Global average sea surface temperatures (SSTs) were consistently high over the past five months, and remained at record high levels for the time of year throughout April, May, June and July 2023. This situation continued into August, which saw both the highest daily global SST in the ERA5 record and the highest monthly average global SST.
The unprecedented SSTs have been associated with marine heatwaves; periods of unusually high ocean temperatures. These can have significant and sometimes devastating impacts on ocean ecosystems and biodiversity, and can lead to socio-economic impacts due to effects on fisheries, aquaculture, tourism and other industries.
Sea ice also plays a fundamental role in polar ecosystems. When the ice melts in the summer, it releases nutrients into the water, stimulating the growth of phytoplankton, the centre of the marine food web. As the ice melts, it exposes ocean water to sunlight, spurring photosynthesis in phytoplankton. When ice freezes, the underlying water gets saltier and sinks, mixing the water column and bringing nutrients to the surface. The ice itself is habitat for animals such as seals, Arctic foxes, polar bears, and penguins.
The influence of sea ice on the Earth is not just regional; it’s global. The white surface reflects far more sunlight back to space than ocean water does. (In scientific terms, ice has a high albedo.) Once sea ice begins to melt, a self-reinforcing cycle often begins. As more ice melts and exposes more dark water, the water absorbs more sunlight. The sun-warmed water then melts more ice. Over several years, this positive feedback cycle (the ice-albedo feedback) can influence global climate. Earth Observatory NASA
Antarctic sea ice extent remained at a record low level for the time of year, with a monthly value 12% below average, by far the largest negative anomaly for August since satellite observations began. Sea ice concentrations were most below-average in the northern Ross Sea and in the South Atlantic and Indian Ocean sectors while above-average concentrations prevailed in the Bellingshausen–Amundsen Sea sector.
Arctic sea ice extent was further below average than in July, at 10% below average, but well above the record minimum from August 2012. While most of the central Arctic Ocean saw below-average sea ice concentrations, a stretch of above-average concentrations persisted between Svalbard and the Laptev Sea. Climate Copernicus
The United Nation’s Climate Change 2023: Synthesis Report reiterates that humans are responsible for all global heating over the past 200 years leading to a current temperature rise of 1.1°C above pre-industrial levels, which has led to more frequent and hazardous weather events that have caused increasing destruction to people and the planet. The report reminds us that every increment of warming will come with more extreme weather events.
The 1.5°C limit is still achievable but critical action is required across sectors and by everyone at all levels.
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