El Niño and La Niña are two opposite weather patterns that occur in the central tropical Pacific Ocean. El Niños are associated with warming trends and La Niñas with cooling trends. The patterns are not that predictable, generally occurring every 2 to 7 years and lasting 1 to 2 years. Scientists sometimes describe “El Nino like conditions” in the Atlantic to explain hurricane intensities and frequencies in that area.
Pacific Decadal Oscillations or PDOs are El Niño like patterns of the Pacific climate, except that they last 20 to 30 years as opposed to the 1 to 2 year cycles of El Niños. In 1977, a major PDO (also known as the Great Pacific Climate Shift) occurred resulting in warmer surface temperatures along the west coast of North America. The effect has been to push the jet stream across North America further north. Scientists are debating if a shift back to a cooler cycle has occurred yet.
Atlantic Multidecadal Oscillations (AMOs) are similar to PDOs except that they occur in the Atlantic in the area between the equator and Greenland. The warming cycles are considered to be responsible for past long droughts in the Midwest and Southwest areas of North America.
Arctic Oscillations are reversals in decade long migration patterns of warmer and more saline ocean currents in the Arctic Ocean. This natural cycle is believed to have amplified the natural warming trend from the late 1970s through at least the 1990s in the Arctic region.
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Also, according to some scientists, the current rate of melting of the massive ice sheets in Greenland and Antarctica and mountain glaciers could cause sea levels to rise by 2 to 6 feet in this century. To put it in perspective, the water volume contained in Greenland’s ice alone is roughly the same as the volume of water in the Gulf of Mexico.
Supporting Websites Science Daily Oceana Union of Concerned Scientists
For example, the melting of glaciers in Montana’s Glacier National Park and Alaska could in large part be attributed to the warm cycle of the Pacific Decadal Oscillation that began in 1977and the Arctic Oscillation that began about the same time. If these long term oscillations have recently reversed as some scientists believe, then we should start seeing a slowing of the rate of glacier melt in this region in the next few years.
On a much longer time scale, ice cores from Greenland and Antarctica have shown large variability and sometimes abrupt changes in temperatures over the past 110,000 years. Greenland’s temperatures have cycled up and down over time. Contradicting current reports on glacial melting, an article in the Heartland Institute website states that “the last two decades of the twentieth century were the coldest decades for Greenland since the 1910s.” A 2008 paper in ICECAP states that “the ice between Canada and southwestern Greenland has reached its highest level in 15 years”. Temperatures of minus 30 degrees Celsius have expanded the ice mass to its most southern extent in 15 years.
Opposing Websites Heartland Institute ICECAP, International Climate and Environmental Change Assessment Project Reason Online Weather Underground: Abrupt Climate Change World Climate Report