New Study Says Many Climatic Factors Caused 2016 Coral Death and Bleaching

The changing climate has been killing off corals. During the El Niño in 2016, warm water threatened the corals in the Great Barrier Reef (GBR). The CIRES or Cooperative Institute for Research in Environmental Sciences assessed the situation and concluded that global warming, in the long run, will bring additional warmth and damage.

The University of Colorado in Boulder atmospheric & oceanic sciences associate professor and CIRES Fellow Kris Karnauskas said in a new study that 2016 saw a heatwave that swept the coast and blanketed the coral reef system, lasting long into the winter months. This resulted in the death of over half of all corals in many areas in the GBR. The study was published on May 18, 2020, in the journal Geophysical Research Letters.

Karnauskas said that the severe 2016 bleaching of the GBR got the attention of the international community, and theories were put forward regarding its cause, ranging from the El Niño to global warming. The roles played by these factors have not been discounted, so Karnauskas decided to weigh in on the issue.

In his analysis, the Coral Sea's hot waters in Northern Australia had a high enough temperature to kill the corals and cause bleaching, which is particularly true in the northern part of the GBR.

Karnauskas applied mathematical computations plus observational data from satellites to detect the causes of the increase in water temperatures and the time it occurred. He concluded that some key factors interacted to produce the heat that killed the corals. A heatwave from the ocean came first, and then a terrestrial heatwave followed it. The two were magnified due to the increased overall temperatures caused by climate change.

The first heat wave involved El Niño, causing the initial increase in water temperatures by driving away clouds that could have blocked the sun. This was made worse by the effect of climate change in increasing ambient temperatures. This exacerbated the intensity of the heat while also extending it over many more months.

Afterwards, the eastern region of Australia experienced a heatwave coming from land, spilling onto the region's waters almost immediately as the marine heatwave ended.

Karnauskas stated that El Niño played a significant role. The temperature was very high due to the extended warm temperatures trend. However, the heat endured for as long as it did because of the heatwave from the land that lingered in eastern Australia. As the heat from the ocean began to wane, the heat from the ground went to the waters. This altered the heat exchange that usually occurs between the air and the ocean, and it kept the ocean warmer for another few months.

The warm waters caused unprecedented mass coral death. Its months-long persistence also extensively damaged the entire ecosystem, which dramatically changed the region's species composition.

Karnauskas said that his study's results showed how climate change could have severe and compounding impacts. He emphasized the need to increase efforts to determine the complex consequences of climate change due to human activities because it will significantly influence future events.