Oceans cover seventy per cent of our planet and store somewhere around a third of carbon dioxide gas released from anthropogenic activities. This has been warming up our ocean and has resulted in acidification and deoxygenation of seawater affecting marine life drastically. However, there is a more serious threat looming over us which can have a direct impact over human lives and that is slowing down of ocean currents. The sluggishness in ocean currents will not only affect marine life but it will also alter the climate systems which have dramatic implications for North America and Europe.
Oceans currents are akin to a conveyor belt which help evenly spread the heat all across the globe. One of the most critical climate systems on earth, these ocean currents transport warm water and precipitation from the equator and tropics towards the poles and the cold water from poles to the tropics. Oceanographers have observed the currents slowing down, specifically the Atlantic Meridional Overturning Circulation (AMOC). This current is responsible for moving a great amount of heat across the globe. A healthy AMOC is critical for the smooth functioning of weather patterns on earth, however, with the rising temperature of our planet, there has been more than the normal inflow of freshwater due to melting of glaciers and ice sheets, which has disturbed the thermohaline circulation in the ocean. This slow down of the currents may have started fifty years ago when the emission due to human activities began to rise. As per scientists, we might have been through similar events of slow ocean currents in the past which would have resulted in ice ages. The Heinrich events are the result of breaking up and melting of huge icebergs over North which were related to the ice age. Our situation could be similar to these past events. The present sluggishness in AMOC could be a result of the melting of glaciers and icebergs in North Atlantic which has poured in a great amount of fresh water in the ocean.
As per a report by Intergovernmental Panel on Climate Change (IPCC), if the temperature of the earth rises above 4°C by 2100, the AMOC could further reduce by 54 per cent. At the present rate of temperature rising, it could decline by one third. In events of dramatic slowdown, the Northern Hemisphere will get cooler and global warming may even reverse for twenty years. As the circulation slows down, the heat would not reach in the Northern regions and Southern Hemisphere will get hotter! The consequences will be worse for North America and Europe when heat from the Tropics would not reach the Northern latitudes. This will bring in colder condition for the region. Even the seasonal rainfall and temperature would be altered which will lead to more floods, sea-level rise and other disturbance in weather systems.
While it is difficult to answer with certainty what may have caused the slow circulation of currents, but the current circulation speed is estimated to go weaker in this century and we must explore ways to adapt ourselves to challenges it will cause.