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Water mass enters the ocean from glaciers such as this along the Greenland coast. NASA/JPL-Caltech

Contributions to the rate of global sea-level rise increased by about half between 1993 and 2014, with much of the increase due to an increased contribution from Greenland’s ice, according to our new research.

Our study, published in Nature Climate Change, shows that the sum of contributions increased from 2.2mm per year to 3.3mm per year. This is consistent with, although a little larger than, the observed increase in the rate of rise estimated from satellite observations.

Globally, the rate of sea-level rise has been increasing since the 19th century. As a result, the rate during the 20th century was significantly greater than during previous millennia. The rate of rise over the past two decades has been larger still.

The rate is projected to increase still further during the 21st century unless human greenhouse emissions can be significantly curbed.

However, since 1993, when high-quality satellite data collection started, most previous studies have not reported an increase in the rate of rise, despite many results pointing towards growing contributions to sea level from the ice sheets of Greenland and Antarctica. Our research was partly aimed at explaining how these apparently contradictory results fit together.

Changes in the rate of rise

In 2015, we completed a careful comparison of satellite and coastal measurements of sea level. This revealed a small but significant bias in the first decade of the satellite record which, after its removal, resulted in a slightly lower estimate of sea-level rise at the start of the satellite record. Correcting for this bias partially resolved the apparent contradiction.

In our new research, we compared the satellite data from 1993 to 2014 with what we know has been contributing to sea level over the same period. These contributions come from ocean expansion due to ocean warming, the net loss of land-based ice from glaciers and ice sheets, and changes in the amount of water stored on land.

Previously, after around 2003, the agreement between the sum of the observed contributions and measured sea level was very good. Before that, however, the budget didn’t quite balance.

Using the satellite data corrected for the small biases identified in our earlier study, we found agreement with the sum of contributions over the entire time from 1993 to 2014. Both show an increase in the rate of sea-level rise over this period.

The total observed sea-level rise is the sum of contributions from thermal expansion of the oceans, fresh water input from glaciers and ice sheets, and changes in water storage on land. IPCC

After accounting for year-to-year fluctuations caused by phenomena such as El Niño, our corrected satellite record indicates an increase in the rate of rise, from 2.4mm per year in 1993 to 2.9mm per year in 2014. If we used different estimates for vertical land motion to estimate the biases in the satellite record, the rates were about 0.4mm per year larger, changing from 2.8mm per year to 3.2mm per year over the same period.

Is the whole the same as the sum of the parts?

Our results show that the largest contribution to sea-level rise – about 1mm per year – comes from the ocean expanding as it warms. This rate of increase stayed fairly constant over the time period.

The second-largest contribution was from mountain glaciers, and increased slightly from 0.6mm per year to 0.9mm per year from 1993 to 2014. Similarly, the contribution from the Antarctic ice sheet increased slightly, from 0.2mm per year to 0.3mm per year.

Strikingly, the largest increase came from the Greenland ice sheet, as a result of both increased surface melting and increased flow of ice into the ocean. Greenland’s contribution increased from about 0.1mm per year (about 5% of the total rise in 1993) to 0.85mm per year (about 25% in 2014).

Greenland’s contribution to sea-level rise is increasing due to both increased surface melting and flow of ice into the ocean. NASA/John Sonntag, CC BY

The contribution from land water also increased, from 0.1mm per year to 0.25mm per year. The amount of water stored on land varies a lot from year to year, because of changes in rainfall and drought patterns, for instance. Despite this, rates of groundwater depletion grew whereas storage of water in reservoirs was relatively steady, with the net effect being an increase between 1993 and 2014.

So in terms of the overall picture, while the rate of ocean thermal expansion has remained steady since 1993, the contributions from glaciers and ice sheets have increased markedly, from about half of the total rise in 1993 to about 70% of the rise in 2014. This is primarily due to Greenland’s increasing contribution.

What is the future of sea level?

The satellite record of sea level still spans only a few decades, and ongoing observations will be needed to understand the longer-term significance of our results. Our results also highlight the importance of the continued international effort to better understand and correct for the small biases we identified in the satellite data in our earlier study.

Nevertheless, the satellite data are now consistent with the historical observations and also with projected increases in the rate of sea-level rise.

Ocean heat content fell following the 1991 volcanic eruption of Mount Pinatubo. The subsequent recovery (over about two decades) probably resulted in a rate of ocean thermal expansion larger than from greenhouse gases alone. Thus the underlying acceleration of thermal expansion from human-induced warming may emerge over the next decade or so. And there are potentially even larger future contributions from the ice sheets of Greenland and Antarctica.

The acceleration of sea level, now measured with greater accuracy, highlights the importance and urgency of cutting greenhouse gas emissions and formulating coastal adaptation plans. Given the increased contributions from ice sheets, and the implications for future sea-level rise, our coastal cities need to prepare for rising sea levels.

Sea-level rise will have significant impacts on coastal communities and environments. Bruce Miller/CSIRO, CC BY

John Church previously received funding from Australian Climate Change Research Program.

Christopher Watson receives funding from the Australian Research Council and the NCRIS Integrated Marine Observing System.

Matt King receives funding from Australian Research Council and Department of Environment.

Xianyao Chen received funding from the National Key Basic Research Program of China and the Natural Science Foundation of China.

Xuebin Zhang received funding from Pacific Climate Change Science Program (PCCSP) and follow-up Pacific-Australia Climate Change Science and Adaptation Planning program (PACCSAP) both of which were funded by the Australian Government’s International Climate Change Adaptation Initiative, and also from Australian Climate Change Science Programme (ACCSP), National Environmental Science Programme (NESP), and Centre for Southern Hemisphere Ocean Research (CSHOR).

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The move follows demonstrations in the city and the decision by China to ban their own trade

Hong Kong has launched a landmark bill to ban its domestic ivory trade, amid accusations that authorities were lagging behind China in phasing out the market.

Hong Kong is home to the world’s biggest retail ivory market, with more items for sale than anywhere else in the world. The majority of buyers are mainland Chinese, who smuggle the worked ivory across the border. Hong Kong is also perpetuating the illegal market: more than a third of licensed ivory dealers have been found to advise buyers on ways to smuggle ivory out of the city, according to a recent report by Traffic.

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Leaders from more than 250 cities gathered at the US Conference of Mayors in Miami Beach to vote on a resolution to reach a 100% clean energy goal

Mayors meeting in Florida are considering an ambitious commitment to have US city governments run entirely on renewable sources such as wind and solar by 2035.

Related: New Orleans mayor: US climate change policy cannot wait for Trump

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A blue shark caused panic on Saturday after being seen by bathers close to the beaches of Cala Major and Can Pastilla. The animal was captured on Sunday, with local media reporting that it was suffering from a head wound, possibly caused by a harpoon

• Blue shark captured after Mallorca beach panic
  

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John Hume to take advantage of court ruling allowing domestic sales of horns, despite international ban

A rhino breeder in South Africa is planning an online auction of rhino horns to capitalise on a court ruling that opened the way to domestic trade despite an international ban imposed to curb poaching.

The sale of rhino horns by breeder John Hume, to be held in August, will be used to “further fund the breeding and protection of rhinos”, according to an auction website.

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National Infrastructure Commission says UK must maintain ties with EU to save key projects such as third runway and HS2

A hard Brexit would be a “calamity” that would spell the end for the Heathrow expansion, according to the chairman of the National Infrastructure Commission.

While the airport has argued that Brexit makes its third runway ever more important, Andrew Adonis said private investment in infrastructure would be off the table unless Britain could maintain ties with the EU.

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In a dig at Trump’s climate change inaction, French president welcomes the green campaigner and says there will be ‘no new exploration licences’

The new French government has sought to further burnish its green credentials with the announcement it is to stop granting licences for new oil and gas exploration.

In his first major intervention since Emmanuel Macron’s election victory, the ecological transition minister, Nicolas Hulot, told the broadcaster BFMTV there would be “no new exploration licences for hydrocarbons”.

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Stiegler Gorge dam on the Selous park, a world heritage site listed as ‘in danger’, will cause irreversible damage, say conservationists

Plans to build a huge hydroelectric dam in the heart of one of Africa’s largest remaining wild areas have dismayed conservationists who fear that the plans will cause irreversible damage to the Selous game reserve in Tanzania.

After many years of delays and false starts, last week the president of Tanzania, John Magufuli, announced that he would be going ahead with the Stiegler’s Gorge dam on the Rufiji river. Magufuli, nicknamed “the Bulldozer”, was elected in 2015 in part on his record of successful road and infrastructure building. The dam will provide 2,100MW of electricity to a country that is currently extremely undersupplied: Tanzania, with a population of approximately 53m to the UK’s 65m, has just 1,400MW of installed grid capacity compared to the UK’s total grid capacity of 85,000MW.

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Although there’s some uncertainty in the distribution among Earth’s ocean basins, there’s no question that the ocean is heating rapidly

As humans put ever more heat-trapping gases into the atmosphere, the Earth heats up. These are the basics of global warming. But where does the heat go? How much extra heat is there? And how accurate are our measurements? These are questions that climate scientists ask. If we can answer these questions, it will better help us prepare for a future with a very different climate. It will also better help us predict what that future climate will be.

The most important measurement of global warming is in the oceans. In fact, “global warming” is really “ocean warming.” If you are going to measure the changing climate of the oceans, you need to have many sensors spread out across the globe that take measurements from the ocean surface to the very depths of the waters. Importantly, you need to have measurements that span decades so a long-term trend can be established.

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The US rocket company makes two launches twice in just over 24 hours.

According to the WWF, we're living off 1.6 Earths' worth of resources. Kevin Gill/Flickr, CC BY-SA

Since the 1970s, humans have used more resources than the planet can regenerate. This is known as overshoot. The WWF Living Planet Report has reported overshoot every two years since 2000.

However, this fact can inspire some confusion. How can it logically be possible for us to use more resources than Earth can produce, for decades on end?

There are two basic concepts at work here. One is our ecological footprint, which can be very loosely understood as a way of tallying up the resources we use from nature. The other is the planet’s ability to provide or renew those resources every year: its “biocapacity”.

When our ecological footprint exceeds Earth’s biocapacity, that’s unsustainable resource use. Unsustainable resource use can occur for some time. The environmental thinker Donella Meadows used a bathtub analogy to explain how.

Imagine a bathtub full of water, with the tap running and the plug out at the same time. It is possible for more water to flow out of the bath than into it for some time without the water in the tub running out. This is because the significant store of water in the bath acts like a buffer. The same goes for nature.

Because nature has accumulated resources – for example, in a forest – it’s possible for us to harvest nature at a greater rate than it can replenish itself for a certain amount of time.

But this leads to the question: if humanity’s ecological footprint exceeds Earth’s biocapacity, how long can we keep going without crossing a tipping point? Our recent research investigates this question.

Explaining the feedback system

It’s important to make the point that nature provides us with literally everything we need, through processes known as ecosystem services. Much of this is obvious because we buy and sell it, as food, shelter and clothing.

Other services go largely unnoticed. Forests provide protection from flooding by slowing down surface water runoff, for example, while mangroves absorb carbon dioxide from the air and store it. Until relatively recently, nature has continued to provide, despite our rapidly increasing ecological footprint.

In part this resilience comes from being able to buffer disturbance with the existing store of resources. But there’s an important mechanism that helps natural systems adjust – to a certain extent – to disruption. This is called a feedback mechanism, and if we take the bathtub analogy one step further we can see how it works.

Say we set up our bathtub so that the tap and the plughole communicate with one another. If more water suddenly starts flowing down the plug, then the tap increases the flow of water into the bath to compensate, thus maintaining the water level. This is an example of a “positive” feedback (more water exiting the bath) being moderated by a “negative” feedback (more water entering from the tap), thus maintaining the state of the system (water in the bath).

Let’s pick a real-world example. Clearing trees from a forest might mean that seeds from the soil have the chance to germinate. If they germinate before the landscape gets too degraded, they can potentially balance out the disturbance.

But harvesting forest also exposes the ground, causing soil loss. In turn, vegetation might find it more difficult to regrow – resulting in yet more soil loss, and so on. This is a “positive” feedback – one that reinforces and exacerbates the original problem.

Negative feedbacks can only adapt to a certain level of disruption. Once the disturbance is too large, they break down. Positive feedback loops can then prevail and the ecosystem is likely to cross a tipping point, resulting in permanent, dramatic and sudden transformation.

Crossing planetary boundaries

In our research, my colleagues and I compared future ecological footprints with research about planetary boundaries (points at which the risks to humanity of crossing a tipping point become unacceptably high). We found the discrepancy between the ecological footprint and biocapacity is likely to continue until at least 2050. We also found that our global cropping footprint is likely to exceed the planetary boundary for land clearing between 2025 and 2035.

This occurs in the context of atmospheric carbon dioxide concentrations that have already crossed the planetary boundary of 350 ppm. (As I write, the carbon dioxide concentration is over 400 ppm.)

By itself, both these points are serious enough. More seriously, we have no idea what happens when two planetary boundaries are approached simultaneously, or two tipping points interact.

We face the permanent loss of essential natural processes, putting, for example, our global food security at risk. Our research shows we need to address gradual, cumulative change, as the global resource buffer shrinks and stabilising feedback mechanisms are overwhelmed.

But there’s good news too. Ecological footprints decrease in response to human decisions. Our current trajectory towards tipping points is not fait accompli at all, but can be influenced by the choices we make now.

Bonnie McBain received ARC funding for this research.

Survey by Energy Institute finds industry professionals think policy is ‘on pause’ and warn Brexit is ‘material concern’

The UK’s ambitious target of slashing carbon emissions by more than half within 13 years is at risk because of government dithering on energy policy, industry professionals have warned.

A survey by the Energy Institute, the professional body for the energy sector, has found that four fifths of its members believe the UK is currently on track to miss the 2030 goal.

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Comins Coch, Aberystwyth Beech leaves moved silkily in the warm wind as though breathing, the only other sounds the stream and distant sheep

Long after midnight, with the temperature well above 20C and humidity high, I gave up attempting to sleep and checked what the night sky might offer in compensation. With the moon yet to rise, the village was in darkness, swathed in a murky blanket of haze that all but obscured the mountains to the east. Looking up, a few stars were just visible above the beech trees – whose leaves moved silkily together in the warm wind as though breathing, the only other sounds those of the stream and a few distant sheep.

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Queensland government edict pushes wholesale prices down; solar costs fall again; Infigen's lousy wind quarter; aspect of limited merits review decision.

Results for South Australia's battery storage tender expected in next week, as state government delays introduction of energy security target and may drop it altogether. Meanwhile, Victoria reports "strong" response for its battery storage tender.

Kenya’s wildlife numbers are plummeting. Reconnecting people to nature is key to the solution.

On May 31st Kenya celebrated the inauguration of the first phase of the new high-speed rail link from Mombasa to Nairobi. Now Kenyans can travel between the two largest cities quickly and cheaply. Accelerated movement of cargo and people will mean more trade, more income generation, and therefore, more jobs, and that’s good for our youthful nation.

Much less widely reported were results of studies by Dr Joseph Ogutu and colleagues at the International Livestock Research Institute (ILRI), which reveal that Kenya’s wildlife numbers are plummeting. Some of our most treasured animals, such as hirola, rhinos, cheetah, lions, and giraffe, are being pushed to the brink of extinction.

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Reality is boring: new technology gets cheap, simple and, increasingly, fit for purpose. There’s nothing magical, mystical or fantastical about this.

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