Global Warming Threatens To End Northern Europe's Mild Climate by 2100, New Study Uncovers

Northern Europe enjoys a relatively mild climate despite its northern latitude. For instance, London, situated north of many major Canadian cities, is warmer than all of them, including Vancouver. However, this warmth might vanish by the century's end due to global warming.

The Atlantic Meridional Overturning Circulation (AMOC), a significant ocean current running from the Gulf of Mexico to near Svalbard, Norway, could halt. This current transports vast amounts of warm water to the North Atlantic, where it cools and sinks before moving southward along Greenland's eastern coast and through the mid-Atlantic. The heat released during this process keeps northern European ports ice-free.

Global warming introduces more freshwater into the northeastern AMOC from Arctic ice melt and increased rainfall. This freshwater reduces the current's density and salinity, diminishing its cooling and sinking in the North Atlantic and thus its southward flow.

In 1995, climate modelers predicted that the AMOC would stop circulating by 2200. Observations since 2004 indicate that parts of the AMOC are indeed slowing down. However, previous climate models couldn't closely examine the AMOC's intricate details.

A recent study using a high-resolution climate model offers a clearer view of the AMOC's future. This model reveals that while some regions experience an abrupt collapse in AMOC activity, others see unexpected increases. These findings were published in Physical Review Letters.

"Our high-resolution model study uncovers a startling twist: the Atlantic Meridional Overturning Circulation (AMOC) may strengthen in the subarctic Atlantic due to warming," said Gerrit Lohmann from the Alfred Wegener Institute at the Helmholtz Center for Polar and Marine Research at the University of Bremen in Germany, "defying the widespread belief that this vital current system is uniformly weakening."

The large global climate models used for projections typically divide land and ocean into 100-kilometer squares. These "low resolution" models can miss smaller physical features like ocean eddies and gyres. Lohmann and his team used a high-resolution model called the Community Earth System Model, which reduced grid sizes to about 17 kilometers.

They assumed a rapid increase in atmospheric carbon dioxide levels—the IPCC's RCP 8.5 scenario—reaching around 1,250 parts per million (ppm) by 2100. Both high- and low-resolution models showed an overall slowdown in AMOC by about 8 million cubic meters per second from 2000 to 2100, with a sharp decline around 2020.

"Advanced climate models now reveal that under extreme greenhouse gas emissions (RCP 8.5), the AMOC could experience sharp declines in some areas while paradoxically increasing in the Arctic," Lohmann said. "This unexpected regional strengthening occurs despite an overall weakening trend in AMOC activity."

The high-resolution model also identified tipping points unknown from lower resolution studies. Subsystems within the climate system have tipping points; for example, research suggests Greenland's Ice Sheet will reach a tipping point if Earth's temperature rises about 2.5°C above preindustrial levels.

The scientists discovered that smaller-scale parts of the AMOC have tipping points not seen in previous general models. "The findings highlight the urgent need to incorporate regional dynamics into AMOC forecasts," said Lohmann. "These localized shifts could have profound impacts on climate and marine ecosystems."

"As we face an uncertain climatic future, these insights underscore the critical importance of advancing climate models to anticipate and respond to dramatic changes in our planet's systems."