気候：海と大気の相互作用が2023年の北大西洋熱波をもたらした

The extreme warming in the North Atlantic Ocean in 2023 was driven by the exchange of heat between the ocean and the atmosphere, research published in Nature suggests. The findings indicate that the factors contributing to this heatwave are likely to continue and that the severity of such heatwaves may worsen in the future.

Marine heatwaves are periods of sustained abnormal warmth that can damage ecosystems and impact human activities. The 2023 North Atlantic marine heatwave occurred in the summer months and was characterized by extreme heat, storms and flooding across Europe, and it contributed to the record global mean temperatures recorded that year. However, the drivers of this 2023 marine heatwave event remain unclear.

Matthew England and colleagues used a suite of models and ocean observations to explore the drivers behind the marine heatwave. They indicate that the transfer of heat between the atmosphere and the shallow mixed layer of the ocean was responsible for the extreme warming event, rather than heat moving within the ocean, which can be a driving agent for marine heatwaves. They propose that the main driver was anomalously weak winds that led to the distinct ocean layers becoming shallower, enabling rapid heating of the surface layer in the North Atlantic. They note that in some locations above-average solar radiation may have also contributed to warming. Some of these locations at mid-latitudes coincided with main shipping lanes, and the authors propose that reduced sulphate emissions, which have been linked to a decline in cloud cover and increased solar radiation, could have played a localised role there.

The authors note that a trend towards shallower ocean layers has been observed over the previous decades and is projected to continue, which could lead to the severity of North Atlantic heatwaves worsening.