 |
||||||||||
|
||||||||||
Australian scientists conclude that winds have increased by 5 to 10% in velocity over the world's oceans during the last 17 years, and that extreme winds (the top one percent of wind speed values) have increased in speed even more than the average winds have. Reporting in the April 22 Science, the three scientists I. R. Young, S. Zieger and A. Babanin of Swinburne University in Melbourne used perhaps the most accurate tool now available, radar altimeters on board the GEOSAT satellites, to map winds and waves over the oceans. The most extreme winds are now 15% stronger over nearly all areas of the ocean. Waves are pushed along by the winds, so it is not surprising that wave heights have also increased over many areas. The relationship is more complex, however, as long-period "sea swell" originates in faraway storms, while local waves are caused by local winds. Where a crest of swell meets a local wave crest, the two waves add such that a high mound of water appears. So average and maximum wave heights are related not just to the strength of the local wind, but also to the power and duration of distant storms. The 23-year trend in wave heights is not as significant nor as easy to explain as the upward trend in wind speeds; in fact, there is no trend for monthly-average wave heights. But the most extreme waves (the top 1% of wave heights) have increased in height, and the increase is statistically significant. Height of these large waves grew by 10% over 20 years (satellites have measured the trend for 23 years), in the temperate latitudes of the oceans, from latitudes 35° to 60° in both Northern and Southern hemispheres. Waves have apparently not grown in most of the Tropical oceans, even though wind speeds have increased on average in the Tropics. In these regions, sea swell affects the wave regime more than locally generated winds do. These findings support the work of Oregon’s Peter Ruggiero, who looked at data from two offshore buoys in the Pacific Ocean 250 miles west of that state. The buoys reported an 18% increase in significant wave height during the 30 years ending in 2007. (The term “significant waves” refers to the highest one-third of all observed waves.) Ruggiero did not examine the causes for the shift in Pacific wave strength. But the Intergovernmental Panel on Climate Change (IPCC) did look at causes that now explain the stronger winds that the Australians found and the stronger waves that both groups found. IPCC scientists documented lower surface air pressure in the Bering Sea and the Arctic Ocean, plus higher air pressure in the subtropical belt, plus a northward shift in the same belt of high pressure. Together, these changes would strengthen the winds over the North Pacific Ocean. The IPCC found the greatest wave size increases in the northeast Pacific Ocean near North America. They considered it likely that the shifts in the pressure pattern were due in part to human influence. We may conclude that the changing wind and wave climate of the oceans is another human influence. CITATIONS:“Global Trends in Wind Speed and Wave Height” by I.R. Young, S. Zieger, and A.V. Babanin (2011). Science, v. 332, 22 April 2011, p. 451–455. “Increasing
wave heights and extreme-value projections: the wave climate
of the U.S. Pacific Northwest” by Peter Ruggiero,
P.D. Komar, and J.C. Allen (2010). Coastal Engineering,
v. 57, May 2010, p. 539-552.
|
Europe’s Hot Summers of 2003/2010 break 500-year recordMuch of the central and eastern two-thirds of the USA is now in the grip of a pronounced heat wave, as of this July. How often has it been exceptionally warm in the first years of the twenty-first century? According to scientists from four European nations, the hot summers of 2010 and 2003 likely exceeded the warmth of any other summer in the last 500 years in one-half of Europe. Their conclusion appeared in the 8 April, 2011 issue of Science ( note, below). The
heat wave of 2003 was responsible for about 70,000 heat-related
deaths in central and western Europe (mainly in France). And last
year, well-populated western Russia and surrounding
countries like the Ukraine and Finland roasted. Some 55,000
people died in Russia from the heat. That country suffered
economic losses of $15 billion, or about 1% of its gross domestic
product, from numerous wildfires and crop failures. The intensity
and extent of the 2010 heat wave surpassed the 2003
event. The European scientists looked at both historical climate records and “proxy” records from sediments, tree rings and other clues since the year 1500. They found that temperatures in the past ten years surpassed those in any other decade since 1500. In other words, the 2003 and 2010 summers were likely hotter than any in the five centuries up to 2000. In the last ten years, the area of Europe that has ever had a summer warmer than 99% of the summers in the 30-year period from 1971 to 2000 has doubled. There may be other clever ways that statisticians can say this; but recent summers have been remarkably hot! Might the summer climate of Europe be influenced by global warming? The authors reviewed climate model experiments and concluded that a summer like 2003 is projected to occur again by mid-century (2050), but not a summer as warm as 2010. However, by the year 2100, a summer like 2010 may occur roughly every eight years in Eastern Europe. CITATION:
|
| ||||||||
