Climate change is slowing Atlantic currents that help keep Europe warm



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Natalie Renier/Woods Hole Oceanographic Institution, Author provided

Peter T. Spooner, UCL

The ocean currents that help warm the Atlantic coasts of Europe and North America have significantly slowed since the 1800s and are at their weakest in 1600 years, according to new research my colleagues and I have conducted. As we’ve set out in a new study in Nature, the weakening of this ocean circulation system may have begun naturally but is probably being continued by climate change related to greenhouse gas emissions.

This circulation is a key player in the Earth’s climate system and a large or abrupt slowdown could have global repercussions. It could cause sea levels on the US east coast to rise, alter European weather patterns or rain patterns more globally, and hurt marine wildlife.

We know that at the end of the last major ice age, rapid fluctuations in the circulation led to extreme climate shifts on a global scale. An exaggerated (but terrifying) example of such a sudden event was portrayed in the 2004 blockbuster film The Day After Tomorrow.

The recent weakening we have found was likely driven by warming in the north Atlantic and the addition of freshwater from increased rainfall and melting ice. It has been predicted many times but, until now, just how much weakening has already occurred has largely remained a mystery. The extent of the changes we have discovered comes as a surprise to many, including myself, and points to significant changes in the future.

The circulation system in question is known as the “Atlantic Meridional Overturning Circulation” (AMOC). The AMOC is like a giant conveyor belt of water. It transports warm, salty water to the north Atlantic where it gets very cold and sinks. Once in the deep ocean the water flows back southwards and then all around the world’s oceans. This conveyor belt is one of the most important transporters of heat in the climate system and includes the Gulf Stream, known for keeping western Europe warm.

Climate models have consistently predicted that the AMOC will slow down due to greenhouse gas warming and associated changes in the water cycle. Because of these predictions – and the possibility of abrupt climate changes – scientists have monitored the AMOC since 2004 with instruments strung out across the Atlantic at key locations. But to really test the model predictions and work out how climate change is affecting the conveyor we have needed much longer records.

Looking for patterns

To create these records, our research group – led by University College London’s Dr David Thornalley – used the idea that a change in the AMOC has a unique pattern of impact on the ocean. When the AMOC gets weaker, the north-eastern Atlantic Ocean cools and parts of the western Atlantic get warmer by a specific amount. We can look for this pattern in past records of ocean temperature to trace what the circulation was like in the past.

Another study in the same issue of Nature, led by researchers at the University of Potsdam in Germany, used historical observations of temperature to check the fingerprint. They found that the AMOC had reduced in strength by around 15% since 1950, pointing to the role of human-made greenhouse gas emissions as the primary cause.

In our paper, which also forms part of the EU ATLAS project, we found the same fingerprint. But instead of using historical observations we used our expertise in past climate research to go back much further in time. We did this by combining known records of the remains of tiny marine creatures found in deep-sea mud. Temperature can be worked out by looking at the amounts of different species and the chemical compositions of their skeletons.

We were also able to directly measure the past deep ocean current speeds by looking at the mud itself. Larger grains of mud imply faster currents, while smaller grains mean the currents were weaker. Both techniques point to a weakening of the AMOC since about 1850, again by about 15% to 20%. Importantly, the modern weakening is very different to anything seen over the last 1,600 years, pointing to a combination of natural and human drivers.

The difference in timing of the start of the AMOC weakening in the two studies will require more scientific attention. Despite this difference, both of the new studies raise important questions regarding whether climate models simulate the historical changes in ocean circulation, and whether we need to revisit some of our future projections.

The ConversationHowever, each additional long record makes it easier to evaluate how well the models simulate this key element of the climate system. In fact, evaluating models against these long records may be a crucial step if we hope to accurately predict possible extreme AMOC events and their climate impacts.

Peter T. Spooner, Research Associate in Paleoceanography, UCL

This article was originally published on The Conversation. Read the original article.

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The shipping sector is finally on board in the fight against climate change



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Australia will have to regulate its considerable shipping industry.
PomInAus/shutterstock.com

Beatriz Garcia, Western Sydney University and Jolene Lin, National University of Singapore

For the first time, the massive global shipping sector has agreed to a 50% reduction in greenhouse gas emissions by 2050, in what’s been called a “historic” moment.

Maritime shipping, which carries about 80% of global trade by volume, contributes around A$9 billion directly to Australia’s gross domestic product, and A$11.8 billion indirectly.




Read more:
Three ways to improve commercial shipping’s environmental footprint


Sea transport has a relatively green image because ships emit less carbon dioxide per tonne and per kilometre than rail, truck or air transport. Yet, given its scale and rapid growth, it’s a major source of carbon emissions. Maritime transport emits around 1,000 million tonnes of CO₂ a year and is responsible for about 2.5% of global greenhouse gas emissions.

The international law

Despite being a major contributor to climate change, the powerful shipping industry has successfully lobbied to be excluded from obligations to reduce emissions under the 1997 Kyoto Protocol and, more recently, the 2015 Paris Agreement.

There are also no sector-wide emission reduction targets in maritime shipping under the United Nations Framework Convention on Climate Change (UNFCCC). In other key policy spaces, such as the International Maritime Organization (IMO) and the United Nations Convention on the Law of the Sea (UNCLOS), there are no obligations imposed on either states or shipping corporations to reduce maritime emissions.

Countries could potentially set emissions targets domestically, but they rarely set sectoral targets, especially for sectors that are heavily exposed to international trade. In this context, the shipping industry has been particularly footloose in its response to climate change.

It is therefore a cause for celebration that decades of negotiation have now yielded this agreement. The deal requires all IMO countries to reduce shipping emissions by 50% compared with 2008 levels.

Ships will be required to be more energy-efficient and to use cleaner energy such as solar and wind electricity generation. Currently, the shipping industry is overwhelmingly reliant on dirty, carbon-rich fuels such as heavy diesel.

Some stormy seas ahead

The climate deal has been described as “historic”, but not all countries are on board. Some, particularly island nations that are vulnerable to sea level rise, wanted a “far, far more ambitious” target. Others, including the United States, Brazil, Panama and Saudi Arabia, are strongly against it. Reconciling these differences will be a difficult task for the IMO.

It has always been technically difficult to accurately calculate the precise amount of fuel used during shipping operations. It’s even harder to allocate maritime emissions to specific countries.

Contributing to the potential confusion is the use of “flags of convenience”. This is where a ship’s owners register the vessel in a country other than their own, and fly the flag of the country where registered.

This is usually done to disguise the relationship between the vessel and its actual owner, due to the attractive, lower regulatory burdens that some open registries offer. Shipping corporations could also use flags of convenience to avoid mandatory emission reduction targets.

The way forward

As a result of the climate deal, states will eventually need to introduce domestic laws setting emission reduction targets for their shipping industry.

These targets could also be applied to ships that call at their ports. The good news is that there is potential synergy between such regulation and existing laws, such as the European Union regulation that requires ship owners and operators to monitor, report and verify CO₂ emissions from certain vessels that dock at European ports.




Read more:
Five ways the shipping industry can reduce its carbon emissions


The new climate deal has the potential to change the way shipping companies operate. It presents an opportunity for the shipping industry to become part of the solution rather than the problem when it comes to climate change.

The ConversationIt’s also a strong signal to other international industries, such as the aviation sector, that have largely escaped emissions reduction targets. If we can reduce emissions in such a large and complex sector as marine transport, it bodes well for the capacity of international frameworks to tackle other difficult problems.

Beatriz Garcia, Lecturer, Western Sydney University and Jolene Lin, Director, Asia Pacific Centre for Environmental Law, National University of Singapore

This article was originally published on The Conversation. Read the original article.