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According to the IPCC’s Report (AR6), the Atlantic Meridional Overturning Circulation (AMOC), is losing its stability.

What is AMOC?

• The AMOC is a large system of ocean currents.
• It is the Atlantic branch of the ocean conveyor belt or Thermohaline circulation (THC), and distributes heat and nutrients throughout the world’s ocean basins.
• AMOC carries warm surface waters from the tropics towards the Northern Hemisphere, where it cools and sinks.
• It then returns to the tropics and then to the South Atlantic as a bottom current. From there it is distributed to all ocean basins via the Antarctic circumpolar current.
• Gulf Stream, a part of the AMOC, is a warm current responsible for mild climate at the Eastern coast of North America as well as Europe.

What happens if AMOC collapses?

• Colder Europe: Without a proper AMOC and Gulf Stream, Europe will be very cold.
• Rainfall decline: Modelling studies have shown that an AMOC shutdown would cool the northern hemisphere and decrease rainfall over Europe.
• El-Nino trigger: It can also have an effect on the El Nino.
• Cooling of Atlantic: AMOC collapse could bring about large, markedly different climate responses: a prominent cooling over the northern North Atlantic and neighboring areas.
• Weaker thermohaline: Freshwater from melting Greenland ice sheets and the Arctic region can make circulation weaker as it is not as dense as salt water and doesn’t sink to the bottom.

Has the AMOC weakened before?

• AMOC and THC strength has always been fluctuating, mainly if you look at the late Pleistocene time period (last 1 million years).
• The extreme glacial stages have seen weaker circulation and slowdown in AMOC, while the glacial terminations have shown a stronger AMOC and circulation.
• AMOC has been relatively stable until the late 19th century.
• With the end of the little ice age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century.

Why is the AMOC slowing down?

• Climate models have long predicted that global warming can cause a weakening of the major ocean systems of the world.
• Last month researchers noted that a part of the Arctic’s ice called “Last Ice Area” has also melted.
• The freshwater from the melting ice reduces the salinity and density of the water. Now, the water is unable to sink as it used to and weakens the AMOC flow.

Influence of Indian Ocean

• Another study suggested that the Indian Ocean may also be helping the slowing down of AMOC.
• As the Indian Ocean warms faster and faster, it generates additional precipitation.
• With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean, leading to higher salinity in the waters of the tropical portion of the Atlantic.
• This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster.
• This acts as a jump start for AMOC, intensifying the circulation.

Now try this:

Q.With reference to Ocean Mean Temperature (OMT), which of the following statements is/are correct? (CSP 2020)

1. OMT is measured up to a depth of 26ºC isotherm which is 129 meters in the south-western Indian Ocean during January-March.
2. OMT collected during January-March can be used in assessing whether the amount of rainfall in monsoon will be less or more than a certain long-term mean.

Select the correct answer using the code given below:

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Post your answers here:

Back2Basics:  Ocean Currents

The Geneva-based Intergovernmental Panel on Climate Change (IPCC) will release the first part of its Sixth Assessment Report, the periodic status check that has now become the most widely accepted scientific view of the state of the Earth’s climate.

What is IPCC?

• The IPCC, an intergovernmental body was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP).
• It was later endorsed by the UN General Assembly. Membership is open to all members of the WMO and UN.
• The IPCC produces reports that contribute to the work of the UN Framework Convention on Climate Change (UNFCCC), the main international treaty on climate change.
• The objective of the UNFCCC is to “stabilize greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic (human-induced) interference with the climate system.”
• The IPCC’s Fifth Assessment Report was a critical scientific input into the UNFCCC’s Paris Agreement in 2015.

What are IPCC reports?

• IPCC reports cover the scientific, technical and socioeconomic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation.
• The IPCC does not carry out original research, nor does it monitor climate or related phenomena itself.
• Rather, it assesses published literature, including peer-reviewed and non-peer-reviewed sources.
• However, the IPCC can be said to stimulate research in climate science.

The Assessment Reports

• The five previous assessment reports that have come out since the IPCC was established in 1988 have formed the basis of international climate change negotiations, and the actions of the governments.
• Their value has been globally acknowledged, and the fourth assessment report, which came out in 2007, won the IPCC the Nobel Peace Prize.
• Each of these voluminous reports, the last couple of them running into thousands of pages, have built upon the previous ones with updated knowledge and understanding of the climate system.
• The reports have presented projections for temperature rise till 2100 under different scenarios and the kind of impacts that can be expected under each of these pathways.

Key projections of the 6^th Report

Apart from incorporating the latest available scientific evidence, the Sixth Assessment Report is also attempting to provide more actionable information to help governments take policy decisions.

• REGIONAL FOCUS: It is expected that this report would likely state what the scenarios for sea-level rise in the Bay of Bengal region is, not just what the average sea-level rise across the world is likely to be.
• EXTREME EVENTS: There is expected to be bigger focus on extreme weather events, like the ones we have seen in the last few weeks.
• CITIES: Densely populated mega-cities are supposed to be among the most vulnerable to impacts of climate change. The report is expected to present specific scenarios the climate change impacts on cities and large urban populations, and also implications for key infrastructure.
• SYNERGIES: IPCC is expected to present a more integrated understanding of the situation, cross-link evidence and discuss trade-offs between different options or pathways, and also likely to cover social implications of climate change action by countries.

Why it matters?

• The IPCC assessment reports have been extremely influential in directing the dialogue and action on climate change.
• The First Assessment Report led to the setting up of the UNFCCC, the umbrella agreement under which international negotiations on climate change take place every year.
• The Second Assessment Report was the basis for the 1997 Kyoto Protocol that ran till last year, and the Fifth Assessment Report, which came out in 2014, guided the Paris Agreement.
• The global climate architecture is now governed by the Paris Agreement, which replaced the Kyoto Protocol from this year.
• There have been enough indications to suggest that global action was far below what was needed to keep the temperatures below 2°C, as mandated under the Paris Agreement.
• In the immediate future, the IPCC report could serve as the most important warning towards the rapidly closing window of opportunity.

Try this PYQ now:

Q.The United Nations Framework Convention on Climate Change (UNFCCC) is an international treaty drawn at:

(a) United Nations Conference on the Human Environment, Stockholm,1972

(b) UN Conference on Environment and Development, Rio de Janeiro, 1992

(c) World Summit on Sustainable Development, Johannesburg, 2002

(d) UN Climate Change Conference, Copenhagen, 2009

Post your answers here:

Back2Basics: UNFCCC

• The UNFCCC established an international environmental treaty to combat “dangerous human interference with the climate system”, in part by stabilizing greenhouse gas concentrations in the atmosphere.
• It was signed by 154 states at the UN Conference on Environment and Development (UNCED), informally known as the Earth Summit, held in Rio de Janeiro from 3 to 14 June 1992.