of sea water, caused by CO2. Even if the warmth of the earth isn't caused by us, it seems like the acidification of the ocean might be. A similarly skeptical look at this would be welcomed.
I am amazed that an article filled with such a vast amount of FUD is frontpaging. But let's go point-by-point, lest the science described in thousands of papers of climate research get lost in the cloud of false skepticism, shall we?
> The models roughly describe the shrinking extent of Arctic sea ice observed over the past two decades, but they fail to describe the comparable growth of Antarctic sea ice, which is now at a record high.
The science of why Antarctic sea ice extent is growing is perfectly well known: the discharge of melting cold water from the Antarctic glaciers forms ice as it hits the coastal winds of the continent. That the models don't necessarily account the extent of this is almost irrelevant, since the sea ice extent has a very minute impact on climate patterns.
Let us note that this is a not-at-all subtle piece of FUD that would appear to account that Antarctic sea ice is compensating for Arctic melting. It's not. There's over 500 Gt of yearly glacier loss in the Antarctic, and the sea ice extent which is, at most, a few meters thick, is absolutely minuscule in comparison to the amount of additional water dissolving into the sea from kilometers-thick walls of ice. Also, the topic has been reasonably well-studied, and the changes in the atmosphere are more than enough to account for the observed effects.
> Even though the human influence on climate was much smaller in the past, the models do not account for the fact that the rate of global sea-level rise 70 years ago was as large as what we observe today—about one foot per century.
It is most definitely increasing, and it is accelerating rapidly, especially if the West Antarctic Ice Sheet accelerates its collapse (http://www.skepticalscience.com/sea-level-rise.htm). The fact that we have been observing linear trends thus far doesn't mean that we'll continue to observe them; evidence points that we're in the beggining of an exponential loss of ice.
> A crucial measure of our knowledge of feedbacks is climate sensitivity—that is, the warming induced by a hypothetical doubling of carbon-dioxide concentration. Today's best estimate of the sensitivity (between 2.7 degrees Fahrenheit and 8.1 degrees Fahrenheit) is no different, and no more certain, than it was 30 years ago. And this is despite an heroic research effort costing billions of dollars.
This is, again, FUD.
First of all, the radiative forcing produced by CO2 is well-known and established by physics. It is known that the Earth's albedo is decreasing, and the certainty that out lower bounds are erroneous has increased substantially.
Moreover, we are now aware of potential feedback loops that we didn't know about. It's interesting that he's never mentioning the Big One: the potential for frozen clathrates in Siberia and the Arctic to release methane that would trigger a certain mass extinction event.
> A transparent rigor would also be a welcome development, especially given the momentous political and policy decisions at stake. That could be supported by regular, independent, "red team" reviews to stress-test and challenge the projections by focusing on their deficiencies and uncertainties; that would certainly be the best practice of the scientific method. But because the natural climate changes over decades, it will take many years to get the data needed to confidently isolate and quantify the effects of human influences.
So, in his opinion, the models clearly described in papers, the data publicly available by NASA and dozens of different government organizations is not enough? A 3000-page report summarizing the findings of hundreds of papers, with multiple, independently corroborated lines of evidence using different data sets isn't enough?
This an obvious attempt to discredit climate scientists. I would suggest anyone who has a shred of doubt as to the integrit...
Still, I would like to thank you for a detailed answer. For me, an outsider to the science and politics of climate affairs, it sheds light on one party of the argument. Perhaps the other party will have an equally eloquent exposition - I have not yet read all the comments in this thread.
I don't know whether it was sarcastic or not, but to clarify: false skepticism is when FUD is cast around on the excuse that it is an attack on an institutional status quo. The reason why it is false is because real skepticism has a knack for rigorously questioning specific points in lines of evidence and proposing why established theories are cargo-culting their data.
As you can see here, none of that is taking place. In fact, the entire article is a massive logical fallacy that implicitly tries to frame the IPCC's current policy proposals as some sort of extreme.
If anything, the IPCC's report is extremely conservative, as it does not analyze the Black Swan events which include methan clathrates and the loss of effectiveness of carbon sinks, or the warming of the deep oceans.
Thus, it frames the debate in a fallacious way.
Actual skepticism has been well-served by the internal debates amongst climate scientists, and if you read the stuff by the emintent experts, you will see that they are shitting their pants in fear.
When climate experts are seriously scared of the possibilities of total extinction, we should be listening, and at best, making thoughtful critiques.
Is funny that a guy who ran a BP renewable energy department is saying not to panic.
BP started panicking when they started a renewable energy department.
Solar death spiral is a phrase from wall street that anyone in the energy industries should be taking heed of and it is going to scupper them far more than any amount of environmental legislation could ever dream of.
My point is that, precisely, such premise is full of crap; scientists are well aware of the limitations of that knowledge, but those limitations are bounded within limits which show a rather limited set of choices as far as valid courses of action to take. All of them indicate that we're doing far too little as it is.
He is not a climate scientist. He's not an applied physicist. He is, apparently, not even an informed layman, and his only critique is about carbon taxes. He has no projections beyond the year 2100 (so that means that he has no even considered the question of the effects of the BAU scenario as far, you know, sustainability goes beyond that, because we all know that after 2100 a magical fairy with technological powers will find the solution to all of this).
This guy's a clown, he freely mixes political leanings with subious science of people with no credentials on the topic, and it honestly looks like another astroturfing effort, no less in the nation of Australia, known for its massive coal lobby which has been pushing hard for the opposition of a carbon tax.
So I'll keep listening to the top climate scientists for advice instead of some paid shill with no understanding in either economy nor climate not environmental sciences.
It seems that the article has a simple thesis.
a) climate is hard
b) human activity is affecting it but because it's hard it's tough to know how much
c) hence it's difficult to know what the correct policies should be.
As an economist might say - without clarity on the positive, it's challenging to resolve the normative.
But I am a little puzzled by the failure to discuss outcomes in terms of mathematical expectation. And of course, the author knows more than I ever will about this.
Hence:
If our activity might just trigger a sequence of events leading to human extinction...(in other words such a sequence is conceivable and credible) then even if the risk is low as estimated by our (weak) ability to assess such risk, then the outcome is surely so hideous that if our policies are taking us in a direction that makes such an outcome more likely (even if we are not sure by how much) then there is cause for caution and re-examination of policy.
It seems to me that our situation at present is of this form. Despite our poor understanding and the fact that things aren't 'settled' (as if they ever will be) this unsettled 'knowledge' is all we have and we have to take it seriously, most particularly if the possible outcomes are ghastly. We can't just wait for better science.
70 comments
[ 3.2 ms ] story [ 124 ms ] threadNor is the crucial question whether humans are influencing the climate. That is no hoax: There is little doubt in the scientific community that continually growing amounts of greenhouse gases in the atmosphere, due largely to carbon-dioxide emissions from the conventional use of fossil fuels, are influencing the climate. There is also little doubt that the carbon dioxide will persist in the atmosphere for several centuries. The impact today of human activity appears to be comparable to the intrinsic, natural variability of the climate system itself...
Society's choices in the years ahead will necessarily be based on uncertain knowledge of future climates. That uncertainty need not be an excuse for inaction."
Much better than I expected of the WSJ. If it consistently took this line instead of buying into absurd conspiracy theories or claiming snow in January means climate change is a hoax, our national discourse would be much healthier, on both sides.
> We are very far from the knowledge needed to make good climate policy
Complete and total horseshit. Even if you'd only assume that the scientists are 90% right any good actuaries will tell you that you should spend about 90% on measures that back up what they've put forward.
Hacker News, I expected something better than this in the #2 spot.
Here, read this: http://www.ipcc.ch/report/ar5/
Or this: http://en.wikipedia.org/wiki/Global_warming
Or this: http://en.wikipedia.org/wiki/Ocean_acidification
Or this one is excellent: http://www.skepticalscience.com/
Edit: Alright, here we go with the downvotes for calling out bullshit regarding climate change on Hacker News. Well, it's not like I expected any better. Next I expect a replies either trying to argue random points about how there were forests in Greenland in the middle ages or some pretensions about being open-minded. While still barely having a grasp of a periphery of relevant facts.
But that's OK, the warriors having upvoted this to the top immediately know best. Or at least as well as Murdoch, publisher of the WSJ who has recently installed a prime minister in Australia who called climate change 'crap' and has abolished a carbon tax a minute fraction of those found in the rest of the OECD.
I am sick to the back teeth of "the sky is falling!" rhetoric.
I refuse to live in mortal fear for the future of humanity.
The climate will change, big deal, we'll adapt -- the range of habitats humans inhabit far exceeds the variation in climate that individual habitats will experience.
On the list of things to worry about climate change should be way down. But wow, you're so vocal -- because you feel that it is an existential threat. Newsflash, it ain't.
Homelessness is a bigger problem. Ditto poverty and starvation. I _welcome_ the push back against the drumbeats and rhetoric and hope climate change disappears off the political agenda entirely. Some hope.
I can't think of things more fundamental to existence or non-existence in this universe than it being the wrong temperature.
Wage your religious battle and set up the caricatures of anyone who might disagree, but you sway no one.
Now replace 'climate science' with astrology on the one hand or astronomy on the other and you might understand why what you're saying is not at all helpful.
That said, if he's bringing something new to the table, then I will lend him three ears. But first the strawman of whether climate science is settled (it won't ever be, just like statistical mechanics won't ever be 'settled', whatever that means), followed by plain wrongness and inaccuracies and only some minor salient points... while calling for what he's calling for is completely out of whack with not only what the IPCC but so many others have determined.
No religion here, mate. And no, I don't think that climate change per se will be the extinction of the human race. If nothing else, we might still have the sulphur dim-the-sun kill switch. And yes, climate science is complicated and, yes, nuclear energy everything. Religion? Please...
I assume the limitation is that all those cells have to be simulated in small time slices for 100 years, and the necessary time slice would scale inversely with the grid size, so computation is O(n^3) on the inverse size of the grid.
Can someone comment on what kind of computer it would take to halve the size of the grid?
Simulations are typically done in one day time-steps or less.
The thing is, there is a lot of physics going on in each cell, and in some respects reducing the cell size makes things more problematic rather than less. For example, the effects of a supercell thunderstorm can dominate the atmosphere over tens of kilometers. With a 100 km (60 mile) scale you can plausibly average over those effects within a cell, as you can reasonably claim that most such "local" phenomena will be happening well away from cell boundaries.
So as you reduce the cell size, you start having to think about the internal details of local disturbances that you were previously averaging away and hoping to catch in your overall parameterizations, and the model complexity goes up tremendously, likely without becoming a whole lot more accurate.
Even at these large scales the amount of physics that goes on within a single cell is huge, and getting all the heat and mass balances right is fantastically difficult, which is where a lot of the computational power goes.
So it isn't really a question of halving the grid size while keeping the physics the same, because you are going to have to substantially revise your model to accommodate the new scale. I'm sure this work is ongoing, but it's extremely complex and difficult.
Compare for example my own short take on the same issues, written two years ago: http://www.tjradcliffe.com/?p=886
You'll see basically similar concerns raised. If you're seriously wedded to the idea that consensus is important to the science, you should dig up the independent opinions of a few other computational physicists (not climate scientists, who are not computational physicists). Having done so, you might find that there is a consensus amongst computational physicists that climate models are problematic in ways that make them questionable guides to policy, although most of us will also say that we should be concerned about the amount of garbage we are dumping into the atmosphere (and there are reasons to want to get off fossil fuels that go beyond the climate change argument.)
Denialists have poisoned the public discourse on climate change, but Warmists have unfortunately responded by digging in their heels in a particularly anti-scientific way. I hope Koonin's piece will help bring the scientific discussion back to fundamentals, and perhaps decouple the policy discussion from models a bit.
For example: we know that carbon taxes work pretty well in reducing CO2 emissions (http://www.theglobeandmail.com/globe-debate/the-insidious-tr...) and we know that carbon taxes can be used to reduce corporate and income taxes. So anyone who is opposed to carbon taxes is necessarily in favour of higher corporate and income taxes.
This is a policy discussion that can and should be had independently of any detailed climate model results, and I invite everyone who is in favour of higher corporate and income taxes to chime in here in support of their position, and explain why those taxes are so much better than the carbon taxes that could partially replace them.
http://www.theguardian.com/environment/climate-consensus-97-...
And can you please stop with the 'Warmist' label? It's stupid, about as much as 'denialist' is narrow for the veritable zoo of opinions - educated or uneducated - that's sprung up in the public discourse.
I've also read your post and 1-2 W/m2 does sound like very little. However, and I quote from Wikipedia:
> Of the ~340 W/m2 of solar radiation received by the Earth, an average of ~77 W/m2 is reflected back to space by clouds and the atmosphere, and ~23 W/m2 is reflected by the surface albedo, leaving about 240 W/m2 of solar energy input to the Earth's energy budget.
That's a change of 0.5%. Doesn't sound like much, does it, but at 273 K that corresponds to about 1.5 degrees already. At the upper end of that and 300 K it's 2.5 degrees. Sure, it's simplistic and it's how to keep it quite that straightforward, but to see that number and be ignorant enough of the context to trivialise it and call it not a big deal is pretty disingenuous. Sure, a 2.5 K (or something like it) rise isn't going to bring the downfall of civilisation per se. But there's more to it than that. And, mind you, 2.5 K is at the lower end of IPCC projections, so there's evidently a lot more ground to cover than the simplistic numbers mentioned here.
well, it did it for Roman Empire - the Mediterranean climate became unsuitable for grain production while Europe north of Alps became drier and comfortable.
Height of the Caliphates ( at 969) http://en.wikipedia.org/wiki/Islamic_Golden_Age coincides with the height of the temperature during middle ages. The caliphates were result of conquest by Arabs from Arabian Peninsula and the caliphates folded back with temperature dropping as the Little Ice Age was coming.
Add to that Vikings (http://en.wikipedia.org/wiki/Viking_Age) whose reach was maximized during about the same time as Caliphates as North Atlantic was more comfortable for sailing in the small open drakars. They reached Greenland and established colony there (which disappeared with Little Ice Age). Vikings are the "Normans" as in Normandy - and we know the key role they played in the history of Western Europe. Vikings founded the Kievana Rus which because of their leadership was pretty strong expanding and aggressive state for hundreds of years, almost until Mongols. Thus the warmth of 1000+ years ago and resulting Vikings outreach were defining factors in shaping the foundation of Western Europe and Russia as we know it.
Getting back to our days - one can only speculate how political landscape of USA for example would change in the next decades when growing corn in Iowa and cattle in Texas would become economically impossible.
The percentages don't change as the sun's output increases. 273K is slightly below freezing. ~290K is closer to the average earth temperature. Look up black body radiation. http://en.wikipedia.org/wiki/Thermal_radiation Radiation is T^4. If incoming energy increases by x temperature increase by x^(1/4). (1.001)^(1/4) = 1.00025. So 1.00025 * 290K = 290.0725K.
PS: This is of course a ridiculously simplified model but a 2.5k rise would take an increase of around ((290+2.5)/290) ^4 - 1 = 3.5%. The sun is no where near that unstable.
I didn't say the sun was - this calculation is past the point of radiation and already in Watt being received by Earth. And I'm pretty sure those Watt are linearly (edit: or at least somewhat like it, given enough time) related to temperature.
Edit: parent had a good point (which may or may not have been edited out) about how radiation from the sun - Black body radiation - is power to the fourth away from translating into temperature. Which, though, I don't think is too relevant here.
I'm clearly on the record as being concerned about climate change and strongly in favour of implementing social policies (including carbon taxes) that will a) reduce GHG emissions and b) protect the most vulnerable, but because I don't quack like precisely the right kind of duck I'm routinely accused of somehow trivializing something, or being the enemy (this is not the first time I've had this kind of discussion, obviously). This is what you see from rival religions, not from scientists. I was involved in the 17 keV neutrino controversy, so I'm no stranger to scientific disagreement, and it simply doesn't have this strange dynamic.
If anyone is trivializing anything, it is Warmists trivializing physics. For example, why anyone would go from a 0.5% change in energy budget to a 0.5% change in absolute temperature is beyond me. Heating and temperature in the atmosphere are connected by complex and non-linear factors, which is one of the reasons we need to do modelling in the first place. Even in the simplest case of a black body the non-linear Stephan-Bolzmann law applies, not Newton's law of cooling (which is linear, but irrelevant to this case.)
So the argument you're making is not even wrong: it simply doesn't speak to the question of what the plausible effect of climate change on the Earth in general and humanity in particular will be.
This kind of argument just feeds the Denialist trolls who are doing so much damage to this discourse, because they will pick up on your errors and cry "hoax!" and other such nonsense rather than "honest, innocent and naive mistake", which in fairness what I think your error most likely is.
Finally, as I said above, I've had this kind of discussion before and it's never ended well, so I'm going to stop here and let you have the last word. Enjoy!
But if I put 1 energy into object x, at the simplest I'll get something about 1 temperature more if that object is in a vacuum, given enough time. Sure, it's never as simple as that, but that's all I was saying, plus/minus several dozen percent, from a bird's eye view. And greenhouse gases don't just trap incoming energy, but also serve to suppress black body radiation... and are 50% higher now than they were some centuries ago. So, point being, do I agree with you that black body radiation is the ultimate end to climate change? Absolutely. But I've just got to look over at Venus and the Sun to see how that dynamic plays out elsewhere and it's much hotter than 300 K.
>it identifies a nearly religious zeal on the part of some non-scientists who insist that anyone who does anything other than repeat the mantra "the science is settled; we must implement every imaginable solution except nuclear power"
Is not a response to what was said. It is a response to a fantasy opponent that was made up.
Based on my experience, the debate about Global Warming is is mostly polemical.
In my opinion, a debate about measurable natural phenomena should be scientific - where a single verifiable fact trumps all previous consensus and conjecture.
But swapping all corporate taxes for a carbon tax? That really is a no brainer, and most policy experts not in the pay of the fossil fuel industry would leap at it. I don't know why we don't see it happen. Maybe because the American political system does not reward risk taking, even if it can substantially improve economic outcomes.
A larger point that was raised by a different lecturer is that solar output has increased drastically over the last 100 years and that the global warming trends we see correlate perfectly with this increase in output. He actually believed that the industrial revolution lining up with this increase in solar output was entirely coincidental.
So to confound the issue further, we may not be responsible for global warming but our production of greenhouse gasses undoubtedly has an impact on our environment/climate that seems unlikely to be positive.
Climate science is a nasty beast.
In a nutshell, CO2 is near enough on the path to increasing by 50% and it's pretty important for the greenhouse effect. Solar variation over millenia is, peak-to-peak, 0.1%.
They are running these on super-computers many many times over and would have no interest in doing exactly the same thing over and over. http://www.climatechange2013.org/images/report/WG1AR5_Chapte...
And yes, they even mention the 15 year hiatus - they don't sweep this under the rug like so many have taken to believing they do. In fact, it's mentioned throughout the AR5. In fact, you can get a sense of them being just eager to tackle it in substantial detail - it's wonderful.
Pages 188-193 summarize why the scientific consensus believes what it does:
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-cha...
Also, while the lead author of that paper is a physicist, looking at his published history he seems firmly biased into the realm of particulate/aerosol driven climate impacts. It would be against his academic interests to publish a paper that at all discounts his historic work.
If you have any knowledge of papers that try to quantify and link solar irradiance changes to global climate change I'd be interested in reading over their methodology. I just didn't see that in here (correct me if I'm wrong).
First of all, did you multiply by the geometric and albedo factors (0.25 and 0.7 respectively)? Because 0.5W/m^2 * 0.25 * 0.7 is 0.9W/m^2 which is within the range given in 5AR in the context of this energy-balance comparison (made in units of radiative forcing):
Effective RF due to all anthropogenic effects: 1.1-3.3W/m^2
Effective RF due to greenhouse gasses: 2.54-3.12W/m^2
Effective RF due to non-CO2 GHGs: 0.43-0.53 W/m^2
RF due to Solar Forcing: 0.05-0.10W/m^2
These numbers indirectly answer your question (solar forcing is estimated to only be accountable for a fraction of the ~1ºC warming we have seen thus far) but I'm afraid that the detailed methodology is buried in a completely different section of the report (probably because it involves models of steady-state equilibrium between energy reservoirs now). I don't have the time to dig it up today and I'm not a subject expert, I am just loath to let people get away with the "scientists haven't considered..." type arguments when they're so blatantly wrong.
5AR (solar forcing on page 688): http://www.climatechange2013.org/images/report/WG1AR5_Chapte...
As far as I know, Cap-and-trade has essentially failed as a policy to reduce carbon emissions and has stimulated a wide variety of dubious speculative enterprises. It is entirely plausible that policies to encourage or discourage the use of different energy types should be as direct as possible - it neither makes that paying for someone else to save resources would work nor has it been proven in practice.
I was a promoter of cap-and-trade for a long time, but the data, which I cited in my original post, suggest that straight carbon taxes work better. They are simpler to implement and demonstrably effective, and allow the reduction of income taxes and corporate taxes.
Am I correct in assuming you are in favour of higher income taxes and corporate taxes? This seems odd to me: I think it makes more sense to tax things we don't want (dumping gigatonnes of garbage into the atmosphere) and lower taxes on things we do want (people making oodles of money.)
The claim that you can't expect emissions reductions from carbon taxes is simply false, on the data. I believe in the data. Why should I believe an unsubstantiated claim to the contrary?
What world do you live in? You know exactly what Koonin's piece will do.
* Maintain standing in the scientific community by presenting a very reasonable, even understated argument that is impossible to refute
* Win political glory, perhaps even funding, by deliberately making himself easy to "misrepresent"
We have to figure out a way to punish people for this kind of bait-and-switch.
His title + soundbytes: 100% against us
Only one of these will matter in the eyes of the public.
If you are missing either of these attributes -- you are in the realm of legends, folklore, and farmer's almanacs.
It's a good article and I'm happy to see it (assuming the information is accurate). But deniers will point to the title to argue that the whole things is a hoax and that we should do nothing.
I'm sure the phenomenon of "Warmists" is a real thing too, and something to watch out for. But it's incredibly hard to talk about the subtle points presented in this article when so many people refuse to believe that anything is happening at all. It's like trying to debate foreign policy with someone who thinks that 9/11 was an inside job.
Obviously climate science as a whole isn't "settled", any more than any other science is "settled".
I am amazed that an article filled with such a vast amount of FUD is frontpaging. But let's go point-by-point, lest the science described in thousands of papers of climate research get lost in the cloud of false skepticism, shall we?
> The models roughly describe the shrinking extent of Arctic sea ice observed over the past two decades, but they fail to describe the comparable growth of Antarctic sea ice, which is now at a record high.
The science of why Antarctic sea ice extent is growing is perfectly well known: the discharge of melting cold water from the Antarctic glaciers forms ice as it hits the coastal winds of the continent. That the models don't necessarily account the extent of this is almost irrelevant, since the sea ice extent has a very minute impact on climate patterns.
Let us note that this is a not-at-all subtle piece of FUD that would appear to account that Antarctic sea ice is compensating for Arctic melting. It's not. There's over 500 Gt of yearly glacier loss in the Antarctic, and the sea ice extent which is, at most, a few meters thick, is absolutely minuscule in comparison to the amount of additional water dissolving into the sea from kilometers-thick walls of ice. Also, the topic has been reasonably well-studied, and the changes in the atmosphere are more than enough to account for the observed effects.
> Even though the human influence on climate was much smaller in the past, the models do not account for the fact that the rate of global sea-level rise 70 years ago was as large as what we observe today—about one foot per century.
It is most definitely increasing, and it is accelerating rapidly, especially if the West Antarctic Ice Sheet accelerates its collapse (http://www.skepticalscience.com/sea-level-rise.htm). The fact that we have been observing linear trends thus far doesn't mean that we'll continue to observe them; evidence points that we're in the beggining of an exponential loss of ice.
> A crucial measure of our knowledge of feedbacks is climate sensitivity—that is, the warming induced by a hypothetical doubling of carbon-dioxide concentration. Today's best estimate of the sensitivity (between 2.7 degrees Fahrenheit and 8.1 degrees Fahrenheit) is no different, and no more certain, than it was 30 years ago. And this is despite an heroic research effort costing billions of dollars.
This is, again, FUD.
First of all, the radiative forcing produced by CO2 is well-known and established by physics. It is known that the Earth's albedo is decreasing, and the certainty that out lower bounds are erroneous has increased substantially.
Moreover, we are now aware of potential feedback loops that we didn't know about. It's interesting that he's never mentioning the Big One: the potential for frozen clathrates in Siberia and the Arctic to release methane that would trigger a certain mass extinction event.
> A transparent rigor would also be a welcome development, especially given the momentous political and policy decisions at stake. That could be supported by regular, independent, "red team" reviews to stress-test and challenge the projections by focusing on their deficiencies and uncertainties; that would certainly be the best practice of the scientific method. But because the natural climate changes over decades, it will take many years to get the data needed to confidently isolate and quantify the effects of human influences.
So, in his opinion, the models clearly described in papers, the data publicly available by NASA and dozens of different government organizations is not enough? A 3000-page report summarizing the findings of hundreds of papers, with multiple, independently corroborated lines of evidence using different data sets isn't enough?
This an obvious attempt to discredit climate scientists. I would suggest anyone who has a shred of doubt as to the integrit...
Still, I would like to thank you for a detailed answer. For me, an outsider to the science and politics of climate affairs, it sheds light on one party of the argument. Perhaps the other party will have an equally eloquent exposition - I have not yet read all the comments in this thread.
As you can see here, none of that is taking place. In fact, the entire article is a massive logical fallacy that implicitly tries to frame the IPCC's current policy proposals as some sort of extreme.
If anything, the IPCC's report is extremely conservative, as it does not analyze the Black Swan events which include methan clathrates and the loss of effectiveness of carbon sinks, or the warming of the deep oceans.
Thus, it frames the debate in a fallacious way.
Actual skepticism has been well-served by the internal debates amongst climate scientists, and if you read the stuff by the emintent experts, you will see that they are shitting their pants in fear.
When climate experts are seriously scared of the possibilities of total extinction, we should be listening, and at best, making thoughtful critiques.
This,in contrast, is stinking bullshit.
BP started panicking when they started a renewable energy department.
Solar death spiral is a phrase from wall street that anyone in the energy industries should be taking heed of and it is going to scupper them far more than any amount of environmental legislation could ever dream of.
Your test for integrity? You have a sense of humor.
http://topher.com.au/about-topher/ is his "story".
He is not a climate scientist. He's not an applied physicist. He is, apparently, not even an informed layman, and his only critique is about carbon taxes. He has no projections beyond the year 2100 (so that means that he has no even considered the question of the effects of the BAU scenario as far, you know, sustainability goes beyond that, because we all know that after 2100 a magical fairy with technological powers will find the solution to all of this).
This guy's a clown, he freely mixes political leanings with subious science of people with no credentials on the topic, and it honestly looks like another astroturfing effort, no less in the nation of Australia, known for its massive coal lobby which has been pushing hard for the opposition of a carbon tax.
So I'll keep listening to the top climate scientists for advice instead of some paid shill with no understanding in either economy nor climate not environmental sciences.
As an economist might say - without clarity on the positive, it's challenging to resolve the normative.
But I am a little puzzled by the failure to discuss outcomes in terms of mathematical expectation. And of course, the author knows more than I ever will about this.
Hence: If our activity might just trigger a sequence of events leading to human extinction...(in other words such a sequence is conceivable and credible) then even if the risk is low as estimated by our (weak) ability to assess such risk, then the outcome is surely so hideous that if our policies are taking us in a direction that makes such an outcome more likely (even if we are not sure by how much) then there is cause for caution and re-examination of policy. It seems to me that our situation at present is of this form. Despite our poor understanding and the fact that things aren't 'settled' (as if they ever will be) this unsettled 'knowledge' is all we have and we have to take it seriously, most particularly if the possible outcomes are ghastly. We can't just wait for better science.