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You may have seen the media images of bays and coastlines along Hurricane Irma’s track, in which the ocean has eerily “disappeared”, leaving locals amazed and wildlife stranded. What exactly was happening?

These coastlines were experiencing a “negative storm surge” – one in which the storm pushes water away from the land, rather than towards it.

Read more: Irma and Harvey: very different storms, but both affected by climate change

Most people are familiar with the idea that the sea is not at the same level everywhere at the same time. It is an uneven surface, pulled around by gravity, such as the tidal effects of the Moon and Sun. This is why we see tides rise and fall at any given location.

At the same time, Earth’s atmosphere has regions where the air pressure is higher or lower than average, in ever-shifting patterns as weather systems move around. Areas of high atmospheric pressure actually push down on the ocean surface, lowering sea level, while low pressure allows the sea to rise slightly.

This is known as the “inverse barometer effect”. Roughly speaking, a 1 hectopascal change in atmospheric pressure (the global average pressure is 1,010hPa) causes the sea level to move by 1cm.

When a low-pressure system forms over warm tropical oceans under the right conditions, it can intensify to become a tropical depression, then a tropical storm, and ultimately a tropical cyclone – known as a hurricane in the North Atlantic or a typhoon in the northwest Pacific.

As this process unfolds, the atmospheric pressure drops ever lower and wind strength increases, because the pressure difference with surrounding areas causes more air to flow towards the storm.

In the northern hemisphere tropical cyclones rotate anticlockwise and officially become hurricanes once they reach a maximum sustained wind speed of around 120km per hour. If sustained wind speeds reach 178km per hour the storm is classed as a major hurricane.

Surging waters

A “normal” storm surge happens when a tropical cyclone reaches shallow coastal waters. In places where the wind is blowing onshore, water is pushed up against the land. At the same time the cyclone’s incredibly low air pressure allows the water to rise higher than normal. On top of all this, the high waves whipped up by the wind mean that even more water inundates the coast.

The anticlockwise rotation of Atlantic hurricanes means that the storm’s northern side produces winds blowing from the east, and its southern side brings westerly winds. In the case of Hurricane Irma, which tracked almost directly up the Florida panhandle, this meant that as it approached, the east coast of the Florida peninsula experienced easterly onshore winds and suffered a storm surge that caused severe inundation and flooding in areas such as Miami.

The negative surge

In contrast, these same easterly winds had the opposite effect on Florida’s west coast (the Gulf Coast), where water was pushed offshore, leading to a negative storm surge. This was most pronounced in areas such as Fort Myers and Tampa Bay, which normally has a relatively low tide range of less than 1m.

The negative surge developed over a period of about 12 hours and resulted in a water level up to 1.5m below the predicted low tide level. Combined with the fact that the sea is shallow in these areas anyway, it looked as if the sea had simply disappeared.

Read more: Predicting disaster: better hurricane forecasts buy vital time for residents.

As tropical cyclones rapidly lose energy when moving over land, the unusually low water level was expected to rapidly rise, which prompted authorities to issue a flash flood warning to alert onlookers to the potential danger. The negative surge was replaced by a storm surge of a similar magnitude within about 6 hours at Fort Myers and 12 hours later at Tampa Bay.

Rising waters are the deadliest aspect of hurricanes – even more than the ferocious winds. So while it may be tempting to explore the uncovered seabed, it’s certainly not wise to be there when the sea comes rushing back.

Darrell Strauss receives funding from an Advance Queensland Research Fellowship in partnership with Griffith University and the City of Gold Coast.

Here's the uncomfortable truth for the federal government: Keeping Liddell open will possibly make electricity prices higher and electricity less reliable. The fuel cost alone is over $60 MWh and may increase.

Wind energy has set new records in Europe, accounting for 20% of all demand, with wind, solar and hydro producing twice as much as coal and gas in afternoon.

Offshore wind auction results means that these projects are close to being subsidy-free, helping shift the conversation from renewables being expensive, towards how cheap, variable zero-carbon power can be integrated into the UK grid.

The latest climate modelling shows more Australians are at risk of being affected by natural disaster, but how resilient are we should the unthinkable occur?

Industry body warns over need for seasonal workers after Brexit as growers face 20% shortfall in supply of labour

UK apple growers are in the grip of a 20% shortfall in the supply of seasonal labour, pushing them towards “a cliff edge” as Brexit nears, the industry has warned.

At the start of the annual British apple harvesting season with more than 20 indigenous varieties going on sale in supermarkets, the main trade body for both apples and pears says worries about future labour availability are at the top of its lobbying agenda.

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Emergency crews have begun an oil spill clean-up after an oil tanker sank close to the island of Salamis.

Melting Antarctic ice can trigger effects on the other side of the globe. NASA/Jane Peterson

Melting of Antarctica’s ice can trigger rapid warming on the other side of the planet, according to our new research which details how just such an abrupt climate event happened 30,000 years ago, in which the North Atlantic region warmed dramatically.

This idea of “tipping points” in Earth’s system has had something of a bad rap ever since the 2004 blockbuster The Day After Tomorrow purportedly showed how melting polar ice can trigger all manner of global changes.

But while the movie certainly exaggerated the speed and severity of abrupt climate change, we do know that many natural systems are vulnerable to being pushed into different modes of operation. The melting of Greenland’s ice sheet, the retreat of Arctic summer sea ice, and the collapse of the global ocean circulation are all examples of potential vulnerability in a future, warmer world.

Read more: Chasing ice: how ice cores shape our understanding of ancient climate.

Of course it is notoriously hard to predict when and where elements of Earth’s system will abruptly tip into a different state. A key limitation is that historical climate records are often too short to test the skill of our computer models used to predict future environmental change, hampering our ability to plan for potential abrupt changes.

Fortunately, however, nature preserves a wealth of evidence in the landscape that allows us to understand how longer time-scale shifts can happen.

Core values

One of the most important sources of information on past climate tipping points are the kilometre-long cores of ice drilled from the Greenland and Antarctic ice sheets, which preserve exquisitely detailed information stretching back up to 800,000 years.

The Greenland ice cores record massive, millennial-scale swings in temperature that have occurred across the North Atlantic region over the past 90,000 years. The scale of these swings is staggering: in some cases temperatures rose by 16℃ in just a few decades or even years.

Twenty-five of these major so-called Dansgaard–Oeschger (D-O) warming events have been identified. These abrupt swings in temperature happened too quickly to have been caused by Earth’s slowly changing orbit around the Sun. Fascinatingly, when ice cores from Antarctica are compared with those from Greenland, we see a “seesaw” relationship: when it warms in the north, the south cools, and vice versa.

Attempts to explain the cause of this bipolar seesaw have traditionally focused on the North Atlantic region, and include melting ice sheets, changes in ocean circulation or wind patterns.

But as our new research shows, these might not be the only cause of D-O events.

Our new paper, published today in Nature Communications, suggests that another mechanism, with its origins in Antarctica, has also contributed to these rapid seesaws in global temperature.

Tree of knowledge The 30,000-year-old key to climate secrets. Chris Turney, Author provided

We know that there have been major collapses of the Antarctic ice sheet in the past, raising the possibility that these may have tipped one or more parts of the Earth system into a different state. To investigate this idea, we analysed an ancient New Zealand kauri tree that was extracted from a peat swamp near Dargaville, Northland, and which lived between 29,000 and 31,000 years ago.

Through accurate dating, we know that this tree lived through a short D-O event, during which (as explained above) temperatures in the Northern Hemisphere would have risen. Importantly, the unique pattern of atmospheric radioactive carbon (or carbon-14) found in the tree rings allowed us to identify similar changes preserved in climate records from ocean and ice cores (the latter using beryllium-10, an isotope formed by similar processes to carbon-14). This tree thus allows us to compare directly what the climate was doing during a D-O event beyond the polar regions, providing a global picture.

The extraordinary thing we discovered is that the warm D-O event coincided with a 400-year period of surface cooling in the south and a major retreat of Antarctic ice.

When we searched through other climate records for more information about what was happening at the time, we found no evidence of a change in ocean circulation. Instead we found a collapse in the rain-bearing Pacific trade winds over tropical northeast Australia that was coincident with the 400-year southern cooling.

Read more: Two centuries of continuous volcanic eruption may have triggered the end of the ice age.

To explore how melting Antarctic ice might cause such dramatic change in the global climate, we used a climate model to simulate the release of large volumes of freshwater into the Southern Ocean. The model simulations all showed the same response, in agreement with our climate reconstructions: regardless of the amount of freshwater released into the Southern Ocean, the surface waters of the tropical Pacific nevertheless warmed, causing changes to wind patterns that in turn triggered the North Atlantic to warm too.

Future work is now focusing on what caused the Antarctic ice sheets to retreat so dramatically. Regardless of how it happened, it looks like melting ice in the south can drive abrupt global change, something of which we should be aware in a future warmer world.

Chris Turney receives funding from the Australian Research Council.

Jonathan Palmer receives funding from the Australian Research Council (ARC).

Peter Kershaw has received fundng from the Australian Research Council.

Steven Phipps receives funding from the Australian Antarctic Science Program, the Australian Research Council, the International Union for Quaternary Research, the National Computational Infrastructure Merit Allocation Scheme, the New Zealand Marsden Fund, the University of Tasmania and UNSW Australia.

Zoe Thomas receives funding from the Australian Research Council.

Lawyers for two anti-fracking campaigners argue in high court that injunction obtained by Ineos curtail’s protester rights

The legality of a wide-ranging injunction obtained against anti-fracking protesters by a multinational firm is to be examined in a three-day court hearing.

Two campaigners have launched a legal challenge against the injunction obtained by Ineos, the petrochemicals giant. Joe Corré, the son of the fashion designer Vivienne Westwood, and Joe Boyd, say it is draconian, oppressive and dramatically curtails protesters’ rights.

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Fertile soil is being lost at rate of 24bn tonnes a year through intensive farming as demand for food increases, says UN-backed study

A third of the planet’s land is severely degraded and fertile soil is being lost at the rate of 24bn tonnes a year, according to a new United Nations-backed study that calls for a shift away from destructively intensive agriculture.

The alarming decline, which is forecast to continue as demand for food and productive land increases, will add to the risks of conflicts such as those seen in Sudan and Chad unless remedial actions are implemented, warns the institution behind the report.

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CCTV footage from under Whitechapel in east London shows a fatberg that weighs as much as 11 double decker buses and is the length of two football pitches blocking the sewer. It is mostly made up of fat, wet wipes and nappies, and is expected to take three weeks to clear

• ‘Total monster’: fatberg blocks London sewage system
  

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Thames Water must break up congealed mass of fat, wet wipes and nappies to prevent raw sewage flooding streets

A fatberg weighing the same as 11 double decker buses and stretching the length of two football pitches is blocking a section of London’s ageing sewage network.

The congealed mass of fat, wet wipes and nappies is one of the biggest ever found and would have risked raw sewage flooding on to the streets in Whitechapel, east London, had it not been discovered during a routine inspection earlier this month.

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The RNLI closed Perranporth beach due to the large number of jellyfish-like creatures.

Trump’s NASA nominee Jim Bridenstine is a climate denier who wants to end the agency’s climate research

According to 2016 election exit polls, only 38% of voters considered Donald Trump qualified to be president. 17% of those who thought him unqualified voted for Trump anyway, perhaps because he promised that as a wealthy businessman, he would be able to hire the best people to advise him. That was a claim his daughter Ivanka explicitly made in her speech at the Republican National Convention:

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Eight to 10 members of a remote indigenous group were allegedly killed by men working for illegal prospectors in Javari Valley

Brazilian authorities are investigating reports of a massacre of up to 10 people from an isolated tribe in the Amazon by illegal gold miners.

The killings, alleged to have taken place in Javari Valley, are claimed to have been carried out by men working for gold prospectors who dredge illegally in the region’s rivers.

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Hurricane Irma destroyed up to 90 per cent of buildings on some of the islands it hit.

The pressure from the Prime Minister on AGL has been described as "Venezuela style" politics.

The Government continues to pressure AGL keep open the Liddell power plant, as the energy company races to come up with an alternative.

A hungry arctic fox, mating sea angels and playful brown bears are among the creatures captured by photographers for this year’s competition. The exhibition opens on 20 October at the Natural History Museum

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David Mariuz/AAP

Pressure is mounting on the government to put an end to energy uncertainty as an Australian Energy Market Operator (AEMO) report warns of looming power shortages over the next few years.

Opposition climate change and energy spokesman Mark Butler has written about the toxic divisions on energy policy in his recent book, Climate Wars. He recognises there are challenges in the Coalition partyroom over the Finkel report, but says Labor will negotiate with the government on an energy framework. It wants to avoid an ALP government inheriting the policy chaos.

Responding to the government’s push to extend the life of the Liddell power station, he says Malcolm Turnbull has unfairly concluded there is only one option.

“With a proper investment framework in place, new investment that will last decades, not just a few more years … could take place. At the moment we have an investment strike and if we can’t end the investment strike then yes in five years time in NSW we will be in a position of supply shortage.”

On the future of coal, Butler says it’s still “a massive part of our system”, and while usage will go down over time, it will be a part of the system for “as far as we politically can see”.

“The problem is not old coal power plants closing, it’s that nothing is being put in to replace them.”

On alternative sources like battery power he is optimistic about their potential, while sceptical of expanding hydro power until the results of a feasibility study are produced.

Michelle Grattan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.