ErseoLi

12/01/2022

A forgotten mangrove forest around remote inland lagoons in Mexico’s Yucatan tells a story of rising seas
The San Pedro River winds from rainforests in Guatemala through the Yucatan Peninsula in eastern Mexico. There, this peaceful river widens into a series of slow-flowing lakes. Along a remote 50-mile (80-kilometer) stretch, thousands of red mangroves – trees commonly found along tropical coastlines – line the river’s banks and gentle waterfalls.

Unlike mangroves elsewhere, these trees grow in freshwater. This means that many other species can grow with them: orchids, bromeliads and other air and land plants that cannot tolerate the saline conditions where red mangroves are normally found. It’s a magical garden, and also a scientific puzzle: How did these mangroves come to be growing some 125 miles (200 kilometers) inland, 85 to 120 feet (25 to 37 meters) above sea level, in an entirely freshwater ecosystem?

I am part of a multidisciplinary team of researchers from Mexico and the U.S. that sought to answer this question by comparing these trees to other mangroves across the broader Yucatan Peninsula region. We also analyzed sediment cores from the San Pedro River terraces, which showed strong indications that the sediments had been created in coastal areas.

We found that the mangroves of the river have been separated from coastal mangroves for around 120,000 years. This coincides with the Last Interglacial – a warm period between ice ages, about 125,000 years ago, when glaciers and polar ice caps melted almost entirely.

During that time, the Earth was even warmer than at present and sea levels were 20 to 30 feet (6 to 9 meters) higher. These mangroves’ ancestors were coastal trees that were left isolated as the planet cooled during the Wisconsin Glaciation – the last era when glaciers expanded across North America. As the glaciers spread, sea levels fell, exposing more land around them. Now, this unique forest, a footprint of the past, is at risk of deforestation and development that could prevent scientists from studying it for more insights into Earth’s climate history.

Fish swim among mangrove roots
Fish and other aquatic life in the San Pedro Martir River in Tabasco, Mexico, amid submerged red mangrove roots. Octavio Aburto, CC BY-ND
Mangroves and fresh water
The red mangrove (Rhizophora mangle) is an iconic tree that is enormously important to commercial and artisanal fisheries around the world. Juvenile fish shelter among mangroves’ tangled roots, feeding and growing until they are large enough to avoid predators.

Our study focused on two inland lagoons created by giant cenotes – natural sinkholes in the Yucatan’s limestone bedrock – near the Caribbean coast. Red mangroves reproduce via seeds that germinate while they are still attached to mother plants, then drop onto a bank or into the water, where they float away and establish themselves on adjacent banks. This adaptation enables mangroves to spread along coastlines, even though saltwater is toxic to most seeds and makes germination very difficult.

We were fascinated to know how the San Pedro mangroves got there. Their seedlings couldn’t float upstream for so many miles, and the forest on the banks was large and well-established, which made it seem highly unlikely that an animal or human could have brought the seeds inland. To our knowledge, the San Pedro River mangroves are unique in existing so far from the coast.

Isolation and fragmentation
One way to determine where plants may have come from is to see whether they are genetically related to colonies of similar plants elsewhere in a region. So we conducted a genetic investigation that looked for single-nucleotide polymorphisms, or “snips” – differences in a single DNA building block between one plant and another.

We found that the closest relatives to the San Pedro River’s isolated mangroves were mangroves at the Terminos Lagoon on the Yucatan’s western coast, along the Gulf of Mexico. Mangroves from both river communities also were closely related to other coastal populations on the Gulf of Mexico. However, they were very distinct from other freshwater inland mangrove populations in cenotes on the Yucatan’s eastern coast along the Caribbean, and those populations are distinct in turn from other coastal mangroves.

We cored the largest mangrove trees at three sites, extracting pencil-shaped samples from their trunks that showed their growth rings, to get a sense of how long these trees lived – about 100 years – and how many generations of trees had lived there. Then we multiplied that figure by a mean genetic mutation rate to estimate how old the San Pedro mangroves were when they diverged genetically from other mangroves, and how long ago that divergence occurred.

We calculated that the San Pedro River and Terminos Lagoon mangrove populations separated genetically approximately 100,000 years ago. This supports our hypothesis that the San Pedro River mangroves are a relict from the last interglacial, some 120,000 years ago.

Our data also suggests that something drastically reduced the size of the isolated inland population of San Pedro River mangroves. This created what scientists call a genetic or population bottleneck, meaning that its gene pool became much smaller. As a result, the current population has a more unique genetic signature than mangroves elsewhere. Amazingly, this change was caused by just 30 feet (9 meters) of change in sea level.

Climate change is raising global sea levels in two ways: water expands as it warms, and ice sheets and glaciers on land are melting.
What else does this unique forest hold?
Our discovery raises an obvious question: Which other species have been isolated in this unique ecosystem for the past 125,000 years? Are there insects? Fungi? We hope scientists who study other types of organisms will explore this area and look for more relicts.

But this special place is at risk. The region was systematically deforested in the 1970s as part of a development plan, but the banks of the San Pedro River escaped the bulldozers because the terrain was challenging. New threats loom today, such as a proposed 950-mile (1,529 km) train route that would carry thousands of visitors to Mayan archaeological sites.

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Mayan river systems contain a wealth of cultural and biological riches. Now, we also know that the story of extreme climate change and sea level rise during the Pleistocene is recorded in the DNA of these plants.

They show how dramatically climate change could alter coastal ecosystems along the Gulf of Mexico and many other shorelines if nations do not take urgent action to reduce greenhouse gas emissions that drive climate change. My colleagues and I believe the San Pedro River deserves protection as a testament to both resilience and adaptation in a changing climate.

12/01/2022

The seas are coming for us in Kiribati. Will Australia rehome us?
Our atoll nation is barely two metres above sea level, and the waters are coming for us.

Despite the progress and momentum of the COP26 climate conference in Glasgow, we are still not moving fast enough to avoid the worst of climate change.

It is heartening that more than 190 countries and organisations agreed to rapidly phase out coal power and end support for new coal power stations. More than 100 countries signed a pledge to cut methane emissions 30% by the end of the decade, and about the same number agreed to stop deforestation on an industrial scale in the same timeframe.

But even with these agreements, we in Kiribati face the death of our homeland. Co-author Anote Tong led our country as president for 15 years, alongside lead author Akka Rimon, who was foreign secretary between 2014 and 2016.

man looks at camera in front of the word
Author Anote Tong, when he was Kiribati president, at the Pacific Islands Forum in 2015. Mick Tsikas/AAP
The problem is speed. Our land is disappearing faster than global action can stem climate change. Delays and a lack of global leadership mean the existence of small island states like Kiribati is now in the balance.

That means we must urgently find ways to rehome our people. It is very difficult to leave our homes, but there is no choice. Time is not on our side. We must prepare for a difficult future.

What we need is a model where displaced people can migrate to host nations when their homes become uninhabitable. Countries like Australia need workers – and we will soon need homes.

This is, increasingly, a question of justice. Australia’s actions, in particular, raise questions over how sincere it is in honouring its recent commitments at COP26.

As the world’s largest exporter of liquefied natural gas and the second largest exporter of coal, Australia’s reluctance to change is putting its neighbours in the Pacific at risk of literally disappearing. It is the only developed nation not committed to cut emissions at least in half by 2030.

In Glasgow, Fiji urged Australia to take real action by halving emissions by 2030. Did it work? No. Australia also refused to sign the agreements on ending coal’s reign, with prominent politicians undermining the COP26 agreement as soon as the conference was over.

We desperately hope the commitments Australia did make at COP26 are not just words on paper. But if they are, that makes our need for certainty even more urgent.

Let us speak plainly: If Australia really does plan to sell as much of its fossil fuel reserves as possible and drag its feet on climate action, the least it can do is help us survive the rising seas caused by the burning of its coal and gas.

Read more: Pacific people have been ‘pummelled and demeaned’ for too long – now they’re fighting back

Satellite image of Tarawa Atoll
Kiribati’s Tarawa Atoll is home to more than half of the island nation’s far-flung population. European Space Agency, Flickr, CC BY-SA
To migrate with dignity
Eighteen years ago, the Kiribati government – then headed by Anote Tong – introduced a “migration with dignity” policy as a way for I-Kiribati people to adapt to climate change.

We gave our I-Kiribati workers international qualifications tailored for jobs in demand overseas. After this, Kiribati, Tuvalu, Fiji, Tonga and New Zealand set up a scheme to allow workers to migrate to New Zealand if they had an offer of a job. Each year prior to COVID, 75 people from Kiribati were able to migrate through the scheme.

New Zealand is the first and only country currently offering a permanent labour migration program from Kiribati. While welcome, we will need more places for I-Kiribati as climate change intensifies.

Like New Zealand, Australia has expanded its seasonal worker schemes for Pacific workers, and is now moving towards a longer stay, multi-visa arrangement under its Pacific Labour Scheme. We expect this scheme will evolve into a permanent migration scheme similar to New Zealand.

While we wait in hope for a true safe haven for our people, our diaspora is growing. I-Kiribati are moving now to Pacific countries higher above the water level such as Fiji, the Cook Islands, Niue, Samoa and Tonga.

Are we scared? Of course. We are on the front line of this crisis, despite having done amongst the least to cause it. It is difficult to leave the only home we have known. But science does not lie. And we can see the water coming.

Labour migration will not solve climate change, but it offers hope to those of us who will be displaced first.

This is a vital question of climate justice. This upheaval is caused by high-emitting economic powerhouses like the US, China, and the European Union. But the vulnerable are paying the full cost. That is not fair.

Read more: Climate crisis: migration cannot be the only option for people living on 'drowning' islands

As climate change worsens, other global leaders must consider how best to support adaptation through labour mobility. Far better to plan for this now than to let climate change rage unchecked and trigger ever-larger waves of refugees.

The question of climate justice
Consider this: in 2018, each person in Kiribati was responsible for 0.95 tonnes of carbon dioxide equivalent. By contrast, each person in the United States was responsible for 17.7 tonnes. Despite this imbalance, the US has taken little responsibility for what is happening to Kiribati and other low-lying nations.

We are hopeful this may change, given US President Joe Biden recently pledged to make his nation a leader in climate finance by supporting nations worst hit by climate change and with the least resources to cope. It’s also encouraging that new laws have been proposed to allow people displaced by climate change to live in America.

We must work to slash emissions and devise solutions for the problems caused by the warming.

Sign saying that the highest point on Kiribati's main island is three metres above sea level
The highest point in Kiribati is 3 metres above sea level, with the average less than 2 metres. Erin Magee, Wikimedia Commons, CC BY
International law must recognise climate displaced populations and create ways we can be rehoused.

While other solutions such as climate-proofing infrastructure or even floating islands have been proposed for Kiribati, these cannot happen overnight and are very expensive. By contrast, labour mobility is fast and advantageous to the host country.

Kiribati’s current government is working to increase skills and employability in our workforce. We are doing our part to get ready for the great dislocation.

When I-Kiribati have to migrate, we want them to be able to do so as first class citizens with access to secure futures rather than as climate refugees.

We are doing all we can to stay afloat in the years of ever angrier climate change. But it will take the global village to save our small village and keep alive our culture, language, heritage, spirits, land, waters and above all, our people.

Correction: an earlier version of this story stated Australia was the largest exporter of fossil gas in the world. It is the largest exporter of liquefied natural gas

12/01/2022

COP26 failed to address ocean acidification, but the law of the seas means states must protect the world’s oceans
The COP26 summit may come to be regarded as a failure or an important milestone, but it certainly failed to address the “other” climate change problem: ocean acidification.

With the exception of rising sea levels, climate change impacts on the oceans have been treated as a peripheral matter at global climate change negotiations. This marginalisation of the oceans largely continued at COP26.

But states, including New Zealand and Australia, nevertheless have an obligation to prevent and mitigate excess carbon dioxide (CO₂) from entering the ocean.

Almost four decades ago, 168 states signed up to the UN Convention on the Law of the Sea (UNCLOS). Under this treaty, they must address CO₂ in the oceans consistent with (but distinct from) their obligations under the climate regime.

Ocean acidification (OA) is caused by excess CO₂ in seawater. Atmospheric concentrations of CO₂ have now reached 414ppm (from about 280ppm in 1750) and the oceans are a major sink, having absorbed nearly half of all anthropogenic emissions since the beginning of the Industrial Revolution some two centuries ago.

Coral reefs in shallow seas off a tropical island.
Acidifying seawater has negative impacts on shell-forming organisms and coral reefs. Shutterstock/Ethan Daniels
But rising levels of CO₂ in the oceans change the acidity of seawater, measured as pH. Ocean acidity has remained remarkably stable for more than 800,000 years, but has increased by about 30% in the last 200 years.

This has negative consequences for shell-forming organisms and coral reefs such as the Great Barrier Reef in Australia. Recent research suggests it may also affect the larvae of fish, including commercially important species such as yellow fin tuna.

Read more: The outlook for coral reefs remains grim unless we cut emissions fast — new research

Climate agreements and the oceans
The climate regime comprises the 1992 UN Framework Convention on Climate Change (UNFCCC), 1997 Kyoto Protocol and 2015 Paris Agreement.

It addresses CO₂ emissions, the primary cause of ocean acidification, but states have significant discretion over what action they take, and there is no explicit requirement to address CO₂ separately from other greenhouse gases.

Although the Paris Agreement sets a target of limiting average global warming to well below 2℃ above pre-industrial levels (and aims to keep it at 1.5℃), it does not set a target for limiting ocean pH change.

However, the Glasgow Climate Pact has, for the first time, explicitly set a target in respect of CO₂ emissions. It calls for a 45% cut relative to 2010 levels by 2030 and net zero by mid-century. This is a positive development in the context of addressing ocean acidification.

Read more: COP26: Scotland's coral reefs are on the line at Glasgow climate change summit

What the law of the sea says
Under part XII of UNCLOS, which has been accepted by all states as part of customary international law, states must take all measures necessary to “prevent, reduce and control” marine pollution from any source. States also have a general obligation to protect and preserve the marine environment.

Carbon dioxide can be classed as pollution under UNCLOS, and therefore states have an obligation to avoid or control it. UNCLOS requires states to prevent pollution from land-based sources and from the atmosphere.

Article 212 is particularly relevant to CO₂ pollution. It requires states to:

… adopt laws and regulations to prevent, reduce and control pollution of the marine environment from or through the atmosphere arising from their territory or vessels under their control.

However, this is a due diligence obligation: it relates to conduct (effort) rather than result. Article 212 does not specify what states must do to meet their obligation, but stipulates they should take into account internationally agreed rules and standards.

International standards
Apart from emissions from vessels, there is no agreement on what these internationally agreed rules and standards are.

It can be argued the climate regime constitutes these standards, and if states comply with their commitments under the Paris Agreement they have met their obligations under Article 212 of UNCLOS. Supporters of this position assert it is unreasonable to expect states to go beyond their commitments under climate agreements, particularly when UNCLOS provides no additional guidance.

On the other hand, if it can be shown that commitments under the Paris Agreement are clearly insufficient to “prevent, reduce and control” ocean acidification, it would be anachronistic to say compliance with those standards constitutes “due diligence” under UNCLOS.

I argue the latter — the due diligence obligation under Article 212 of UNCLOS is not met by compliance with climate regime commitments, except where those commitments expressly relate to ocean acidification or CO₂ reductions. This conclusion is arguably supported by the UN’s 2015 adoption of the Sustainable Development Goal 14: Life in the Oceans.

One of the goal’s targets calls for states to explicitly address ocean acidification. This recognises that commitments under the Paris Agreement do not adequately address the issue.

Damselfish hovering around a coral colony.
The law of the sea requires states to protect the oceans. Shutterstock/Ethan Daniels
COP26 confirmed the climate regime is the main forum for addressing the consequences of climate change. But it is not the only game in town or the only legally relevant regime.

UNCLOS requires states to protect the oceans. These obligations must be expressly considered and incorporated into commitments made by states, including New Zealand and Australia, in international climate agreements and their actions to implement these at the domestic level.

COP27, to be held in Egypt next year, provides the next opportunity to address ocean acidification and to support a more integrated approach under both the climate change regime and the law of the seas.

12/01/2022