Wednesday, June 9, 2010

The consequences of an ice-free Arctic, part one: Loss of biodiversity

Has anyone actually explained exactly WHY and HOW an ice-free Arctic is such a disaster? And for whom would it be a disaster? And in what way it would be a disaster? --Kevin Cave

Though we are accustomed to think of the Arctic as cold and lifeless, except perhaps for a few polar bears, the Arctic is home to a large and diverse group of plant and animal species. Few of them would survive an ice-free Arctic.

It's perfectly possible to stop right there, and acknowledge that it is morally reprehensible to wipe out unique and irreplaceable species, making our world poorer in strangeness and in wonder, and destroying creatures that, whether you believe them to be shaped by God or by evolution, are fantastically sophisticated and beautiful. But we will assume or questioner has little interest in the welfare of species other than humans. So let's look at the anthropocentric argument.

This would represent a heavy loss of biodiversity, which would decrease the resilience of our biosphere as a whole.

Put in the dimpliest possible terms, the millions of species on earth represent a reservoir of genetic strategies which work in different ways and in different places. The greater your biodiversity, the "deeper" your "bull pen" when things change. Climate change, disease, habitat loss, natural disasters, invasive species -- lots of things can "go wrong" with a particular ecosystem. The species in that ecosystem adapt, and the balance of species may change.

Most people who have had high school biology are familiar with one form of adaptation: natural selection. Less successful organisms fail to reproduce; more successful ones to so avidly, and the species as a whole becomes "fitter" -- which just means better suited to the conditions that exist.

However, this is only one of the many forms of adaptation which are necessary for life -- including human life -- to continue to exist in changing circumstances. Natural selection for complex organisms is pretty slow. If you aren't a bacteria, you don't spit out a new generation every five minutes. Fast adaptation is often needed.

Species are also restricted by their genetic program in terms of how far they can go. A small fish may involve into a bigger fish, but no matter what the evolutionary pressures, in a million years that fish still will not be a bird. Meaning, if an ecological niche for birds develops, those birds need to come from somewhere. That ecosystem will "borrow" birds from another range -- they won't make them from scratch out of sloths, or what have you.

So an important part of adaptation is having a much of species on hand to swap in and out of different roles. Just like genes in DNA, a species may play a minor role (a small range in the Arctic, say) under current conditions, but a shift may cause them to play a more important role over a different area. In the Arctic are fish with anti-freeze for blood, for example. Someday, that tactic or a variation on it may be crucial to the food webs that keep us alive. Eliminate the species, and you eliminate some of life's tricks for survival. That's a bad idea.

Still too abstract? Let's look at an example that's unfolding today:

Two new forms of a devastating wheat fungus, known as Ug99 stem rust, have shown up in South Africa, a study has found.

The two South African forms are able to overcome the effects of two resistance genes in wheat that normally prevent stem rust from taking hold. The genes cause plant cells around the infection site to die, stopping the fungus from further infecting the plant. They are two of the most important genes in wheat because they are selected for in crop-breeding programmes across the world.

In the last hundred years, humans have gone from getting most of our calories from several hundred species to getting 80% from just 20 species, including maize, rice, wheat, and sorghum. The benefit of this has been dramatically improved output, but the cost is that our food supply to much more subject to any disruptions of a particular crop, such as that affecting wheat, noted above. Another example:

About eight hundred million people in Africa, Asia and South America eat cassava. The plant is a major source of food energy and a major food security crop. It can survive in poor soil and without much water. Also, the root can stay in the ground for as long as three years, so it can be harvested as needed.

But in East Africa the plant is under attack. Cassava brown streak disease is a more destructive form of cassava mosaic. The mosaic has been active in East Africa for about one hundred years. It limits plant growth. But brown streak can destroy a crop. The virus was identified in Uganda in two thousand four and has spread fast in areas extending from Lake Victoria.

So far, brown streak has not jumped to Nigeria, the world's largest producer of cassava. But it threatens more than thirty million tons a year of production in East Africa. In some areas of Uganda, rates of brown streak reached more than eighty-five percent in two thousand five and two thousand eight.

Eight hundred million people. A single crop. Disease strikes -- what do you do? We have seen this movie before.

When a species falls to disease, or other environmental changes (such as rising temperatures!) other species try to occupy that niche. We, as humans, if a ecosystem's productivity is important to us, can hasten this process through deliberate introduction of new species or even via genetic engineering. But when we allow species to be wiped out (particular species, like many in the Arctic, with unique adaptations to extreme environments) we lose the raw material of adaptation. We lobotomize nature. That's a problem, because even if you worship skyscrapers and loathe polar bears, we all have to eat. All seven billion of us. Anything that makes our food supply less secure is a disaster in the making.

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