The past seven years, from 2015 to 2021, have been the seven warmest years on record.
Last year in 2021, the global annual mean temperature was around 1.11°C above the 1850-1900 pre-industrial average.
The World Meteorological Organisation (WMO) has released the latest State of the Global Climate report revealing that four key climate change indicators have set new records for 2021.
These are greenhouse gas concentrations, sea-level rise, ocean heat, and ocean acidification, and together clearly signify the planetary scale of changes that are being caused by human activities.
Here are the records and what they mean:
Greenhouse gases include carbon dioxide, methane, nitrous oxide, naturally occurring water vapour and synthetically produced fluorinated gases.
Together these gases act like a blanket, trapping in more of the heat produced by solar radiation within the Earth's atmosphere.
In 2020, greenhouse gas concentrations reached new global records of 413 parts per million for carbon dioxide (CO2), 1,889 parts per billion of methane, and 333.2 parts per billion of nitrous oxide. Respectively, these represent 149 per cent, 262 per cent and 123 per cent of the pre-industrial levels.
Greenhouse gases are one of the main drivers of climate change, not only having environmental impacts, but with implications for human health, agriculture and the economy.
Atmospheric methane is of particular concern, as it is a hazardous pollutant, and causes one million premature deaths every year through exposure.
"The report highlights that atmospheric CO2 has now surpassed 420 ppm (parts per million) in 2022. To put this into perspective, ice core records in Antarctica suggest that atmospheric CO2 naturally fluctuates between 150 and 300 ppm," says Dr Tom Mortlock, Senior Analyst at Aon and Adjunct Fellow at Macquarie University.
"We are now probably 40 per cent above natural levels of CO2 experienced over the last million years of Earth's history, and this has all happened in the past 150 years."
Global sea-level rise is caused by global warming in two different ways. The higher temperatures of the air and ocean cause glaciers and ice sheets to melt, which contribute more water to the ocean. As seawater warms up (see Ocean Heat below), it expands and takes up a greater volume than cold seawater.
From 1993 to 2002, the global mean sea level rose by 2.1mm per year on average. From 2013-2021 this has increased to 4.5mm per year, mostly due to the accelerated loss of ice sheets.
These rapidly rising sea levels have resulted in the loss of at least five islands in the Pacific, exposing communities to more king tides, tropical cyclones, drought and soil salinity, which leads to more crop failures and the collapse of marine resources.
Most of the excess heat (over 93 per cent) from greenhouse gasses are absorbed by the ocean, leading to rises in ocean temperatures. Ocean heating has reached a record high: in 2021, the oceans absorbed 231 zettajoules (ZJ) - or 231 sextillion (1021) joules - of heat, 14 ZJ more than last year (221 ZJ).
The average rate of ocean warming from 1958 to 2021 has been 5.7ZJ per year, with a particularly accelerated rate over the past two decades, with the warmth penetrating increasingly deeper levels of ocean.
Ocean warming can lead to extreme weather events, melting of the polar ice shelves, accelerating sea level rise, and massive disruption of marine ecosystems.
As the oceans warm, their heat charges weather systems, resulting in more intense rainfall, and more powerful storms. This can result in extreme flooding and snowfall events.
Rising ocean temperatures also cause coral bleaching, and the loss of breeding grounds for marine species. With fishing and aquaculture providing 4.3 billion people with 15 per cent of their animal protein supply, the economic loss due to ocean warming for the seafood industry alone is likely to be in the billions of dollars.
The ocean helps mitigate climate change effects by absorbing around 23 per cent of the annual emission of anthropogenic CO2 that would otherwise rise into the atmosphere. However, this reacts with seawater and reduces the pH of the ocean.
The ocean pH has now dropped below 8.06, from 8.11 in the late 1980s.
The report concludes 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."
With greater ocean acidification, and thus a lower pH, there are less available ions available for organisms to build their hard structures. If the pH gets too low, shells and skeletons can even start dissolving.
The global value production of oysters in Australian alone is over $100 million per year, while tourism of the Great Barrier Reef contributes around $5.4 billion annually and employs around 69,000 people.
"It is just a matter of time before we see another warmest year on record," says WMO secretary-general Petteri Taalas. "Our climate is changing before our eyes. The heat trapped by human-induced greenhouse gases will warm the planet for many generations to come.
Sea level rise, ocean heat and acidification will continue for hundreds of years unless means to remove carbon from the atmosphere are invented.
Some glaciers have reached the point of no return and this will have long-term repercussions in a world in which more than two billion people already experience water stress."
This new report also provides information and practical examples for policy-makers on how climate indicators have changed globally in recent years, and what impacts have been felt at national and regional levels in 2021.
"We have to make enormous progress towards net zero this decade if we are to have even a 50 per cent chance of limiting warming to 1.5°C. Net-zero by 2050 is too late to avoid 2°C warming with certainty." Says Professor Pete Strutton from the Institute for Marine and Antarctic Studies at the University of Tasmania.
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