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Scientists from the ARC Centre of Excellence for Coral Reef Studies document the worst mass coral bleaching event ever recorded.
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Fourth mass bleaching event strikes Great Barrier Reef

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Scott Sutherland
Meteorologist/Science Writer

Thursday, March 16, 2017, 6:41 PM - The Great Barrier Reef is suffering through yet another mass coral bleaching, NASA logs February 2017 as the 2nd warmest February on record, and sea ice at both poles suffers through historic lows.

Yet another mass bleaching for the Great Barrier Reef

It was only around a year ago that ocean scientists revealed the extent of the damage suffered by the Great Barrier Reef, as its northern sections underwent the worst mass coral bleaching event ever witnessed. 

As The Weather Network reported at the time:

Flying up and down the northeastern coastline of Australia, scientists with the ARC Centre of Excellence for Coral Reef Studies have been documenting the conditions on the Great Barrier Reef, and have now returned with the dire news.
Over 900 coral reefs were surveyed, with the worst of the bleaching located in the northern region.
"Between 60 and 100 per cent of coral are severely bleached on 316 reefs, nearly all in the northern half of the Reef," Terry Hughes, director of the ARC Centre, said in a press release.
In addition, scientists have reported nearly 50 per cent coral death in the northern reef. Meanwhile, most of the reefs in the southern end have minor to moderate bleaching and should soon recover.
”Of all the reefs surveyed, only 7 per cent have escaped bleaching," added Hughes.

Warm ocean waters off the northern and northeastern coast of Australia, partially elevated by the effects of a record-setting El Niño event going on at the time, were forcing the corals of the reef to expel the colourful algae that inhabit them. This caused large regions of the reef to turn white - the natural colour of the corals - and without the algae, which provide the corals' most important food source, many areas of the reef died. 

That was the third mass bleaching event in the past 20 years, as scientists observed large sections of the Great Barrier Reef turn white in 1998, 2002 and then again in 2016.


The extent and severity of the past three mass coral bleachings, as measured by aerial survey. Dark green = < 1% of corals bleached, light green = 1–10%, yellow = 10–30%, orange = 30–60%, red = > 60%. Credit: Hughes, et al.

Discussing the 2016 event, Terry Hughes, of the ARC Centre of Excellence for Coral Reef Studies, told the New York Times on Wednesday, "We didn’t expect to see this level of destruction to the Great Barrier Reef for another 30 years."

"In the north, I saw hundreds of reefs -- literally two-thirds of the reefs were dying and are now dead," Hughes said.

In a study published in Nature on Wednesday, in which Hughes led an international team of 45 other scientists to examine the severity of these mass bleaching events and their relation to global warming, the authors found that:

• only 9 per cent of the corals in the Great Barrier Reef had escaped these three events without some level of bleaching,
• no adaptation or resistance to bleaching was observed in corals that were affected by more than one event,
• heat stress due to rising ocean temperatures was the primary cause and are affording corals less recovery time, and
• urgent and rapid action to reduce global warming is needed to prevent more frequent and severe bleaching events.

In addition, the paper discussed the likelihood of another mass bleaching event occurring in the next decade or two, but as it turns out, the word now is that yet another mass bleaching event is currently affecting the Great Barrier Reef.

"Mass bleaching is occurring on the Great Barrier Reef for the second consecutive year," Dr. David Wachenfeld, the director of reef recovery for the Great Barrier Reef Marine Park Authority, said in an Australian Institute of Marine Science (AIMS) press release last week.

"How this event unfolds will depend very much on local weather conditions over the next few weeks," he said.


Alert areas for the waters off northeastern Australia, from Dec 16, 2016 to March 15, 2017. The colours denote alert levels, which rose dramatically as ocean temperatures in the region increased over the past 90 days. Credit: NOAA Coral Reef Watch

"We are seeing a decrease in the stress tolerance of these corals. This is the first time the Great Barrier Reef has not had a few years between bleaching events to recover," Dr. Neal Cantin, from AIMS, said in the press release.

NASA reports: February 2017 2nd warmest on record

It will be tough to beat the record temperatures set across the globe in 2016, but 2017 isn't falling too far behind, so far.


Global temperature anomalies for February 2017, showing extreme heat over eastern North America, eastern Siberia and across the Arctic. Credit: NASA GISS

Having tallied their records for the month, NASA's Goddard Institute for Space Sciences ranks February 2017 as the 2nd hottest month of February in the record books, going back 137 years. It came in at 1.1oC warmer than the 1951-1980 February mean temperature (a period used as it provides a good representation of 20th century average temperatures), and 0.2oC cooler than February 2016.


NASA's GISTEMP monthly temperature anomalies, superimposed on a 1980-2015 mean seasonal cycle. Credit: NASA GISS

With the equatorial Pacific Ocean slipping into a La Niña pattern towards the end of last year, it was assumed that 2017 would not continue the trend of "new warmest year on record" that we have seen from 2014-2016. However, with La Niña calling it quits in mid-February, global temperatures lagging only slightly behind 2016, and now the possibility that we will see another El Niño develop later this year, there is the wonder if that brief episode of cooling across the Pacific will have a big enough impact.

We'll be watching closely in the months to come, to see where the temperature trend is going.

Record low Antarctic Sea Ice, and new record low for the Arctic?

Based on records kept by the U.S. National Snow and Ice Data Center, on March 3, 2017, Antarctic sea ice reached its lowest summer minimum extent on the books, going back to 1979.


Antarctic sea ice extent, in millions of square kilometres. Credit: NSIDC/S. Sutherland

As shown in the graph, sea ice extent in the southern ocean waxes and wanes throughout each year, reaching a maximum extent around the end of the southern winter (September-October) and a minimum extent around the end of the southern summer (late Feb - early March).

In recent years, sea ice extents around Antarctic were seen to reach some record or near-record high levels, however that changed in 2016, as the extent skirted the lower end of the range seen in the records, and then dropped into a record low streak that has lasted from November to the present day.

Looking to the other end of the Earth, on March 7, 2017, Arctic sea ice extent appeared to reach its winter maximum for the year, and if so - if sea ice extent in the North does not increase significantly before the end of the season - this will be a new record for lowest winter maximum extent seen in the dataset.


Arctic sea ice extent, in millions of square kilometres. Credit: NSIDC/S. Sutherland

If this is the highest extent the ice reaches in the Arctic for this winter, it will be the third consecutive lowest winter maximum on record.

Sources: NYTARC Centre of Excellence for Coral Reef Studies | AIMS | NOAANASA | NSIDC

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