What Greenland’s record-breaking rain means for the planet


Willow Hallgren, Griffith UniversityFor three days this month, 7 billion tonnes of rain fell across Greenland — the largest amount since records began in 1950. It’s also the first time since then that rain, not snow, fell on Greenland’s highest peak.

This is alarming. Greenland’s ice sheet is the second largest on the planet (after Antarctica) and any rain falling on its surface accelerates melting. By August 15, the amount of ice lost was seven times greater than is normal for mid-August.

This is just the latest extreme climate event on the island, which sits in the North Atlantic Ocean. In a single day in July this year, the amount of ice that melted in Greenland would have covered the US state of Florida with 5 centimetres of water. And last October, research showed ice in Greenland is melting faster than at any other time in the past 12,000 years.

Melting in Greenland threatens to significantly hamper humanity’s efforts to mitigate climate change. That’s because, after a certain point, it may create catastrophic “feedback loops”. Let’s look at the issue in more detail.

Rising temperatures in the Arctic

Greenland’s vast ice sheet comprises almost 1.7 million square kilometres of glacial land ice. It covers most of the territory and contains enough ice to raise sea levels by more than 7 metres if melted.

The Greenland and Antarctica ice sheets lost a combined 6.4 trillion tonnes of ice between 1992 and 2017. Melting in Greenland has contributed to 60% (17.8 millimetres) of the Earth’s overall sea-level rise due to melting ice sheets, even though Greenland is much smaller than Antarctica.

This may be partly because half of Greenland’s melting is the result of rising air temperatures, which cause surface melting. In Antarctica, most ice loss is from ocean water melting glaciers that spill from land into the sea. And the rate of ice loss in both Greenland and Antarctica is accelerating — increasing sixfold since the 1990s.

Rain falling on ice exacerbates this process. So what’s behind the recent unprecedented weather?

Temperatures in the Arctic are rising twice as quickly as the rest of the planet for a number of reasons, including changes in cloud cover and water vapour, the reflectivity of the surface, and how weather systems transport energy from the tropics to the polar regions. This has made extreme weather events more common.




Read more:
Climate explained: why is the Arctic warming faster than other parts of the world?


In recent years in Greenland, rain has fallen further north, and more rain has fallen in winter. This is not normal for these regions, which usually get snow, not rain, in below-freezing temperatures.

This month’s rain is the result of warm, moist air flowing up from south-west of Greenland and remaining for several days. In the morning of August 14, temperatures at the 3,216-metre summit of Greenland’s ice sheet surpassed freezing point, peaking at 0.48℃. Rain fell on the summit for several hours that morning and on August 15.

This was particularly shocking given the above-freezing temperatures occurred so late in Greenland’s normally short summer. At this time of year, large areas of bare ice are exposed from a lack of snow, which leads to greater runoff of rainwater and meltwater into the oceans.

Temperatures rarely surpass freezing at Greenland’s highest point.
Shutterstock

When melting is self-reinforcing

Rainfall makes the ice sheet more prone to surface melt since it exacerbates the so-called “ice-albedo positive feedback”. In other words, the melting reinforces itself.

When rain falls, its warmth can melt snow, exposing the underlying darker ice, which absorbs more sunlight. This increases temperatures at the surface, leading to more melting.

Unfortunately, this isn’t the only positive feedback loop destabilising the Greenland ice sheet.

The “positive melt-elevation feedback” is another, where the lower height of the ice sheet leads to faster melting because higher temperatures occur at lower altitudes.

Also worrying is when higher temperatures cause coastal glaciers to thin, allowing more ice to slip into the sea. This both speeds up the rate of glacier flow towards the sea and lowers the ice surface, exposing it to warmer air temperatures and, in turn, increasing melting.

The rate of ice loss in both Greenland and Antarctica is accelerating.
Shutterstock

What does this mean for the planet?

These positive feedbacks can lead to tipping points — abrupt and irreversible changes in the climate system after a certain threshold is reached. We are more likely to reach these tipping points as emissions increase and global temperatures rise.

While the science on tipping points is still emerging, the most recent report from the Intergovernmental Panel on Climate Change said they cannot be ruled out. The report identified likely tipping points such as widespread Arctic sea-ice melting and the thawing of methane-rich permafrost.




Read more:
‘Failure is not an option’: after a lost decade on climate action, the 2020s offer one last chance


Recent studies show what humanity may be up against. A study from May this year showed a substantial part of the Greenland ice sheet is either at, or about to reach, a tipping point where melting will accelerate, even if global warming is stopped. Scientists are concerned reaching this point may trigger a cascade effect, leading to other tipping points being reached.

Melted ice from both the Arctic Ocean and Greenland have caused an influx of freshwater into the North Atlantic Ocean. This has contributed to the slowing of a system of crucial ocean currents, which carry warm water from the tropics into the colder North Atlantic. This current, called the Atlantic Meridional Overturning Circulation (AMOC), has slowed by 15% since the 1950s.

If the AMOC slows down any further, the consequences for the planet could be profound. It could destabilise the West African monsoon, cause more frequent drought in the Amazon rainforest and accelerate ice loss in Antarctica.

An existential threat

The rising likelihood of tipping points being reached beyond 1.5℃ of warming represents a potential, looming existential threat to human civilisation. However, even if we’ve already crossed some tipping points, as some scientists suggest, how fast the impacts unfold is still within our control.

If we limit global warming to 1.5℃ this century, we give ourselves longer to adapt to heating already locked into the Earth’s system. But the window is rapidly closing; estimates indicate we may reach the crucial 1.5℃ threshold as soon as the mid-2030s.

The message for humanity is urgent: hard science, not cloying political spin, needs to dictate climate action in the coming years. As with COVID-19, listening to the scientists gives us the best hope of saving the planet.




Read more:
When Greenland was green: rapid global warming 55 million years ago shows us what the future may hold


The Conversation


Willow Hallgren, Adjunct Research Fellow, Centre for Planetary Health and Food Security, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia’s record-breaking winter warmth linked to climate change


File 20170901 27714 7nsuln
This winter had some extreme low and high temperatures.
Daniel Lee/Flickr, CC BY-NC

Andrew King, University of Melbourne

On the first day of spring, it’s time to take stock of the winter that was. It may have felt cold, but Australia’s winter had the highest average daytime temperatures on record. It was also the driest in 15 years.

Back at the start of winter the Bureau of Meteorology forecast a warm, dry season. That proved accurate, as winter has turned out both warmer and drier than average.


Read more: Australia’s dry June is a sign of what’s to come


While we haven’t seen anything close to the weather extremes experienced in other parts of the world, including devastating rainfalls in Niger, the southern US and the Indian subcontinent all in the past week, we have seen a few interesting weather extremes over the past few months across Australia.

Much of the country had drier conditions than average, especially in the southeast and the west.
Bureau of Meteorology

Drier weather than normal has led to warmer days and cooler nights, resulting in some extreme temperatures. These include night-time lows falling below -10℃ in the Victorian Alps and -8℃ in Canberra (the coldest nights for those locations since 1974 and 1971, respectively), alongside daytime highs of above 32℃ in Coffs Harbour and 30℃ on the Sunshine Coast.

During the early part of the winter the southern part of the country remained dry as record high pressure over the continent kept cold fronts at bay. Since then we’ve seen more wet weather for our southern capitals and some impressive snow totals for the ski fields, even if the snow was late to arrive.

This warm, dry winter is laying the groundwork for dangerous fire conditions in spring and summer. We have already had early-season fires on the east coast and there are likely to be more to come.

Climate change and record warmth

Australia’s average daytime maximum temperatures were the highest on record for this winter, beating the previous record set in 2009 by 0.3℃. This means Australia has set new seasonal highs for maximum temperatures a remarkable ten times so far this century (across summer, autumn, winter and spring). The increased frequency of heat records in Australia has already been linked to climate change.

Winter 2017 stands out as having the warmest average daytime temperatures by a large margin.
Bureau of Meteorology

The record winter warmth is part of a long-term upward trend in Australian winter temperatures. This prompts the question: how much has human-caused climate change altered the likelihood of extremely warm winters in Australia?

I used a standard event attribution methodology to estimate the role of climate change in this event.

I took the same simulations that the Intergovernmental Panel on Climate Change (IPCC) uses in its assessments of the changing climate, and I put them into two sets: one that represents the climate of today (including the effects of greenhouse gas emissions) and one with simulations representing an alternative world that excludes our influences on the climate.

I used 14 climate models in total, giving me hundreds of years in each of my two groups to study Australian winter temperatures. I then compared the likelihood of record warm winter temperatures like 2017 in those different groups. You can find more details of my method here.

I found a stark difference in the chance of record warm winters across Australia between these two sets of model simulations. By my calculations there has been at least a 60-fold increase in the likelihood of a record warm winter that can be attributed to human-caused climate change. The human influence on the climate has increased Australia’s temperatures during the warmest winters by close to 1℃.

More winter warmth to come

Looking ahead, it’s likely we’re going to see more record warm winters, like we’ve seen this year, as the climate continues to warm.

The likelihood of winter warmth like this year is rising. Best estimate chances are shown with the vertical black lines showing the 90% confidence interval.
Author provided

Under the Paris Agreement, the world’s nations are aiming to limit global warming to below 2℃ above pre-industrial levels, with another more ambitious goal of 1.5℃ as well. These targets are designed to prevent the worst potential impacts of climate change. We are currently at around 1℃ of global warming.

Even if global warming is limited to either of these levels, we would see more winter warmth like 2017. In fact, under the 2℃ target, we would likely see these winters occurring in more than 50% of years. The record-setting heat of today would be roughly the average climate of a 2℃ warmed world.

While many people will have enjoyed the unusual winter warmth, it poses risks for the future. Many farmers are struggling with the lack of reliable rainfall, and bad bushfire conditions are forecast for the coming months. More winters like this in the future will not be welcomed by those who have to deal with the consequences.


Climate data provided by the Bureau of Meteorology. For more details about winter 2017, see the Bureau’s Climate Summaries.

The ConversationYou can find more details on the specific methods applied for this analysis here.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

This article was originally published on The Conversation. Read the original article.