New Delhi, Sept. 5 -- In Part I of the article, we covered the major ocean current systems as well as the warm and cold currents in the three largest oceans and Antarctica. In this article, we will examine how climate change is interfering with the natural rhythms of the oceans and how this is impacting rainfall, wind speeds, temperatures, marine ecosystems and agriculture around the world.
Climate Change and Ocean Currents
Climate change has disrupted the manner in which ocean currents carry heat/cold and nutrients from one part of the world to another through the 'Global Conveyor Belt'. This has happened through the warming of ocean waters and the melting of glaciers, such as those in Greenland, which has led to a lower density of ocean water. This has disrupted the 'thermohaline' circulation discussed in the first article. Further, lower salinity means acidification of the oceans, compounded by ocean water absorbing excess carbon dioxide from the air (this forms carbonic acid and makes the ocean acidic). Let us discuss the more specific aspects:
Freshwater from melting ice sheets in Greenland is weakening the AMOC, causing shifts in temperature, rainfall patterns, wind speeds, marine ecosystems and agricultural practices. Higher temperatures are also warming the oceans and slowing the sinking of cold water, thus weakening the AMOC. In short, the following climate impacts are likely:
A colder Europe and North Atlantic and warmer tropics (in particular, Africa and South Asia).
Interference in global monsoon systems, leading to weakened monsoons in West Africa and South Asia, including India.
Warmer tropics also lead to more intense hurricanes.
A slower AMOC means slower circulation and a lower capacity of the oceans to sequester carbon dioxide.
A slowing AMOC leads to lower upwelling of nutrients, putting marine ecosystems, including fisheries, under stress.
If continued emissions accelerate global warming and ocean warming, a tipping point could be reached where the AMOC collapses, leading to unprecedented climate impacts around the world.
Warming oceans could intensify the ENSO system and lead to stronger El Niño and La Niña currents. A stronger ENSO will result from enhanced feedback loops between ocean surface temperatures and atmospheric winds in the Pacific Ocean (also called the Bjerknes effect). A more intense El Niño would mean greater-than-usual warming of Pacific waters and weaker trade winds, while a stronger La Niña would mean colder Pacific waters and more intense trade winds. Thus, a stronger El Niño would lead to more extreme cyclones and heavy rainfall in South and North America, but droughts and reduced monsoons in India, Indonesia and Australia. A stronger La Niña would produce the opposite effects: droughts and colder-than-usual winters in South and North America and flooding in Asia and Australia. These changes would put agriculture, soil conditions, food security and human health under stress.
Climate change threatens to warm the Antarctic and lead to a loss of its vast ice sheets, releasing huge quantities of freshwater into the ocean. This reduces ocean salinity and density, creating a lighter surface layer and preventing upwelling from the deep oceans. It also alters wind patterns over the ocean. These factors threaten to disrupt the Antarctic Circumpolar Current, which, in turn, reduces the ocean's capacity to absorb carbon dioxide, leading to further warming and setting up a vicious feedback loop.
Climate change is also causing disruptive changes to important warm and cold ocean currents. The normal patterns of the Gulf Stream, Kuroshio, Labrador, Agulhas and Humboldt currents are being affected by ocean warming, ice melt from Greenland and the poles, altered winds and changing surface currents, as well as the weakening of nutrient upwelling.
Conclusion
Climate change is disrupting ocean current systems as well as warm and cold ocean currents. This is adversely impacting marine ecosystems and agricultural productivity through erratic rainfall patterns and unseasonal droughts. Agriculture is also affected by increased soil erosion caused by excessive and heavy rainfall and changes in crop-growing seasons, with implications for food security. This also has implications for flood-protection works in coastal areas and the maintenance of shipping lanes for world trade.
Published by HT Digital Content Services with permission from Millennium Post.