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Over the past 60 years land clearing has seen the loss of more than 90 per cent of the Brigalow forests between Townsville and northern NSW.

Clouds over Australia's Davis Research Station, containing ice particles that activate ozone-depleting chemicals, triggering the annual ozone hole. Barry Becker/BOM/AAD, Author provided

This weekend marks the 30th birthday of the Montreal Protocol, often dubbed the world’s most successful environmental agreement. The treaty, signed on September 16, 1987, is slowly but surely reversing the damage caused to the ozone layer by industrial gases such as chlorofluorocarbons (CFCs).

Each year, during the southern spring, a hole appears in the ozone layer above Antarctica. This is due to the extremely cold temperatures in the winter stratosphere (above 10km altitude) that allow byproducts of CFCs and related gases to be converted into forms that destroy ozone when the sunlight returns in spring.

As ozone-destroying gases are phased out, the annual ozone hole is generally getting smaller – a rare success story for international environmentalism.

Back in 2012, our Saving the Ozone series marked the Montreal Protocol’s silver jubilee and reflected on its success. But how has the ozone hole fared in the five years since?

Read more: What is the Antarctic ozone hole and how is it made?.

The Antarctic ozone hole has continued to appear each spring, as it has since the late 1970s. This is expected, as levels of the ozone-destroying halocarbon gases controlled by the Montreal Protocol are still relatively high. The figure below shows that concentrations of these human-made substances over Antarctica have fallen by 14% since their peak in about 2000.

Past and predicted levels of controlled gases in the Antarctic atmosphere, quoted as equivalent effective stratospheric chlorine (EESC) levels, a measure of their contribution to stratospheric ozone depletion. Paul Krummel/CSIRO, Author provided

It typically takes a few decades for these gases to cycle between the lower atmosphere and the stratosphere, and then ultimately to disappear. The most recent official assessment, released in 2014, predicted that it will take 30-40 years for the Antarctic ozone hole to shrink to the size it was in 1980.

Signs of recovery

Monitoring the ozone hole’s gradual recovery is made more complicated by variations in atmospheric temperatures and winds, and the amount of microscopic particles called aerosols in the stratosphere. In any given year these can make the ozone hole bigger or smaller than we might expect purely on the basis of halocarbon concentrations.

Launching an ozone-measuring balloon from Australia’s Davis Research Station in Antarctica. Barry Becker/BOM/AAD, Author provided

The 2014 assessment indicated that the size of the ozone hole varied more during the 2000s than during the 1990s. While this might suggest it has become harder to detect the healing effects of the Montreal Protocol, we can nevertheless tease out recent ozone trends with the help of sophisticated atmospheric chemistry models.

Reassuringly, a recent study showed that the size of the ozone hole each September has shrunk overall since the turn of the century, and that more than half of this shrinking trend is consistent with reductions in ozone-depleting substances. However, another study warns that careful analysis is needed to account for a variety of natural factors that could confound our detection of ozone recovery.

The 2015 volcano

One such factor is the presence of ozone-destroying volcanic dust in the stratosphere. Chile’s Calbuco volcano seems to have played a role in enhancing the size of the ozone hole in 2015.

At its maximum size, the 2015 hole was the fourth-largest ever observed. It was in the top 15% in terms of the total amount of ozone destroyed. Only 2006, 1998, 2001 and 1999 had more ozone destruction, whereas other recent years (2013, 2014 and 2016) ranked near the middle of the observed range.

Average ozone concentrations over the southern hemisphere during October 1-15, 2015, when the Antarctic ozone hole for that year was near its maximum extent. The red line shows the boundary of the ozone hole. Paul Krummel/CSIRO/EOS, Author provided

Another notable feature of the 2015 ozone hole was that it was at its biggest observed extent for much of the period from mid-October to mid-December. This coincided with a period during which the jet of westerly winds in the Antarctic stratosphere was particularly unaffected by the warmer, more ozone-rich air at lower latitudes. In a typical year, the influx of air from lower latitudes helps to limit the size of the ozone hole in spring and early summer.

The 2017 hole

As noted above, the ozone holes of 2013, 2014 and 2016 were relatively unremarkable compared with that of 2015, being close to the long-term average for overall ozone loss.

In general respects, these ozone holes were similar to those seen in the late 1980s and early 1990s, before the peak of ozone depletion. This is consistent with a gradual recovery of the ozone layer as levels of ozone-depleting substances gradually decline.

This year’s hole began to form in early August, and the timing was similar to the long-term average. Stratospheric temperatures during the Antarctic winter were slightly cooler than in 2016, which would favour enhancement of the chemical changes that lead to ozone destruction in spring. However, temperatures climbed above average in mid-August during a disturbance to the polar winds, delaying the hole’s expansion. As of the second week of September, the warmer-than-average temperatures have continued but the ozone hole has grown slightly larger than the long-term average since 1979.

Read more: Saving the ozone layer: why the Montreal Protocol worked.

While annual monitoring continues, which includes measurements under the Australian Antarctic Program, a more comprehensive assessment of the ozone layer’s prospects is set to arrive late next year. Scientists across the globe, coordinated by the UN Environment Program and the World Meteorological Organisation, are busy preparing the next report required under the Montreal Protocol, called the Scientific Assessment of Ozone Depletion: 2018.

This peer-reviewed report will examine the recent state of the ozone layer and the atmospheric concentration of ozone-depleting chemicals, how the ozone layer is projected to change, and links between ozone change and climate.

In the meantime we’ll watch the 2017 hole as it peaks then shrinks over the remainder of the year, as well as the ozone holes of future years, which will tend to grow less and less large as the ozone layer heals.

Andrew Klekociuk is employed by the Australian Antarctic Division and is funded by the Department of the Environment and Energy of the Australian government.

Paul Krummel is employed by CSIRO and receives funding from MIT, NASA, Australian Bureau of Meteorology, Department of the Environment and Energy, and Refrigerant Reclaim Australia.

New federal government-funded study finds exposure to a key air pollutant is significantly influenced by race, far more than by income, age or education

People of color are still far more likely to suffer from harmful air pollution than white people across the US and this disparity has barely improved in recent years, despite overall improvements in air quality, a new federal government-funded study has found.

Related: London’s black communities disproportionately exposed to air pollution – study

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The case for new nuclear power stations is fatuous now offshore wind power has come down in cost so much, says Ian Hill. Yes, writes Will Taylor, but don’t forget the potential of tidal energy. Hold on a minute before rejecting nuclear, argue Tim Chittenden and Jim Waterton

Your excellent editorial on the reducing cost of offshore wind power (13 September) is timely in identifying the increasingly futile case for new nuclear build. It does, however, repeat the fallacy that nuclear power “is a zero-carbon technology”. The carbon emissions involved in building such immense structures, in mining and transporting uranium, and in the transport, reprocessing and storage of waste, contribute to a considerable carbon burden. Estimates vary considerably, but studies suggest that the emissions from nuclear generation could be one-10th of those of fossil fuels, but twice those of wind power.

Furthermore, the need for a continuous supply is of only limited use when consumption patterns become distorted by, for example, the increased need to charge electric vehicles overnight, as your leader identifies. What is needed now, alongside continued investment in the latest generation of renewable production, is increased investment into a wide range of storage technologies, and further research and investment into the production of renewable heat.

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Scientists explain how they discovered a water ocean beneath the ice shell of Saturn's moon Enceladus.

New inquiry will look into the viability of deposit schemes and taxes as ways to reduce impact of plastic waste on the environment

MPs are to mount a new inquiry into plastic bottles amid growing calls for a deposit scheme to reduce the impact of plastic waste in the ocean.

The investigation will also examine whether charges or taxes should be put on single-use plastic bottles and takeaway coffee cups to reduce their contribution to litter.

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Scary-looking fish found on a Texas beach after Hurricane Harvey is identified as a fangtooth snake-eel with the help of social media

The mystery of an eyeless fanged sea monster washed ashore by Hurricane Harvey has been solved by social media.

Preeti Desai, a science communicator, found the sinister-looking fish on a beach in Texas City after the storm, and asked Twitter users to help identify it.

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The conservation status of the elusive snow leopard is downgraded from "endangered" to "vulnerable".

It took seven years for the US-European mission to get to the ringed planet, launching in 1997.

North American ash trees, that face extinction due to an invasive beetle, and African antelope join the latest IUCN list that includes 25,000 species at risk of extinction

• Red list: ash trees and antelopes on the brink of extinction

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David Malin has spent four decades photographing space. Now retired, he has held a competition to inspire other astrophotographers.

Scientists warn once-common species are disappearing faster than they can be counted as North America’s ash trees join IUCN’s list of endangered species due to threat of an invasive beetle

• In pictures: once-common ash trees and antelope added to red list

Native ash trees, abundant across North America, are on the brink of extinction as an invasive beetle ravages forests, according to the new red list of threatened species from the International Union for Conservation of Nature (IUCN).

The list now includes more than 25,000 species at risk of extinction and the scientists warn that species, such as the American ashes and five African antelopes, that were thought to be safe, are now disappearing faster than they can be counted.

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British athlete Mark Beaumont is expected to complete his world tour on Monday after 79 days in the saddle, smashing the previous record of 123 days

Endurance cyclist Mark Beaumont is expected to arrive in Paris on Monday 18 September, 79 days after setting off on his attempt to cycle around the world in 80 days.

The Guardian joined Beaumont in Lisbon on Wednesday, where he arrived on an overnight flight from Halifax in Canada to start the final leg of his record-breaking challenge. Despite cycling an average of 240 miles over 16 hours every day since 2 July, he looked fresh and sounded upbeat as we ticked off more miles on our way to the Spanish border. Yet he admitted the ride has taken its toll on him, both mentally and physically.

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An Aboriginal group in Tasmania says a state government plan to reopen drive tracks that run through the Tarkine would see areas of significant cultural and historical value destroyed.

Environmental activist group says it is detaining vessels for Timorese police after Chinese-owned fleet allegedly targeted sharks

The ocean activist group Sea Shepherd says it has delivered armed Timor-Leste police on to a Chinese-owned fishing vessel in a dawn raid and is detaining the vessels for the police after it was found targeting sharks.

Following a two-week hunt for the Pingtan Marine Enterprises fleet, the Sea Shepherd boat M/Y Ocean Warrior found the vessels 150km south of Timor-Leste, allegedly fishing with gill nets anchored to the bottom of the sea, which would suggest they were targeting bottom-dwellers such as sharks.

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Chair of newly formed Energy Security Board, Kerry Schott, says that by harnessing demand management in Australia, "we can all stop worrying about building new plants of any description."

Sandy, Bedfordshire A leave-taking of Britain is playing out in the skies as swifts and martins fuel up for their epic journey

Through these last weeks of summer, the autumn migration has played out in the skies, though it goes largely unnoticed by most below. A trickle of an exodus began over the bank holiday with three dark specks, way, way up in the blue. Specks, yes, but you could see, from the wings curved like taut bows, that they were unmistakably swifts.

Hatched on northern ledges they had become citizens of heaven. They deviated on insect-chasing sallies in all directions, but were overall tracking south-west.

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The Australian energy statistics provides annual energy consumption, production and trade statistics and analysis.

Wirsol Energy adds ready-to-build 110MW Wemen solar farm near Mildura to its planned 1GW by 2020 pipeline.

A pair of giraffes with leucism, a condition that inhibits pigmentation in skin cells, have been filmed by conservationists for the first time

A pair of rare white giraffes have been spotted in Kenya, to the delight of local residents and conservationists.

The reticulated giraffes, a mother and child, suffer from a genetic condition called leucism, which inhibits pigmentation in skin cells. Unlike albinism, animals with leucism continue to produce dark pigment in their soft tissue, which explains the white giraffes’ dark eyes and other colouring.

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