Environment

New records were set in 2021 for rising sea levels, greenhouse gas and ocean heat

Four out of seven "key climate indicators" hit records levels in 2021, scientists have revealed.

A diver observes coral bleaching.

High ocean temperatures lead to coral bleaching. Image: Ocean Agency / XL Catlin Seaview Survey / Richard Vevers

Greenhouse gas levels, ocean heat, ocean acidification and sea level rise all hit new records in 2021, according to a new report released by the World Meteorological Organisation (WMO).

The report, examining the state of the global climate, found that previous records were smashed for four out of seven key climate indicators in 2021, underlining the need for urgent action on climate change

The WMO said the report was “yet another clear sign” of human-induced changes to the planet, with “harmful and long-lasting ramifications”.

Seven indicators are used by the WMO to track the impact of climate change on the planet. These indicators are:

  • Surface temperature (i.e. the temperature near the surface of the Earth)
  • Ocean heat
  • Greenhouse gases
  • Ocean acidification
  • Sea level
  • Glaciers
  • Arctic and Antarctic sea ice extent

These measures allow organisations to measure the changes driven by climate change without focusing on temperature change alone. 

Here’s what it means for the planet. 

Greenhouse gases 

Greenhouse gases are the main driver of climate change, and are produced by a number of human activities – namely, burning fossil fuels. 

In 2021, the concentration of carbon dioxide in the atmosphere reached a new high, with 419.13 parts per million recorded at Mauna Loa in Hawaii in May 2021.

In 1958, when scientists first began collecting CO2 data at Mauna Loa, the highest month of the year had just 317.51 ppm.

Although greenhouse gas emissions temporarily fell during the Covid-19 pandemic, levels have now rebounded as normal human activities have resumed. 

Ocean heat 

It’s not just surface temperatures that heat up as climate change accelerates. The world’s oceans are also getting hotter.

In 2021, a new record high was set for ocean heat, with warming penetrating to deeper levels than ever before.

Much of the surface ocean experienced at least one ‘strong’ marine heatwave at some point in 2021.

Ocean heating can have a devastating impact on ocean ecosystems, which are vital in supporting life on Earth. Coral reefs, for instance, bleach in high temperatures. 

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Ocean acidification

The ocean is a vital absorber of the CO2 which humans release into the atmosphere, but this comes at a cost to the health of the ocean.

When too much CO2 is absorbed, it reacts with seawater and leads to acidification of the oceans, threatening ecosystems and the vital services they provide us. 

As the pH of the ocean decreases, its capacity to absorb CO2 from the atmosphere also declines. 

In a recent report, the Intergovernmental Panel on Climate Change concluded that “there is very high confidence that open ocean surface pH is now the lowest it has been for at least 26,000 years and current rates of pH change are unprecedented since at least that time.”

Sea level

The global average (mean) sea level reached a new record high in 2021, and increased at an average 4.5 mm per year over the period 2013 -2021. 

This is more than double the rate of between 1993 and 2002 and the change in rate is mainly due to the accelerated loss of ice mass from the ice sheets, the WMO said. 

Rising sea levels threaten millions of communities, people and animals who live along the world’s coastlines. 

What about the other indicators? 

Though the three other indicators didn’t break records in 2021, surface temperatures and the extent of glaciers and sea ice exceeded normal levels.

And 2021 was cooler than some recent years, but the WMO report noted that the past seven years remain the warmest on record. 

Glaciers and sea ice also continue to melt at rapid rates, contributing to global sea level rise and threatening life that depends on their existence.

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