Wild Cards of Global Warming
By S. Tom Bond, Resident Farmer, Lewis County, WV
There are several “wild cards” connected with global warming. These are phenomena, which may result in “positive” feedback and thus increase earth warming more than would happen by human addition of greenhouse gases alone.
I The Amazon River Basin
The Amazon river basin in South America is huge, about the size of the continental U. S. A. It looks smaller on many maps because it is on the equator, and the U. S. is enlarged because those maps are a flat projection of a spherical earth.
As everyone knows, the Amazon area is hot and wet. It harbors a great diversity of life, typically 200 species of trees per square mile, compared to two dozen at our distance from the equator, and perhaps 5 or 6 species in the far northern forests. The diversity of other species is similar, with untold numbers of insect species and tiny plants.
It is both a huge store of carbon and a mighty air cleanser. All plants take water and carbon dioxide from the air and with sunlight make sugar, but the many huge trees and warm climate make the trees especially effective. The sugar is both a source of energy for growth and a starting material for synthesis of cellulose and all the other compounds a plant needs. The tree is largely carbon, which it retains while giving pure oxygen back to the air. That carbon storage includes the roots and the attendant microorganisms, too.
Dr. Sassan Saatchi and coworkers estimate, writing in Global Change Biology, these trees, including their roots and the microorganisms which attend them in the soil store about 82 billion metric tons (gigatons) of carbon. For comparison, 7.5 gigatons of carbon was emitted as CO2 in 2011, so the Amazon holds about 11 times the carbon all sources emitted in 2011.
This is vast carbon deposit is vulnerable in several ways. In the not too distant past it was being cut down at a high rate for pasture, soybean growth and other agricultural use. When cleared, most of the carbon goes to CO2 by burning or rotting. The carbon in crops is much less than in the trees – there is even some question if there is enough carbon left in crops so a rainforest could be restored.
This has been slowed in recent years, but an even more serious threat has emerged. Droughts in 2005 and in 2010, both ”once in a century droughts” have turned the Amazon from a sink for carbon into a source. The dead and decaying growth produced more CO2 than it absorbed.
One of the predictions of global warming is stronger el niño’s due to warmer ocean water. This pushes the tropical front northward, producing droughts in Amazonia. Will the Amazon give up its carbon, equivalent to ten times the world’s present emission rate?
II Methane hydrates and melting permafrost
Methane hydrates, some times called clanthrates, are cage compounds, methane enclosed in a framework of water molecules. The most common one involves a ratio of 4 methane molecules to 29 water molecules. The hydrate forms when methane comes in contact with water that is cold enough and under sufficient pressure. If pure it looks like ice, but burns. 167 volumes of gas are present in one volume of the hydrate.
It is found along the ocean shore out where it is deep, even in warm climate, because the ocean deep is cold. One of the most studied is off the Carolinas. The deposits are wide spread, because methane is produced by microorganisms in the sea. They accumulate over millions of years. The most shallow deposit is in about 900 feet in the Beaufort Sea, north of Alaska. A good map of deposits is located here.
Japan has shown interest in mining a deposit Northeast of its land, because it is extremely resource poor, but most other nations are content simply to study the subject.
The hydrates can decompose if pressure is removed or temperature goes up. The fear is that global warming, particularly when it reaches the sea, will release vast amounts of methane into the atmosphere. The deposits have been estimated to hold in the range of 10,000 gigatons of carbon, while the atmosphere holds only 750 gigatons of carbon.
The fear is that some significant part of it may be released by global warming. Since methane is some 30 times as powerful as carbon dioxide in warming the atmosphere, only a small fraction of the total would be a “significant part.”
Some methane hydrate deposits are found in and under permafrost. This is the permanently frozen part of the world’s surface that in some places is 2100 feet thick. Permafrost is found in the far north and in high mountains. It covers about 24% of the earths exposed land surface.
Permafrost is melting, there are plenty of pictures of the far North to demonstrate this to any reasonable person’s satisfaction. They include eroding coast lines, damaged housing, effects on terrain on roads, pipelines and rail lines and many other effects. Sources show pictures of methane bubbles keeping pools open in Arctic lakes and caught under winter ice that escapes when melting occurs. Records show the Arctic and alpine areas are warming twice as fast as the rest of the world.
In addition to escaping methane, there are huge reservoirs of carbon in Arctic soils which will be converted to carbon dioxide by decay when the soils thaw. The UN Environment Programme predicts that the melting Arctic could emit 43 to 135 gigatons of carbon equivalent by 2100.
This author concludes some of the above is chance of emission, but some is for sure, in addition to other sources we hear a great deal about. We have not reached the equilibrium temperature caused by the past emissions. In other words, we will experience further warming, even if additions to the atmosphere stopped today, due to the carbon dioxide already in the atmosphere!
– - – . . . To be continued . . . – - -