Just what is going on with our wacky weather? Why do the summers seem hotter, the winters seem colder, and the storms, floods, and droughts seem worse each year? Answers are beginning to emerge...
No doubt you have noticed that one popular topic of conversation of late is the weather: it seems to be getting steadily stranger and more extreme. Despite the claims that greenhouse gases are heating up the planet, our winters seems to be colder and snowier than ever. Yes, summers have been hotter than we can remember, too, but it's not possible that these two opposite effects can flow from the same cause, is it? To find the answer, let's consider the measurable conditions and their causes, and then dig a bit deeper.
We know that the planet must indeed be heating, not only because of the retreat of Arctic Ocean ice and hundreds of shrinking glaciers worldwide, but also because we measure the planetary temperature using satellites. But the reality is that the large majority of additional heat being retained by increased carbon dioxide, methane, and other greenhouse gases is not held in the atmosphere, but is absorbed by the oceans. Since CO2 is up by a third, and methane by half, there is little doubt that the atmosphere is retaining heat that would normally radiate into space. But the heat hasn't stayed in the atmosphere. Numerous studies indicate that as much as 80% of the measurable increase in temperature is within the oceans. The result is that the warmer waters, with less ice cover, release more heat through evaporation, so that the humidity of the atmosphere increases. Since water vapor is actually the biggest single retainer of atmospheric heat, this creates an effective 'feedback mechanism' that results in further heat gain, and thus further oceanic warming in a repetitive cycle.
Increased moisture naturally results in increased rainfall. The effect is most noticeable in the many record rainfall events which have caused extreme flooding in locations in every region of the globe. This week that has been Queensland, Australia, where over four feet of rain fell, resulting in unprecedented floods. In 2010 alone, similar situations have occurred in western Tennessee, New England, Arkansas, and the Dakotas as well as the catastrophic flooding that inundated the majority of Pakistan. "100-year flood" events have occurred twice in 10 years in some places.
Heavier snowfall is the parallel effect in winter. As atmospheric moisture increases, winter storms have much more available moisture to create snow. That condensation process also deepens and intensifies the storm itself.
According to the National Oceanic and Atmospheric Administration, "Northern Hemisphere snow cover during December 2009 was the second largest extent, behind 1985, on record. North American snow cover for December 2009 was the largest extent since satellite records began in 1967."
Although final numbers are not available, it is possible that December 2010 has surpassed 2009 in both snowfall and snow cover.
In one of my earlier blog posts I attempted to explain how these events develop as a result of the 'jet stream', a virtual river of 100 to 250 mile-per-hour winds that circle the globe in the mid-latitudes at altitudes of five to seven miles. First discovered in the 1940's, it is now known that this phenomenon has a major effect on world weather.
Normally the jet stream moves in a 'zonal' or west-to-east direction in a fairly straight line, from San Francisco to Denver to Atlanta, for example. Occasionally, however, the jet stream develops significant kinks, or oscillations, that cause it to bend into strange patterns, for example, moving from Los Angeles to Alberta, Canada, and then back south to New Orleans. This alignment would bring unseasonably warm air to Canada, and sharply colder weather to the Gulf coast. Sometimes these patterns become 'locked in' for days or even weeks, causing truly extreme effects, such as the crop-and-forest-destroying heat wave of last summer in Russia, and the simultaneous severe flooding that struck India, China, and especially Pakistan.
Now comes Dr. Judah Cohen, Director of Seasonal Forecasting at Atmospheric and Environmental Research, a private consulting firm, with an expansion of my earlier observations. According to an article published in the New York Times Sunday December 26, he suggests that there is very likely a more direct link between warmer oceans and the brutally cold winters we have all been experiencing. He explains this phenomenon clearly, eliminating short-term variations:
"Annual cycles like El Niño/Southern Oscillation, solar variability and global ocean currents cannot account for recent winter cooling. And though it is well documented that the earth’s frozen areas are in retreat, evidence of thinning Arctic sea ice does not explain why the world’s major cities are having colder winters.
"But one phenomenon that may be significant is the way in which seasonal snow cover has continued to increase even as other frozen areas are shrinking. In the past two decades, snow cover has expanded across the high latitudes of the Northern Hemisphere, especially in Siberia, just north of a series of exceptionally high mountain ranges, including the Himalayas, the Tien Shan and the Altai."
Dr. Cohen logically points out that the extremely high topography of the Asian plateau has always been an initiating cause of the jet stream oscillations, since it rises more than two miles into the atmosphere. Winds that normally flow west to east push up against the mountains, and are diverted both over and around them. This process, not unlike the standing waves caused by boulders in a fast-flowing river, is the genesis of a great deal of the turbulence in the jet stream. Those waves propagate
both horizontally and vertically in the atmosphere.
Dr. Cohen advances the further theory, based on observable conditions, that the increasingly heavy snow cover in Siberia and the Asian plateau is caused by the greater moisture available from the defrosted Arctic Ocean. By reflecting more sunlight, the surface air mass over Siberia becomes colder and denser, and so increases the deflecting effects of the plateau, in essence creating an even larger boulder in the stream. The amplified oscillations then ripple around the globe, causing further downstream effects that lead, for example, to extreme snowfall events in New Jersey or London. Since these events are short-term, extreme phenomenon, there is no chance that they will somehow tip the planet into a new ice age. They are simply the reflection of the warmer oceans, which are now massively tipped against a cooling cycle.
Some speculate, in fact, that, had the industrial revolution and our massive release of stored carbon not occurred, we might otherwise be beginning a new cycle of glaciation in the northern hemisphere. They cite the 'Little Ice Age' of the 16th through 19th centuries. Our planetary climate, and the land uses that it dictates, have been in a period of relative stability, slowly warming, since that time. Now that slow warming trend is accelerating, and is approaching a tipping point at which further rapid warming will result from a number of feedback mechanisms. The most threatening is the release of methane clathrates, which could warm the entire globe beyond the tolerable range for most species, including humans.
As is now in evidence, small changes in ocean temperatures can trigger major changes to the entire planetary climate system. The current growing increases in greenhouse gases are no doubt upsetting a number of balances, not only directly in the atmosphere, but also in the pattern of ocean currents. As new patterns emerge and new regimes are established, every species on Earth is likely to be impacted, and forced to adapt to very challenging changes.
Dr. Cohen is an astute observer and predictor of global weather, and has predictions for the immediate future in the U.S. It will be interesting to see how they will play out this winter.