Greenhouse gas levels, surface temperatures, ocean heat and acidification, sea level rise, Antarctic sea ice cover and glacier retreat reached new highs
The year 2023 smashed multiple climate records with greenhouse gas levels, surface temperatures, ocean heat and acidification, sea level rise, Antarctic sea ice cover and glacier retreat reaching new highs, according to the World Meteorological Organization’s (WMO) State of the Global Climate 2023 report.
“Sirens are blaring across all major indicators… Some records aren’t just chart-topping, they’re chart-busting. And changes are speeding-up,” United Nations Secretary-General António Guterres said in a statement.
The WMO confirmed that the global mean near-surface temperature in 2023 was 1.45 ± 0.12°C above the 1850-1900 average.
This makes it the warmest year in the 174-year observational record, surpassing the previous record holders — 2016 at 1.29 ± 0.12 °C and 2020 at 1.27±0.13 °C — by a clear margin. The past nine years, 2015-2023, were the nine warmest years on record.
“Never have we been so close — albeit on a temporary basis — to the 1.5°C lower limit of the Paris Agreement on climate change,” WMO Secretary-General Celeste Saulo wrote in the report.
This rapid rise in temperature from 2022 to 2023 can be partly explained by the shift from La Nina to El Nino conditions in the middle of 2023.
El Nino and La Nina are the warm and cool phases of a recurring climate pattern across the tropical Pacific—the El Nino-Southern Oscillation (ENSO). The year 2023 marked the end of the three-year-long run of La Nina and the beginning of El Nino.
The global average sea-surface temperatures were also at a record level between late spring in the Northern Hemisphere and the end of the year.
In 2022, the three main greenhouse gases — carbon dioxide, methane, and nitrous oxide — reached record-high levels.
Average concentrations for carbon dioxide were 417.9 ± 0.2 parts per million (ppm), methane at 1923 ± 2 parts per billion (ppb) and nitrous oxide at 335.8 ± 0.1 ppb. This is 150 per cent, 264 per cent and 124 per cent of pre-industrial (1750) levels, respectively.
Among these gases, the rate of increase of methane was the second highest on record and the highest on record for nitrous oxide.
However, the rate of increase of carbon dioxide was slightly below the 10-year average. This, according to the WMO, typically occurs in years starting with La Nina, as it did in 2022.
The total amount of heat stored by the oceans (ocean heat content) was the highest on record in 2023, the WMO highlighted.
The ocean has been showing warming trends in the past two decades. The rate of warming for the top 2000 m layer of the ocean was 0.7 ± 0.1 W·m-2 (Watt per square metre) from 1971-2023 on average, but 1.0 ± 0.1 W·m-2 from 2005-2023.
Sea-level rise also reached a record high in 2023 since 1993. This is due to continued ocean warming as well as the melting of glaciers and ice sheets.
The sea level rise rate has more than doubled since the start of the satellite observation, increasing from 2.13 millimetres per year (mm yr-1) between 1993 and 2002 to 4.77 mm·yr-1 between 2014 and 2023.
At the end of 2023, most of the global ocean from roughly 20°North to South of the equator had seen a marine heatwave — periods of persistent anomalously warm ocean temperatures.
The average daily coverage of marine heatwaves in the global ocean was 32 per cent, overtaking 2016’s record of 23 per cent.
Increase in acidity of the ocean is also increasing. The ocean absorbs around 25 per cent of the annual emissions of anthropogenic carbon dioxide to the atmosphere. The greenhouse gas, in turn, reacts with seawater, resulting in a decrease in acid levels referred to as “ocean acidification”. This has negative consequences for organisms and ecosystem services, including food security, by reducing biodiversity, degrading habitats and endangering fisheries and aquaculture.
The Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change noted with high confidence that the acidity in the open oceans is now the lowest it has been for at least 26,000 years.
However, the WMO added that there are regional variations in the rate of change in ocean acidification, its pattern and scale. It called for high-resolution, long-term observation.
The Arctic sea ice extent stayed below normal in 2023, with the annual maximum and annual minimum extents being the fifth and sixth lowest in the 45-year satellite record, respectively.
At the South Pole, the Antarctic sea ice extent reached an absolute record low for the satellite era (1979 to present) in February.
Preliminary data showed that the amount of mass gained or lost by global glaciers for the hydrological year 2022-2023 or the annual mass balance was negative 1.2 metres of water equivalent (mwe).
This is nominally the largest loss since 1950. The WMO said this was likely driven by the extremely negative mass balance in both western North America and Europe. In Switzerland, glaciers lost around 10 per cent of their remaining volume in the past two years.
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