World's oceans absorbed the same amount of heat last year as 150 MILLION 'Little Boy' atomic bombs that destroyed Hiroshima
- Top portion of ocean absorbed the same energy as 150million Hiroshima bombs
- The world's oceans absorbed 19.67 x 10²² Joules of energy in 2018
- This is the most heat absorbed by the world's oceans since the 1950s
- Experts say ocean temperatures and heat absorption is one of the most robust measurements of greenhouse emissions and global warming
Last year the world's oceans absorbed the same amount of heat as 150million Hiroshima bombs, a new study claims.
Scientists also found 2018 was the worst year for ocean warming since the 1950s.
The top 6,500 feet (2,000 metres) of ocean absorbed 19.67 x 10²² Joules of energy, 388 times more than the total electricity generated in China during 2017.
Following 2018 as the hottest oceanic years on record are 2017, 2015, 2016 and 2014, in descending order.
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Last year the world's oceans absorbed the same amount of heat as 150million Hiroshima bombs, a new study has found. Scientists also found 2018 was the worst year for ocean warming since the 1950s (stock image)
Values from the study are based on ocean temperature analysis conducted by the Institute of Atmospheric Physics (IAP) at Chinese Academy of Sciences.
They collated information from previous studies for the research which included data from the National Oceanic and Atmospheric Administration and the National Center for Environmental Information (NOAA/NCEI).
Latest measurements were aided after 2005 when the Argo observing network was established to significantly improve the reliability and accuracy of ocean measurements.
Observations below 6,500 feet (2,000 metres) are sparse due to technological restrictions and therefore information on ocean heat absorption at these depths remains widely unknown.
Study co-author Dr John Abraham, a Professor of thermal sciences at the University of St. Thomas School of Engineering in the United States, said: 'Over the past year, oceans have absorbed about 150,000,000 Hiroshima bombs worth of heat.'
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A team of academic found the world's oceans absorbed 19.67 x 10²² Joules of energy in 2018.
Little Boy, the atomic bomb dropped on the city of Hiroshima in 1945, released 6.3 x 10¹³ Joules of energy in comparison.
A joule is a standard measurement for 'work done' over a period of time. For example, one Watt of energy is expended when one Joule of energy is expended over one second.
Researchers believe changes in ocean heat content to be one of the best measures of climate change driven by greenhouse gas emissions.
Scientists say because global warming is driven by the Earth's 'energy imbalance' due to more greenhouse gasses in the air, more than 90 per cent of global warming heat is deposited in the world's oceans.
A replica of the atomic bomb nicknamed Little Boy. The captain that dropped the real version of the bomb said it made 'the greatest explosion man has ever witnessed'
They found the ocean heat record is also less impacted by natural fluctuations and is a robust indicator of climate change and therefore act as direct evidence' for global warming.
Study lead author Dr Lijing Cheng said: 'The new data, together with a rich body of literature, serve as an additional warning to both the government and the general public that we are experiencing inevitable global warming.
'The ocean and global warming have already taken place and caused serious damage and losses to both the economy and society.'
He warned that action needs to be taken 'immediately' to minimise future warming trends.
The researchers also highlight that the increases in ocean water heat are 'causes for additional concern' to both the scientific community as well as the public at large.
The findings were published in the journal Advances in Atmospheric Sciences.
WHAT ARE MARINE HEATWAVES AND WHAT DO WE KNOW ABOUT THEM?
On land, heatwaves can be deadly for humans and wildlife and can devastate crops and forests.
Unusually warm periods can also occur in the ocean. These can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries.
Yet until recently, the formation, distribution and frequency of marine heatwaves had received little research attention.
Long-term change
Climate change is warming ocean waters and causing shifts in the distribution and abundance of seaweeds, corals, fish and other marine species. For example, tropical fish species are now commonly found in Sydney Harbour.
But these changes in ocean temperatures are not steady or even, and scientists have lacked the tools to define, synthesize and understand the global patterns of marine heatwaves and their biological impacts.
At a meeting in early 2015, we convened a group of scientists with expertise in atmospheric climatology, oceanography and ecology to form a marine heatwaves working group to develop a definition for the phenomenon: A prolonged period of unusually warm water at a particular location for that time of the year. Importantly, marine heatwaves can occur at any time of the year, summer or winter.
Unusually warm periods can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries worldwide (pictured)
With the definition in hand, we were finally able to analyse historical data to determine patterns in their occurrence.
Analysis of marine heatwave trends
Over the past century, marine heatwaves have become longer and more frequent around the world. The number of marine heatwave days increased by 54 per cent from 1925 to 2016, with an accelerating trend since 1982.
We collated more than 100 years of sea surface temperature data around the world from ship-based measurements, shore station records and satellite observations, and looked for changes in how often marine heatwaves occurred and how long they lasted.
This graph shows a yearly count of marine heatwave days from 1900 to 2016, as a global average.
We found that from 1925 to 1954 and 1987 to 2016, the frequency of heatwaves increased 34 per cent and their duration grew by 17 per cent.
These long-term trends can be explained by ongoing increases in ocean temperatures. Given the likelihood of continued ocean surface warming throughout the 21st century, we can expect to see more marine heatwaves globally in the future, with implications for marine biodiversity.
'The Blob' effect
Numbers and statistics are informative, but here's what that means underwater.
A marine ecosystem that had 30 days of extreme heat in the early 20th century might now experience 45 days of extreme heat. That extra exposure can have detrimental effects on the health of the ecosystem and the economic benefits, such as fisheries and aquaculture, derived from it.
A number of recent marine heatwaves have done just that.
In 2011, a marine heatwave off western Australia killed off a kelp forest and replaced it with turf seaweed. The ecosystem shift remained even after water temperatures returned to normal, signalling a long-lasting or maybe even permanent change.
That same event led to widespread loss of seagrass meadows from the iconic Shark Bay area, with consequences for biodiversity including increased bacterial blooms, declines in blue crabs, scallops and the health of green turtles, and reductions in the long-term carbon storage of these important habitats.
Examples of marine heatwave impacts on ecosystems and species. Coral bleaching and seagrass die-back (top left and right). Mass mortality and changes in patterns of commercially important species s (bottom left and right)
Similarly, a marine heatwave in the Gulf of Maine disrupted the lucrative lobster fishery in 2012. The warm water in late spring allowed lobsters to move inshore earlier in the year than usual, which led to early landings, and an unexpected and significant price drop.
More recently, a persistent area of warm water in the North Pacific, nicknamed 'The Blob', stayed put for years (2014-2016), and caused fishery closures, mass strandings of marine mammals and harmful algal bloom outbreaks along the coast. It even changed large-scale weather patterns in the Pacific Northwest.
As global ocean temperatures continue to rise and marine heatwaves become more widespread, the marine ecosystems many rely upon for food, livelihoods and recreation will become increasingly less stable and predictable.
The climate change link
Anthropogenic, that is human-caused, climate change is linked to some of these recent marine heatwaves.
For example, human emissions of greenhouse gases made the 2016 marine heatwave in tropical Australia, which led to massive bleaching of the Great Barrier Reef, 53 times more likely to occur.
Even more dramatically, the 2015-16 marine heatwave in the Tasman Sea that persisted for more than eight months and disrupted Tasmanian fisheries and aquaculture industries was over 300 times more likely, thanks to anthropogenic climate change.
For scientists, the next step is to quantify future changes under different warming scenarios. How much more often will they occur? How much warmer will they be? And how much longer will they last?
Ultimately, scientists should develop forecasts for policy makers, managers and industry that could predict the future impacts of marine heatwaves for weeks or months ahead. Having that information would help fishery managers know when to open or close a fishery, aquaculture businesses to plan harvest dates and conservation managers to implement additional monitoring efforts.
Forecasts can help manage the risks, but in the end, we still need urgent action to curb greenhouse gas emissions and limit global warming. If not, marine ecosystems are set for an ever-increasing hammering from extreme ocean heat.
Source: Eric Oliver, Assistant Professor, Dalhousie University; Alistair Hobday, Senior Principal Research Scientist - Oceans and Atmosphere, CSIRO; Dan Smale, Research Fellow in Marine Ecology, Marine Biological Association; Neil Holbrook, Professor, University of Tasmania; Thomas Wernberg, ARC Future Fellow in Marine Ecology, University of Western Australia in a piece for The Conversation.
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