The Point of No Return
New Zealand’s glaciers showed signs of an unusually severe summer in 2018. Every year, scientists from New Zealand’s National Institute for Water and Atmospheric Research (NIWA) fly over the Southern Alps of New Zealand to record the condition of the country’s glaciers. This year, they noticed that no snow remained from the previous winter.
New Zealand has 3,200 glaciers, and scientists have been observing these glaciers since the late 1970s. Out of 3,200 glaciers, 50 were selected by glaciologist Trevor Chinn to serve as a sample data set representing all of New Zealand’s alps. Of these 50 glaciers, 30 were unable to retain snow from the previous winter.
The “snow line” is the elevation at which the snow from the previous winter sits above exposed ice, but in 2018 the snow kept melting. In other words, 30 of the mountains were not tall enough to reach the potential “snow line.” Unfortunately, this means that these mountains lost snow which could have potentially become the ice necessary for nourishing these glaciers.
Over one-third of all the snow and ice in the Southern Alps melted in recent decades, with warmer temperatures making it difficult for the mountains to retain snow through the summer. In fact, the total volume of ice has decreased by 34 percent since the late 1970s. The Southern Alps of New Zealand have continuously receded at an uneven pace. Some years the glaciers have receded quicker than other years. However, research indicates that the rate at which glaciers are shrinking has accelerated over the past 15 years.
What Made This Summer so Severe?
The same climate scientists from NIWA and others from Victoria University of Wellington argue that the increase in temperature is being caused by a marine heat wave. This is the first time scientists have made a connection between marine heat waves and glacial retreat. A marine heat wave is characterized by extreme sea surface temperatures (SSTs) that last for several months. However, unlike the El Niño-Southern Oscillation (ENSO), which also has extreme SSTs, marine heat waves are not limited to the tropical eastern Pacific Ocean. In fact, marine heat waves have occurred in different locations around the world. It turns out marine heat waves have been around for quite some time, but it is only recently that they have caught the attention of the scientific community.
According to a recent study, one of the earliest significant marine heat waves on record took place in 2003 around the northwestern part of the Mediterranean Sea. The warm pool reached anywhere between three to five degrees Celsius above the 1982 to 2016 reference period. Since then, there have been a total of seven other significant marine heat waves based on the metrics of the study.
What is truly troubling about the frequency of these heat waves is that three out of the eight significant heat waves happened in 2016 alone. That’s not including the other smaller marine heat waves similar to the one which directly affected the glaciers in New Zealand. There seems to be an increasing trend in marine heat waves around the world.
According to another study, the warming and the frequency could be due to anthropogenic forcing. Eric Oliver of the Department of Oceanography at Dalhousie University claims that, according to his findings, heat waves in the region are made 53 percent more likely due to human-induced climate change.
The Dangers of Marine Heat Waves
The most significant marine heat wave to date was nicknamed “the blob.” This marine heatwave stretched all the way from Alaska to Panama and got its name from the way its massive heat signature registered on the map. Between 2013 and 2015 this massive heat wave cost the lives of millions of sea stars, over one hundred thousand seabirds, and thousands of sea lions. In June 2015, over a dozen whales died and washed ashore. Similarly, in a single month, 79 sea otters reportedly died. At one point the heat wave even caused a toxic bloom of algae so large that it shut down California’s crab industry.
The video above explains what caused large numbers of sea otters to die during the marine heat wave (Source: National Geographic).
Off the southeast coast of Australia, another heat wave was recorded shortly after “the blob.” According to another study, between 2015 and 2016, Australia had its longest and most intense heat wave ever recorded. It lasted between 251 days, with heat reaching up to 2.9 degrees Celsius higher than normal. This marine heat wave killed off over one-fifth of the coral in the Great Barrier Reef. The same marine heat wave resulted in the worst mangrove die-off in the world. Over 7,000 hectares of mangroves died during that marine heat wave.
Marine heat waves also have a significant economic impact. A marine heat wave between 2010 and 2013 off the western coast of Australia destroyed 90 percent of the kelp forests in the Great Southern Reef, affecting major fisheries including rock lobsters and abalone fisheries. More recently, the 2016 marine heat wave in the region caused an outbreak of an oyster disease, closing local hatcheries all over the region.
How are Marine Heat Waves Formed?
The term marine heat wave was only coined fairly recently in 2011. Scientists are starting to study the causes of marine heat waves and the extent of their impact on the environment. Some scientists argue that certain marine heat waves are affected by El Niño. For example, “The blob” has been closely associated with the weak 2014-2015 El Niño event. According to studies conducted by researchers at the Georgia Institute of Technology and the National Oceanic and Atmospheric Administration (NOAA), the beginning of the marine heat wave may have started toward the end of 2013 and start of 2014. In 2014, high pressure over the Pacific Ocean led to weaker winds. The winds were unable to bring cooler air from the north which contributed to a slight rise in temperatures in the region. Then, around the middle of 2014, an El Niño event occurred and further intensified the heat wave allowing the warmer temperatures to expand all along the Pacific coast.
On the other hand, Oliver’s research argues that the convergence of heat is somehow linked to the anomalous southward flow of the East Australian Current (EAC) and enhanced kinetic energy which coincided with the 2015 to 2016 marine heat wave off the coast of Australia. The EAC brings warm water down the East coast of Australia into the Tasman Sea.
According to Oliver’s study, a temperature budget, in which “horizontal advection and sea-air heat flux” were also considered, indicated that southward advection was indeed the main cause of the anomalous temperatures. The study goes on the point out that the southward advection was consistent with a stronger southward extension of the EAC. Meanwhile, NIWA forecaster Ben Noll argues that one of the factors that researchers may wish to consider would be the atmospheric pressure. Higher atmospheric pressure in the region keeps the weather conditions calm above the water and fail to produce the winds necessary to churn up cold water from deep in the ocean. This therefore allows warm pools to build up over time.
Researchers and scientists are still trying to understand the causes behind marine heat waves around the world. However, it remains clear that the chances of marine heat waves occurring will continue to increase in the near future, affecting not just marine life but even glaciers.