16 March 2016, The Conversation ,Droughts and flooding rains: it takes three oceans to explain Australia’s wild 21st-century weather. Australia is a land of extremes, and famously of “droughts and flooding rains”. That’s been truer than ever in the 21st century; since 1999 the country has see-sawed from drought to deluge with surprising speed. There was the millennium drought, which lasted more than a decade and culminated in disasters such as Victoria’s Black Saturday bushfires in 2009. Then, in 2011, Cyclone Yasi struck Queensland and a large swathe of Australia exploded under a green carpet of grasses, shrubs and trees. Filming of the movie Mad Max: Fury Road was moved from outback Australia to Namibia after the big wet of 2010-11, because Australia’s luxurious growth of wildflowers and metre-high grasses didn’t quite match the post-apocalyptic landscape the movie’s producers had in mind. In Alice Springs, the Henley-on-Todd Regatta was almost cancelled in 2011 because there was water in the normally dry river. Globally, the big wet on land caused a 5 mm drop in sea levels as large amounts of rain were deposited on Australia, South America and Africa. This coincided with an unprecedented increase in carbon stored in vegetation, especially in arid and semi-arid regions of the southern hemisphere. The greening of Australia in particular had a globally significant impact. Meteorologists have struggled to explain these wild variations in Australia’s weather. Dry years with disappointing crops have been linked to the Pacific Ocean’s El Niño phase (part of a cycle called the El Niño-Southern Oscillation (ENSO)). But despite its huge influence, not even ENSO can fully account for Australia’s extreme rainfall patterns. Our research, published this week in Nature’s Scientific Reports, offers an explanation. We found that conditions in the three oceans that surround Australia – the Pacific, Indian and Southern Oceans – combine to amplify each other’s influences on Australian weather. Read More here
Tag Archives: oceans
14 March 2016, The Guardian, Severe coral bleaching worsens in most pristine parts of Great Barrier Reef. Expert blames global warming, as coral bleaches when water temperatures go above a certain threshold for an extended period of time. Damage to parts of the Great Barrier Reef has worsened, leading authorities to raise the alert to the second-highest level, indicating severe local coral bleaching. The bleaching is worst in the most pristine and remote parts of the reef north of Cairns, according to Terry Hughes, convenor of the National Coral Taskforce. “It’s the jewel in the crown of the Great Barrier Reef and it’s now getting a quite a serious impact from this bleaching event,” he said. “The northern reefs are bleaching quite badly now.” Hughes said it appeared there was some coral death occurring in northern reefs. Russell Reichelt, the chairman of the Great Barrier Reef Marine Park Authority said the area around Lizard Island, 250km north of Cairns, and sites further north, had fared the worst. The US National Oceanographic and Atmospheric Administration predicts bleaching conditions to worsen over the coming weeks. The world is currently in the grips of the third global coral bleaching event. Coral bleaches when water temperatures are raised above a certain threshold for an extended period of time. Hughes, director of the ARC centre of excellence for coral reef studies at James Cook University, said although the strong El Niño occurring now is partly to blame for the bleaching event, the real culprit is global warming caused by carbon emissions. Read More here
14 March 2016, The Conversation, Tipping point: how we predict when Antarctica’s melting ice sheets will flood the seas. Antarctica is already feeling the heat of climate change, with rapid melting and retreat of glaciers over recent decades. Ice mass loss from Antarctica and Greenland contributes about 20% to the current rate of global sea level rise. This ice loss is projected to increase over the coming century. A recent article on The Conversation raised the concept of “climate tipping points”: thresholds in the climate system that, once breached, lead to substantial and irreversible change. Such a climate tipping point may occur as a result of the increasingly rapid decline of the Antarctic ice sheets, leading to a rapid rise in sea levels. But what is this threshold? And when will we reach it? What does the tipping point look like? The Antarctic ice sheet is a large mass of ice, up to 4 km thick in some places, and is grounded on bedrock. Ice generally flows from the interior of the continent towards the margins, speeding up as it goes. Where the ice sheet meets the ocean, large sections of connected ice – ice shelves – begin to float. These eventually melt from the base or calve off as icebergs. The whole sheet is replenished by accumulating snowfall. Floating ice shelves act like a cork in a wine bottle, slowing down the ice sheet as it flows towards the oceans. If ice shelves are removed from the system, the ice sheet will rapidly accelerate towards the ocean, bringing about further ice mass loss. A tipping point occurs if too much of the ice shelf is lost. In some glaciers, this may spark irreversible retreat. Read More here
14 March 2016, Nature Geoscience, Impacts of warm water on Antarctic ice shelf stability through basal channel formation. Antarctica’s ice shelves provide resistance to the flow of grounded ice towards the ocean. If this resistance is decreased as a result of ice shelf thinning or disintegration.1 , acceleration of grounded ice can occur, increasing rates of sea-level rise. Loss of ice shelf mass is accelerating, especially in West Antarctica, where warm seawater is reaching ocean cavities beneath ice shelves 2 . Here we use satellite imagery, airborne ice-penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding Antarctica. The highest density of basal channels is found in West Antarctic ice shelves. Within the channels, warm water flows northwards, eroding the ice shelf base and driving channel evolution on annual to decadal timescales. Our observations show that basal channels are associated with the development of new zones of crevassing, suggesting that these channels may cause ice fracture. We conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas. Read More here. See also Washington Post article here