Since 2007, the Arctic Ocean has been experiencing a significant change due to Arctic marine heatwaves. These are periods when the sea surface temperature (SST) rises unusually high for a long time. This study investigates how much these heatwaves are linked to greenhouse gas (GHG) emissions.
It turns out that a major factor behind the heatwaves is the increase in sea surface temperature caused by the ocean absorbing more heat, especially in shallow areas near the Arctic margins where ice melts rapidly. Notably, up to 82% of the temperature changes in these areas can be connected to this process. This indicates a strong link between human-made emissions and the extreme temperature changes in the Arctic.
The research points out that the main trigger for Arctic marine heatwaves is the rapid melting of sea ice, happening at the same time as the largest amount of heat from the sun reaches the ocean. The 2020 heatwave, lasting 103 days with a peak temperature of 4°C, stands out as the most intense example. The analysis suggests that such severe heatwaves are very unlikely to occur without the influence of GHG emissions. Moreover, the study warns that if GHG emissions keep increasing, and the Arctic ice continues to melt, then these moderate but frequent Arctic marine heatwaves will likely become a regular phenomenon.
The study also delves into the mechanisms behind these heatwaves. One key factor is the increase in solar energy absorbed by the ocean, particularly in areas where sea ice has melted. Shallow waters, mostly covered by new ice formed each year (first-year ice), are particularly prone to these heatwaves. The heat from the sun is absorbed more in these areas, leading to higher sea temperatures.
Using advanced methods to attribute these events to specific causes, the study finds that any Arctic marine heatwave with a temperature increase of more than 1.5°C would almost certainly not happen without GHG emissions. This means that while GHG emissions are necessary for such intense heatwaves to occur, they alone do not guarantee their occurrence. However, for less intense heatwaves (0.5–1°C), GHG emissions are a likely cause, indicating that these events could become more common if GHG levels continue to rise.
In summary, the study provides strong evidence that GHG emissions are a key driver of Arctic marine heatwaves. These heatwaves are part of a larger trend of increasing sea temperatures in the Arctic, which are expected to lead to more frequent and intense heat events. This trend has serious implications for the Arctic environment, including faster melting of sea ice, and highlights the urgent need to address GHG emissions.