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Earth’s Ocean Absorbed 338 Zettajoules Of Heat Energy From 1991 To 2016

[Estimated read time: 3 minutes]
  • Between 1991 and 2016, Earth’s ocean absorbed 150 times more heat energy than the energy produced by humans as electricity annually. 
  • Oceans took up nearly 13 zettajoules of heat energy every year.

Earth has more than 332,519,000 cubic miles of water, as per the U.S Geological Survey. About 97% of this volume can be found in oceans, and less than 1% of all Earth’s water is fresh. A small fraction of water is present in our atmosphere in the form of vapor.

The ocean is the primary source of thermal inertia in the environmental system. Over the last couple of decades, the heat absorbed by the ocean has been calculated by hydrographic temperature measurement and Argo float project. However, these calculations rely on inaccurate ocean datasets and uncertainties that arise due to sparse coverage, especially before 2007.

Recently, researchers at Princeton University tried to measure the precise amount of heat energy world’s oceans have absorbed. They found that for each year between 1991 and 2016, the oceans absorbed 150 times more heat energy than the energy produced by humans as electricity annually. The reports indicate that our planet is more sensitive to fossil-fuel emission than previous estimations.

More specifically, the oceans took up nearly 13 zettajoules — one zettajoule is sextillion (1021) joules — of heat energy every year. This is 60% greater than what was published by the United Nations Intergovernmental Panel on Climate Change (IPCC) in the 2014 Fifth Assessment Report.

The Average Temperature Of Oceans Is Rising Significantly

According to this report, if the Earth’s ocean was only 9 meter deep, its temperature would have increased by 6.5°C every 10 years since 1991. Since world’s oceans absorb almost 90% of all the excess energy generated as Earth warms, calculating the exact quantity of energy could help researchers determine the surface warming and climate sensitivity that is used to measure acceptable emission for mitigation approaches.

Over the last 10 years, scientists have agreed that if the average temperature of Earth goes beyond pre-industrial scales by 2 degree Celsius, people will certainly face hazardous consequences of global warming.

To prevent temperatures from exceeding this threshold, it is necessary to reduce greenhouse gas and carbon dioxide emission by 25% compared to earlier estimations.

Reference: Nature | doi:10.1038/s41586-018-0651-8 | Princeton University

Techniques Used For Calculating Heat Content In The Ocean

This is the first time someone has used an independent measuring method to estimate how much heat oceans absorbed during the past quarter century.

Earlier studies interpolated millions of spot measurements of ocean climate to find out the total amount of heat content. However, gaps in coverage weren’t certain, leading to inaccurate calculations.

Ocean Absorbed Heat Energy in Zettajoules

This time, they have used Argo — a mesh of robotic sensors — to make comprehensive measurements of oceans’ salinity and temperature. However, it only contains datasets of after 2007 and only accounts for the upper half of the ocean. In the last few couples of years, numerous reassessments have been made regarding heat content, including the Argo project, which has finally lead to the revision of IPCC reports.

To accurately calculate the amount of heat oceans have stored (during 1991-2016), researchers utilized high-precision measurements of carbon dioxide and oxygen. They analyzed the combined amount of  COand  O2 in air and gave it a name APO (short for atmospheric potential oxygen).

The mechanism relies on the fact that both carbon dioxide and oxygen are less soluble in warm water. These compounds release into the air as the temperature of ocean increases, raising APO levels. Also, burning fossil fuels greatly affects the APO levels.

Read: 15 Facts About Global Warming That Show Climate Change Is Real

Researchers compared these APO changes with the changes caused by CO2  update and fossil-fuel use, to evaluate the amount of APO emanated from the ocean. The amount matches the ocean’s heat-energy content.

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