Record Hot Summer Wreaks Havoc: Low Ice and Coral Bleaching

Eli Kintisch Science Now 15 Sep 10;

Record-breaking summer temperatures and the warmest year to date in 131 years are wreaking havoc on the global environment, say climate scientists.

The National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, is about to report near-record loss of sea ice this summer, and modelers say total ice volume is at a record low. Meanwhile, the National Oceanic and Atmospheric Administration (NOAA) has issued warnings about coral bleaching throughout the Caribbean, a problem exacerbated by high water temperatures in the Atlantic Ocean.

According to NASA's Goddard Institute for Space Studies, the first 8 months of 2010 is the warmest such January-to-August period in climate records stretching back 131 years. This period was nearly 0.7˚C warmer than the average temperature from 1951 to 1980. (NOAA announced roughly the same finding today, using many of the same temperature stations but a different analysis method.) Scorching summer temperatures set records across the United States, and nighttime temperatures hit record highs in 37 U.S. states this summer, the Natural Resources Defense Council will announce in a new report tomorrow.

Science has learned that NSIDC expects this summer to yield the third lowest area of ice "extent" in the Arctic. The ice has reached its yearly minimum, which generally occurs in September.

"Extent" means the area of icy water—essentially, areas with more than 15% of the surface covered with ice. The past 4 years have yielded the four smallest extents of sea ice in the Arctic, says NSIDC.

NSIDC climatologist Julienne Stroeve told ScienceNOW that warmer-than-average ocean temperatures were a factor in this summer's sea-ice losses, but so are circulation patterns that push sea ice toward the pole, opening up water that can be warmed by the sun. In addition, she notes, "there's a lot less of the old ice" in the Arctic due to its recent formation and relative thinness.

Arctic experts at the University of Washington use temperature, satellite, and weather data in a computer model to estimate the total volume of ice in the area. According to their model, the total ice volume in the Arctic is now at an all-time low, nearly 10,000 cubic kilometers less than the average of the past 30 years. "We think there is a lot of thin ice up there, but there's little data to validate [that]," says Ron Lindsay of the University of Washington, Seattle. Overall, he says, the model suggests a stunning 17% loss of ice volume per decade.

A moderate El Niño event that began last year and ended earlier this summer has contributed to rising global ocean temperatures. El Niño periods, characterized by a redistribution of heat in the Pacific Ocean, lead to warming on the western and eastern sides of the Pacific and the western Atlantic. A very vigorous 1997–98 El Niño led to record-setting temperatures over the oceans and land. Even though this year's warming due to El Niño is smaller, trends in ocean temperature have roughly matched 1997–98 thus far due to an overall warmer system. The trend is especially clear in waters near the equator.

The biggest immediate effect of warmer ocean temperatures in the tropics has been the extraordinary death of corals, as Science laid out 3 weeks ago:

Reefs on both sides of the Thai Peninsula were hit, with up to 100% of some coral species bleached, says James True, a coral biologist at Prince of Songkla University in Hat Yai, Thailand. He expects at least 80% of the most sensitive species to die. "A few inshore reefs got so badly damaged, they probably won't ever come back to the way they were," he says. Among surviving corals, "disease is rampant," True says, with two to three times the usual incidence of necrotic lesions and growth anomalies. Similar reports of "quite extensive bleaching" have come from Vietnam and through the heart of the Coral Triangle in Indonesia and the Philippines.

Experts told Al Jazeera that up to 20% of the coral off the shore of Malaysia could die this fall. A dive instructor interviewed there said he had seen neither bleached coral nor 34˚C water in 6 years of working there. The Malaysian government has closed 13 sites to divers and snorkelers to try to mitigate the damage.

Meanwhile, in the Caribbean, according to a new bulletin put out by NOAA last week:

The NOAA Coral Reef Watch (CRW) satellite coral bleaching monitoring shows sea surface temperatures continue to remain above average throughout the wider Caribbean region. Large areas of the southeastern Caribbean Sea are experiencing thermal stress capable of causing coral bleaching. The western Gulf of Mexico and the southern portion of the Bahamas have also experienced significant bleaching thermal stress. The CRW Coral Bleaching Thermal Stress Outlook ... indicates that the high stress should continue to develop in the southern and southeast Caribbean until mid-October . Bleaching stress in the western Gulf of Mexico and southern Bahamas should dissipate quickly in the next couple of weeks.

A reprieve from the sweltering temperatures is coming, but it will only be temporary. Columbia University's Richard Seager says the now-ended El Niño phase has been followed by a La Niña phase, which usually means cooler average global ocean and land temperatures. El Niño will eventually return. More importantly, as the planet's average temperature warms, Seager says, the El Niño-La Niña cycles "cancel one another out."