Winter storms are speeding up the loss of Arctic sea ice



A scientist checks cracks in the Arctic sea ice after a storm (April 2015, N-ICE2015 expedition).
Amelie Meyer/NPI, Author provided

Amelie Meyer, University of Tasmania

Arctic sea ice is already disappearing rapidly but our research shows winter storms are now further accelerating sea ice loss.




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The research is based on data we gathered during an expedition on a small Norwegian research vessel, the Lance, that was left to drift in the Arctic sea ice for five months in 2015.

Time series of air temperature anomalies in the Arctic for the period 1981-2010: Temperatures in the Arctic in May and June 2019 period were the warmest in the satellite records.
Zack Labe (@ZLabe)

The expedition was intense and felt more like going to the Moon than going on a typical research cruise. What took us by surprise were the many winter storms that battered the ice (and our ship and ice camp).

It has taken us years to collate these data but now we know the winter storms play a key role in the fate of Arctic sea ice, particularly in the Atlantic sector of the Arctic.

Norwegian research vessel ‘Lance’ frozen in the Arctic sea ice in February 2015 during the N-ICE2015 expedition.
Paul Dodd (NPI)

How winter storms amplify climate change

On average, about 10 extreme storms will reach all the way to the North Pole each winter. While these winter storms are short (they last on average 6-48 hours), they can be incredibly intense.

During a storm in winter 2015 we saw the air temperature rise from -40℃ (-40℉) to 0℃ (32℉) in just a day, and then fall back to -30℃ (-22℉) the next day, when cold Arctic air returned after the storm.

These storms bring heat, moisture and strong winds into the Arctic, and next we look at how they impact sea ice and its surroundings.

Warming and weakening the ice

The heat from the storms warms up the air, snow and ice, slowing down the growth of the ice. Moisture from the storms falls as snow on the ice. After the storm, the blanket of snow insulates the ice from the cold air, further slowing the growth of the ice for the remainder of winter.

The strong winds during the storms push the ice around and break it into pieces, making it more fragile and deforming it, more like a boulder field.

The strong winds also stir the ocean below the ice, mixing up warmer water from deeper waters to the surface where it melts the ice from below. This melting of the ice in the middle of winter can happen for several days after the storms when the air is already back to well below freezing.

Processes related to Arctic winter storms. In the first storm phase, strong southerly winds compress the ice cover and transport warm air, moisture, and bring strong winds. In the second phase, northerly winds transport ice southwards. After the storm has passed, cold and calm conditions return, allowing new ice to grow in leads. When the next winter storm arrives, it further drives the ice cover into a relatively thin-ice, snow-covered mosaic of strongly deformed ice floes. These new conditions impact surrounding ecosystems by shaping habitats and light conditions.
Graham et al., 2019 (Scientific Reports)

Thinner ice, shelter for life and accelerated melting

The breakup of the ice opens big passages of open water between ice floes, called leads. In winter these passages end up refreezing rapidly, generating new super-thin ice.

These thinner refrozen patches of ice let more light through in the following spring, allowing ocean plants (phytoplankton) to bloom earlier.

The rougher sea ice landscape becomes a shelter for many ice-associated Arctic organisms, including ice algae, becoming biological hot spots in the following spring.

The broken up and deformed ice drifts faster, reaching warmer waters where it melts sooner and faster.

So really, winter storms precondition the ice to a faster melt in the following spring with an impact that continues well into the following season.

Why is Arctic sea ice declining?

Winter sea ice cover in the Atlantic sector of the Arctic has been retreating at a record breaking pace, especially in the Barents Sea off Norway and Russia.

Average September Arctic sea ice extent from 1979 to 2018. Black line shows monthly average for each year; blue line shows the trend.
National Snow and Ice Data Center

The Arctic is particularly sensitive to human driven climate change. We know the decrease in sea ice is due to both the warming of the Arctic (air and ocean) and changing wind patterns that break up the ice cover.

But there are also amplifying mechanisms or “feedback” mechanisms, in which one natural process reinforces another. Their role in the decrease of sea ice is hard to predict. We now know winter storms in the Arctic contribute to these feedback mechanisms.

More storms ahead

Arctic winter storms are increasing in frequency and this is likely due to climate change.

With the thinner Arctic sea ice cover and shallower warmer water in the Arctic Ocean, the mechanisms we observed during the winter storms will likely strengthen and the overall impact of winter storms on Arctic ice is likely to increase in the future.

Two weeks ago, the Arctic sea ice reached its minimum extent for 2019, after another winter of intense winter storms. The minimum ice extent was effectively tied for second lowest since modern record-keeping began in the late 1970s, along with 2007 and 2016, reinforcing the long-term downward trend in Arctic ice extent. Arctic sea ice has been declining for at least 40 years, and amplifying mechanisms such as the winter storms are accelerating this retreat.

Arctic sea ice extent just reached its annual minimum extent for 2019 on September 18. This season was a tie for the 2nd lowest on record, along with 2007 and 2016 and behind 2012, which holds the overall record minimum.
Zack Labe (@ZLabe)

As highlighted in the recent IPCC Ocean and Cryopshere report, these changes in September sea ice are likely unprecedented for at least 1,000 years.

Remember also that changes in the Arctic don’t just affect the immediate region: Arctic warming has been linked to the polar vortex, and weather extremes across central Europe and north America.




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As we start taking into account feedback mechanisms like the winter storms, our predictions for the first Arctic sea ice free summer are indicating it will likely happen before 2050.The Conversation

Amelie Meyer, Research fellow, University of Tasmania

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

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The winter was dry, the spring will likely be dry – here’s why


Jonathan Pollock, Australian Bureau of Meteorology and Andrew B. Watkins, Australian Bureau of Meteorology

Winter still has a few days to run, but it’s highly likely to be one of Australia’s warmest and driest on record. While final numbers will be crunched once August ends, this winter will probably rank among the top ten warmest for daytime temperatures and the top ten driest for rainfall.

While it was drier than average across most of the country, it was especially dry across South Australia, New South Wales and southern Queensland. Small areas of South Australia and New South Wales are on track for their driest winter on record.




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In contrast, parts of southern Victoria, western Tasmania and central Queensland were wetter than usual.

Preliminary winter 2019 rainfall deciles.
Bureau of Meteorology

Thirsty ground

Soil moisture normally increases during winter (except in the tropics, where it’s the dry season), and while we saw that in parts of Victoria, for most of Queensland and New South Wales the soil moisture actually decreased.

Dry soils leading into winter have soaked up the rain that has fallen, resulting in limited runoff and inflows into the major water storages across the country.

A glass half empty

Sydney’s water storages dropping below 50% received considerable public attention, and unfortunately a number of other regional storages in New South Wales and the Murray Darling Basin are much lower than that.

The winter ‘filling’ season in the southern Murray Darling Basin has been drier than usual for the third year in a row, and storages in the northern Murray Darling basin are extremely low or empty with no meaningful inflows.

Some rain in the west

Some regions did receive enough rainfall to grow crops this cool season. However, northern New South Wales and southern Queensland didn’t see an improvement in their severe year-to-date rainfall deficiencies over winter.

In fact, the area of the country that is experiencing year-to-date rainfall in the lowest 5% of historical records expanded.

In better news, the severe year-to-date deficiencies across southwest Western Australia shrank during winter.

Indian Ocean Dipole the culprit

Sustained differences between sea surface temperatures in the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole (IOD). The IOD impacts Australian seasonal rainfall and temperature patterns, much like the more well known El Niño–Southern Oscillation.

Warm sea surface temperatures in the tropical western Indian Ocean and cool sea surface temperatures in the eastern Indian Ocean, along with changes in both cloud and wind patterns, have been consistent with a positive Indian Ocean Dipole since late May.

International climate models, some of which forecast the positive IOD as early as February, agree that it is likely to continue through spring.

Typically, this means below average rainfall and above average temperatures for much of central and southern Australia, which is consistent with the current rainfall and temperature outlook from the Bureau’s dynamical computer model. The positive IOD is likely to be the dominant climate driver for Australia during the next three months.

Comparison of international climate model forecasts of the IOD index for November 2019.
Models from the Australian Bureau of Meteorology, Canadian Meteorological Centre, European Centre for Medium-Range Weather Forecasts, Meteo France, National Aeronautics and Space Administration (USA) and the Met Office (UK)

A dry end to 2019 likely

Chances are the remainder of 2019 will be drier than normal for most of Australia. The exceptions are western Tasmania, southern Victoria and western WA, where chances of a wetter or drier than average end to the year are roughly equal.

The spring 2019 outlook showing low chances of above average rainfall for most of the country.
Bureau of Meteorology

Warmer than average days are very likely (chances above 80%) for most of the country except the far south of the mainland, and Tasmania.

Nights too are likely to be warmer than average for most of the country. However, much of Victoria and Tasmania, and southern parts of South Australia and New South Wales have close to an even chance for warmer than average minimum temperatures.

Due to the warm and dry start to the year, the east coast of Queensland, New South Wales, Victoria and Tasmania, as well as parts of southern Western Australia, face above normal fire potential this coming bushfire season.

More outlooks more often

The term weather describes conditions over shorter periods, such as from minutes to days, while the term climate describes the more slowly varying aspects of the atmosphere.

From today, the Bureau of Meteorology is closing the forecast gap between weather and climate information with the release of weekly and fortnightly climate outlooks.

For the first time, rainfall and temperature outlooks for the weeks directly after the 7-day forecast are available. One- and two-week outlooks have been added to complement the existing 1-month and 3-month outlooks.




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The new outlook information for the weeks ahead also features how much above or below average temperatures are likely to be, and the likelihood of different rainfall totals.

The Bureau’s outlook videos explain the long-range forecast for the coming months.
Bureau of Meteorology


You can find climate outlooks and summaries on the Bureau of Meteorology website here.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology and Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology

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

Winter is coming, and it’s looking mighty mild



File 20180531 120502 ay6jq9.jpg?ixlib=rb 1.1
Brrr! It’s cold in here!
Alpha/Flickr, CC BY-SA

Jonathan Pollock, Australian Bureau of Meteorology and Andrew B. Watkins, Australian Bureau of Meteorology

After an exceptionally warm and dry autumn, it’s time to look ahead to see what’s in store for winter. The Bureau of Meteorology’s climate outlooks for winter, issued today, shows above-average temperatures and below-average rainfall are likely across southern Australia. While some of us will relish the prospect of a mild winter, the dry isn’t necessarily good news for everyone.




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Warm lead-up to winter

Summer-like conditions continued into early autumn for much of southern Australia, including an exceptional heatwave in early April. Temperatures in autumn were warmer than average across much of the continent. New South Wales, South Australia, Western Australia and Victoria all experienced one of their warmest autumns since at least 1900. Overnight temperatures have also been warmer than average in most parts.

Autumn maximum temperature map.
Bureau of Meterology

Very dry autumn for the southern mainland

For many southern areas autumn wasn’t just warm, it was also extremely dry. New South Wales, Victoria, southwest Western Australia and South Australia all had one of their driest autumns on record.

Many farmers in southern Australia look to the autumn break – the first significant rain event (25mm or more) after summer – to kick off the crop and pasture growing season. The autumn break arrived by mid-May across southern Victoria, eastern New South Wales and southwest coastal Western Australia. However, farmers in northwest Victoria, inland New South Wales, eastern South Australia and much of inland Western Australia didn’t receive an autumn break this year.

One of reasons for the warm and dry autumn in the south was higher than average pressure over southern Australia. The high pressure meant rain bearing cold fronts from the Southern Ocean couldn’t push up into southern Australia.

Autumn rainfall map.
Bureau of Meterology

No strong influence from Pacific or Indian Ocean this winter

So, will this pattern of warm and dry continue? Two of the major drivers of Australia’s climate, the El Niño–Southern Oscillation (ENSO) in the Pacific Ocean, and its equivalent in the Indian Ocean, the Indian Ocean Dipole (IOD), were neutral during autumn, and are likely to remain so throughout winter.




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Of the eight international climate models surveyed by the Bureau of Meteorology, seven predict winter will see ENSO-neutral sea surface temperatures in the central Pacific, with only one model forecasting a warming to El Niño levels by August.

Models also suggest the Indian Ocean Dipole (IOD) will remain neutral through winter. But there is quite a range of scenarios from the international modelling centres the Bureau assesses. One model is predicting a positive IOD over winter, one model predicting a negative IOD in spring, and the other four are neutral. Typically, when the ENSO and IOD are both neutral there is no strong shift in the outlook towards widespread wetter or drier conditions across most of Australia.




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Most international model outlooks for the ENSO sea surface temperature index in the central Pacific Ocean (NINO3.4) remain neutral in August.
Model outlooks provided by: BoM (Bureau of Meteorology), CanSIPS (Canadian Seasonal to Interannual Prediction System), ECMWF (European Centre for Medium-Range Weather Forecasts), JMA (Japan Meteorological Agency), Météo France, NASA (National Aeronautics
Most international model outlooks for the IOD sea surface temperature index remain neutral in August.
Model outlooks provided by: BoM (Bureau of Meteorology), CanSIPS (Canadian Seasonal to Interannual Prediction System), ECMWF (European Centre for Medium-Range Weather Forecasts), Météo France, NASA (National Aeronautics and Space Administration), and the

However, when these major drivers are neutral, other factors can have a greater influence on Australian rainfall and temperature patterns. For instance, forecast warmer-than-usual temperatures in the Tasman Sea and the associated lower-than-normal air pressure this winter is likely to contribute to a weakening of westerly winds over southern Australia that would normally draw cold fronts up from the Southern Ocean.




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So, what’s the outlook for winter?

As a result of the weakened westerly winds, below-average winter rainfall is likely for western parts of Western Australia, and for most of New South Wales extending across the border into southern Queensland and northern Victoria. For most other parts, the outlook is neutral, meaning roughly equal chances of above- or below-average rainfall.

The outlook for June is looking particularly dry across most of the southern mainland.

The likely reduction in cold fronts, and clearer skies over much of the continent means warmer-than-average temperatures are favoured across southern Australia, with the strongest likelihood (about 80%) in the southeast.

The model suggests there is also an above-normal likelihood of winter “mildwaves” – periods of very mild weather – along Australia’s southeast coast.




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So, what does this all mean? For farmers and those working in the agricultural sectors, the warmer temperatures mean soils will stay warm longer. This is likely to keep the crop and pasture growing window open a little longer before the cold of winter. Dry conditions are likely to mean a slow and possibly late start to the growing season, potentially pushing the crop harvest later into the warmer months of 2018, when heatwaves can become a problem.

What does this mean for the snow season?

For skiers, a later start to the season becomes more likely with a warm and dry June expected. On the other hand, neutral ENSO conditions typically bring snow cover that’s a little deeper than average by mid-season.

This is a contrast to strong El Niño or La Niña phases, which both typically mean less snow than usual, but for different reasons. El Niño phases mean less rainfall and warmer days during the snow season. La Niña years usually have more rain, but temperatures can be too high for snow to form.

This has happened more often in recent decades because of climate change. Historically, neutral years have had more consistent good snow depths than either El Niño or La Niña years, so late winter should be a good time to hit the slopes.


The ConversationFor more details on the long-range forecast for winter, visit our Climate Outlooks website and subscribe to Climate Outlooks to stay on top of what’s happening with the climate. A complete set of Climate Summaries covering May and autumn 2018 will be available on 1 June.

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology and Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology

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