CORALS ON Australia’s Great Barrier Reef that survived bleaching from rising sea temperatures were more resistant to another bout of hot conditions the following year, scientists said Tuesday, a “silver lining” for the embattled ecosystem.

The 2,300-kilometre Unesco World Heritage-listed reef off Australia’s northeastern coast was hit by back-to-back bleaching events in 2016 and 2017.

Bleaching occurs when abnormal environmental conditions, such as warmer sea temperatures, cause corals to expel tiny photosynthetic algae, draining them of their colour. Corals can recover if the water temperature drops and the algae are able to recolonise them.

A dead and eroding section of reef following back-to-back bleaching events. 

Swathes of coral died or were damaged in the unprecedented successive events, particularly the more heat-susceptible branching corals that are shaped like tables.

But Professor Terry Hughes of James Cook University, who has been leading the surveys of bleached corals, found in the latest study, published in Nature Climate Change, that the response of the reef was different between the two years.

“We were astonished to find less bleaching in 2017, because the temperatures were even more extreme than the year before,” Hughes said.

The northern part of the reef, which was worst-affected in 2016, bleached “much less” in 2017 even though some of the reefs underwent similar levels of heat stress in both summers.

In the central regions, the levels of bleaching for both years were observed to be the same, even though the heat exposure was higher in 2017, the researchers said.

Meanwhile, in the southern region – the least-affected – corals that suffered minor bleaching in the first year showed no bleaching in the second.

“It looks like the history of their experience in year one has toughened them up so that they’ve acclimatised to moderate levels in year two of heat exposure … It’s something of a silver lining.”

Hughes said it was too early to say whether the reef could be hit by another bleaching event in early 2019, after a spring heatwave in adjacent Queensland state.

Global coral reefs risk catastrophic die-offs if Earth’s average surface temperature increases two degrees Celsius above pre-industrial levels, earlier research has shown.

Coral reefs make up less than one per cent of Earth’s marine environment, but are home to an estimated 25 per cent of ocean life, acting as nurseries for many species of fish.

FORMED IN the shadow of Mount Everest, the turquoise depths of Nepal’s Imja glacial lake would be a breathtaking miracle of nature to behold – were they not a portent of catastrophic floods.

Scientists warn that as climate change causes Himalayan glaciers to melt at an alarming rate, lakes like Imja could swell further and eventually collapse, triggering a terrifying deluge in Nepal, an impoverished nation at the mercy of a warming planet.

Those tasked with staving off disaster fear a “glacial lake outburst flood” – sending torrents of water, mud and rock hurtling downstream– could reach as far as Nepal’s densely populated southern plains, wiping out roads, vital energy projects and entire villages in its path.

Nepalese resident Ngawang Tshering Sherpa speaks during an interview with AFP in Shurke village in Solukhumbu district, some 140km northeast of Kathmandu.

“The risk is getting bigger,” says Arun Bhakta Shrestha, a climate scientist from the Kathmandu-based International Centre for Integrated Mountain Development.

“These valleys are getting more populated, and infrastructure is developing rapidly.”

Hundreds of these lakes have appeared out of nowhere in the Himalayas in recent decades. A 2014 survey found one quarter of Nepal’s glaciers shrunk between 1977 and 2010, leaving behind 1,466 lakes.

Twenty-one have been identified as potentially dangerous and Nepal is racing to stay a step ahead of disaster, as global warming reshapes its mountain geography.

“As a small country, there is little we can do to stop what is happening to our glaciers,” says Rishi Ram Sharma, the director general at Nepal’s department of hydrology and meteorology.

“But we have to do what we can do to adapt and protect our people.”

Nepal’s fastest-growing lake, Imja once posed little threat to the villagers of Surke, a picturesque hamlet perched high in the Everest region.

In the early 1980s, the small lake at the foot of the Imja glacier at 5,010 metres was unremarkable.

But by 2014, it had more than tripled in size, contained only by a natural wall of debris, known as a moraine, which experts warned might not hold back the waters much longer.

A year later, when a massive earthquake struck Nepal, villagers in Surke assumed Imja had collapsed and would soon bury them all.

“We were terrified the quake would trigger a flood from the lake. All of us ran for safety,” villager Phudoma Sherpa recalls.

The lake miraculously held – sparing the 12,000 people directly in its path.

But the quake served as a wake-up call for policymakers.

Experts told the government that the gigantic glacial lakes were effectively a ticking time bomb.

With thousands of lives at stake, a massive undertaking began in late 2016 to drain Imja, which then measured 150 metres deep and two kilometres long.

Only the second operation of its kind in Nepal’s history, the project was a testament to the monumental challenge posed by glacial lakes, which are often remote and very difficult to access.

The Imja glacial lake controlled exit channel in the Everest region of the Solukhumbu district, some 140km northeast of Kathmandu.

Yaks and helicopters transported materials and teams of workers to the high-altitude region, where they toiled in thin air for six months until a drainage canal and early-warning system were installed.

The lake was lowered by 3.5 metres, draining more than five million cubic metres of water.

“Now, you have a channel. So any water that accumulates is drained out. That is how the risk is lowered,” explains Deepak KC, a climate change analyst from the United Nations Development Programme that backed the project.

The project cost $7.4 million (Bt57.4 million), an expensive commitment for a nation heavily reliant on its wealthier neighbours and on

international aid that contributed 12 per cent to its GDP in the last fiscal year.

In this case, more than 80 per cent of the money came from the Global Environment Facility, an international fund that provides green financing to developing countries. The rest was covered by UNDP.

With a paltry economy and 26 million people, Nepal has a tiny carbon footprint compared to its giant patrons China and India, major polluters that are home to a third of humanity.

Melting glaciers from climate change pose a huge threat to Nepal – as well as an undeserved extortionate burden, authorities say.

“We feel as if we have been penalised for the mistakes we never made,” President Bidya Devi Bhandari told world leaders at a climate summit in Poland this month.

“We are compelled to spend (a) significant amount of our national income in addressing disasters-induced problems.”

Nepal is asking the global community for further assistance to fight climate change.

For those no longer living under Imja’s shadow, the cost is well worth it.

“There was a sense of fear before, but we feel a lot safer now,” Sherpa says.