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Over the weekend, more than 170 countries signed an accord in Rwanda that will see the damaging synthetic greenhouse gases usually found in refrigerators and car air conditioners gradually curbed over the next 30 years.

A bar-tailed godwit on the mudflats may be on her way from the Arctic to sub-Saharan Africa. But she’s a lightweight compared to her New Zealand cousins

A long-billed, long-legged wader stands on the edge of the mud, waiting for the tide to recede so she can begin to feed. Nothing about her stands out: she isn’t strikingly pied like the avocets; she doesn’t have the curlew’s impossibly long, curved bill; and she isn’t flying around while yelling a frantic, urgent call like the redshanks.

Yet she has a far better story to tell than any of them. For she is a bar-tailed godwit: one of the greatest of all the bird world’s global travellers. She has already flown here to the river Parrett, that muddy river flowing into the Bristol Channel, from her breeding grounds far to the north – somewhere on the Arctic tundra in Scandinavia or Northern Russia.

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Tropical Cyclone Carlos approaches Western Australia in February 2011. NASA Goddard Space Flight Center/Flickr, CC BY

Northern Australia is likely to experience an average or above-average number of tropical cyclones this summer, according to the Bureau’s annual Tropical Cyclone Season Outlook, issued last week. Given current climate drivers, that means we’re likely to see 11 or more tropical cyclones in the Australian region, and typically around four of those will cross the coastline.

The season will almost certainly be more active than the last. And that means it’s time to prepare, because the likelihood of damage from a tropical cyclone is high in any season.

Last year was certainly nothing like a normal season, so you don’t want to be caught out. The Australian region saw only three tropical cyclones in total (easily beating the old record minimum of five set in the El Niño years of 1987 and 2006 from our data back to 1969-70), none reached severe status (Category 3 or above; this has never occurred) and only one crossed the coast (the equal lowest number on record).

But why do we expect such a different season this time around?

Tracking cyclones

When a cyclone develops, the Bureau issues short-term weather forecasts on the cyclone’s likely track and strength. But for the tropical cyclone season as a whole, we can only look at the chances of more or less cyclones than average forming in Australian waters because cyclones and their tracks are so sensitive to subtle and fine-scale changes in the atmosphere and ocean.

When considering how many tropical cyclones may form over a season, we currently use a statistical model that considers the long-term relationship between cyclones and the state of El Niño or La Niña (properly known as El Niño–Southern Oscillation or ENSO). This particularly focuses on ocean temperatures and atmospheric circulation over the tropical Pacific Ocean.

The model uses the Southern Hemisphere Best Track Cyclone database. This historical record extends back to 1969 and is jointly-maintained by the Bureau, Météo France (La Reunion), Fiji Meteorological Service and Meteorological Service of New Zealand. These four agencies are assigned by the World Meteorological Organization to issue cyclone forecasts in the southern hemisphere.

What makes a cyclone?

Tropical cyclones form in regions with very warm surface waters — generally greater than 26℃. The location of this warm water in the tropical Pacific Ocean and around Australia’s northern coast is affected by ENSO.

During El Niño years the warmest water in the tropics (and associated tropical weather) tends to be located away from Australia, in the eastern tropical South Pacific. In La Niña years, this warm water tends to be located in Coral Sea, between Australia and the Solomon Islands.

Plots of observed cyclone density in the southern hemisphere with ENSO phase. The observed density of cyclones during La Niña years is subtracted from the observed density during El Niño years. Australia Bureau of Meteorology

The image above shows that during El Niño years, cyclones are more likely to occur away from Australia, closer to the dateline and in the eastern south Pacific, as well as in the western Indian Ocean.

This is why 2015 - which was also one of the strongest El Niño events on record, arguably behind only 1982–83 and 1997–98 - resulted in such a quiet tropical cyclone season for Australia. It is also why the eastern Pacific at the same time experienced its second most active (eastern) Pacific Hurricane season on record.

Cyclones for Christmas

Conversely, during La Niña years, cyclones are more likely to form in the western Pacific/Coral Sea, and in the eastern Indian Ocean. As La Niña also tends to bring warmer-than-average waters around Australia’s coastline, the Australian region experiences more cyclones overall. Of course ocean temperatures are just one factor that drives the formation of cyclones. Changes in the atmosphere also encourage tropical cyclones, including higher humidity and more favourable winds.

Because tropical cyclones form closer to the coast during La Niña years, and there tends to be more winds guiding them towards land in some areas, there is a greater chance of more cyclones making landfall. The first crossing also typically comes earlier. History shows that, on average, the first tropical cyclone to make landfall during a La Niña year is around December 10, more than two weeks earlier than the average date across all cyclone seasons; December 25. Typically, Australia’s western coastline sees the first crossing of the year.

The record number of tropical cyclones to cross the coast occurred in the La Niña season of 1970–71, when eight crossed the Australian coastline. The most cyclones on record for an Australian season were in the La Niña summer of 1973–74 and the neutral 1983–84, when 18 tropical cyclones formed. This highlights why a benign season like 2015–16 should not make us complacent.

As this season starts, ENSO is neutral. But a La Niña “watch” is current, meaning a La Niña certainly cannot be ruled out before the end of the year.

The latest observations show the Pacific Ocean has several indicators that have exceeded La Niña thresholds. El Niño and La Niña develop slowly, and likewise their impacts don’t appear suddenly.

With warmer water around Australia’s northern coastline – a classic La Niña-like pattern – the odds rise of an above-average tropical cyclone season.

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond the academic appointment above.

No amount of spin or legal obfuscation can reconcile the UK government’s clamour for shale gas with its obligations as enshrined in the Paris climate change agreement. Consequently, when the UK’s communities secretary, Sajid Javid, gave the go-ahead for fracking in Lancashire (Report, 7 October), he was making a clear statement that the government has no interest in abiding by either the spirit or the maths of the Paris agreement.

Shale gas is a high carbon energy source. When used for generating electricity its emissions of carbon dioxide are about 30-90 times higher than the full lifecycle emissions of either renewables or nuclear. Given the rapid phase-out of the UK’s existing coal power stations, shale gas will not be produced at sufficient scale and in the necessary timeframe for it to be a substitute for coal.

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Europe’s Schiaparelli spacecraft is ejected by its “mothership” and is now on a direct course to try to land on Mars on Wednesday.

China is poised to launch a rocket carrying two astronauts to its orbiting space station on Monday morning.

Every day, one in nine people around the world do not have enough food to support a healthy, active lifestyle. The problem has been compounded by climate change, which often has a devastating impact on food security. Severe drought across three continents has led to shortages of food, water and energy in recent months. Tearfund is helping communities to grow crops, find alternative sources of food or fuel, and increase resilience to climate change

Photographs: Tearfund

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Wildlife photojournalist of the year exposes the plight of the endangered scavenger

Vultures are rarely viewed as the poster boys and girls of the natural world. They have repulsive eating habits and are strikingly ugly. Nevertheless, they play a critical role in maintaining the ecological health of many parts of the world.

Vultures consume animal carcasses more effectively than any other scavengers and because their digestive juices contain acids that neutralise pathogens such as cholera and rabies they prevent diseases spreading. They act as dead-end hosts for numerous unpleasant ailments. But many ecologists are now warning that vultures across the planet are under serious threat thanks to habitat loss, deliberate and accidental poisoning, and use of the birds’ body parts as traditional medicine cures.

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Experts emphasize that the incident, in which a great white broke through a cage holding a diver, was a ‘one in a million occurrence’

Shark enthusiasts are concerned about the impact of a viral video that showed a great white shark breaking into a cage occupied by a diver in Mexico.

The diver survived, but the harrowing video shed light on a decades-old tourism industry that allows people to be within an arm’s length of great white sharks, separated only by the sea and some metal bars.

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The deal done in Rwanda on Saturday will cut greenhouse gases. We assess its global significance

They went to Kigali to eliminate hydrofluorocarbons (HFCs) and take 0.5C out of future global warming, and the 170 countries that successfully negotiated an amendment to the Montreal protocol treaty agreed to get rid of 90% of them. Not bad for four days and three long nights of hard work.

The Kigali deal on HFCs is in fact fiendishly complicated and has taken years to negotiate in various technical and political forums. The final agreement, announced on Saturday morning caps and reduces the use of HFCs in a gradual process beginning in 2019.

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HFCs deal is vital for reducing emissions but poorer countries rely on old coolant technologies and will now have to upgrade

They went to Kigali to eliminate hydrofluorocarbons (HFCs) and take 0.5C out of future global warming, and the 170 countries who successfully negotiated an amendment to the Montreal Protocol agreed to get rid of 90% of them. Job done. Not bad for four days and three long nights’ work.

In fact the Kigali deal on HFCs, announced on Saturday morning, is fiendishly complicated and has taken years to negotiate in different technical and political forums. It was only struck by an ambitious agreement to give countries different timescales to phase them out, alongside major chemical and big food companies accepting change, the personal determination of the US secretary of state, John Kerry, to get a deal before the election and developing countries agreeing to invest heavily in new technologies.

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Polish mathematicians who laid the groundwork for cracking the WW2 Nazi Enigma code, are being honoured at the country's embassy in London.

Delegates celebrate a global deal to limit the use of hydrofluorocarbon gases, in a major effort to combat climate change. The agreement was reached at a climate conference in the Rwandan capital Kigali on Saturday morning. US secretary of state John Kerry hails it a ‘monumental step forward’

• Climate change: global deal reached to limit use of hydrofluorocarbons

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Professor John Goodenough, whose work led to the lithium-ion battery, on the Samsung problems.

The continuing refugee crisis in Europe, #FeesMustFall protests in South Africa, the aftermath of Hurricane Matthew – the best photography in news, culture and sport from around the world this week

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The worst drought for decades in Ethiopia’s northern highlands has ended, but unusually heavy downpours threaten to ruin crops and exacerbate food insecurity as flash flooding turns roads to rivers and swamps fields

Photographs by James Whitlow Delano/USAid

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One year on from collapse of the Samarco dam, which killed 19 people and polluted one of the country’s most important rivers, and communities are still suffering

• Samarco dam collapse: one year on from Brazil’s worst environmental disaster

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Countries meeting in Rwanda have agreed a "monumental" deal to phase out gases used in fridges that are worsening global warming.

Global deal on HFCs – greenhouse gases far more powerful than carbon dioxide – seen as ‘largest temperature reduction ever achieved by single agreement’

A worldwide deal has been reached to limit the use of greenhouse gases far more powerful than carbon dioxide in a major effort to fight climate change.

The talks on hydrofluorocarbons, or HFCs, have been called the first test of global will since the historic Paris Agreement to cut carbon emissions was reached last year. HFCs are described as the world’s fastest-growing climate pollutant and are used in air conditioners and refrigerators.

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Almost half of all plastic bottles used in the home end up in landfill sites, research shows, with huge impacts on marine life

British households are failing to recycle as many as 16m plastic bottles every day – a “staggering” number and nearly half the total of more than 35m which are used and discarded daily – according to new research.

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