What are marine heat waves, which have gripped parts of the world’s oceans this summer?

Source: The post is based on the article “What are marine heat waves, which have gripped parts of the world’s oceans this summer?”  published in Indian Express on 24th July 2023.

What is the News?

Since April 2023, ocean temperatures have remained at record-high levels giving rise to Marine Heat Waves (MHWs) around the globe.

What are Marine Heat Waves (MHWs)?

A marine heat wave is an extreme weather event. It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degree Celsius above the average temperature for at least five days. MHWs can last for weeks, months or even years.

What is the impact of marine heat waves on ocean life?

An increase of 3 or 4 degrees Celsius in average temperatures may not impact humans a lot.But it can be catastrophic for marine life. 

For instance, MHWs along the Western Australian coast during the summer of 2010 and 2011 caused unexpected death of many fish or other aquatic animals over a short period of time.

– Another example is when high ocean temperatures in the tropical Atlantic and Caribbean in 2005 led to a massive coral bleaching event.A 2010 study showed that more than 80% of surveyed corals had bleached and over 40 per cent of the total surveyed had died. 

– MHWs also fuel the growth of invasive alien species, which can be destructive to marine food webs.

How do marine heat waves affect humans?

Higher ocean temperatures, which are associated with MHWs, can make storms like hurricanes and tropical cyclones stronger. 

With warmer temperatures, the rate of evaporation escalates and so does the transfer of heat from the oceans to the air.When storms travel across hot oceans, they gather more water vapour and heat. 

This results in more powerful winds, heavier rainfall and more flooding when storms reach the land — meaning heightened devastation for humans.

How is global warming affecting marine heat waves and oceans?

According to a 2018 study titled ‘Marine heatwaves under global warming’ due to increase in global temperatures, MHWs have become longer-lasting, more frequent and intense in the past few decades. The study has also attributed 87 percent of MHWs to human-induced warming.

Moreover, according to Copernicus Climate Change Service, oceans have absorbed 90% of the additional heat caused by the release of greenhouse gases into the atmosphere from burning fossil fuels and deforestation in recent decades.This has increased the global mean sea surface temperature by close to 0.9 degree Celsius since 1850.

Hence, as global air temperatures increase, so will ocean temperatures leading to more MHWs.