An Inconvenient Triumph: Climate Change and the Indian Subcontinent

I just saw An Inconvenient Truth and I think it's beautifully done -- I would strongly recommend it. Even if you don't love Al Gore as a politician, the science is convincing and all the pictures of vanishing glaciers and dried-up inland lakes (Lake Chad!; the Aral Sea!) are terrifying.

In the film, Gore refers several times to the potential catastrophic consequences of Global Warming in the Indian subcontinent. It's somewhat ironic, because countries on the Indian subcontinent are far smaller contributors of greenhouse gases than the developed countries (India's per capita emissions are one sixth the world average) but you can be sure that the subcontinent will feel its effects. As I understand it, there are two major consequences of global warming for the Indian subcontinent that are essentially guarantees, and a third which seems to me to be a maybe:

First guarantee: significant amounts of land in the Bay of Bengal are going to disappear if oceans rise even 1 foot, as is predicted to occur in the next 50 years. Most estimates I've found give the number at about 15% of the total landmass of Bangladesh, with a comparable loss of land in West Bengal on the Indian side. As many as 60 million people will be displaced in both countries.

In Orissa, the receding coastline is already a fact of life. In the Satabhaya region of the Orissa coastline, according to this article, the shore has moved 2.5 km inland over the past 25 years, displacing a number of villages. And it continues to move. (The article doesn't specify what could be causing the rising sea levels in that specific part of the state.)

In the short run, scientists are already noting a pattern of a growing number of low pressure systems (leading to cyclones) in the Bay of Bengal in the post-Monsoon season. These are expected to worsen -- meaning that extreme storms may force mass evacuations of coastal regions well before the land itself disappears. (See this article for more.) Also, erosion caused by the storms is already seriously affecting these regions. As Banglapedia puts it:

Flooding and erosion/sedimentation Bangladesh experiences moderate to severe flooding every year. Frequent storm surges also cause severe coastal flooding. The flood situation is further aggravated by the high tide in the Bay of Bengal. It has been seen with a 1.4m rise in sea level water level rises to about 6m near the meghna estuary. Even with a 0.2m rise in sea level, water level rises between 4.5 and 5m near the estuary. Since most of the coastal area is below 1.5m above mean sea level (MSL) and the area near the confluence of the ganges and Meghna is below 3m above MSL, both depth and area of inundation will increase extensively. However, the water level in the Ganges and Upper Meghna also increases significantly due to backwater effect as a result of changes in the hydrodynamics of flow. Hence the severity and extent of flooding will increase even in the upstream portion of the river. On the other hand, a rise in sea level will also move the shoreline landward and this will result in loss of farmland, leading to the shifting of agriculture, reduced crop yields, and loss of cultivable areas. Increased flooding will cause problems with existing irrigation and drainage system too. (link)

Even small changes in the mean sea level could lead to a cascade of problems for the Bengal delta, because the water systems are all interdependent. Even before the land disappears, the damage caused by increased flooding is expected to make a lot of coastal land essentially uninhabitable.

Tyler Cowen, when he was in India a couple of years ago, did a thought experiment on this. It's a little in the "heartless economist" vein, but it's worth reading.

And here's a Salon article about attempts that are being made in Bangladesh to raise awareness about the coming catastrophe.

The second guarantee: The glaciers will disappear, leaving all of the subcontinent's major rivers dry. Abhi already posted on this last fall, though he didn't get much of a response to this shocking fact at the time. These rivers, as everyone knows, provide the vast majority of water to India, Pakistan, Nepal, and Bangladesh. (And glacial water also feeds China; in total, 40 percent of the world's population is dependent on water from the Himalayas.) The retreat of the Himalayan glaciers is not a prediction; it's happening. The only question is when the effects will start to kick in. But I would say that even if it takes 100 years for the water supply to crash, it's not to early to start doing something about it.

But here's the irony: in the short run, the rapidly melting glaciers may actually cause flooding in the plains.

The third "maybe" consequence is that the whole weather pattern could change if ocean currents change as a result of rising water temperatures. The monsoon could disappear entirely (or it could double in intensity!). There's not much to say about this -- because no one really knows -- except that it reminds us how little we really know about what is happening.

In An Inconvenient Truth Gore talks about an instance where scientists were surprised by the rapidity of change. In Antarctica, in 2002, the Larsen ice shelf collapsed over the course of a few weeks. No one predicted that a chunk of solid ice the size of Rhode Island could break up so fast. But now scientists think it was probably caused by earlier partial melting, leading to the creation of 'moulins' under the ice, that exponentially speed up the break-up of ice shelves. Those same moulins are being observed in Greenland, suggesting that large melt-offs may be imminent there too.

In effect, the predictions for ocean level rise over the next fifty years may be understatements: it could be much sooner than that. Scientists have been unpleasantly surprised by things like this before, and may be again.

[Cross-posted at Sepia Mutiny]