Category Archives: ocean circulation

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New research suggests signs of an ocean circulation collapse

A new study published in the journal Nature Communications, suggests that the Gulf Stream system, known as the Atlantic Meridional Overturning Circulation (AMOC), could collapse as soon as 2025.AMOC diagram

AMOC plays a crucial role in carrying warm ocean water northwards, driving the Atlantic’s currents. However, increasing freshwater influx from melting ice caps, especially from Greenland, is disrupting these currents.

The consequences of an AMOC collapse would be catastrophic, affecting rainfall patterns in India, South America, and West Africa, increasing storms and lowering temperatures in Europe, raising sea levels on the eastern coast of North America, and endangering the Amazon rainforest and Antarctic ice sheets.

The AMOC ocean currents are currently at its weakest state in the last 1,600 years due to global heating, and warning signs of a tipping point were observed and reported on in 2021.

The research suggests the collapse could occur between 2025 and 2095, with an estimated central point of 2050 if global carbon emissions are not reduced.

The study utilised sea surface temperature data to estimate the timing of the tipping point based on a type of tipping point called a “saddle-node bifurcation.”

Some scientists have expressed concerns about uncertainties in data and assumptions about tipping points, they agree that the potential collapse of AMOC should urge rapid cuts in carbon emissions.

The Intergovernmental Panel on Climate Change (IPCC) most recent assessment concluded that AMOC would not collapse this century, but researchers argue that their models may be overly conservative.

The new study emphasises the need for further research and a collective effort to address the risks associated with AMOC collapse.

Find out more about AMOC and the risks it poses

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Summer 2023 shows extreme weather effects from climate change

2023 has seen wildfires, heatwaves, and major floods. Meanwhile, ocean temperatures are increasing, with average surface temperatures reaching unprecedented levels for June and sea ice failing to regrow in the Antarctic.antarctic ice graph

Throughout July, extreme weather has caused havoc across the planet, with temperatures breaking records in China, the United States and southern Europe, sparking forest fires, water shortages and a rise in heat-related hospital admissions.

World Weather Attribution is an initiative where scientists attempt to quantify how climate change influences the intensity and likelihood of an extreme weather event. Their latest research suggests human-induced climate change has played clear role in the extreme heatwaves that have swept across North America, Europe and China in July 2023. 

El Nino has probably also contributed to the extreme heatwaves. El Nino is a band of warm ocean water that develops in the central and east-central equatorial Pacific, but rising greenhouse gases were the major factor, the scientists said, and heatwaves will become increasingly likely if emissions are not slashed.heatwave maps The July 2023 heatwaves would have been “virtually impossible without climate change”, said researchers who stressed that extreme weather events would occur with greater frequency if the world continues to warm. Find out more

IPCC climate predictions graphAccording to new research from Oxford University’s Environmental Change Institute, an impact of more than $122 billion on economic activity is anticipated, with a staggering $81 billion impact in international trade. Parts of northern Europe, the western United States, Southern Australia, the Middle East and West Africa are particularly expected to feel the effects to cross-border trade, mainly because of dependencies on East Asian ports.  Find out more

As part of its digital data dashboard developments, the Teaching the Future project has used UN Intergovernmental Panel on Climate Change (IPCC) data to examine how future generations will experience the warming created by climate change. This data summarises advanced climate research from hundreds of leading scientists. It suggests the risks of warming are even greater than was thought at the time of the last assessment in 2014. The IPCC report has been signed off by governments worldwide, but a lack of political commitment was a major barrier to progress.

Graphics showing the IPCC global climate predictions can be freely downloaded from the IPCC Web site.

The UN secretary-general António Guterres had confirmed “The 1.5C limit is achievable. But it will take a quantum leap in climate action.”  “Our world needs climate action on all fronts: everything, everywhere, all at once,” he said, urging richer countries to significantly improve their net zero greenhouse gas emissions targets, and strive to achieve the goal by as close to 2040 as possible, rather than by 2050.

 

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Changes in Global Ocean Circulation

The Atlantic Meridional Overturning Circulation (AMOC) is a large system of ocean currents that carry warm water from the tropics northwards into the North Atlantic.ocean circulation image

It acts like a conveyor belt, driven by differences in temperature and salt content – the water’s density. As warm water flows northwards it cools and some evaporation occurs, which increases the amount of salt. Low temperature and a high salt content make the water denser, and this dense water sinks deep into the ocean.

The cold, dense water slowly spreads southwards, several kilometres below the surface. Eventually, it gets pulled back to the surface and warms in a process called “upwelling” and the circulation is complete.

This global process makes sure that the world’s oceans are continually being mixed, and that heat and energy are distributed around the earth. This, in turn, contributes to the climate we experience today.

Oceanographers have been continuously measuring the AMOC since 2004. These measurements have shown that the AMOC varies from year to year, and it is likely that these variations have an impact on the weather in western Europe. However it is too early to say for sure whether there are any long term trends.

Before 2004 the AMOC was only measured a few times, and to go back further into the past we need to look at indirect evidence (for example from sediments on the sea floor). The indirect evidence doesn’t always agree on the details, but it seems likely that there have been some large, rapid changes in the AMOC in the past (for example around the end of the last ice age).

Some scientists believe the changes to this ocean circulation poses a huge risk for Europe.  The devastating droughts last summer were caused by the AMOC being at its lowest point in 1200 years, and now they say it is the weakest it has been in the last 1600 years. Watch the video which explains findings from recent research.

An example of their potential impact

However, according to the UK Met Office, climate models suggest that the AMOC will weaken over the 21st Century as greenhouse gases increase. This is because as the atmosphere warms, the surface ocean beneath it retains more of its heat. Meanwhile increases in rainfall and ice melt mean it gets fresher too. All these changes make the ocean water lighter and so reduce the sinking in the ‘conveyor belt’, leading to a weaker AMOC. So the AMOC is very likely to weaken, but it’s considered very unlikely that large, rapid changes in the AMOC, as seen in past times, will happen in the 21st Century.

Educators need to be careful not to exaggerate the impact of such processes as teachers should try to keep to the facts and data, as AMOC has only been measured regularly since 2004 – we simply do not know, nor can we yet predict with any accuracy, what the future will bring. But it is an important issue that we ought to teach about and its impact on the development of previous ice ages for example as polar ice melted.

Find out more about the AMOC