Ok sunshine, you explain how 2000 scientists can contribute to a paper.
By that I mean physically contribute, review and discuss.
First of all, it wasn’t a paper, but a report. Secondly, various scientists contributed to formulating different sections of the report. It’s really not all that hard to understand how that many scientists could have contributed in that way.
Giving the independent-mindedness of most scientists, this is an apt analogy. Based on this, the near-unanimity of the scientific community on the subject at this point does argue very strongly for the reality of the report’s conclusions. I might add, this strong consensus on the subject is evident in scientific conferences I have attended as well as in the peer-reviewed literature.
Some individuals, maybe.
It’s absolutely fascinating, if depressing, this ability of some humans to completely disregard science in their thinking processes.
2000 scientists probably got together to make this declaration because the poor fools thought that people might actually pay attention if enough scientists spoke out together. I guess not many of them are versed in psychology and the phenomenon of cognitive dissonance.
Fortunately, it appears that the majority of people in Canada and the USA and likely elsewhere as well are concerned about the environment so the weight of the opinions of those who refuse to acknowledge there’s a problem will shrink until it’s insignificant. They can then join the ranks of the Luddites and the Flat-Earthers and have conventions or something.
The greater than 90% probability is not being assigned to the notion that humans are having some effect. It is being assigned to the notion that humans are responsible for most of the net warming that has occurred over the last half century. And, in addition to this, there is more warming that is predicted to already be “in the pipeline”…i.e., even if we were to stop emitting greenhouse gases tomorrow, the earth would continue to warm just to fully equilibrate with the amount presently in the atmosphere. Furthermore, we have likely offset (in a sense “hidden”) some of the warming due to increased greenhouse gas concentrations by also increasing the concentrations of sulfate aerosol pollutants that have a net cooling effect. Unfortunately, since these particles are not very pleasant to breath, it is unlikely that we can continue to increase the concentration of these particles (and, in fact, in First World countries like the U.S., we are already dramatically decreasing our emission of these pollutants due to the Clean Air Act, while rapidly developing countries like China are still increasing theirs with all the attendant pollution effects). [Furthermore, since the sulfate aerosols have a shorter lifetime in the atmosphere, one has to keep emitting more and more in order to increase concentrations whereas with CO2 the lifetime is long enough that even if we hold our CO2 emissions constant at current values, the concentration of CO2 will continue to increase for a long time. So, in the end, the greenhouse effect tends to win over the sulfate aerosol cooling effect.]
Yes, it will be pretty gradual…although in low-lying areas like Bangladesh or southern Florida, rather small changes in sea level can result in losses of quite large areas of land, so it may not be as gradual as it sounds to those of us whose distance above sea level is measured in hundreds of feet rather than in feet or even in inches. Also, it is worth noting that although the IPCC predictions only go to 2100, the sea levels will continue to rise for hundreds to thousands of years because the equilibration times for the melting of the glacial ice and for the increase in sea temperatures is so long.
Furthermore, as Colibri has noted, the IPCC official estimates of sea level rise has chosen to specifically exclude the possibility that the breakup of some of the glacial land ice could occur much faster than models predict because of highly non-linear processes, such as meltwater seeping underneath the ice and lubricating it so that it slides off into the sea rather than just gradually melting away.
Scientists have never claimed that all aspects of this problem are easy to model. (In fact, they have never claimed that hardly any aspects are easy.) It turns out that the modeling of the breakup of the ice sheets is exceeding difficult, as I explained briefly in the post above. However, as noted, the IPCC document is conservative in that its estimate of sea level rise only includes a small contribution from the melting of ice sheets (most of it instead coming from the simple thermal expansion of the sea water as it heats up, something that is quite well-understood from basic physics).
If the ice sheets were to break up much more quickly due to highly nonlinear processes, then the seas could start to rise considerably faster. And, as Jim Hansen notes, it is not at all encouraging that the historical record seems to suggest that the sea level rise at the end of the last ice age was very rapid…I believe much more rapid than can be accounted for by the models of ice sheet dynamics that are generally being used.
And yet, I imagine if I were to offer you a bet, giving you 1000:1 odds that it will be warmer 6 months from now in Rochester than it is here today, you would still refuse to take that bet. Why is that? Perhaps it is because you know that although the weather on a day 6 months in advance can’t be accurately predicted, we can still say something about the climate…i.e., the weather in some suitably-averaged sense.
Those who run the climate models (and weather forecast models) know very well that they cannot use these models to predict the weather on a particular day 100 years, or even 1 year, from now. In fact, they can see these in those very models by making very tiny perturbations in the initial conditions and seeing that this leads to different results. However, they find that while the details may be different, the simulations run with increasing greenhouse gases consistently show a warmer climate than those run without.
Are the models definitely very accurate in their predictions? I agree that this can’t be said with too much certainty because what the paleoclimate evidence suggests is that the climate can sometimes change quite quickly and dramatically in ways that are difficult for climate models to mimic. However, this idea of abrupt threshholds is hardly re-assuring. I.e., what it suggests is that the climate models are giving the basic climate response in the absence of some dramatic positive feedback effects that suddenly send the climate off to a very different state. That is to say, they are likely to be erring more on the conservative side.
Just to clarify and elaborate on this point a little more: In this case, what we are talking about is the seasonal climate and perhaps a better analogy to the climate change predictions would be if I offered to bet that the average temperature for the entire month of August in Rochester would be warmer than the month of February. However, in this particular case, the climatic difference is so large that I can make a prediction about the weather on a particular day just because the probability of a day in early August being colder than this below-average-temperature day in February is infinitesimally small.
By the way, there is a good article [url=]here in the New York Times about the question of whether the IPCC’s predictions of the sea level rise are too conservative:
[It sounds like this article was actually written before the IPCC report was officially released and I believe the final compromise was to stay with the more conservative estimate but to also explicitly note that this estimate is excluding effects that could occur if ice breakup occurs in the more dramatic ways that the current evidence seems to be suggesting might happen. I have only heard this 2nd-hand as I haven’t had the chance to actually read it yet.]
The [url=]main article on the IPCC report in the New York Times, which is very good and highly-recommended, also has a bit of discussion on the issue of melting land ice and sea level rise:
Cite? Here’s the actual PDF report, which I read, and quoted one line of. I admit that one line of the report supports this but other lines say that they really have no idea what % of overall change is caused by Anthropogenic change. Note that the report also concedes a considerable cooling effect due to an increase in aerosols, so you need to see what the NET anthropongenic change is, not take one line out of context.
http://ipcc-wg1.ucar.edu/wg1/docs/WG1AR4_SPM_PlenaryApproved.pdf
“The observed widespread warming…support the conclusion that it is extremely unlikely that the global climate change of the past 50 years can be explained without external forcing,and very likely that it is not due to *natural causes alone”.
The US Senate has heard views contrary to global warming (warning, one of the links therein plays music).
Thanks, but I’ll continue to listen to both sides. Neither has me convinced.
Gosh, a committee chaired (until recently) by a vehement opponent of even considering some human responsibility for global warming has been far more favorable to deniers than anyone else? Color me surprised.
If the way you flagrantly misread that BBC report you linked to is any indication, I doubt that you are actually really listening to both sides.
Wrong. Did you read the bolded paragraph immediately before the two bullet points from which you took you that quote?
“Most of the observed increase in globally averaged temperatures since the mid 20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”
That’s their emphasis, not mine, btw.
Just curious, Quartz, but are you a Creationist by any chance? The logic you’re applying to global warming seems largely identical to the logic they apply to evolution.
Climatology is a hard science in the sense that it deals with real and, for the most part, verifiable numbers. However, the interpretation of the meaning of the numbers, and extrapolation of them via predictive models of future behavior are less than completely rigorous. However, over the past decade there has been increasingly inarguable evidence of a large global warming trend which is unprecidented in recent history, and the only obvious proximate cause is the increase in so-called “greenhouse gases” that are a result of industrialization. Note that this isn’t an exclusive argument; there could be other causes, or for all we know, carbon emissions could be a nonissue, but that argument seems unlikely at best; even if the models can’t specifically predict future trends, there is a growing technical consensus that the extant levels of CO[sub]2[/sub] in the atmosphere have to be causing some climate distrubances.
Unfortunately, like evolution, space exploration, or the nuclear winter effect, this is an extremely polarizing, highly politicized issue that is almost impossible to bring up in public discourse because (a) it evokes strong and often irrational impulses, (b) the arguments on both sides are often amplified for dramatic “newsworthy” effect, and © the vast majority of people, even advocates of one side or the other, are technically ignornant on the topic, rendering an attempt at intelligent discussion into and attempt at lecture and monologue drowned out by energetic proselytizing.
Climate change will happen eventually regardless, and even if the current trend is anthropgenic in origin it’s unlikely that we can do much to significantly forestall it (at least, with extant technologies), although there would certainly be some abatement value in dramatically reducing carbon emissions. But there are also other excellent and frankly pressing reasons to reduce the use of fossil fuels, chief among them is the finite reserves of said energy sources and from a nationalist standpoint the control that resource holders have over dependent nations. We can cope with climate change–although the effects upon nations which have small natural resources and large populations in low-lying and equatorial regions may suffer greatly–but we can’t keep growing and transporting crops without fuel. There are persuasive technical arguments for developing nuclear power and, where applicable and effective, solar and wind.
I find it interesting that there is such a focus and concern regarding climate change (which is something that we can at least cope with) but very little public awareness at groundwater contamination and aquifer depletion, which in combination seriously threaten industrial society en masse, and the effects of which could be rapid and devestating, especially since there is no easy way to replenish or repair overdepleted underwater aquifers and no ready way to move fresh water inland for irrigation and residential use, even if you could develop some kind of effective, low energy desalination process.
Stranger
John Mace has already pointed to the place where they very clearly say that is is very likely (which, as explained in their footnotes, means >90% chance in their estimation) that most of the warming since the mid-20th century is due to the increase in greenhouse gas concentrations. And, far from the offset by aerosols saving you from this conclusion, they only take you deeper in the sense that the report points out that there would have been even more warming seen due to greenhouse gases except that some of it was offset by aerosols. Or, to quote straight from the source:
(“Likely” in IPCC-speak means >66% chance.)
Well, I will. My brother the engineer (software design, not nuclear, but he’s broadly sophisticated about technology) tells me nuclear-power technology is much more safe and reliable now than it was in the '70s. I see no reason to doubt it. France gets most of its power from nuke plants, and when was the last time they had a meltdown? As for the waste, ship it to Yucca Mountain. Worst-case scenario, we lose Vegas – BFD. 
Unfortunately, decommissioning the coal-fired power plants and replacing them with nuclear plants only solves part of the greenhouse-gas problem. You can’t run cars on nuclear power. And I’m skeptical about how far we can get with electric cars or hydrogen-powered cars.
There’s really no good reason to ship waste anywhere, or at least, not any further than the reprocessing facility down the road. There are a variety of breeder-type reactors that actually produce more fuel than they initially use. (This seems counterintuitive, but it’s a natural result of atomic decay and binding energies.) The more significant problem is the large amounts of low-level waste which can’t be processed into any kind of fuel but post a moderate but long-term environmental hazard for disposal.
With extant technologies, not too well; and remember, we’d have to add not only energy generating capability to replace the existing network of coal- and oil-fired plants, but also enough to serve for transportation usage. (Certain types of transport, like marine, would still require gas or some other portable, high energy/low bulk fuel or energy source regardless.) But advances in fuel cells or chemical production of artificial, low emission fuels might make this more viable. (I doubt pure “dry cell” battery technologies will be viable in the foreseeable future for the purposes of long range off-grid transportation, especially over-the-road hauling.) Also, a shift to more rail-based public transport would alieviate demands on off-grid energy requirements, but this would require extensive dense urbanization as seen in many European nations.
Nuclear may seem “free” of pollution in the chemical sense (ignoring the small amount of high level waste which is easily contained, and the afformentioned low level waste), but you are going to have to find or somehow make cooling capabilities for these plants; this is traditionally done by building the plant on a bank of a river or very large lake and using a heat exchanger (with or without cooling towers) to dump waste heat to the environment. There’s a limit to how much heat you can dump without detrimentally effecting the local ecosystem, though. So you have to figure out that problem, too; either using big radiant heat exchangers, somehow converting some of the waste heat to mechanical or chemical energy, or otherwise managing the thermal rejection problem in a way that doesn’t screw up someone’s lifestyle.
So, in short, there’s no easy answer to reducing emissions; even nuclear has some significant hurdles quite aside from the whole political issue of waste disposal or reprocessing.
Stranger
Sure you can. We’re maybe 20 years away from workable hydrogen car, but when we do get there, you need electricity to create the fuel cells.
But transportation emissions are not the main contributor to greenhouse gases-- they only account for about 14%, although you do have to count the extraction, refining and transportation as well. However, if we could tackle the power generation issue that will be a huge deal, as it will spill over into some of the other sources of greenhouse gases, too.
What’s “wrong”? I said “I admit that one line of the report supports this…” Are you saying that this quote is “wrong”: “The observed widespread warming…support the conclusion that it is extremely unlikely that the global climate change of the past 50 years can be explained without external forcing,and very likely that it is not due to natural causes alone”.
Or that I am wrong when I say "so you need to see what the NET anthropongenic change is, not take one line out of context. "? So, what’s “wrong”?
Read the whole report, everyone.