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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Positives and negatives of global warming

What the science says...

Select a level... Basic Intermediate Advanced

The consequences of climate change become increasingly bad after each additional degree of warming, with the consequences of 2°C being quite damaging and the consequences of 4°C being potentially catastrophic.

Climate Myth...

It's not bad

"By the way, if you’re going to vote for something, vote for warming. Less deaths due to cold, regions more habitable, larger crops, longer growing season. That’s good. Warming helps the poor." (John MacArthur)

Global Warming Impacts

The 2007 IPCC Fourth Assessment Report (AR4) summarizes the magnitudes of impact of various degrees of warming here, and graphically in Figure 1, relative to ~1990 temperatures (~0.6°C above late 19th Century temperatures).

fig spm.2

Figure 1: Illustrative examples of global impacts projected for climate changes (and sea level and atmospheric carbon dioxide where relevant) associated with different amounts of increase in global average surface temperature in the 21st century. The black lines link impacts, dotted arrows indicate impacts continuing with increasing temperature. Entries are placed so that the left-hand side of the text indicates the approximate onset of a given impact. Quantitative entries for water stress and flooding represent the additional impacts of climate change relative to the conditions projected across the range of Special Report on Emissions Scenarios (SRES) scenarios. Adaptation to climate change is not included in these estimations. Confidence levels for all statements are high.  IPCC AR4 WGII Figure SPM.2.

Some adverse impacts are expected even before we reach the 2°C limit, such as hundreds of millions of people being subjected to increased water stress, increasing drought at mid-latitudes (as we recently discussed here), increased coral bleaching, increased coastal damage from floods and storms, and increased morbidity and mortality from more frequent and intense heat waves (see here), floods, and droughts.  However, by and large these are impacts which we should be able to adapt to, at a cost, but without disastrous consequences.

Once we surpass the 2°C limit, the impacts listed above are exacerbated, and some new impacts will occur.  Most corals will bleach, and widespread coral mortality is expected ~3°C above late 19th Century temperatures.  Up to 30% of global species will be at risk for extinction, and the figure could exceed 40% if we surpass 4°C, as we continue on the path toward the Earth's sixth mass extinction.  Coastal flooding will impact millions more people at ~2.5°C, and a number of adverse health effects are expected to continue rising along with temperatures.

Reasons for Concern

Smith et al. (2009) (on which the late great Stephen Schneider was a co-author) updated the IPCC impact assessment, arriving at similar conclusions.  For example,

"There is medium confidence that ~20–30% of known plant and animal species are likely to be at increased risk of extinction if increases in global average temperature exceed 1.5 °C to 2.5 °C over 1980–1999"

"increases in drought, heat waves, and floods are projected in many regions and would have adverse impacts, including increased water stress, wildfire frequency, and flood risks (starting at less than 1 °C of additional warming above 1990 levels) and adverse health effects (slightly above 1 °C)"

"climate change over the next century is likely to adversely affect hundreds of millions of people through increased coastal flooding after a further 2 °C warming from 1990 levels; reductions in water supplies (0.4 to 1.7 billion people affected with less than a 1 °C warming from 1990 levels); and increased health impacts (that are already being observed"

Smith et al. updated the 2001 IPCC report 'burning embers' diagram to reflect their findings (Figure 2).  On this figure, white regions indicate neutral or low impacts or risks, yellow indicates negative impacts for some systems or more significant risks, and red indicates substantial negative impacts or risks that are more widespread and/or severe.  They have grouped the various climate change consequences into 'reasons for concern' (RFCs), summarized below.

smith embers

Figure 2:  Risks from climate change, by reason for concern (RFC). Climate change consequences are plotted against increases in global mean temperature (°C) after 1990. Each column corresponds to a specific RFC and represents additional outcomes associated with increasing global mean temperature. The color scheme represents progressively increasing levels of risk and should not be interpreted as representing ‘‘dangerous anthropogenic interference,’’ which is a value judgment. The historical period 1900 to 2000 warmed by 0.6 °C and led to some impacts. It should be noted that this figure addresses only how risks change as global mean temperature increases, not how risks might change at different rates of warming. Furthermore, it does not address when impacts might be realized, nor does it account for the effects of different development pathways on vulnerability.

  • Risk to Unique and Threatened Systems addresses the potential for increased damage to or irreversible loss of unique and threatened systems, such as coral reefs, tropical glaciers, endangered species, unique ecosystems, biodiversity hotspots, small island states, and indigenous communities.
  • Risk of Extreme Weather Events tracks increases in extreme events with substantial consequences for societies and natural systems. Examples include increase in the frequency, intensity, or consequences of heat waves, floods, droughts, wildfires, or tropical cyclones.
  • Distribution of Impacts concerns disparities of impacts.  Some regions, countries, and populations face greater harm from climate change, whereas other regions, countries, or populations would be much less harmed—and some may benefit; the magnitude of harm can also vary within regions and across sectors and populations.
  • Aggregate Damages covers comprehensive measures of impacts. Impacts distributed across the globe can be aggregated into a single metric, such as monetary damages, lives affected, or lives lost. Aggregation techniques vary in their treatment of equity of outcomes, as well as treatment of impacts that are not easily quantified.
  • Risks of Large-Scale Discontinuities represents the likelihood that certain phenomena (sometimes called tipping points) would occur, any of which may be accompanied by very large impacts. These phenomena include the deglaciation (partial or complete) of the West Antarctic or Greenland ice sheets and major changes in some components of the Earth’s climate system, such as a substantial reduction or collapse of the North Atlantic Meridional Overturning Circulation.

All of these reasons for concern enter the red (substantial negative impact, high risk) region by 4°C.  Aggregate impacts are in the red region by 3°C, and some types of concerns are in the red region by 1°C.

For more details we also recommend Mark Lynas' book Six Degrees, which goes through the climate impacts from each subsequent degree of warming, based on a very thorough review of the scientific literature.  A brief review of the book by Eric Steig and summary of some key impacts is available here.  National Geographic also did a series of videos on the Six Degrees theme, which no longer seem to be available on their websites, but which can still be found on YouTube.

This is Why Reducing Emissions is Critical

We're not yet committed to surpassing 2°C global warming, but as Watson noted, we are quickly running out of time to realistically give ourselves a chance to stay below that 'danger limit'.  However, 2°C is not a do-or-die threshold.  Every bit of CO2 emissions we can reduce means that much avoided future warming, which means that much avoided climate change impacts.  As Lonnie Thompson noted, the more global warming we manage to mitigate, the less adaption and suffering we will be faced with in the future.

Realistically, based on the current political climate, limiting global warming to 2°C is probably the best we can do.  However, there is a big difference between 2°C and 3°C, between 3°C and 4°C, and anything greater than 4°C can probably accurately be described as catastrophic, since various tipping points are expected to be triggered at this level.  Right now, we are on track for the catastrophic consequences (widespread coral mortality, mass extinctions, hundreds of millions of people adversely impacted by droughts, floods, heat waves, etc.  But we're not stuck on that track just yet, and we need to move ourselves as far off of it as possible by reducing our greenhouse gas emissions as soon and as much as possible.

There are of course many people who believe that the planet will not warm as much, or that the impacts of the associated climate change will be as bad as the body of scientific evidence suggests.  That is certainly a possiblity, and we very much hope that their optimistic view is correct.  However, what we have presented here is the best summary of scientific evidence available, and it paints a very bleak picture if we fail to rapidly reduce our greenhouse gas emissions.

If we continue forward on our current path, catastrophe is not just a possible outcome, it is the most probable outcome.  And an intelligent risk management approach would involve taking steps to prevent a catastrophic scenario if it were a mere possibility, let alone the most probable outcome. 

Climate contrarians will often mock 'CAGW' (catastrophic anthropogenic global warming), but the sad reality is that CAGW is looking more and more likely every day.  But it's critical that we don't give up, that we keep doing everything we can do to reduce our emissions as much as possible in order to avoid as many catastrophic consequences as possible, for the sake of future generations and all species on Earth.  The future climate will probably be much more challenging for life on Earth than today's, but we still can and must limit the damage.

Advanced rebuttal written by dana1981

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Additional video from the MOOC

Interviews with  various experts


Last updated on 5 July 2015 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Further reading

National Geographic have an informative article listing the various positives and negatives of global warming for Greenland.

Climate Wizard is an interactive tool that lets you examine projected temperature and precipitation changes for any part of the world.

A good overview of the impacts of ocean acidification is found in Ken Caldeira's What Corals are Dying to Tell Us About CO2 and Ocean Acidification

Denial101x video

Here is a related video lecture from Denial101x - Making senses of climate science denial


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Comments 1 to 25 out of 425:

  1. This NY Times article apparently refers to the following document: “Estimating Future Costs for Alaska Public Infrastructure At Risk from Climate Change”
    Response: Many thanks, I've updated the link (under Economical) - always good to go direct to the source!
  2. Malaria spread? It already reaches the Arctic circle how much more could it spread? I know tongue in cheek but some of these things are mutually exclusive.
  3. Malaria is one among others. Italy recently had a brush with Chikungunya (more fun to pronounce, if not to experience). Dengue fever is also to be considered Furthermore, "skeptics" take as fact the idea of "CO2 fertilization" popularized heavily by the propaganda site called CO2Science. However, that fact may not be nearly as much good news as they imagine. Those positives and negatives are still pretty much open to speculation, I remain quite skeptical of the "CO2 fertilization" idea in light of the open air experiments conducted so far.
  4. "Those positives and negatives are still pretty much open to speculation, I remain quite skeptical of the "CO2 fertilization" idea in light of the open air experiments conducted so far." 1. Every last open air experiment so far has CONFIRMED the fertilization effect. 2. Open air experiments may appear to be "streetwise" but they are very much likely to UNDERESTIMATE the CO2-fertilisation effect. Open air experiments sound to me like an appalling waste of money. You either control a factor in an experiment or you do not. Piping CO2 into the area isn't going to have the same effect as having the CO2 homogenised in the air. Since the plant is accessing the CO2 at the molecular level and not at the level of little eddies and wisps of unhomogenised CO2. What looks at first like the streetwise simulation on second thoughts appears to be hopelessly unrealistic. And it appears to underestimate the massive and universal benefit of extra CO2. But nonetheless these experiments CONFIRM this universal benefit. They underestimate the benefit but still they confirm the benefit.
  5. What makes you think that the limits on Rubisco Activase will not manifest themselves? How could it be good to shift the ratio of ATP/ADP toward ADP? Since CO2 level is already quite a bit higher, those bumper crops should already start to show up. Examples? Universal benefit? How is it universal?
  6. And if you dig, you find stuff about methane hydrates and the P/T extinction, so it is a stretch to say there is no justification whatsoever of dire predictions. I'd say that it would be as much of an exaggeration than to predict bumper crops on the basis of the existing CO2 fertilization alone.
  7. In other words Malaria should be removed from the list. Maybe there are other diseases but Malaria which already exists in the Arctic is not one of the bugs that is likely to increase its range due to climate change so its inclusion here is simply wrong. Other diseases would also have to be evaluated case by case and there are many if not more illnesses associated with low temperatures. I haven't had time to research many of these claims but the few I have researched on the negative side are very doubtful, like polar bears being threatened, which is directly contradicted by the available data. This is an old salesman trick of inflating the number of arguments on your side and minimizing the number on your opponents side. It doesn't impress me and it does the AGW argument more harm than good.
  8. Mostly pure speculation; extrapolation without including negative feedbacks is useless and as WA. says, harmful to the argument. ? expanding desert areas? Look at the existing deserts and tell me how they formed and grew BEFORE any AGW effects. Oh, and right now Egypt has drilled over 100 wells into the Sahara bedrock and (so far) found sufficient fresh water for the next 500 years. Thank you satellite radar imaging which showed the underlying ancient river courses and lakes. The same technology shows similar ancient water deposits in Darfur ( the war there is directly attributable to scarcity of water) and the government there has been offered the expertise to explore it...which could end that conflict and turn the country into an oasis. My Point? All the doom and gloom projections NEVER NEVER can account for paradigm shifts caused by technology. ( NY was predicted to end up knee deep in horse **** in the 1800's because of exponential increases in the use of never happened, instead, the automobile did). My point?
  9. What about global warming reduces heating fuel consumption? Philippe: We should hold very lightly info that doesn't have empirical data tacked onto Co2 fertilisation ( or lack of it) Jasper Ridge have been conducting controlled experiments on plants for the past 3 yrs and their data shows 1/3rd increase in biomass if CO2 alone is increased, and up to 85% increase if water/minerals/ temp are optimised WITHOUT extra CO2.
  10. From the Ministry of Ag, Ontario: "The benefits of carbon dioxide supplementation on plant growth and production within the greenhouse environment have been well understood for many years... For the majority of greenhouse crops, net photosynthesis increases as CO2 levels increase from 340–1,000 ppm (parts per million). Most crops show that for any given level of photosynthetically active radiation (PAR), increasing the CO2 level to 1,000 ppm will increase the photosynthesis by about 50% over ambient CO2 levels. For some crops the economics may not warrant supplementing to 1,000 ppm CO2 at low light levels. For others such as tulips, and Easter lilies, no response has been observed." Commercial growers all over the world have invested millions of $ into CO2 enhancement of greenhouses: Given that they are businessmen, if there was no appreciable crop increase they wouldn't be doing it- No? Now I would call a 50% increase in crop mass substantial, maybe not BUMPER, but clearly enough to warrant the cash investment. So there is plenty of empirical, current, evidence that raising levels of CO2 causes plants to grow bigger and faster. It isn't an issue, it's a fact. Just as clear is that concentrations up to 1000ppm the Rubisco Activase limit does not manifest.
  11. Can Carbon Dioxide Be A Good Thing? Physicist Explains Benefits Of Carbon Dioxide June 1, 2007 — A physicist from Colorado State University and his colleagues from the North American Carbon Program (NACP) have discerned and confirmed the unforeseen advantages of rising carbon dioxide levels. Through the processes of photosynthesis and respiration, scientists have been able to elucidate why plants are growing more rapidly than they are dying. The NACP is employing methods, such as the use of cell phone and aircraft towers to monitor and retrieve carbon data for their continuing study.
  12. Well John after much reading I think this is a thread where you are likely wrong. I have read a lot of claims that CO2 increasing yields is a myth, however in controlled experiments it really tends to have a large positive effect. Some have even claimed that it doesn't work in the "Real World".. A good argument sometimes but one that doesn't work very well here. If CO2 increases yields under controlled conditions but this is not seen in the real world that would in fact strongly suggest that our readings of CO2 increasing were incorrect not that CO2 doesn't help. That would be an interesting thing to investigate.
  13. Lets look at this from a logical perspective. Warmer means more like the world that we evolved in during the PETM (when prosimians first appear) in Asia. Colder means more like the world that came close to driving us to extinction (glacial maximum) in Africa. We are from a tropical paradise, no polar ice caps and green pole to pole. Which do we wan't for our offspring? Warm and abundant or cold and starvation?
  14. #14....Most of the examples of increased CO2 giving increased plant growth have come from environments where the CO2 level is artificially held at around 1000ppm. In the real world the levels have risen from around 260ppm (1000AD) through 290ppm (1900AD) to 380ppm (2005), in other words the increase over the period we have started taking interest in what's going on is at best 100ppm. Roughly, doubling the level gives a 50% increase in growth, so adding a third (real world) isn't going to show up much at the small scale level. Globally, however, the increase may be significant, although probably unquantifiable
  15. A good book on this topic: This book has hundreds of references to objective peer-reviewed studies on the effects of global warming, at each degree C in global temperature rise. Essentially, costs immediately exceed benefits. With each degree of warming, the cost-benefit gap expands greatly.
  16. Millions of years ago, climate conditions were such that plant life grew rapidly on a global scale. CO2 and WV levels were high enough to sustain this growth and during this period much of the FF's we now burn were laid down. Plant life sequestered CO2 and locked it up as FF, thereby reducing the CO2 levels, although at times, 'natural' events such as vulcanic erutions/forest fires would have temporarily offset this sequestration. The end result is that CO2 levels hit (possibly) an all time low of around 200ppm and stayed there. As this level is close to the minimum C3 plants can tolerate, further growth and investment of new habitat were resticted. At this time, only C3 plants existed (fossil records of C4 plants indicate their emergence around 8mya) and C3 plants, in order to prosper, require CO2 levels higher than 200ppm. If the levels fall below this figure, then growth effectively halts as does sequestration. One can argue that the emergence of C4 plants was 'caused' by persistent low levels of CO2 - an adaptation of metabolic process to environmental pressures - and since they are more efficient in their use of CO2,(they had to be) they began to colonise and modify habitats where C3 plants could no longer compete effectively. C4 plants are grasses, and include the cereals. The rise of civilisation was made possible only because of these plants and man's ability to husband them, so we actually owe our existence to low levels of atmospheric CO2. Current concern is directed at enhanced CO2 levels through burning FF's, and the (modelled) effects this may have on climate, and the consequent impact on man's habitat. The current level of around 380ppm, whilst nearly double that during the period C3 plants were dominant, is still towards the lower level of tolerance for them. It can therefore be argued that further increases of CO2 will be beneficial to this class of plants and not detrimental to C4's until levels exceed 1000ppm; in other words, our CO2 emissions are helping C3 plants, and quite possibly helping (in some small way) to offset the losses incurred by de-forestation. Yes, they may be disadvantages to mankind and his preferred lifestyle/habitat from CO2 enhancement, but there are benefits to the biosphere at large.
  17. High Carbon Dioxide Boosts Plant Respiration, Potentially Affecting Climate And Crops ScienceDaily (Feb. 10, 2009) "The leaves of soybeans grown at the elevated carbon dioxide (CO2) levels predicted for the year 2050 respire more than those grown under current atmospheric conditions, researchers report, a finding that will help fine-tune climate models and could point to increased crop yields as CO2 levels rise."
  18. "This book has hundreds of references to objective peer-reviewed studies on the effects of global warming, at each degree C in global temperature rise. Essentially, costs immediately exceed benefits. With each degree of warming, the cost-benefit gap expands greatly." How much colder should the earth be to idealize the benificial ascpect for man. Of course I am most intested as to what "peer reviewed" studies have concluded. Another thing I am most intersested in is what "peer revied studies" have concluded thet the DOW jones should be at by the year 2025. Dont you alarmists have any sense of humility as to what you think you know. For the record "peer review" is simply a call for rudimentary error checking - it is not thesis confirming and it is by no means systematic, thorough, or even unbiased. It has its place but it is neither an essential nor required component of sound science. Theory confirmation is derived by outcome - not opinions of self proclaimed "experts"
  19. Some of your pros and cons listed above and not correct. The longer geological record contradicts statements made by the IPCC and other climatologists, because the IPCC and other climatologists don't usually bother to consult the longer geological record, and the usual argument from climatologists is that 'geologists are not climate scientists', which is false; climate is a subset of geology (earth science), not the other way around, (with both ultimately a subset of astronomy). The longer geological record has much to say about the lists you have given above, for eg: -Increased desertification corresponds to globally cool periods, NOT warm periods, in the geological past, (which is the opposite of what the IPPC projects). This genrally means that African and the US, and some Asian crop yields will increase with warming, not decrease. Globally, there is more rainfall. Africa, for example, began to become drier with the onset of glacial periods several million years ago, with larger areas of savannah and reduced rainforest cover, (which may well have led to the evolution of the savannah-ape line-that's us). -Warm periods do not correspond with increased extinction in the geological record, rather, biodiversity increases (which is the opposite of what the IPCC projects) -Coral reefs thrive during sea level rise, whilst sea level falls produce extinction. -Coral reefs thrive during warmer periods, and oceans do not become acidic from greatly increased C02; there were many periods of thriving corals and other marine life in the geological record when C02 was much higher than today. -Polar bear populations have survived the many warm interglacials in the last several hundred thousand years, warmer periods do NOT promote their extinction. The bigger threats to polar bears are ecotourists, bureaucrats, and hunters. -The Tibetan plateau began to rise around 30-40 million years ago; changes in short -term climate are paradoxical and not thought to greatly affect water supply/runoff in this region as much as longer period changes in elevation; as during globally warmer periods snow (and rain) precipitation increases along with seasonal meltwaters-particularly on the Chinese (cooler) side, whilst in cooler periods ice and snow cover increases but overall precipitation and seasonal meltwater generally decreases. Other points: -Crop yields at all latitudes increase with increased C02, (already an estimated 15% since about 1850), the same goes for tropical rainforests,(the Carboniferous period had high vegetation levels and high C02-much higher than at present) -Both Europe and USA have thrived in warmer periods, both ecologically (in the past) and economically during human occupation eg reduced energy consumption for heating, increased rainfall, less droughts, less deserts (USA). -Lakes do no "vanish" on a global scale during globally warmer periods; if anything it is generally the opposite (point 1 above-lower desertification occurs during warmer periods). I could dig up alot of other longer geological record indices, but again, what surprises me is the complete ignorance amongst many who promote various global warming scenarios/projections on what the actual record of the earth itself has to say on these matters. A similar thing occurs with creation scientists, and in various discussions and debates within biology about evolution; the longer geological record is usually ignored (other than the usual-'the fossil record is incomplete'), when it was the geological record that formed the general foundation about thinking about evolution in the first place, and has alot to say about it. Another related topic is the long history of debates around catastrophism and uniformitariaism-which also have much to say about current issues/debate concerning global warming-but that is for another day and another thread. In general, there needs to be more input/integration from the actual geological record on various climate change scenarios/issues, which directly contradict some of the (surmised/projected) points in your list above.
  20. Plants can't grow any better than their limiting factor, which might be not CO2, but nitrogen, water, light,.... Some plants grow worse at higher temperature, offsetting gains from CO2 spurring growth. Even if they do grow "better," the betterment often is not to the advantage of farmers; for example, the extra mass can go into non-consumable woody stalk, which makes the crop more expensive to process than any extra grain/fruit value. And weeds such as poison ivy and kudzu respond much "better" to increased CO2 than do many crops, but "better" is not better for people, and not better for plants that those weeds compete with. For details see the U.S. Department of Agriculture's report on climate change.
  21. I feel that the positives vs. negatives are somewhat biased toward the negative side. For instance, on negative, it says decreased water levels three times, and specifies each individual area where the water supplies will decrease each time: * Decreasing human water supplies... (Solomon 2009) * Decreased water supply in the Colorado River Basin (McCabe 2007) * Decreasing water supply to the Murray-Darling Basin (Cai 2008) However, on positive, it only says: Improved agriculture in some high latitude regions (Mendelsohn 2006) It does not specify what countries or regions, which could inflate it to several points. Seeing as that has been done with the decreasing water supply, I think the same should be done for the positives.
    Response: This is solely because I'm referencing individual papers. I suggest you take a leaf out of Shawnhet's book and find some positive papers focusing on benefits in specific regions.
  22. Re Glacier Melt, Barnett 2005, Kehrwald 2008 and 'Severe consequences for one-sixth of world's population dependent on glacial melt for water supply': I wasn't going to bother with this tabulation any more (for reasons already given) but I can't let this slide. Barnett's 'one sixth of the world's population' refers to both snowmelt and icemelt - mostly the former, of course. Kehrwald's 'one sixth' is either a misattributed misrepresentation of Barnett or pure invention. Either way, it's gibberish. If you're genuinely interested in presenting a fair picture of the science, the least you can do is remove the Kehrwald reference and add something that highlights the importance of snowmelt to this alleged one sixth. Personally, I'd remove the whole thing. Barnett was based on a very dodgy analysis.
    Response: I notice Kehrwald 2008 cites the IPCC AR4 as their source so until I track down the IPCC's peer-reviewed source (most likely Barnett 2005), I've removed Kehrwald. I find it interesting that you'd 'remove the whole thing' - do you think the whole issue of threatened water resources for such a large proportion of the population is not worthy of concern?
  23. JC: 'I notice Kehrwald 2008 cites the IPCC AR4 as their source so until I track down the IPCC's peer-reviewed source (most likely Barnett 2005), I've removed Kehrwald.' Would that help? Kehrwald et al. offers several contradictory estimates of the number of people in South and East Asia who rely on water from melting glaciers. Would a peer-reviewed source for any of them really confer legitimacy on self-evident nonsense? Kehrwald's largest estimate: 'TP ice fields are a critical resource for one sixth of the world’s population'. 'TP' is 'Tibetan Plateau'. In Kehrwald, 'Tibetan Plateau' has at least three different meanings. Let's assume that this one was 'Himalayas plus Karakorams plus Hindu Kush plus Pamirs plus the Tibetan Plateau proper and the mountains on its western and northern rims'. Are the glaciers in this large region a 'critical resource for one sixth of the world’s population'? Er, no. Does any peer-reviewed literature say that they are? Probably. Does Kehrwald's cited source say that they are? No. The 'one-sixth' claim was attributed to AR4 WG2 Chapter 10, which says nothing of the kind. If not pure invention, it was probably a misattributed mangling of Barnett, which claimed (on very dodgy grounds) that 'more than one-sixth of the Earth’s population [relies] on glaciers and seasonal snow packs for their water supply'. Snow *and* glaciers. Worldwide, not just 'TP'. And note that Barnett's 'one-sixth' didn't include people living on the Gangetic plain. (He got something right.) The only other attributed claim in Kehrwald (750 million seriously affected) comes, it is said, from the Stern Review via WG2 Ch10. Stern did say something like that but its cited sources didn't support it. Things get complicated here, so I won't go further unless you insist. JC: 'I find it interesting that you'd 'remove the whole thing' - do you think the whole issue of threatened water resources for such a large proportion of the population is not worthy of concern?' I find it interesting that you are happy to accept that the water resources of such a large proportion are threatened. Peer-reviewed crap is still crap.
  24. Vinny Burgoo at 11:37 AM on 11 March, 2010 When assessing the importance of any single component of a population's water supply, it is important to remember that water needs to be available always, and the available quantity required at any given time is bounded by definite lower limits. I've seen a lot of criticism of water supply impacts based on the notion that "only" 20%, 10% or 5% of a given total regional water supply is sourced by glacial and snowpack meltwater. If during certain times of the year the component that is only 20% of an annual supply represents 50% of the instantaneous available flow, the perspective of persons depending on that supply will be rather different than for those of us sitting in our armchairs at safe remove, wondering what the problem is. Not to be repetitious, but tell an engineer that you're going to remove reservoirs supplying 20% of a water utility's capacity and he should not worry because the annual total amount of water passing by his system will remain the same and that engineer will think you crazy. As to the rather arbitrary separation of snow and ice meltwater sources, if as we can expect glacier disappearance is accompanied by more rapid melting of snow the current budgetary components of melt water sources are of less use in predicting future impacts of glacier loss. This hair-splitting about impacts of changes in regional water supplies resulting from warming is at the end of the day not very flattering to so-called skeptics. Rummaging around for minor flaws in citations is not a robust counter-argument.
  25. Robust counter-argument against what, doug_bostrom? It's certainly a good argument against political overreaction. Does it really not concern you that bogus claims are being made about the water supplies of one-sixth of the world's population? (Yes, I did read your lecture about seasonal flows etc. Meltwater from Kehrwald's 'TP' glaciers mostly coincides with the monsoon, when the glacial component is more like 2%, not 20%. So where is this one-sixth of the world's population? Not in the oases of Western China, which do rely to some extent in summer on glacial melt. That's most likely bad news for tens or scores of millions who live there but 100 million is not 1000 million. Exaggeration is neither scientific nor big nor clever. Also, your conflation of snow- and glacier-melt was... unhelpful.) Like many of your stripe, you are hung up on the denial of the theoretical basis for AGW. Things have moved on. Impacts are what matter and the science of predicting impacts is demonstrably weak and overstated. The whole field is less than scientifically kosher and large areas of it are politicised. It really shouldn't be up to ordinary 'hair-splitting' citizens to sort this out. It takes hours and days for a non-specialist to track back a single claim to its source and evaluate it. The IPCC is supposed to have done all that for us. It hasn't. I'm pissed off. Don't be surprised that a lot of other people are pissed off. And if you're not pissed off too, that isn't very flattering to you, especially when you're posting on a website called Skeptical Science. (Pre-emption: Yes, Kehrwald et al was published post-AR4. Will it be in AR5, though? Let's bloody hope not. Barnett too.)

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