Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


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.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


Return to the Himalayas

Posted on 29 June 2010 by Doug Bostrom

Guest post by Doug Bostrom

Seemingly eons ago in the Internet gossip universe yet a scant six months past in solar time here on physical Earth, the IPCC was taken to task for employing a sadly squishy and wrong reference having to do with Himalayan glaciers and their hypothetical shrinkage rate. Self-professed anthropogenic global warming skeptics jumped on this fault with both feet, helping to fuel and then briefly basking in an explosion of negative press coverage emphasizing this single error in thousands of references, found in the WGII section of the 2007 IPCC Fourth Assessment Report. John Cook treated this blemish on an otherwise nearly faultless record here on Skeptical Science in a blog post.

Despite the IPCC's established "four nines" citation reliability and generally scrupulous and circumspect nature, the Himalayan brouhaha encouraged the organization to review its processes with an eye to even better diligence, while ignoring some vitriolic and arguably irrational demands by pundits and enthusiast doubters of mainstream science for shaming and dismissal of IPCC personnel and scientific talent. The dust-up also illustrated how our state of knowledge about the Himalayan glaciers and how they're responding to global warming needs further work. This was news to many of us but not to scientists who as we shortly will read carried on with the topic, appropriately ignoring public opinion. 

Before continuing our return to the Himalayas, let's think about how we're going to travel. 

From a bystander's perspective the collective mechanism of scientific progress may resemble a pachinko machine. At top is the area of relative ignorance and at the bottom lies a state of better information. Akin to a pachinko machine's little balls, scientific inquiries begin from ignorance and inexorably rattle their way to enlightenment via often tortuous paths. It's vanishingly rare that a line of inquiry springing from a viable hypothesis gets intractably "stuck", unable to progress to answers lying at the bottom of the course. Equally it's rare that two researchers should choose the same precise steps of investigation and arrive at identical results when observational and other limitations impose uncertainties. Despite this seemingly chaotic lack of organization, our human compulsion to gain insight invariably leads to better understanding of our world. As with a pachinko machine's payoff, as inquiries wend their way to conclusions they may land at more or less valuable results but unlike a pachinko machine the ultimate worth of research findings is not random.

All pachinko balls are created equal but the value of a researcher's work product is guided by a diverse set of skills, including those of posing tractable questions or formulating testable hypotheses, enrolling collaborators, reliance when needed on other complementary investigations, and choosing and successfully employing appropriate investigative methods. Perhaps as important as any other attributes, successful researchers combine ample self-confidence tempered with a healthy dose of humility and awareness of disciplinary limitations.

Now let's return to the promised topic of this post, where we find science has been quietly progressing while heated words were flying elsewhere in the world. 

While IPCC reports encompass many areas of still-active research, the matter of the Himalayas is exemplary of how research progresses. Different investigators follow slightly different paths while seeking the same general destination, drawing on other previous work and suspicious of large discontinuities between their own findings and those of others. John's article explored some past research on Himalayan glaciers and their impact on regional hydrology and human culture. Now come Walter Immerzeel et al (Climate Change Will Affect the Asian Water Towers, Science 11 June 2010: Vol. 328. no. 5984, pp. 1382 - 1385 ) who have followed their curiosity about the Himalayas by employing a new combination of methods, thereby presenting us with some fresh information and possibly improving on earlier results. They refine estimates of rain, snowfall and glacial hydrological contributions to stream flow and ultimately agriculture in regions fed by many Himalayan glaciers as well as taking a stab at reducing uncertainty surrounding the future condition of those glaciers. Both arenas of learning are thus mapped a little more thoroughly, one more than the other.

The abstract:

More than 1.4 billion people depend on water from the Indus, Ganges, Brahmaputra, Yangtze, and Yellow rivers. Upstream snow and ice reserves of these basins, important in sustaining seasonal water availability, are likely to be affected substantially by climate change, but to what extent is yet unclear. Here, we show that meltwater is extremely important in the Indus basin and important for the Brahmaputra basin, but plays only a modest role for the Ganges, Yangtze, and Yellow rivers. A huge difference also exists between basins in the extent to which climate change is predicted to affect water availability and food security. The Brahmaputra and Indus basins are most susceptible to reductions of flow, threatening the food security of an estimated 60 million people.

Some of the public discussion ensuing from the IPCC's Himalayan citation error focused on  significance for humans of loss of glacial ice. How much do these glaciers count in the supply of water for consumption downstream by agriculture and other uses? Does rainfall dominate the hydrology? What about snowpack?

For assessing the relative importance of meltwater from snow versus ice Immerzeel uses a measure known as "Normalized Melt Index" (NMI), defined in the paper as "...the volumetric snow and glacier upstream discharge divided by the downstream natural discharge." NMI is considered a superior metric compared to meltwater fractions of total discharge, being less susceptible to distortions by impoundments and midcourse withdrawals.

The authors describe their findings on relative proportions of water contributions by meltwater type:

Results from the NMI analysis indicate that for the present-day climate, meltwater plays an important role in the Indus and Brahmaputra river basins. This is most evident in the Indus: Discharge generated by snow and glacial melt is 151% of the total discharge naturally generated in the downstream areas. In the Brahmaputra basin this amounts to 27%. The contribution of snow and glacier water to the Ganges (10%), Yangtze (8%), and Yellow (8%) rivers is limited owing to comparatively large downstream areas, limited upstream precipitation, smaller glaciers, and/or wet monsoon-dominated downstream climates. In the Indus and Ganges basins, about 40% of the meltwater originates from glaciers, whereas in the other basins the glacial melt contribution is much less.

Graphically, the proportional contributions appear like so:

What about the glaciers' fate? Well, we already knew they were not going to shrivel out of sight by 2035. Immerzeel applies GRACE-derived gravimetry to gain more insight on the state of Himalayan glaciers. We learn a bit more, it is confirmed that the health of the ice in the Himalayas is regionally diverse, is in a state of decline on the whole, is not at imminent threat of disappearance but will likely decline sufficient to have a sizable impact on certain major rivers fed by the Himalayan hydrological system. We can  surmise that investigations of this topic will continue because results are ambiguous, leaving an unsatisfied hunger for more information:

We used the DMT-1 GRACE gravity model in combination with derived precipitation trends to identify large-scale trends in snow and ice storage in each of the five basins. Results were inconclusive. We identified a negative trend of -0.22 +/- 0.05 m year-1 only in the Ganges basin. A positive trend of 0.19 +/- 0.02 m year-1 was observed in the Indus basin, while in the other basins no discernable trends were identified. On the basis of this review, we conclude that there is a general decrease in the ice volumes of Asian basins, although regional anomalies exist and, as regional quantification of these trends is lacking, the uncertainty about these trends is substantial.

Pursuant to our pachinko analogy, beyond Immerzeel a number of other lines of inquiry on glacier status in the Himalayas have proceeded since IPCC 2007 published the synthesis of research done prior to that year. Other researchers use the same or different data than does Immerzeel and arrive at roughly consistent but not identical conclusions. While zooming our viewpoint from the macro to the micro scale we can visit a few of many recent publications and summarize that withal we see a number of indicators of declining glacial health and some hints of acceleration of the process.  Matsuo and Heki (Earth and Planetary Science Letters Volume 290, Issues 1-2, 15 February 2010, Pages 30-36) also resort to GRACE data-- as with Immerzeel attempting to account for anthropogenic groundwater withdrawal-- and report a regional ice loss of 47 +/- 12 Gton/year, equivalent to sea level rise of some 0.13mm/year, as well as significant loss acceleration over the past 40 years. Scrutinizing from space a single specimen, the Hailuogou glacier in Tibet, Zhang et al (Journal of Glaciology, Vol. 56, No. 195, 2010) find thinning of about 1m/year, again with apparent acceleration in recent decades. Direct water flow measurements from the same glacier are performed by Qiao et al (Journal of Glaciology, Vol. 56, No. 196, 2010) and are consistent with remote sensing results, showing an increasing annual meltwater surge correlated with rising temperatures at nearby weather stations. 

No rest for us laypersons looking to clench arguments about exactly how much ice will vanish by when, but nonetheless we see fresh research findings appearing to support and better resolve earlier rougher results suggesting regional loss of ice in the Himalaya accompanied by acceleration. Our collective dissatisfaction with our acuity on this subject can be measured by scholarly activity; an unscientific indication of the intensity of effort in this narrow area is that a Google Scholar search on the term "himalayan glacial mass balance" reports over 1,000 publications since 2009. We can be confident that our comprehension is steadily improving and we'll be able to track progress by watching the decline of research productivity on the general topic of Himalayan glacial mass balance.

Turning back to Immerzeel, because they are reasonably confident with GCM applications his team goes on to make projections about what's in store for Himalayan water sources and downstream consumers:

We made projections of future upstream discharge using a hydrological modeling approach that incorporates uncertainty about the cryospheric response by employing a scenario analysis. The hydrological model SRM simulated the present-day discharge with acceptable accuracy. To provide a multimodel assessment of future water availability from the upstream river basins, we forced the SRM model with outputs from five general circulation models (GCMs) for the SRES A1B scenario over the period 2046 to 2065. In addition, two different scenarios of future glacier size were modeled: (i) a best guess based on glacier mass-balance calculations assuming trends in degree days and snowfall between current time and 2050 (calculated by the GCMs) to be linear, and (ii) an extreme (and unlikely) scenario with total disappearance of all glaciers to serve as a reference.

As many of us have speculated, the response of individual rivers to changing climatic conditions will vary, because the situation upstream for each river is diverse in terms of rain, snowpack and glacial contributions to flow as well as different climate regimes downstream. Indications of future behavior of affected rivers are summarized:

The best-guess glacier scenario resulted in a modeled decrease in mean upstream water supply from the upper Indus (-8.4%), the Ganges (-17.6%), Brahmaputra (-19.6%), and Yangtze rivers (-5.2%). Although these changes are considerable, they are less than the decrease in meltwater production would suggest, because this reduction is partly compensated for by increased mean upstream rainfall (Indus +25%, Ganges +8%, Brahmaputra +25%, Yangtze +5%, Yellow +14%). The analysis even shows a notable 9.5% increase in upstream water yield in the Yellow River because this basin depends only marginally on glacial melt

Annual future streamflow model results in graphical form:

Overall there's at least some good news here, if the models the paper relies on are reasonably predictive. Immerzeel suggests that unlike some other emerging scenarios the IPCC AR4 report may have overestimated impacts of climate change on the overall hydrological system fed in part by the Himalayas. The Yellow River in particular may experience a longterm improvement in flow characteristics.

Not all change is good. In this case the result of the accidental modification of the Himalayan hydrological regime looks to be distinctly negative for two major rivers:

Regardless of the compensating effects of increased rainfall in the two basins with the largest NMI, the Indus and the Brahmaputra, summer and late spring discharges are eventually expected to be reduced consistently and considerably around 2046 to 2065 after a period with increased flows due to accelerated glacial melt.

What's the net result in terms of impact on people living in the region? We're not looking at a direct threat to the feeding of half a billion persons, a few millions may see actual improvement in food supply but we're left with a "residual" of some sixty million persons whose access to food will be degraded:

By relating changes in upstream water availability to net irrigation requirements, observed crop yields, caloric values of the crops, and required human energy consumption, one can estimate the change in the number of people that can be fed. The results (based on a best guess of 2050 glacier area) show a sizable difference between the five basins. Estimates range from a decrease of -34.5 +/- 6.5 million people that can be fed in the Brahmaputra basin to -26.3 +/- 3.0 million in the Indus basin, -7.1 +/- 1.3 million in the Yangtze basin, and -2.4 +/- 0.2 million in the Ganges basin, and an increase of 3.0 +/- 0.6 million in the Yellow River basin. In total, we estimate that the food security of 4.5% of the total population will be threatened as a result of reduced water availability.

Immerzeel finishes with some sobering remarks, including that "...Asia's water towers are threatened by climate change, but that the effects of climate change on water availability and food security in Asia differ substantially among basins and cannot be generalized." The analogy of Asia's high altitude water resources to a "water tower" is elegant and useful. It's easy to dismiss the loss of ten percent of a region's water supply as insignificant in the grand scheme of things, but imagine proposing to an engineer responsible for the operation of a municipal water district that ten percent of his reservoir capacity was to be removed for no reason but an anticipated accident that might be avoided. What would he say and how would we justify allowing the accident to happen? Just as many natural features are in a state of equilibrium with their environment, so is much of human culture. Our systems and behaviors are adapted to our environment and if those surroundings change too rapidly we'll be stressed, often with needless suffering.

Immerzeel's paper has some things to tell us of a more general nature having to do with our perceptions. With respect to the unusual degree of public attention on the process and progress of science as it relates to climate research, the paper is a fine example of how-- despite our often overenthusiastic cheering and razzing from the stands with wild speculations about motivations and biases-- scientists are not participants in a team sport but instead are following paths largely transcending the buffeting of politics and human affairs. Although it appears to circumscribe the most recent IPCC report's projections with refined, conservative and possibly better results, Immerzeel et al are published in AAAS' journal Science, a top-ranked, elite publication; "Groupthink" does not seem to be in evidence here.  As we'd expect on a continuum of better cognition this paper does not suddenly overturn previous findings but rather largely improves upon them. Immerzeel's research will be incorporated according to its merits into our pyramid of information and will likely be accounted for in the next IPCC report now in its nascent stages. From all this we may reasonably conclude that despite our fixation with defects, regardless of scientific inquiry's intrinsically unorganized and sometimes to the layperson confusing features, science functions effectively, rattling its way forward regardless of noise in the gaming hall of human society at large.

As a parenthetical note, New Scientist will probably manage to continue fueling irrelevant controversy on this matter, indirect though their original involvement was. In their coverage of Immerzeel et al New Scientist manages to both over and understate the conclusions, starting with the headline Himalayan ice is stable, but Asia faces drought and concluding with the observation " 2050, 60 million fewer people-- 4.5 per cent of the world's population-- will be able to feed themselves using water from the Brahmaputra, Ganges, Yangtze and Indus, which supports the world's largest irrigation system." Astute SkS readers will no doubt be delighted to point out the problems in that presentation.

0 0

Printable Version  |  Link to this page


1  2  Next

Comments 1 to 50 out of 52:

  1. Sorry for the off-topic nitpicking, but you've misspelled "pachinko (パチンコ)" in an otherwise excellent post. (I hope the katakana reproduces in other browsers and machines.) And please don't accuse me of pedanticness. The word is "pedantry".
    0 0
  2. Thank you, Johnny. Indeed you're right, I don't know how I missed that; I actually read the Wikipedia article while selecting my analogy. Scurrying to correct it...
    0 0
  3. Well, 4.5% of the current world population would be 301,376,432; in forty years it'll be something like 420,000,000. So, math FAIL. Also you can't "feed" yourself using water.. not for long, anyway.
    0 0
  4. Ding-dong-ding! Paul gets the prize for being first to winnow a New Scientist error. In fairness I think it was down to some ambiguous language in Immerzeel, who refers to "total population" without a reminder that the term refers to the region under scrutiny. I made the same mistake when reading the paper but had the luxury of having time for my intuition to illuminate a caution lamp and consequently check the figure.
    0 0
  5. Try feeding yourself WITHOUT using water, Paul Daniel Ash. In a rice field it takes around 2,500 litres of water to grow a single kilogram of rough rice.
    0 0
  6. You have not quite come back to the Himalayas, but to the greater mountainous region of the Central Asia. Let us tentatively call it the greater Himalayas. There were actually two problems in the Asian chapter (Chapter 10) of IPCC AR4 WG2. One was the outlook of diminishing glaciers in the (proper) Himalayas in the Section 10.6.2. It was really erroneous. Another thing was the estimate of population who depend on glacier meltwater of the "greater Himalayas". In Section, it was written that "Climate change -related melting of glaciers could seriously affect half a billion people in the Himalaya-Hindu-Kush region and a quarter of a billion people in China who depend on glacial melt for their water supplies (Stern, 2007)". Stern Review may be a good reference for economic matters, but not an original reference suitable here. In Stern Review, it appears in Chapter 3 "How climate change will affect people around the world", section "3.2 water", page 63. It refers to the following paper in the Note 23 and it is surely the source of the information. Barnett, T.P., J.C. Adam and D.P. Lettenmaier, 2005: Potential impacts of a warming climate on water availability in snow-dominated regions. Nature, 438, 303 - 309. IPCC AR4 WG2 directly refers to Barnett et al. (2005) in Chapter 3 (Freshwater resources and their management), Sections 3.4.1 (Surface waters) and 3.4.3 (Floods and droughts). The paper by Barnett et al. is a peer-reviewed article. And its estimate of population who depend on meltwater from snow seems to be reasonable, though it is different from the estimate of population who are likely to be affected by decrease of snowpack associated with global warming. But it did not distinguish snowmelt and glacier-melt. But Stern Review and consequently IPCC AR4 WG2 Chapter 10 mis-interpreted it as mainly glacier-melt. Also there is a problem in the paper of Barnett et al. that their numbers about glacial meltwater and population are not fully substantiated by their references 40, 41, 42 and 43. It seems to be an issue of sloppiness in the editorial process of the "Nature" magazine rather than of IPCC. The study by Immerzeel et al. (2010) is very welcome and it will supercede Barnett et al. (2005) in terms of estimate of population who depend on snow and glacier meltwater. But we should note that Immerzeel studied five large river basins. We should also look at inland river basins to the north of the Tibatan Plateau, where glacier meltwater has the largest relative role, though the human population density is relatively low.
    0 0
  7. Thank you for your remarks, Kooiti. You make a fair point about the distinction between the Himalayas and the region covered by Immerzeel. In fact, the title of the article I feature is "Climate Change Will Affect the Asian Water Towers" and I now see that not only does my title not reflect that but I actually managed to -not- mention the article title once in my little writeup. The latter I'll somehow fix but I think I'll leave the title as-is because I think it's helpful to give folks an explicit pointer to updated information behind the Himalaya reference fiasco. Thanks also for your remarks about population details as well as your taking time to supply some pointers for people wanting to go further with that. In a way your points are complementary to mine in that we can see how resolution of this sort of information improves over time. W/regard to Barnett's own issues w/cites as well as "data bruising" as information is passed from one publication to another I have (is it any surprise) an opinion about that but not I think one that is very controversial in terms of intent, though it could become significant when viewed from the perspective of relying on reviews if not handled properly. The least ambiguous and most accurate description of any research paper's content is harbored in the original paper itself. By necessity not all information from a paper is conveyed when another researcher or reviewer dips into a given paper for supporting information and so real diligence must be practiced in this crucial hand-off. Unless the dependency in question is unusually atomic there is room for ambiguity and even error to creep in; ambiguity accompanies insufficient characterization as does error. Authors of reviews and synthesis reports are at the end of a longer foodchain, the information they draw from has passed through more hands and thus is more susceptible to damage. I think it's safe to say this problem of conclusion creep or divergence is one reason why it's such a good thing that IPCC has built what appears to laypersons as a pathologically obsessive review process, drawing on the awareness of publishing scientists of how easy it is to mess up information as it is passed along. Cases of error in spite of fanatical attention to details are a cue to how demanding this process really is. Apparently IPCC is going to amp-up their reviewer scrutiny still farther, a sign of the relative urgency attached to the task of keeping the IPCC synthesis up to date even while drawing on active avenues of inquiry. Time appears of the essence in this case, we don't have 100 years to wait for dust to collect on researchers' work before before being supplied with information to assist with mitigation and adaptation.
    0 0
  8. Thanks Doug, I'll just offer this new paper for now which raises the idea that the Himalayan catchment areas may be less susceptible to glacier mass balance changes than believed. Suggesting precipitation dominates the hydrological system of the region.
    0 0
  9. "It's easy to dismiss the loss of ten percent of a region's water supply as insignificant in the grand scheme of things, but imagine proposing to an engineer responsible for the operation of a municipal water district that ten percent of his reservoir capacity was to be removed for no reason but an anticipated accident that might be avoided." I'm not accusing you of anything here Doug but there seems buried in this comment one of the bigger problems of developing nation. They are more susceptible to the variations that nature can throw at them no matter what the underlying reason. One way to mitigate any future water shortages might be for these nations to produce more water engineers and take control of their water supplies. It's ironic dam projects in China and India, which might help these nations gain better control of this resource have often been criticized by the environmental lobby. On a more general point. It does seem the problem with this science is now it is expected to give more black and white answers to problem thrown at it by policy and politics were in fact the situation is more grey. Maybe New Scientist is pandering to much to this rather than remaining firmly buried in the science.
    0 0
  10. Thanks for the pointer to the paper, HR. More refinement with cautious conclusions. For me the takeaway on was that future behavior of monsoons is going to be a key determinant of how stable the region remains for cultivation, more so for those areas where solid-state storage counts and diminishes, and we need to understand monsoons better. W/regard to engineered structures they can certainly help but for me to the extent we can avoid stressing both nature and ourselves by avoiding the need to create dams and the like the better. I'm personally a fan of dams but we've sometimes been pretty thoughtless about where they're implemented and of course they cost money. As well, they sit in a nest of complications when transnational rivers are involved. For a truly astonishing example of engineered responses to climate change see this example: Chinese engineers propose world's biggest hydro-electric project in Tibet Comes with strings attached, because nothing's simple in the hands of us humans. China-India history, new dams across upper reaches of Brahmaputra, rationality about net effects downstream may well take a back seat to festering wounded feelings.
    0 0
  11. I don't know where you live Doug but Western Europe has 'controlled' and reshaped every major river system in the region. And yet the earth continues to turn and the sun continues to rise. Those opposed to dams and the like need to realise we could be denying developing nations the benefits that have come with this successful Western European experiment.
    0 0
  12. Hi HR, sorry I did not notice your comment until now. Funny thing is, I live in a place where nearly all our "juice" comes from hydropower. Turns out we overdid it a bit and it appears we will be selectively removing a few dams because they've seriously interfered w/salmon runs, causing negative impacts on some sectors of the local economy. Choosing to remove these dams has been a delicate decision process because their utility has of course been integrated into our local systems in a way that needs unraveling without excessive harm. It's all a question of balance and poise, I believe.
    0 0
  13. At the moderator's request, I am posting here.

    On this thread: Global Warming in a Nutshell

    Gary M writes:

      What happens when the planet gets warmer? ...receding glaciers have consequences, such as ... disappearing fresh water supplies for billions of people.

    I replied:

    If a glacier disappears, it will still rain and snow in the watershed where the glacier was and the rivers in such watersheds will still flow.

    This answer followed:

    The amount of water that flows in a river is a function of the precipitation that falls in the water shed minus evaporation and plus or minus the contribution of receding or advancing glaciers if there are any.

    Currently many glaciers are receding, and as such more water flows in the rivers than is falling as rain or snow. When the glaciers either stop receding, or disappear, flow of water in the rivers will decrease.

    If "Global Warming" schemes actually prove out to be successful in stopping the recession of the world's glaciers, the reduction of water flow in these areas will occur sooner.

    This discussion will eventually boil down the difference in melt rates between ice and snow.

    0 0
  14. Steve @ 13... "This discussion will eventually boil down the difference in melt rates between ice and snow." Don't you think this is exactly the problem? Warming is anticipated to enhance the hydrological cycle. That means both wetter and drier conditions. Glaciers, as I understand it, act to buffer the normal variation in wet/dry cycles of weather. This would act to keep the water supplies downstream more consistent, and is why large populations have developed in these regions. If we deplete that source of fresh water then those downstream populations will be subject to greater extremes. Times of extreme flooding and times of extreme low water conditions. Being that many of these populations are also poor their capacity to adapt to the extremes is very limited, which brings on a whole host of other problems.
    0 0
  15. Steve Case#13: There are sufficient data to show without question that diminishing snowpack results in decreased river flow. See this SciAm article about the western US: Snowpack in the northern Rocky Mountains has shrunk at an unusually rapid pace during the past 30 years, according to a new study. ... the plummeting snowpack could have serious consequences for more than 70 million people who depend on water from the runoff-fed Columbia, Colorado and Missouri rivers. So no, your "If a glacier disappears, it will still rain and snow in the watershed where the glacier was and the rivers in such watersheds will still flow" is wishful thinking at best.
    0 0
  16. Rob Honeycutt "Warming is anticipated to enhance the hydrological cycle. That means both wetter and drier conditions" No comment. Muoncounter So are glaciers disappearing due to a lack of precipitation or a warming climate? If it's a lack of precipitation then you have to deal with the fact as I pointed out earlier in the other thread, the IPCC tells us that in a warmer world there will be more precipitation. If they're disappearing due to warming, and precipitation is at least the same, then you have deal with the question of what happens to the water. The claim was that fresh water supplies would disappear.
    0 0
  17. Steve, you make a specious point. It is quite possible for glaciers to gain mass in a warming world (even though the majority of the world's glaciers are in retreat). Glaciers can put on mass as long as the gains made in their accumulation zone outweigh the losses from their ablation zone. In the case of many of the Himalayan glaciers, increased precipitation in the accumulation zones is causing some to gain mass, despite increased losses in their ablation zones. These glaciers serve as storage depots for a great portion of the world's populations, buffering them against the lack of rainfall during the non-monsoon seasons. Despite the hand-waving to the contrary, this is all well-understood and well-documented. And non-controversial, despite the best efforts at denialists to manufacture controversy.
    0 0
  18. Steve Case#16: "the IPCC tells us that in a warmer world there will be more precipitation." Indeed. But there's no prediction of the sort you made that precipitation will fall where you'd like it to. See "The wet get wetter, the dry get drier." Precipitation is projected to increase in the near-equatorial regions, which tend to be wet in the present climate. In subtropical land areas — places that are already relatively dry — precipitation is projected to decrease during the 21st century.
    0 0
  19. Get ready for another onslaught from the echo chamber: Some Asian glaciers 'putting on mass' Prediction: The use of models to reach this conclusion will be ignored. And this tidbit will also be under-reported: ... between 1999 and 2008 the mass of the glaciers in this 5,615 sq km (2,168 sq miles) region of the Karakoram increased marginally, although there were wide variations between individual glaciers. See the Nature article here.
    0 0
  20. You know what's particularly annoying about that piece in the BBC - it's the headline that's on the front page of BBC "Asian glaciers 'putting on mass' " Now, what message do you take from such a headline? 1: That the mass balance of some glaciers in part of the Himalayas (one small region of Asia), measured over just nine years, slightly increased, contrary to the overall regional trend. 2: Or if you're casually browsing the intertubes, do you think that those darn scientists were wrong again about the glaciers, as it looks like Asia's glaciers (a big area) are all gaining mass, contradicting all earlier research? [This of course assumes you don't read the article] I don't know if the short headline is Richard Black's (the article author's) doing, but as so often happens on BBC climate articles, they can't quite manage to escape throwing a bone to contrarians, despite their very own Jones Report on impartiality. Here, the main article is also a decidedly mixed bag, notably failing to mention the context of worldwide accelerating loss of glacier/ice sheet ice mass.
    0 0
  21. skyw, Nor should this new report be a surprise. Scherler et al 2011: More than 65% of the monsoon-influenced glaciers that we observed are retreating, ... In contrast, more than 50% of observed glaciers in the westerlies-influenced Karakoram region in the northwestern Himalaya are advancing or stable. Our study shows that there is no uniform response of Himalayan glaciers to climate change and highlights the importance of debris cover 'No uniform response' ... that's a subtlety that won't play well in the echo-chamber, where all the answers are simple. Nuance need not apply.
    0 0
  22. Dead right mc - but as it would appear, the skeptic echochamber is desperate to twist any research these days, be it about Antarctic ikaites or CO2 during deglaciation. Their discomfort with the truth grows all the time, and they have no coherent explanations...
    0 0
  23. "These glaciers serve as storage depots for a great portion of the world's populations, buffering them against the lack of rainfall during the non-monsoon seasons." And the obvious question is: When a non-monsoon season comes along, how do we release the water from these great storage depots?
    0 0
  24. "When a non-monsoon season comes along, how do we release the water from these great storage depots?" They take in snow in the accumulation zone and rain in the ablation zone. They emit water from the lower reaches via the internal plumbing all glaciers have. This goes on for as long as the glacier has mass in the ablation zone (even in the non-monsoon season).
    0 0
  25. sky, Seems this story has been around. Here's Nature Climate Change in March 2010: Karakoram glaciers seem to buck the trend, however. Several studies of a handful of glaciers in Pakistan have found that many glaciers there are steady at their snouts, and some have even advanced. ... But it makes sense that the Karakoram glaciers would respond differently from those in the Himalayas, says Armstrong. “It's colder. It's higher latitude,” up to ten degrees latitude farther north than Nepal. This figure accompanies the article, but doesn't separate out Karakoram: --source The marginal increase in a small area clearly cancels this more widespread downtrend.
    0 0
  26. Steve... I checked. Your comment was not deleted. But I do take exception to your "no comment" response at 16. An enhanced hydrological cycle means both more evaporation and more precipitation. Wetter and drier conditions.
    0 0
  27. muoncounter @ 19... The Guardian actually did a good job with this one. The glaciers are still shrinking – and rapidly
    0 0
  28. wow - what a difference between the Guardian and BBC articles. You could use them as an educational example of how to place a story into context and how not to. Of course, one author is a science writer, the other a glaciology professor, and the difference in understanding is stark. Well done Prof Bamber!
    0 0
  29. Daniel Bailey at 10:07 AM on 16 April, 2012

    How does the process of taking in snow in the accumulation zone, rain in the ablation zone and emitting water from the lower reaches vary all that much from melting snowpack and rain?

    I had said that this discussion would boil down to the difference between the melt rate of ice and snow.

    0 0
  30. #30 - many of these regions are dry for extended periods of the year. With a glacier present upstream, there's a water supply all year round, even in long dry periods. The ice cube is a reservoir that lasts through the dry season, holding back the precipitation that fell earlier in the year and gradually releasing it through the dry season. Snowpack is a much weaker and less stable form of this, often diappearing quite quickly in the melting season, leaving you with no water reservoir. Remove the ice cube altogether, and your river flow is much less reliable in the dry season. you might have a season with lots of snowpack and be fine, but how many season with little snowpack will you even survive?
    0 0
  31. Steve Case#16: "the IPCC tells us that in a warmer world there will be more precipitation." Rather than arguing from first principles, it would be better to see if you can find any peer-reviewed studies that support your opinions. The predicted effects of climate change are well studied and the conclusions don't generally match yours. Your starting point is correct, that a warmer world also tends to be a wetter world *in general* and the Earth has *in general* dried as it has cooled in the Cenozoic (with the emphasis on “in general”). However, things are not quite so simple as to be able to conclude from that the effects will be beneficial to humanity. There are a number of other, complicating, factors that make the picture less rosy. First of all, where will the extra precipitation fall? Not everywhere will receive more rain – some will receive less. If, as is predicted, already wet regions receive more rain and snow while dry ones, especially in the subtropics, receive less, that would be extremely damaging for agriculture. It is predicted that precipitation will increase in the equatorial and sub-polar regions which are generally regions of excess moisture but decrease in the subtropics, where most of the world’s arid and semi-arid regions are found. Secondly, as temperature rises so does water loss and so more rainfall is needed. Would any increase in precipitation be sufficient to compensate for increased water loss? Think of say England, generally a ‘green and pleasant land’ where crops grow without irrigation, naturally covered in woodland (now mainly cleared). London has an average annual rainfall of 602mm, but is in world terms not exactly a hot city. By comparison, in tropical regions, around 1800mm of rainfall is needed per year to support woodland growth where the trees do not need to drop their leaves for part of the year for lack of water. At equatorial temperatures 602mm of rainfall wouldn’t go far and there would be many brown, parched months. Thirdly, one needs to think of when in the year the precipitation comes. Part of the reason for England’s greenness is that the rainfall is distributed fairly evenly through the year. If it mainly fell in the winter half of the year with little in the summer, the picture would be very different. Models of climate change predict greater seasonality of rainfall. Indeed, studies of the Palaeocene-Eocene Thermal Maximum (PETM), a period of extreme global warming thought to have been brought about by massive greenhouse gas release, show evidence of greatly increased seasonality with long dry periods followed by violent downpours. At the height of the PETM in the Bighorn Basin of Wyoming moist woodland was replaced with seasonally dry, open forest, similar perhaps to that found today in parts of Central America. Fourthly, if some regions become more suitable for agriculture and others less there are many associated problems even if there is little or no net change (or even a net positive change). Imagine if agriculture were to fail in say Kenya but open up new possibilities in Russia. Would it be possible for Kenyan farmers to simply up sticks and move to Russia? Would the Russians welcome them? Would they adapt? Or would we just decide that the Kenyans’ loss was balanced by the Russians’ gain and therefore famine in Kenya didn't matter because there were bumper harvests in Russia? I think you can see that the problem wouldn’t be trivial.
    0 0
  32. skywatcher #30

    You wrote:

      ...The ice cube is a reservoir that lasts through the dry season, holding back the precipitation that fell earlier in the year and gradually releasing it through the dry season. Snowpack is a much weaker and less stable form of this, often diappearing quite quickly in the melting season ...

    I said in my first post that this discussion would boil down to the difference in melt rate between ice and snow. I've been making this argument on different boards for some time now and I always wind up dealing with assertions like yours above. Last year I even did some crude experimentation:

    I got an "It depends answer" Packed snow outlasted the ice and fluffy snow does not.

    0 0
  33. Steve Case @33, you are ignoring the fact that snow pack comes in drifts of a few feet thick while glaciers are tens of meters thick. The result is that relative to snow pack, the glaciers have a much larger volume relative to surface area which accounts for their slow melt rate. I should also note that snow pack, even thickly packed snow is permeable to the air. That is of little consequence when air temperatures are below freezing, but for temperatures significantly above freezing, I strongly suspect it will result in the packed snow melting faster than the ice of the same mass.
    0 0
  34. Tom, Over time, measured in years, the flow in the river of any watershed is a function of the precipitation that falls in that watershed. The presence of a glacier ultimately has nothing to do with it. If the glacier is advancing year to year, the flow will be less than precipitation. If it's receding, the flow will be more. If the glacier is static or there is no glacier then flow will the same as precipitation. Those four cases are all minus evaporation. Packed snow permeable to air? Well, that's an assertion. As I've said a few times now, this whole thing will revolve around the difference in melt rate between ice and snow.
    0 0
  35. Steve Case @34, you are quite correct that the flow of the river is a function of precipitation. Essentially, if all the precipitation is rainfall, it is a function of the average precipitation over the preceding week or so, with run off being delayed by vegetation. With very heavy precipitation, you get a greater proportion of run off, and hence a more immediate response to precipitation but the idea is valid. With snow pack, run off in the spring is a function of precipitation during the preceding winter, plus the precipitation during spring. In most river systems, by summer most of the snow will have melted, so river flow will be a function of summer rainfall. With glaciers, runoff is a function of precipitation averaged over several preceding years or even decades. Consequently, where you have heavy winter precipitation and light summer and spring precipitation, if precipitation is as rain, you will have flooding in winter, while in spring and summer the river will run low. With snow pack fed rivers, you will instead have flooding in spring, with winter and summer river levels being low. While with glacier fed rivers you will have near constant river flows throughout the year, with a peak in summer due to the faster rate of melting with summer temperatures. Specific situations will of course vary based on specific details of geography and meteorology in the area; but the basic pattern will hold. Packed snow is known to be permeable to air, both from the well known survival trick of burying yourself in snow to stay warm. If the snow was not permeable, that would not be a survival trick, but an invitation to death by suffocation. Further, studies related to measuring the trapped atmosphere in ice cores have measured the permeability of the firn to air, and found it is still permeable for up to 100 years (in the case of the South Pole). How quickly it becomes impermeable will depend on the rate of deposition of new snow, and hence the rate of compression of the firn, but periods in excess of 30 years are still common even in areas of very heavy deposition. Consequently the assumption that seasonal snow pack is still permeable to air is very safe. Finally, you say repeatedly that it will come down to the rate at which snow and ice melt. That formulation is, however, nonsensical. Snow is just a particular form of ice. What is relevant are the particular details of heat transfer, and how it effects the rate of ice melt given the different structure of snow and ice. Air is an excellent insulator. Consequently in cold weather, the many air spaces in snow will help insulate the inner layers from warming due to conduction or radiation on the outer layers. Without the air spaces, ice blocks have no such insulation. Consequently, in cold air conditions ice blocks heated by conduction or radiation will melt relatively faster. Against this, the snow has a larger surface area for a given mass which would encourage more rapid melting. Apparently in late winter and early spring with snow still on the ground, the balance of extra surface area vs better insulation is unfavourable for loosely packed snow, but favourable for densely packed snow. In April and May, however, the warmer air will penetrate the snow through those air gaps, hastening melt rather than retarding it. Consequently, if you carried out the same experiment in each month of the year, you would get different results in each month. And your experiment ignores the obvious facts that glaciers have a very large mass (and hence heat capacity) per unit surface area, while snow which is scattered thinly over the side of the mountain has a very large surface area per unit mass. If you are serious about your experimentation, you need to first control air temperature and mass and change surface area to see what effect that has. You then need to control for surface area and mass, and change air temperature and see what effect that has. Until you do so, your experiment is irrelevant, and certainly does not provide evidence that you can set against the observations of hydrologists on the actual impact of glaciers and snow packs of flow rates in rivers.
    0 0
  36. Steve Case - Sudden floods after rainfall are not helpful for agriculture, as most of the runoff is simply lost downstream. Steady water supply throughout the summers requires significant snowpack or glacier melt throughout the year. Declines in that late season water will affect huge agricultural areas. [Source]
    0 0
  37. Steve Case - Your point? My telepathy is in the shop, and your post is a bit content-light. Observations indicate less total snow volume, the temperature records clearly show warmer/earlier springs, and both are affecting spring/summer snowpacks feeding agriculture downhill.
    0 0
  38. This whole thread is getting quite off-topic and derailed. Steve's most recent comment being "case" in point. And subject to deletion as not being compliant with the posting policy of this site. Mauri sent me some info for a post on the Himalayan glaciers. I will try to put that into shape over the next few days to try to put to bed some of this nonsense.
    0 0
  39. It seems to me that California, where I live, can be a good case in point with regards to this subject. The SF Bay area's water supply, as well as farming in the central valley, are reliant upon the snow pack from the previous winter. That snow pack can be very different season to season. A year or two in succession with low snow pack can quickly deplete the bay area's reservoir systems and then we are subject to water rationing. If it were not for the reservoir system which buffers these swings we would have dramatic swings in water supply. Glaciers operate similarly to buffer the water supply to vast down stream populations (much greater than SF, by far). Currently the glaciers of the Himalayas act as reservoirs for those populations. There can be normal swings in the snow pack from season to season but overall they are going to have a constant supply of water because of the buffering effect of the glaciers. What we are doing with climate change is, we're effectively dismantling that glacial reservoir system, AND we are increasing the variability of season to season precipitation. The situation is clearly a looming crisis. I have no doubt that we have already committed to melting the Himalayan glaciers completely over the next 2-300 years. The only possible response will be to build a series of massive dams in those same basins to mimic what the glaciers naturally do.
    0 0
  40. Snow is more susceptible to sublimation than thick glacier ice, so, other things being equal, a given mass of snow will contribute less to the runoff than the same mass of glacier ice. It's a question of how much surface area of the frozen water cystals is exposed to the air and direct sunlight. Anyone who has experienced a Chinook wind has seen snow disappear into thin air quite quickly, while any ice on the ground lingers longer. Some of the water vapor produced by sublimating snow will, of course, re-precipitate locally as rain or snow.
    0 0
  41. Steve Case, your "crude" experiment is too crude to yield any useful result; whatever you observed while doing it can not be applied to this discussion. I don't know that it can be applied to anything. The snow and ice blocks are of different sizes and obviously different densities. What are the beginning and ending water masses for each? What are the surface to volume ratios for each? What results do you get if you start with identical masses (i.e. kg of water in snow form and 1 kg of water in ice form)? The angles of the pictures and the distance to the subjects are different for the before-melt and after-melt, and the blocks also appear to have been moved, as the background is not the same.
    0 0
  42. Steve Case avoided the crucial point, mentioned by KR in #36 and myself in #30. The problem is not about whether snow melts/sublimates quicker or slower than ice, the problem is the reliability of the runoff through the year. Some years will have lots of snow, and thus there will be snowmelt runoff throughout the year, whoopee... but other years will have relatively little snow, or the snow will be spread thinly, or for whatever reason will melt early in the dry season. What happens then? How many years will it take for the late-season lack of runoff to make a real mess of local agriculture? In places like the Himalayas, and elsewhere, the reliability of runoff is the absolutely crucial factor to agriculture, and that is where having a mass of glacier ice that will survive every summer, providing runoff through the year every year, is more valuable than relying on the vagiaries of annual snowfalls. Some years all the snow will melt and some of the stored glacier ice will melt too, other years not even all the snow will melt (so the glacier gains mass), but every single year there is runoff through the whole year.
    0 0
  43. Philippe Chantreau at 09:48 AM on 18 April, 2012 I ran two variables, all with the same volume of snow and same weather conditions. I packed snow into two identical plastic tubs and weighed them to make sure the same mass of snow was in each. One went in the freezer, the other the microwave to melt the snow. Then it went in the freezer when it was frozen out they came and went on the wall. I did the same with loosely packed or fluffy snow. Fluffy snow melted faster than the same mass of ice and packed snow melted slower. The different volume you see is that of the ice, the loosely packed fluffy snow produced a smaller volume of ice. The test ran over several days. You assert that there are no useful results from I did. What experiments have you done? What experiments have you found in the literature addressing the issue that are useful? If the moderators know of a more appropriate thread for this topic, I would appreciate their input.
    0 0
  44. skywatcher at 10:26 AM on 18 April, 2012 You of course have a point. If the snow in the mountains varies year to year some of that variability will be reflected in the runoff. A 100% direct relationship or something less? Do natural and manmade impoundments modify the flow? How about ground water? Besides, there are lots of watersheds that don't have glaciers or very large ones and people live there. Is this "Problem" so absolutely crucial that I must change my life style? Just remember this conversation started out because LarryM wrote in Global Warming in a Nutshell that receding glaciers have consequences, such as disappearing fresh water supplies for billions of people. I object to the claim that fresh water supplies will disappear for billions of people because of receding glaciers. And once again, the IPCC tells us that in a warmer world there will be more precipitation.
    0 0
    Moderator Response:

    [DB] "And once again, the IPCC tells us that in a warmer world there will be more precipitation."

    And, once again, you take an overly simplistic view of things. As was pointed out to you earlier (did you not read it?), some areas will stay the same, some will further dry and some will get even wetter.

    In the case of the Himalayas, much of the area (if not all) is projected to receive both less precipitation and to warm even more.

    Precipitation Changes:


    PDSI Changes:


  45. 43, Steve, While I won't discount your experiment as uninteresting or useless, it does little to add to an understanding of the problem. In a nutshell, looking through your comments, your understanding of glaciers is insufficient and is tainted with 'real world, common sense' assumptions that are in many cases wrong or at best incomplete. If the topic interests you as much as it seems, I'd suggest that you spend an afternoon looking for (reputable) information on what glaciers are and how they work. They're a fascinating, varied and surprising area of study. It's well worth the time spent. Then, armed with a better understanding of the complex mechanics behind glaciers and their behaviors, you can revisit some of the scientific statements concerning how they will be impacted by climate change, in order to arrive at a better understanding of what those statements mean and eventually to arrive at a point where you can answer your own questions.
    0 0
  46. Steve Case#44: "I object..." The issue here is not seasonal melt that clearly provides fresh water. The issue is long term loss of ice mass - and that fresh water is on its way to being salt water. These concerns are stated very clearly: “Glaciers serve as a natural regulator of regional water supplies,” ... "Glacier changes, especially recent melting, can affect agriculture, drinking water supplies, hydroelectric power, transportation, tourism, coastlines, and ecological habitats." ... ... as the world’s glaciers continue to melt and shrink, over time there will be less water to sustain the communities that have come to depend on that meltwater. This seems an obvious point; what is the basis for your continued objection? "in a warmer world there will be more precipitation. " Once again, indeed. But you cannot count on that increased precipitation falling on the same areas that were dependent on glacial melt for their freshwater.
    0 0
  47. muoncounter at 03:11 AM on 20 April, 2012 In a round about way you are making the argument that the glaciers are the source of fresh water. Precipitation and nothing else is the source. And you know what the IPCC says about precipitation in a warmer world. You tell me that we can't count on precipitation falling on the same areas that were dependent on glacial melt for their freshwater. (-snip-). Glacier melt snowmelt or rain may very well flow to an arid region. Just because a glacier is gone or becomes static, doesn't mean the rain and snow that falls won't continue to flow there.
    0 0
    Moderator Response:

    [DB] Now you are just being argumentative. Precipitation is the source of glacial mass. In a warming world, glacial accumulation zones shrink and their ablation zones increase. Glaciers are declining in mass with much greater losses to come.

    All of this has been pointed out to you previously, but still you persist in what amounts to an agenda of stubbornness and patent refusal to learn.

    Off-topic diversions snipped.

    Just because answers and information are provided to Steve doesn't mean that he will then deign to learn from it.

  48. Steve, If I may, the important thing to remember is that for all intents and purposes a glacier (in terms of water supplies) is like a reservoir. It holds a vast amount of water. In times of increased precipitation the amount of water it holds can grow. In times of decreased precipitation the amount of water is holds will shrink, but its mere existence continues to provide water to human communities with a fairly steady flow. It is only the complete destruction (evaporation or physical drainage) of a reservoir that spells trouble, even if the amount of precipitation remains the same, because without the reservoir, the water is not necessarily there for the taking when you need it. The same thing applies to water fed to communities or ecosystems by glaciers. Glaciers are like regulators. When precipitation is high, they trap the water for later. When precipitation is low they continue to deliver water at a steady rate. When the glacier is gone, this natural regulation goes away with it. The reservoir is gone, and the inhabitants must live or die at the mercy of the uneven nature of the weather.
    ...receding glaciers have consequences, such as ... disappearing fresh water supplies for billions of people.
    Does that statement make more sense now, given this context?
    0 0
  49. Steve Case #47: Nonsense; I make no mention of the 'source.' The source is irrelevant - what matters is that many people derive their freshwater from meltwater-fed rivers. Both references I've posted here and here suggest the same thing: Take away the water impounded as snow and ice and you go thirsty. It would be beneficial to the discussion if you could produce some source material to support your opinions. "Just because a glacier is gone or becomes static, doesn't mean the rain and snow that falls won't continue to flow there." I have no idea what that even means. However, if you are suggesting that glacial meltwater falls as precipitation solely on the same catchment, you are sorely mistaken. Compiled by UNEP's Polar Research Centre GRID-Arendal and experts from research centers in Asia, Europe, Latin America and North America, the report says the larger glaciers may take centuries to disappear but many low-lying, smaller glaciers, which are often crucial water sources in dry lands, are melting much faster. -- emphasis added
    0 0
  50. Sphaerica @48, Unless humans respond by building reservoirs.
    0 0

1  2  Next

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us