Fact vs Fiction: Is it all a fairy tale?

Throughout this blog I hope to look at some of the major factors that affect the distribution of glaciers and their contribution in causing oscillations in glacial extent over time. Palaeoclimatic evidence indicated substantial fluctuations in global glacial extent throughout the late quaternary (Lehmkuhl and Owen, 2005). It is generally accepted that last global peak in ice extent occurred during the Last Glacial Maximum around 18ka BP in radio-carbon dating (or marine isotope stage II) (Lowe and Walker, 1997). Since then, repeated advances and retreats have occurred responding to exogenous (solar insolation, volcanoes), and endogenous forcings (atmospheric GHG concentration, dust cover and atmospheric circulation patterns) with the last glacial advance occurring during the neoglacial or 'Little Ice Age' between 1550 to 1850 AD (Junglclaus, 2000).  

It is this period after 1850AD, the period classed by some as the 'anthropocene' (Crutzen, 2000) that has gained particular attention from glaciologists and other scientists studying changes to the global environment. Ice core-analyses show rises in carbon dioxide concentrations from the mid-18th century corresponding with the start of the Industrial Revolution (Steffen et al., 2011). Since then, atmospheric carbon dioxide concentrations have risen (see previous blog), surpassing natural Holocene variability and are at their highest concentration at any time point during the Holocene. Alongside this increase global mean annual temperature has risen by approximately 0.55 ºC since 1860 (see Figure 1), and it is anticipated to continue in the 21st century (IPCC, 2007).



Figure 1: Global temperature change from a) 1860-2007, b) 1000 AD to present. In the top panel the global mean surfac temperature is shown year-by-year (red bars with very likely ranges as thin black whiskers) and approximately decade-by-decade (continuous red line). Analyses take into account data gaps, random instrumental errors and uncertainties, uncertainties in bias corrections in the ocean surface temperature data, and also in adjustments for urbanization over the land. The lower panel merges proxy data (year-by-year blue line with very likely ranges as grey band, 50-year-average purple line) and the direct temperature measurements (red line) for the Northern Hemisphere. The proxy data consist of tree rings, corals, ice cores, and historical records that have been calibrated against thermometer data. Insufficient data are available to assess such changes in the Southern Hemisphere. (Source: IPCC, 2007).

 
The literature disputes the amount that natural variability and anthropogenic forcing contributes to the observed warming in the atmosphere. Lean et al., (1995) state that the contribution of natural and anthropogenic forcing to global warming has a temporal element, with solar forcing accounting for about 50% of the observed warming since 1860, which falls to a third post-1970. However, Crowley (2000) argues that the contribution of natural forcings (volcanism and solar forcing) only accounts for 25% of the 20th century warming. The key observation to be drawn from these studies is that not all of the warming since 1850 AD can be explained by natural variability alone. This is an essential point to consider in order to understand the potential impacts that global warming and other climate changes may have on glaciers and other ecosystems, the former of which I shall discuss in the oncoming weeks.

BACK TO BASICS: What is a glacier?

Glaciers are a mass of snow and ice which, if it accumulates to sufficient thickness deforms under its own weight and flows. There are three main types of glacier: ice sheet/ice cap; ice shelf; and mountain glaciers (Thomas and Goudie, 2000). Mountain glaciers, which are constrained by the underlying topography of the mountains will be the focus of this blog, with particular attention to the Himalayan glaciers in central Asia.

GLACIERS AND CLIMATE CHANGE

Understanding how glaciers could be affected by climate change is of substantial socio-economic relevance. Significant retreat of glaciers could have wide-ranging impacts causing sea-level rise, an increased risk of glacial lake outburst floods (GLOF) and alterations to runoff affecting the discharge of rivers sourced by glacial meltwater.
This is of greatest concern in the Himalayas. The Himalayas are one of the largest bodies of ice outside of the polar regions covering approximately a 33,000 square km area (Space Application Centre, 2010: 7). Meltwater and rainfall from this region feed major rivers such as the Indes, Ganges and Brahmaputra, supporting over one-sixth of the world's population that inhabit the Indio-Gangetic Plain (Prasad et al., 2009).

In recent years there have been mixed reviews over the rate that these glaciers are declining compared to other regions of the world. Bolch et al., (2011) study using a combination of stereo and aerial images and satellite data, concluded that all of the ten Himalayan glaciers studies had lost an average mass of 0.32±0.08 m w.e.a^-1, despite of their thick debris cover. Though this was statistically greater that earlier time periods (though this may have been partially due to improvements in the resolution of the data), this value was not found to be higher than the global average (0.32m w.e.a^-1) estimated by Zemp et al., (2009) using 30 reference glaciers from around the world. In contrast, Prasad et al., (2009) suggest Himalayan glaciers to be among the fastest receding glaciers in the world. Despite these mixed conclusions, it was the fourth IPCC report published in 2007 that brought this debate to the centre stage, encouraged by extensive coverage by the global media (Barley, 2010; Pearce, 2010).

THE IPCC FOURTH REPORT: When facts are not always facts.

The claim:

'Himalayan glaciers are receding at a faster rate than in any other part of the world and if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps warming at its current rate' (IPCC, 2007)

This controversial and alarmist statement was later withdrawn after it was found it had been founded on grey literature published by WWF in 2005 (Pearce, 2010).

THE REALITY CHECK!

Though it is highly unlikely that the Himalayas will have completely disappeared by 2035, the long term outlook still is not good.
Taking rainfall predictions into account Immerzel ( cited in Barley, 2010) found that by 2050, 60 million fewer people (4.5% of the world's population) will be able to support themselves on the main rivers supplied by the Himalayas. Therefore, although the loss of these 'water towers' may not occur within the next few decades, in general, most Himalayan glaciers are in a state of retreat (Scherler et al., 2011). In the short-term, glacial melt may result in an increase in meltwater discharge to rivers such as the Indes, Ganges and Brahmaputra, but in the long-term the water security in these regions is likely to come under threat (Bolch et al., 2011).

With the IPCC projecting potential global temperature rises of 1.1-6.4 ºC by the end of the 21st century, it seems Himalayan glaciers will only continue to retreat. The key question now is at what rate and how is this impacted by other forcings such as dust cover and monsoon-rainfall? Conclusions from the Snow and Glacial Studies Report (2010) show spatial disparities in the number of glaciers in retreat, advance or observed as no change (2184, 435, 148 of the 2767 glaciers studied respectively). This suggests local climatic variations and glacial characteristics may also affect their resilience to changes in climate, some of which will be discussed in the oncoming weeks. Case studies will also give an insight to regional disparities caused by variations in glacial characteristics which add to the complex picture of estimating changes in the mass balance of these ice giants.

Reference:
Barley, S. (2010) 'Himalayan glaciers good for a while yet', New Scientist, 206, 2765: 1.

Bolch, T., T. Pieczonka and D.I. Benn (2011) 'Multi-decadal mass loss of glaciers in the Everest area (Nepal Himalaya) derived from stereo imagery' The Cryosphere, 5: 349-358.

Crowley, T. J. (2000) 'Causes of climate change over the past 1000 years', Science, 289: 270-277.

Crutzen, P.J. (2002) 'Geology of mankind' Nature, 415, 1:23.

IPCC (2007) Climate Change 2007: Impacts, Adaptation and Vulnerability, in M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (Eds) Contributions of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press: Cambridge.

Jungclaus, J. H. (2009) 'Lessens from the past Millennium', Nature Geoscience, 2: 468-488.

Lean, J. J. Beer and R. Bradley (1995) 'Reconstructions of solar irradiance since 1610: Implications for climate change', Geophysical Research Letters, 22: 3195-3198.

Lehmkuhl, F. and L.A. Owen (2005) 'Late quaternary glaciation of Tibet and the bordering mountains: a review', Boreas, 34: 87-100.

Mayewski, P.A. and P.A. Jeschike (1979) 'Himalayan and trans-himalayan glacier fluctuations since AD1812', Arctic and Alpine Research, 11, 3: 267-287.Pearce, F (2010) 'Debate heats up over IPCC melting glaciers claim. How did a 10 year old speculative comment over disappearing Himalayan glaciers come to be included in an IPCC report?', NewScientist, 11th January 2010.
Prasad, A.K., K.-H.S. Yang, H.M. El-Askary and M. Kafatos (2009) 'Melting of major glaciers in the western Himalayas: evidence of climatic changes from long ter, MSU derived tropospheric temperature trend (1978-2008)', Annuals of Geophysics, 27: 4505-4519.

Scherler, D., B. Bookhagen and M.R. Strecker (2011) 'Spatially variable response of Himalayan glaciers to climate change affected by debris cover', Nature Geoscience, 4,3: 156-159.Space Application Centre (2010) Snow and Glacier Studies Report, Ministry of Environment and Forests Department of Space of India.
Steffen, W., J. Grinewald, P. Crutzen and J. McNeill (2002) 'The Anthropocene: conceptual and historical perspectives', Philosophical Transactions of the Royal Society of London A, 369: 842-867.Thomas, D.S.G., and A. Goudie (2000) The Dictionary of Physical Geography (Eds) Blackwell Publishers: Oxford.

Zemp, M., M. Hoelzle and W. Haeberli (2009) 'Six decades of glacier mass balance observations- a review of the worldwide monitoring system', Annuals of Glaciology, 50:501-511.  (see link to UNEP long-term monitoring of glaciers around the world).