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 "...by 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.