There seem to be conflicting reports on whether glaciers around the world are retreating or not, and the rates at which they are retreating. What are your views on this subject?

I personally feel that there is no real conflict in the scientific community on this matter. The scientific community predominantly believes that glaciers throughout the world are retreating. However, ambiguity in measuring glacier retreat does come up, mainly because of differing interpretations of how glacier mass changes with glacier retreat. 

Change in glacier mass with glacier retreat is a complex phenomenon controlled by numerous factors – terrain, geomorphology, and other physical aspects of glaciers. If one does not understand or account for such factors comprehensively, one may come to the erroneous conclusion that glaciers are not retreating. Oftentimes, when glaciers lose mass and their volumes reduce, the change takes a long time to reflect on glacier length, which could lead to people believing that glaciers are not retreating. There is also a huge variation in the rate at which glaciers retreat – some retreat fast, others slowly, and some appear to be stagnant. But a close look at the global or international picture shows that glaciers all over the world are retreating. 

I believe it is futile to continue arguing whether glaciers are retreating or not; it would be a better use of our energies to make necessary contingency plans to secure water security for India.

In direct contrast to the global picture of glacier retreat, the Karakoram glaciers seem to be stable, a phenomenon that has been dubbed ​“The Karakoram anomaly”. Could you explain why this is a special case?

As far as the Karakorams are concerned, the situation is unique. In glacier research, there is a concept called the equilibrium line altitude (ELA) – this is the altitude at which mass loss in a glacier is zero, that is, ice accumulation from snow is equal to ice lost in melting. Parts of the glacier that lie above the ELA will accumulate ice since mass lost through melting is lesser than the amount of snowfall received. Since the Karakoram mountains are at a very high altitude, much of the glacier mass in this area lies above the ELA. Because of this, these glaciers still have a small positive mass balance, which means they are either growing or are not retreating as of now. However, some of our work shows that with the current rate of climate change, even the Karakoram glaciers will begin to retreat within the next 20 – 25 years.

How does one measure ​“glacier health”?

Fundamentally, glacier health is a measure of how stable a glacier is. We can estimate glacier health using four parameters – mass loss, debris on the glacier, glacier thickness and glacier length. Every glacier has a certain amount of ice of a certain thickness, which is determined by how much snowfall it receives in winter and how much ice melts in summer. If a glacier is losing more ice mass than it gains as snow, it will have negative mass-balance, and such glaciers are in a retreating phase – such glaciers are not healthy. 

Another component in determining glacier health is the amount of debris on the glacier. In the Himalayas, valleys where glaciers are formed, have huge side walls adjacent to them. Because of weathering, rock from these walls fall on the glaciers. If glaciers are healthy, they have only a small amount of debris on them since the fallen rocks are quickly brought down to exit at the glacier terminus. However, if glacier thickness is reduced, the amount of debris keeps increasing, which is another sign of an unhealthy glacier. 

The other factors – glacier ice thickness and length, are also key factors of glacier health. However, all these parameters must be used in conjunction to estimate glacier health. Any one alone will not give an accurate measure of whether a glacier is retreating or not.

What are the difficulties facing researchers working on glaciers? Is there some way of overcoming them?

One must understand that most field work on glaciers, especially in the Himalayas, is very difficult. Because of their extremely remote location, it is very demanding for anyone to physically go there to take measurements. Any such study would require a few days’ trekking to get there, and special mountaineering skills and equipment are a must. Because of such conditions, there are obvious limitations to how much one can observe or measure, which could leave such studies open to erroneous interpretations. 

One of the main difficulties in studying Himalayan glaciers is the that many parameters cannot be physically obtained. However, we have overcome some issues by using other techniques – satellite images and UAVs (unmanned aerial vehicles) to make measurements and observations. One of the very difficult tasks in the past was to determine the aerial extent of glaciers. But now, with the advances in satellite technology and India’s excellent satellite program, we have images and multispectral data which makes it much easier to map a glacier. These advances, which have come about in the last 10 to 15 years, allow us to know the aerial extent of glaciers with good accuracy. 

What we don’t have information on now, is the depth of glaciers. Satellite remote sensing cannot measure the depth of glaciers, one needs special radars for such studies that cannot be launched on a satellite. As going to each glacier to physically measure its depth is quite an impossible task, we have such measurements only for a few glaciers. Now, the challenge we face is to understand how best we can use those few observations to account for the entire Himalayan mountain range. For this, we are working on theoretical modelling systems that explores measured depths and predicted depths of glaciers. 

We, at the Divecha centre and IISc are very keen on solving this problem, and so we have developed a new model which is based on field observations, satellite observations and theoretical models. Using that now, we hope we can estimate the spatial distribution of glacial depth. 

I will give you an example of how risky glacier studies can be, from my own experience. It was, I think, the year 1987 when I had gone on my first glacier-studying expedition, organised by the Wadia Institute of Himalayan Geography. I was supposed to take the spectral reflectance of various snow and ice features for a better interpretation of satellite images – where a glacier ends, or where it begins, based on reflectance characteristics. 

I was very young then, and even though I had had mountaineering training– by then, I was a certified mountaineer – I wasn’t entirely prepared for what happened. In the mountains, we have a very small window of time to study reflectance- only about two hours on a daily basis. This made staying at a base camp and taking the apparatus to the field site for measurements is virtually impossible.

So, being young and adventurous, I decided that we would stay at the field site itself. We were at a very high altitude, around 5,500 meters in an area near the Sara Ugma Pass, and the Chhota Shigri glacier. That night, a huge snow storm started, one that had such fierce winds that my entire tent got uprooted, and I was moved away from my campsite. I was quite an ordeal, and I somehow survived it. The incident taught me that the mountains always have something new to teach you, and that to research glaciers, you must have an adventurous spirit and a strong survival streak.

How well are glaciers and glacial lakes in India inventoried? Does this data make it possible to predict or mitigate glacial lake outburst floods (GLOFs)?

Overall, because of our excellent satellite program, the Himalayan glaciers and glacial lakes in India are quite well inventoried. Now, the big challenge is to reduce the risk of GLOFs or to mitigate the effects of one. To do this, we need to know the amount of water in the glacial lake – we know size of the lake via data on its aerial extent. By using various sonar techniques, we can also estimate the depth of such lakes. With this data, we can apply a hydrodynamic model to understand the consequences of a lake burst under different conditions – be it heavy rainfall, an avalanche or under natural ground subsidence. Knowing how much water is likely to be released downstream under these situations, one can assess probable damage and prepare for such situations. 

Beyond this, it is also possible to mitigate the effects of a flood by simply reducing the amount of water in glacial lakes such that even in the event of an outburst, the damage downstream is minimal. Such projects are being undertaken in Sikkim by dewatering glacial lakes. 

What is the likely impact of glacial retreat on runoff in the Himalayan rivers in the near future? 

This is a very tricky question to answer, mainly because the amount of retreat is not equal across glaciers. So, when I look at this problem, I perceive it in two ways. One view is from the perspective of the small communities living in the mountains. The other viewpoint is of the people living in the plains, where the waters from the Himalayas come into the Indo-Gangetic plain, the fertile region where our agriculture and water security need to be sustained. The two situations are very different, and will fan out very differently. 

People who live in the mountains, usually live around small streams fed by small glaciers of 4 – 5 Km length – they have agriculture and pastures there. These small glaciers are also the ones that are going to face the maximum effects of climate change in the near future. Some of our investigations have shown that from 1980s onwards, till now, almost 70% of such small glaciers have lost quite a lot of mass. One of the reasons for this is that there has been a reduction in snow cover. Snow melt has started to set in early, almost in the middle of winter, due to which many streams are drying up very early, and the whole ecosystem of the mountains is changing dramatically. I think we require a major program to understand the effects of climate change on the mountain communities, and to think of mitigation measures before it reaches a crisis stage. 

With regard to the communities in the plains, that depend on the larger glaciers for water, the situation is also growing critical. For example, in Pakistan, almost 70% of the water that irrigates a vast majority of their agricultural plains comes from snow and glacier melt. If a significant number of such glaciers melt away, there is going to be a huge impact on the food and water security of the country. However, this may be quite far off in the future — it may not happen in this lifetime, or perhaps not even in the next two generations, but it will happen sometime in the future especially if climate change keeps on at the present pace. 

Is it possible to mitigate glacier loss?

There have been some projects – called ice towers or ice stupas that are being tested in Ladakh and Sikkim. Such mitigation measures are important and hugely useful for small mountain communities, but their sustainability over an extended period of time is still under question. As temperatures keep rising with climate change, ice towers will also melt faster. But such projects do have the potential to mitigate water problems in places like Leh, Ladakh and perhaps Sikkim. 

But this kind of mitigation is not going to be a solution at a large scale. In the Himalayas, we have about 40 to 50,000 square km of ice, and we cannot create snow and ice cover at that scale. So, it is crucial that we begin planning to take measures to create water security through other means for India.