Oceans are warming twice as fast than the 1960s and it could get much worse

Oceans are warming twice as fast than the 1960s and it could get much worse

Subject : Geography

Context: The rate at which oceans are globally warming has doubled from the 1960s to the 2010s, a recent study has found. The top 2,000 metres of the global ocean has gained 351 zettajoules during 1958-2019. For context, a zettajoule is 10 to the power of 21 or 1,000,000,000,000,000,000,000 joules.

Concept:

• As humans emit greenhouse gases into the atmosphere, it causes the Earth to warm. The vast majority of the heat ends up in the ocean (more than 90 per cent). So, to understand how fast the Earth’s climate is changing, we must look to the ocean and track ocean heat content change.
• The rate of warming increased from 5 to 10 ZJ per year from the 1960s to the 2010s, it said.
• The Atlantic Ocean is warming the fastest, reporting the largest area-averaged warming at 1.42 joule per square metre. The Southern Ocean is next, at 1.40 joule per square metre for the upper 2,000 m from 1958–2019.
• The relentless increase in the ocean heat content has direct implications for the frequency, intensity and extent of marine heat waves (MHW) and other hotspots within the ocean.

Marine heat waves (MHW)

• Marine heat waves (MHW) are periods of increased temperatures overseas and oceans for extended period of time impacting marine life.
• Such heat waves are caused by an increase in the heat content of oceans, especially in the upper

What causes marine heat waves?

The most common drivers of marine heatwaves include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere. Winds can enhance or suppress the warming in a marine heatwave, and climate modes like El Niño can change the likelihood of events occurring in certain regions.

Worldwide, they are one of the major results of human-induced global warming.

During an MHW, the average temperatures of the ocean surface (up to a depth of 300 feet) goes 5-7 degrees Celsius above normal.

Climate change and Marine Heat Wave:

• Human-induced global warming and higher ocean heat content lead to more abundant, extensive and longer-lasting MHW. This has a huge impact on ocean ecosystems and marine life.

Impact of Marine Heat Waves:

• The prolonged MHW in the northeast Pacific and Gulf of Alaska from 2014 and 2016, known as ‘the blob’ saw seabird die-offs, declines in forage fish populations, and the appearance of subtropical marine taxa (ocean sunfish, skipjack tuna) in the northern Gulf of Alaska.
• About 62,000 dead or dying common murres, a dominant fish-eating seabird of the North Pacific, washed ashore between the summer 2015 and spring 2016 on beaches from California to Alaska. Scientists estimated that the total mortality was around 1 million birds.
• Ocean warming also has an effect on tropical cyclones and associated changing ocean surface currents can indirectly affect pathways of storms. In August 2017, the Gulf of Mexico became the warmest on record to that point in the summertime.
• The Gulf of Mexico ocean heat loss during Harvey matched the latent heat released by Harvey rainfall and thereby fuelled the storm, said a May 9, 2018 study published in Earth’s Future. Ocean heat content was the highest on record just before the northern summer of 2017, supercharging Atlantic hurricanes Harvey, Irma and Maria.