The North American heatwave shows we need to know how climate change will change our weather

Christian Jakob, Monash University and Michael Reeder, Monash UniversityEight days ago, it rained over the western Pacific Ocean near Japan. There was nothing especially remarkable about this rain event, yet it made big waves twice.

First, it disturbed the atmosphere in just the right way to set off an undulation in the jet stream – a river of very strong winds in the upper atmosphere – that atmospheric scientists call a Rossby wave (or a planetary wave). Then the wave was guided eastwards by the jet stream towards North America.

Along the way the wave amplified, until it broke just like an ocean wave does when it approaches the shore. When the wave broke it created a region of high pressure that has remained stationary over the North American northwest for the past week.

This is where our innocuous rain event made waves again: the locked region of high pressure air set off one of the most extraordinary heatwaves we have ever seen, smashing temperature records in the Pacific Northwest of the United States and in Western Canada as far north as the Arctic. Lytton in British Columbia hit 49.6℃ this week before suffering a devastating wildfire.

What makes a heatwave?

While this heatwave has been extraordinary in many ways, its birth and evolution followed a well-known sequence of events that generate heatwaves.

Heatwaves occur when there is high air pressure at ground level. The high pressure is a result of air sinking through the atmosphere. As the air descends, the pressure increases, compressing the air and heating it up, just like in a bike pump.

Sinking air has a big warming effect: the temperature increases by 1 degree for every 100 metres the air is pushed downwards.

The North American heatwave has seen fires spread across the landscape.
NASA

High-pressure systems are an intrinsic part of an atmospheric Rossby wave, and they travel along with the wave. Heatwaves occur when the high-pressure systems stop moving and affect a particular region for a considerable time.

When this happens, the warming of the air by sinking alone can be further intensified by the ground heating the air – which is especially powerful if the ground was already dry. In the northwestern US and western Canada, heatwaves are compounded by the warming produced by air sinking after it crosses the Rocky Mountains.

How Rossby waves drive weather

This leaves two questions: what makes a high-pressure system, and why does it stop moving?

As we mentioned above, a high-pressure system is usually part of a specific type of wave in the atmosphere – a Rossby wave. These waves are very common, and they form when air is displaced north or south by mountains, other weather systems or large areas of rain.

Rossby waves are the main drivers of weather outside the tropics, including the changeable weather in the southern half of Australia. Occasionally, the waves grow so large that they overturn on themselves and break. The breaking of the waves is intimately involved in making them stationary.

Importantly, just as for the recent event, the seeds for the Rossby waves that trigger heatwaves are located several thousands of kilometres to the west of their location. So for northwestern America, that’s the western Pacific. Australian heatwaves are typically triggered by events in the Atlantic to the west of Africa.

Another important feature of heatwaves is that they are often accompanied by high rainfall closer to the Equator. When southeast Australia experiences heatwaves, northern Australia often experiences rain. These rain events are not just side effects, but they actively enhance and prolong heatwaves.

What will climate change mean for heatwaves?

Understanding the mechanics of what causes heatwaves is very important if we want to know how they might change as the planet gets hotter.

We know increased carbon dioxide in the atmosphere is increasing Earth’s average surface temperature. However, while this average warming is the background for heatwaves, the extremely high temperatures are produced by the movements of the atmosphere we talked about earlier.

So to know how heatwaves will change as our planet warms, we need to know how the changing climate affects the weather events that produce them. This is a much more difficult question than knowing the change in global average temperature.

How will events that seed Rossby waves change? How will the jet streams change? Will more waves get big enough to break? Will high-pressure systems stay in one place for longer? Will the associated rainfall become more intense, and how might that affect the heatwaves themselves?

From climate change to weather change

There is one thing we do know for sure: we need to up our game in understanding how the weather is changing as our planet warms, because weather is what has the biggest impact on humans and natural systems.

To do this, we will need to build computer models of the world’s climate that explicitly include some of the fine detail of weather. (By fine detail, we mean anything about a kilometre in size.) This in turn will require investment in huge amounts of computing power for tools such as our national climate model, the Australian Community Climate and Earth System Simulator (ACCESS), and the computing and modelling infrastructure projects of the National Collaborative Research Infrastructure Strategy (NCRIS) that support it.

We will also need to break down the artificial boundaries between weather and climate which exist in our research, our education and our public conversation.

Christian Jakob, Professor in Atmospheric Science, Monash University and Michael Reeder, Professor, School of Earth, Atmosphere and Environment, Monash University

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

100 degrees in Siberia? 5 ways the extreme Arctic heat wave follows a disturbing pattern

This Arctic heat wave has been unusually long-lived. The darkest reds on this map of the Arctic are areas that were more than 14 degrees Fahrenheit warmer in the spring of 2020 compared to the recent 15-year average.
Joshua Stevens/NASA Earth Observatory

Mark Serreze, University of Colorado Boulder

The Arctic heat wave that sent Siberian temperatures soaring to around 100 degrees Fahrenheit on the first day of summer put an exclamation point on an astonishing transformation of the Arctic environment that’s been underway for about 30 years.

As long ago as the 1890s, scientists predicted that increasing levels of carbon dioxide in the atmosphere would lead to a warming planet, particularly in the Arctic, where the loss of reflective snow and sea ice would further warm the region. Climate models have consistently pointed to “Arctic amplification” emerging as greenhouse gas concentrations increase.

Well, Arctic amplification is now here in a big way. The Arctic is warming at roughly twice the rate of the globe as a whole. When extreme heat waves like this one strike, it stands out to everyone. Scientists are generally reluctant to say “We told you so,” but the record shows that we did.

As director of the National Snow and Ice Data Center and an Arctic climate scientist who first set foot in the far North in 1982, I’ve had a front-row seat to watch the transformation.

Arctic heat waves are happening more often – and getting stuck

Arctic heat waves now arrive on top of an already warmer planet, so they’re more frequent than they used to be.

Western Siberia recorded its hottest spring on record this year, according the EU’s Copernicus Earth Observation Program, and that unusual heat isn’t expected to end soon. The Arctic Climate Forum has forecast above-average temperatures across the majority of the Arctic through at least August.

Arctic temperatures have been rising faster than the global average. This map shows the average change in degrees Celsius from 1960 to 2019.
NASA-GISS

Why is this heat wave sticking around? No one has a full answer yet, but we can look at the weather patterns around it.

As a rule, heat waves are related to unusual jet stream patterns, and the Siberian heat wave is no different. A persistent northward swing of the jet stream has placed the area under what meteorologists call a “ridge.” When the jet stream swings northward like this, it allows warmer air into the region, raising the surface temperature.

Some scientists expect rising global temperatures to influence the jet stream. The jet stream is driven by temperature contrasts. As the Arctic warms more quickly, these contrasts shrink, and the jet stream can slow.

Is that what we’re seeing right now? We don’t yet know.

Swiss cheese sea ice and feedback loops

We do know that we’re seeing significant effects from this heat wave, particularly in the early loss of sea ice.

The ice along the shores of Siberia has the appearance of Swiss cheese right now in satellite images, with big areas of open water that would normally still be covered. The sea ice extent in the Laptev Sea, north of Russia, is the lowest recorded for this time of year since satellite observations began.

The loss of sea ice also affects the temperature, creating a feedback loop. Earth’s ice and snow cover reflect the Sun’s incoming energy, helping to keep the region cool. When that reflective cover is gone, the dark ocean and land absorb the heat, further raising the surface temperature.

Sea surface temperatures are already unusually high along parts of the Siberian Coast, and the warm ocean waters will lead to more melting.

The risks of thawing permafrost

On land, a big concern is warming permafrost – the perennially frozen ground that underlies most Arctic terrain.

When permafrost thaws under homes and bridges, infrastructure can sink, tilt and collapse. Alaskans have been contending with this for several years. Near Norilsk, Russia, thawing permafrost was blamed for an oil tank collapse in late May that spilled thousands of tons of oil into a river.

Thawing permafrost also creates a less obvious but even more damaging problem. When the ground thaws, microbes in the soil begin turning its organic matter into carbon dioxide and methane. Both are greenhouse gases that further warm the planet.

In a study published last year, researchers found that permafrost test sites around the world had warmed by nearly half a degree Fahrenheit on average over the decade from 2007 to 2016. The greatest increase was in Siberia, where some areas had warmed by 1.6 degrees. The current Siberian heat wave, especially if it continues, will regionally exacerbate that permafrost warming and thawing.

A satellite image shows the Norilsk oil spill flowing into neighboring rivers. The collapse of a giant fuel tank was blamed on thawing permafrost.
Contains modified Copernicus Sentinel data 2020, CC BY

Wildfires are back again

The extreme warmth also raises the risk of wildfires, which radically change the landscape in other ways.

Drier forests are more prone to fires, often from lightning strikes. When forests burn, the dark, exposed soil left behind can absorb more heat and hasten warming.

We’ve seen a few years now of extreme forest fires across the Arctic. This year, some scientists have speculated that some of the Siberian fires that broke out last year may have continued to burn through the winter in peat bogs and reemerged.

A satellite images shows thinning sea ice in parts of the East Siberian and Laptev Seas and wildfire smoke pouring across Russia. The town of Verkhoyansk, normally known for being one of the coldest inhabited places on Earth, reported hitting 100 degrees on June 20.
Joshua Stevens/NASA Earth Observatory

A disturbing pattern

The Siberian heat wave and its impacts will doubtless be widely studied. There will certainly be those eager to dismiss the event as just the result of an unusual persistent weather pattern.

Caution must always be exercised about reading too much into a single event – heat waves happen. But this is part of a disturbing pattern.

What is happening in the Arctic is very real and should serve as a warning to everyone who cares about the future of the planet as we know it.

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Mark Serreze, Research Professor of Geography and Director, National Snow and Ice Data Center, University of Colorado Boulder

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

5 big environment stories you probably missed while you’ve been watching coronavirus

Rod Lamberts, Australian National University and Will J Grant, Australian National University

Good news: COVID-19 is not the only thing going on right now!

Bad news: while we’ve all been deep in the corona-hole, the climate crisis has been ticking along in the background, and there are many things you may have missed.

Fair enough – it’s what people do. When we are faced with immediate, unambiguous threats, we all focus on what’s confronting us right now. The loss of winter snow in five or ten years looks trivial against images of hospitals pushed to breaking point now.

As humans, we also tend to prefer smaller, short-term rewards over larger long-term ones. It’s why some people would risk illness and possible prosecution (or worse, public shaming) to go to the beach with their friends even weeks after social distancing messages have become ubiquitous.

But while we might need to ignore climate change right now if only to save our sanity, it certainly hasn’t been ignoring us.

So here’s what you may have missed while coronavirus dominates the news cycle.

Heatwave in Antarctica

Antarctica is experiencing alarmingly balmy weather.
Shutterstock

On February 6 this year, the northernmost part of Antarctica set a new maximum temperature record of 18.4℃. That’s a pleasant temperature for an early autumn day in Canberra, but a record for Antarctica, beating the old record by nearly 1℃.

That’s alarming, but not as alarming as the 20.75℃ reported just three days later to the east of the Antarctic Peninsula at Marambio station on Seymour Island.

Bleaching the reef

The Intergovernmental Panel on Climate Change has warned a global average temperature rise of 1.5℃ could wipe out 90% of the world’s coral.

As the world looks less likely to keep temperature rises to 1.5℃, in 2019 the five-year outlook for Australia’s Great Barrier Reef was downgraded from “poor” to “very poor”. The downgrading came in the wake of two mass bleaching events, one in 2016 and another in 2017, damaging two-thirds of the reef.

And now, in 2020, it has just experienced its third in five years.

Of course, extreme Antarctic temperatures and reef bleaching are the products of human-induced climate change writ large.

But in the short time since the COVID-19 crisis began, several examples of environmental vandalism have been deliberately and specifically set in motion as well.

Coal mining under a Sydney water reservoir

The Berejiklian government in New South Wales has just approved the extension of coal mining by Peabody Energy – a significant funder of climate change denial – under one of Greater Sydney’s reservoirs. This is the first time such an approval has been granted in two decades.

While environmental groups have pointed to significant local environmental impacts – arguing mining like this can cause subsidence in the reservoir up to 25 years after the mining is finished – the mine also means more fossil carbon will be spewed into our atmosphere.

Peabody Energy argues this coal will be used in steel-making rather than energy production. But it’s still more coal that should be left in the ground. And despite what many argue, you don’t need to use coal to make steel.

Victoria green-lights onshore gas exploration

In Victoria, the Andrews government has announced it will introduce new laws into Parliament for what it calls the “orderly restart” of onshore gas exploration. In this legislation, conventional gas exploration will be permitted, but an existing temporary ban on fracking and coal seam gas drilling will be made permanent.

The announcement followed a three-year investigation led by Victoria’s lead scientist, Amanda Caples. It found gas reserves in Victoria “could be extracted without harming the environment”.

Sure, you could probably do that (though the word “could” is working pretty hard there, what with local environmental impacts and the problem of fugitive emissions). But extraction is only a fraction of the problem of natural gas. It’s the subsequent burning that matters.

Trump rolls back environmental rules

Meanwhile, in the United States, the Trump administration is taking the axe to some key pieces of environmental legislation.

One is an Obama-era car pollution standard, which required an average 5% reduction in greenhouse emissions annually from cars and light truck fleets. Instead, the Trump administration’s “Safer Affordable Fuel Efficient Vehicles” requires just 1.5%.

The health impact of this will be stark. According to the Environmental Defense Fund, the shift will mean 18,500 premature deaths, 250,000 more asthma attacks, 350,000 more other respiratory problems, and US$190 billion in additional health costs between now and 2050.

And then there are the climate costs: if manufacturers followed the Trump administration’s new looser guidelines it would add 1.5 billion tonnes of carbon dioxide to the atmosphere, the equivalent of 17 additional coal-fired power plants.

And so…

The challenges COVID-19 presents right now are huge. But they will pass.

The challenges of climate change are not being met with anything like COVID-19 intensity. For now, that makes perfect sense. COVID-19 is unambiguously today. Against this imperative, climate change is still tomorrow.

But like hangovers after a large celebration, tomorrows come sooner than we expect, and they never forgive us for yesterday’s behaviour.

Rod Lamberts, Deputy Director, Australian National Centre for Public Awareness of Science, Australian National University and Will J Grant, Senior Lecturer, Australian National Centre for the Public Awareness of Science, Australian National University

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

Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month

Dana M Bergstrom, University of Wollongong; Andrew Klekociuk, University of Tasmania; Diana King, University of Wollongong, and Sharon Robinson, University of Wollongong

While the world rightfully focuses on the COVID-19 pandemic, the planet is still warming. This summer’s Antarctic weather, as elsewhere in the world, was unprecedented in the observed record.

Our research, published today in Global Change Biology, describes the recent heatwave in Antarctica. Beginning in late spring east of the Antarctic Peninsula, it circumnavigated the continent over the next four months. Some of our team spent the summer in Antarctica observing these temperatures and the effect on natural systems, witnessing the heatwave first-hand.

Antarctica may be isolated from other continents by the Southern Ocean, but has worldwide impacts. It drives the global ocean conveyor belt, a constant system of deep-ocean circulation which transfers oceanic heat around the planet, and its melting ice sheet adds to global sea level rise.

Antarctica represents the simple, extreme end of conditions for life. It can be seen as a ‘canary in the mine’, demonstrating patterns of change we can expect to see elsewhere.

A heatwave in the coldest place on Earth

Most of Antarctica is ice-covered, but there are small ice-free oases, predominantly on the coast. Collectively 0.44% of the continent, these unique areas are important biodiversity hotspots for penguins and other seabirds, mosses, lichens, lakes, ponds and associated invertebrates.

This summer, Casey Research Station, in the Windmill Islands oasis, experienced its first recorded heat wave. For three days, minimum temperatures exceeded zero and daily maximums were all above 7.5°C. On January 24, its highest maximum of 9.2°C was recorded, almost 7°C above Casey’s 30-year mean for the month.

The arrival of warm, moist air during this weather event brought rain to Davis Research Station in the normally frigid, ice-free desert of the Vestfold Hills. The warm conditions triggered extensive meltwater pools and surface streams on local glaciers. These, together with melting snowbanks, contributed to high-flowing rivers and flooding lakes.

By February, most heat was concentrated in the Antarctic Peninsula at the northernmost part of the continent. A new Antarctic maximum temperature of 18.4°C was recorded on February 6 at Argentina’s Esperanza research station on the Peninsula – almost 1°C above the previous record. Three days later this was eclipsed when 20.75°C was reported at Brazil’s Marambio station, on Seymour Island east of the Peninsula.

What caused the heatwave?

The pace of warming from global climate change has been generally slower in East Antarctica compared with West Antarctica and the Antarctic Peninsula. This is in part due to the ozone hole, which has occurred in spring over Antarctica since the late 1970s.

The hole has tended to strengthen jet stream winds over the Southern Ocean promoting a generally more ‘positive’ state of the Southern Annular Mode in summer. This means the Southern Ocean’s westerly wind belt has tended to stay close to Antarctica at that time of year creating a seasonal ‘shield’, reducing the transfer of warm air from the Earth’s temperate regions to Antarctica.

But during the spring of 2019 a strong warming of the stratosphere over Antarctica significantly reduced the size of the ozone hole. This helped to support a more ‘negative’ state of the Southern Annular Mode and weakened the shield.

Other factors in late 2019 may have also helped to warm Antarctica. The Indian Ocean Dipole was in a strong ‘positive’ state due to a late retreat of the Indian monsoon. This meant that water in the western Indian Ocean was warmer than normal. Air rising from this and other warm ocean patches in the Pacific Ocean provided energy sources that altered the path of weather systems and helped to disturb and warm the stratosphere.

Is a warming Antarctica good or bad?

Localised flooding appeared to benefit some Vestfold Hills’ moss banks which were previously very drought-stressed. Prior to the flood event, most mosses were grey and moribund, but one month later many moss shoots were green.

Given the generally cold conditions of Antarctica, the warmth may have benefited the flora (mosses, lichens and two vascular plants), and microbes and invertebrates, but only where liquid water formed. Areas in the Vestfold Hills away from the flooding became more drought-stressed over the summer.

High temperatures may have caused heat stress in some organisms. Antarctic mosses and lichens are often dark in colour, allowing sunlight to be absorbed to create warm microclimates. This is a great strategy when temperatures are just above freezing, but heat stress can occur once 10°C is exceeded.

On King George Island, near the Antarctic Peninsula, our measurements showed that in January 2019 moss surface temperatures only exceeded 14°C for 3% of the time, but in 2020 this increased fourfold (to 12% of the time).

Based on our experience from previous anomalous hot Antarctic summers, we can expect many biological impacts, positive and negative, in coming years. The most recent event highlights the connectedness of our climate systems: from the surface to the stratosphere, and from the monsoon tropics to the southernmost continent.

Under climate change, extreme events are predicted to increase in frequency and severity, and Antarctica is not immune.

Dana M Bergstrom, Principal Research Scientist, University of Wollongong; Andrew Klekociuk, Adjunct Senior Lecturer, University of Tasmania; Diana King, Research officer, University of Wollongong, and Sharon Robinson, Professor, University of Wollongong

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

Shark Bay: A World Heritage Site at catastrophic risk

File 20190207 174880 9uo53z.jpg?ixlib=rb 1.1 — Shark Bay was hit by a brutal marine heatwave in 2011.
W. Bulach/Wikimedia Commons, CC BY-SA

Matthew Fraser, University of Western Australia; Ana Sequeira, University of Western Australia; Brendan Paul Burns, UNSW; Diana Walker, University of Western Australia; Jon C. Day, James Cook University, and Scott Heron, James Cook University

The devastating bleaching on the Great Barrier Reef in 2016 and 2017 rightly captured the world’s attention. But what’s less widely known is that another World Heritage-listed marine ecosystem in Australia, Shark Bay, was also recently devastated by extreme temperatures, when a brutal marine heatwave struck off Western Australia in 2011.

A 2018 workshop convened by the Shark Bay World Heritage Advisory Committee classified Shark Bay as being in the highest category of vulnerability to future climate change. And yet relatively little media attention and research funding has been paid to this World Heritage Site that is on the precipice.

Shark Bay.
Openstreetmap.org/Wikimedia Commons, CC BY-SA

Shark Bay, in WA’s Gascoyne region, is one of 49 marine World Heritage Sites globally, but one of only four of these sites that meets all four natural criteria for World Heritage listing. The marine ecosystem supports the local economy through tourism and fisheries benefits.

Around 100,000 tourists visit Shark Bay each year to interact with turtles, dugongs and dolphins, or to visit the world’s most extensive population of stromatolites – stump-shaped colonies of microbes that date back billions of years, almost to the dawn of life on Earth.

Commercial and recreational fishing is also extremely important for the local economy. The combined Shark Bay invertebrate fishery (crabs, prawns and scallops) is the second most valuable commercial fishery in Western Australia.

Under threat

However, this iconic and valuable marine ecosystem is under serious threat. Shark Bay is especially vulnerable to future climate change, given that the temperate seagrass that underpins the entire ecosystem is already living at the upper edge of its tolerable temperature range. These seagrasses provide vital habitat for fish and marine mammals, and help the stromatolites survive by regulating the water salinity.

Stromatolites are a living window to the past.
Matthew Fraser

Shark Bay received the highest rating of vulnerability using the recently developed Climate Change Vulnerability Index, created to provide a method for assessing climate change impacts across all World Heritage Sites.

In particular, extreme marine heat events were classified as very likely and predicted to have catastrophic consequences in Shark Bay. By contrast, the capacity to adapt to marine heat events was rated very low, showing the challenges Shark Bay faces in the coming decades.

The region is also threatened by increasingly frequent and intense storms, and warming air temperatures.

To understand the potential impacts of climatic change on Shark Bay, we can look back to the effects of the most recent marine heatwave in the area. In 2011 Shark Bay was hit by a catastrophic marine heatwave that destroyed 900 square kilometres of seagrass – 36% of the total coverage.

This in turn harmed endangered species such as turtles, contributed to the temporary closure of the commercial crab and scallop fisheries, and released between 2 million and 9 million tonnes of carbon dioxide – equivalent to the annual emissions from 800,000 homes.

Some aspects of Shark Bay’s ecosystem have never been the same since. Many areas previously covered with large, temperate seagrasses are now bare, or have been colonised by small, tropical seagrasses, which do not provide the same habitat for animals. This mirrors the transition seen on bleached coral reefs, which are taken over by turf algae. We may be witnessing the beginning of Shark Bay’s transition from a sub-tropical to a tropical marine ecosystem.

This shift would jeopardise Shark Bay’s World Heritage values. Although stromatolites have survived for almost the entire history of life on Earth, they are still vulnerable to rapid environmental change. Monitoring changes in the microbial makeup of these communities could even serve as a canary in the coalmine for global ecosystem changes.

The neglected bay?

Despite Shark Bay’s significance, and the seriousness of the threats it faces, it has received less media and funding attention than many other high-profile Australian ecosystems. Since 2011, the Australian Research Council has funded 115 research projects on the Great Barrier Reef, and just nine for Shark Bay.

Coral reefs rightly receive a lot of attention, particularly given the growing appreciation that climate change threatens the Great Barrier Reef and other corals around the world.

The World Heritage Committee has recognised that local efforts alone are no longer enough to save coral reefs, but this logic can be extended to other vulnerable marine ecosystems – including the World Heritage values of Shark Bay.

Safeguarding Shark Bay from climate change requires a coordinated research and management effort from government, local industry, academic institutions, not-for-profits and local Indigenous groups – before any irreversible ecosystem tipping points are reached. The need for such a strategic effort was obvious as long ago as the 2011 heatwave, but it hasn’t happened yet.

Due to the significant Aboriginal heritage in Shark Bay, including three language groups (Malgana, Nhanda and Yingkarta), it will be vital to incorporate Indigenous knowledge, so as to understand the potential social impacts.

And of course, any on-the-ground actions to protect Shark Bay need to be accompanied by dramatic reductions in greenhouse emissions. Without this, Shark Bay will be one of the many marine ecosystems to fundamentally change within our lifetimes.

Matthew Fraser, Postdoctoral Research Fellow, University of Western Australia; Ana Sequeira, ARC DECRA Fellow, University of Western Australia; Brendan Paul Burns, Senior Lecturer, UNSW; Diana Walker, Emeritus Professor, University of Western Australia; Jon C. Day, PSM, Post-career PhD candidate, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Scott Heron, Senior Lecturer, James Cook University

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

Farmed fish dying, grape harvest weeks early – just some of the effects of last summer’s heatwave in NZ

File 20190128 108348 ycw7kr.jpg?ixlib=rb 1.1 — Queensland groper, typical of coral reefs off Queensland at 27°S were found in the Bay of Islands, north of Auckland, at 35°S.
from http://www.shutterstock.com, CC BY-ND

Jim Salinger, University of Tasmania and James Renwick, Victoria University of Wellington

As the Australian heatwave is spilling across the Tasman and pushing up temperatures in New Zealand, we take a look at the conditions that caused a similar event last year and the impacts it had.

Last summer’s heatwave gave New Zealand its warmest summer and the warmest January on record. It covered an area of four million square kilometres (comparable to the Indian subcontinent), including the land, the eastern Tasman Sea and the Pacific east of New Zealand to the Chatham Islands.

In our research, we looked at what happened and why, and found that the heatwave affected many sectors, leading to early grape harvests and killing farmed fish in parts of the country.

Drivers of warmer than average conditions

We used a combination of land and ocean temperature observations, large-scale analyses of the atmospheric circulation, and ocean modelling to understand the drivers of the 2017/18 summer heatwave. It was memorable for a number of extreme events and statistics.

The average air temperature was 2.2°C above the 1981-2010 normal of 16.7°C, and it was the warmest summer ever recorded in more than 150 years. The number of extreme warm days and warm nights was also the highest recorded, going back several decades.

The peak month was January 2018, 3.2°C above normal and the warmest month recorded in observations as far back as 1867. Ocean surface temperatures were similarly extreme, with a marine heatwave that lasted about five months, at 2.0°C above normal at its peak.

The combined New Zealand annual land and sea surface temperature record, in °C, from 1867 to 2018, compared with the 1981-2010 average. The blue bars represent individual years, and the red line trends over groups of years.
Jim Salinger, CC BY-ND

The warming was mostly the result of very settled conditions over the country, especially to the east, bringing light winds, plenty of sun, and warm air from the subtropics. Such conditions in summer are associated with the positive phase of a polar ring of climate variability known as the Southern Annular Mode (SAM), which brings high pressures (anticyclones) to New Zealand and parts of other southern hemisphere countries in the mid-latitudes, including southern Australia and Tasmania, southern Chile and Argentina.

The SAM was strongly positive throughout last summer, especially in January, and weak La Niña conditions were prevalent in the tropics. The light winds in the New Zealand region allowed the ocean surface to warm rapidly, without the usual turbulent mixing to transport the heat away. The warmest waters in the Tasman Sea formed an unusually thin layer near the surface.

Impacts and repercussions

New Zealand was affected by more than its normal share of ex-tropical cyclones, notably Fehi and Gita. They brought strong winds, storm surges and heavy rainfalls that caused flooding as they passed through. The warm ocean waters around New Zealand would have helped maintain the intensity of the storms and supply moisture to drive the heavy downpours.

The warm conditions caused massive ice loss in South Island glaciers, estimated to be the largest annual loss of glacier ice in nearly 60 years of records for the Southern Alps. Satellite data from end-of-summer snowline measurements at the Tasman Glacier suggest that the Southern Alps lost 9% of glacier ice during last summer alone.

The Franz Josef glacier on New Zealand’s West Coast advanced during the 1980s and 1990s but is now retreating.
Andrew Lorrey/NIWA, CC BY-ND

Warm air temperatures had a marked effect on managed and natural ecosystems. The Marlborough grape harvest was unusually early in 2018, two to three weeks ahead of the normal maturation time. Marine ecosystems were significantly disrupted. Coastal kelp forests struggled to grow in the warm sea. In southern New Zealand, the temperature threshold was breached three times, resulting in substantial losses of kelp canopies.

For the first time, Atlantic salmon had to be imported as farmed fish died in salmon farms in the Marlborough Sounds. Commercial fishers reported that snapper was spawning approximately six weeks early off the South Island coast, and Queensland groper was reported in northern New Zealand, 3000km out of range.

Past and future

The summer of 2017/18 shared some characteristics with another hot summer, way back in 1934/35. That season was so warm that it prompted a special report by the New Zealand Meteorological Service. Conditions were similar: persistent high-pressure systems in the New Zealand region, positive SAM conditions, light winds over and around New Zealand, warm ocean surface and air temperatures. While those two summers shared some natural variations in the local climate, the recent summer was warmer for two reasons.

First, climate in the region is now more than half a degree warmer now than in the 1930s. Second, the SAM has been trending towards its positive phase over the last few decades, making settled conditions over New Zealand more frequent now than in the 1930s. That trend is mostly related to the ozone hole that occurs in spring and early summer, cooling the polar atmosphere and driving the strongest winds farther south towards Antarctica, leaving lighter winds and higher pressures over New Zealand.

Looking to the future, we can compare the conditions experienced in 2017/18 with what climate models predict for the future. We estimate that the extreme warm conditions of New Zealand’s last summer would be typical summer conditions by the end of the century, for an emissions scenario associated with a couple of degrees of global warming above pre-industrial temperatures. If emissions keep increasing as they have done in recent years, last summer will seem cool by the standards of 2100.

Jim Salinger, Honorary Associate, Tasmanian Institute for Agriculture, University of Tasmania and James Renwick, Professor, Physical Geography (climate science), Victoria University of Wellington

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

Coastal seas around New Zealand are heading into a marine heatwave, again

File 20190121 100292 m58bim.jpg?ixlib=rb 1.1 — This summer, coastal seas to the north and east of New Zealand are even warmer than during last year’s marine heat wave.
from http://www.shutterstock.com, CC BY-ND

Craig Stevens, National Institute of Water and Atmospheric Research and Ben Noll, National Institute of Water and Atmospheric Research

As New Zealanders are enjoying their days at the beach, unusually warm ocean temperatures look to be a harbinger of another marine heatwave.

Despite the exceptional conditions during last year’s heatwave in the Tasman Sea, this summer’s sea surface temperatures to the north and east of New Zealand are even warmer.

The latest NIWA climate assessment shows that sea surface temperatures in coastal waters around New Zealand are well above average. Marine heatwave conditions are already occurring in parts of the Tasman Sea and the ocean around New Zealand and looking to become the new normal.

Changing sea surface temperature anomalies (conditions compared to average) in the oceans around New Zealand during the first two weeks of January – comparing 2009 to 2019. Source: NIWA

What’s in a name

Currently, marine heatwaves are defined as periods that last for five or more days with temperatures warmer than the 90th percentile based on a 30-year historical baseline. Given we are likely to experience many more such events as the oceans continue to warm, it is time to understand and categorise the intensity of marine heat.

The names Hurricane Katrina, tropical cyclone Giselle (which sank the ferry Wahine 50 years ago), tropical cyclone Winston give a malevolent personality to geophysical phenomena. Importantly they get graded into categories, so we can rapidly assess their potential impact.

An Australian team has developed a classification scheme for marine heatwaves. The team used an approach similar to that used for hurricanes and cyclones – changing conditions can be slotted into to a sequence of categories. At the moment it looks like we are in marine heat wave category one conditions, but potentially entering category two if it continues to warm.

Turning the heat up on marine life

A marine heatwave is potentially devastating for marine ecosystems. It is also an indication that the hidden buffer in the climate system – the fact that the oceans have absorbed 93% of the excess heat – is starting to change. Individual warm seasons have always occurred, but in future there will be more of them and they will keep getting warmer.

The Great Barrier Reef has already been hit hard by a succession of marine heatwave events, bleaching the iconic corals and changing the structure of the ecosystem it supports.

Further south, off Tasmania’s east coast, a number of species that normally occur in tropical waters have extended their range further south. A number of fish species, lobster and octopus species have also taken up residence along the Tasmanian coast, displacing some of the species that call this coast home. Mobile species can escape the warmer temperatures, but sedentary plants and animals are hardest hit.

In New Zealand, aquaculture industries will find it more difficult to grow fish or mussels as coastal waters continue to warm. If the same trends seen off Tasmania occur here, areas with substantial kelp canopies will struggle and start to be replaced by species normally seen further north. But the impacts will likely be very variable because the warming will be heavily influenced by wind and ocean currents and different locations will feel changes to a greater or lesser extent.

NIWA’s research vessel Kaharoa has deployed Argo floats in the Southern Ocean and in waters around New Zealand.
NIWA, CC BY-ND

Predicting the seasons

As important as it is to identify a marine heatwave at the time, reliable predictions of developing conditions would help fishers, aquaculture companies and local authorities – and in fact anyone living and working around the ocean.

Seasonal forecasting a few months ahead is difficult. It falls between weather and climate predictions. In a collaboration between the National Institute of Water and Atmospheric Research and the Australian Bureau of Meteorology, we are examining how well long-term forecasts of ocean conditions around New Zealand stack up. Early forecasts suggested this summer would not be as warm as last year. But it now looks like this summer will again be very warm in the ocean.

One of the important points to keep in mind is that when we are at the beach, we are sampling only the surface temperature. The same is true of satellites – they monitor less than the top millimetre of the ocean.

Sea surface temperatures are several degrees above normal at the moment. But in deeper waters, because of the high heat content of water, even a tenth of a degree is significant. Temperature in the deeper ocean is monitored by a network of moored buoys on and off the continental shelf along the Australian coast. New Zealand has almost nothing that would be comparable.

Measuring temperature in real time

What we can look to, in the absence of moored buoys, is a fleet of ocean robots that monitor temperature in real time. Argo floats drift with ocean currents, sink to two kilometres every ten days and then collect data as they return to the surface.

These data allowed us to identify that the 2017/18 marine heatwave around New Zealand remained shallow. Most of the warmer water was in the upper 30 metres. Looking at the present summer conditions, one Argo robot off New Zealand’s west coast shows it is almost four degrees above normal in the upper 40 metres of the ocean. On the east coast, near the Chatham Islands, another float shows warmed layers to 20 metres deep. To the south, the warming goes deeper, down to almost 80 metres.

Our work using the Australian Bureau of Meteorology forecast model highlights how variable the ocean around New Zealand is. Different issues emerge in different regions, even if they are geographically close.

The research on categories of marine heatwaves shows we will have to keep shifting what we regard as a heat wave as the ocean continues to warm. None of this should come as a surprise. We have known for some time that the world’s oceans are storing most of the additional heat and the impacts of a warming ocean will be serious.

Craig Stevens, Associate Professor in Ocean Physics, National Institute of Water and Atmospheric Research and Ben Noll, Meteorologist/forecaster, National Institute of Water and Atmospheric Research

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

The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations

File 20180725 194140 1cri4pn.jpg?ixlib=rb 1.1 — Some fish fared better than others amid the extreme temperatures of the 2016 heatwave.
Rick Stuart-Smith/Reef Life Survey

Rick Stuart-Smith, University of Tasmania; Christopher Brown, Griffith University; Daniela Ceccarelli, James Cook University, and Graham Edgar, University of Tasmania

The 2016 marine heatwave that killed vast amounts of coral on the Great Barrier Reef also caused significant changes to fishes and other animals that live on these reefs.

Coral habitats in the Great Barrier Reef (GBR) and in the Coral Sea support more than 1,000 fish species and a multitude of other animals. Our research, published in Nature today, documents the broader impact across the ecosystem of the widespread coral losses during the 2016 mass coral bleaching event.

While a number of fish species were clearly impacted by the loss of corals, we also found that many fish species responded to the increased temperatures, even on reefs where coral cover remained intact. The fish communities in the GBR’s southern regions became more like those in warmer waters to the north, while some species, including parrotfishes, were negatively affected by the extreme sea temperatures at the northern reefs.

The loss of coral robs many fish species of their preferred food and shelter. But the warming that kills coral can also independently cause fish to move elsewhere, so as to stay within their preferred temperature range. Rising temperatures can also have different effects on the success, and therefore abundance, of different fish populations.

One way to tease apart these various effects is to look at changes in neighbouring reefs, and across entire regions that have been affected by bleaching, including reefs that have largely escaped coral loss.

We were able to do just this, with the help of highly trained volunteer divers participating in the Reef Life Survey citizen science program. We systematically surveyed 186 reefs across the entire GBR and western Coral Sea, both before and after the 2016 bleaching event. We counted numbers of corals, fishes, and mobile invertebrates such as sea urchins, lobsters and giant clams.

Sea temperatures and coral losses varied greatly between sites, which allowed us to separate the effects of warming from coral loss. In general, coral losses were much more substantial in areas that were most affected by the prolonged warmer waters in the 2016 heatwave. But these effects were highly patchy, with the amount of live hard coral lost differing significantly from reef to reef.

For instance, occasional large losses occurred in the southern GBR, where the marine heatwave was less extreme than at northern reefs. Similarly, some reefs in the north apparently escaped unscathed, despite the fact that many reefs in this region lost most of their live corals.

Sea temperatures the culprit

Our survey results show that coral loss is just one way in which ocean warming can affect fishes and other animals that depend on coral reefs. Within the first year after the bleaching, the coral loss mostly affected fish species that feed directly on corals, such as the butterflyfishes. But we also documented many other changes that we could not clearly link to local coral loss.

Much more widespread than the impacts of the loss of hard corals was a generalised response by the fish to warm sea temperatures. The 2016 heatwave caused a mass reshuffling of fish communities across the GBR and Coral Sea, in ways that reflect the preferences of different species for particular temperatures.

In particular, most reef-dwelling animals on southern (cooler) reefs responded positively to the heatwave. The number of individuals and species on transect counts generally increased across this region.

By contrast, some reefs in the north exceeded 32℃ during the 2016 heatwave – the typical sea temperature on the Equator, the hottest region inhabited by any of the GBR or Coral Sea species.

Some species responded negatively to these excessive temperatures, and the number of observations across surveys in their northernmost populations declined as a consequence.

Parrotfishes were more affected than other groups on northern reefs, regardless of whether their local reefs suffered significant coral loss. This was presumably because the heatwave pushed sea temperatures beyond the level at which their populations perform best.

Nothing to smile about: some parrotfishes don’t do well in extreme heat.
Rick Stuart-Smith/Reef Life Survey

Local populations of parrotfishes will probably bounce back after the return of cooler temperatures. But if similar heatwaves become more frequent in the future, they could cause substantial and lasting declines among members of this ecologically important group in the warmest seas.

Parrotfishes are particularly important to the health of coral reef ecosystems, because their grazing helps to control algae that compete with corals for habitat space.

A key message from our study is not to overlook the overarching influence of temperature on coral reef ecosystems – and not to focus solely on the corals themselves.

Even if we can save some corals from climate change, such as with more stress-tolerant breeds of coral, we may not be able to stop the impacts of warming seas on fish.

Future ecological outcomes will depend on a complex mix of factors, including fish species’ temperature preferences, their changing habitats, and their predators and competitors. These impacts will not always necessarily be negative for particular species and locations.

One reason for hope is that positive responses of many fish species in cooler tropical regions may continue to support healthy coral reef ecosystems, albeit in a different form to those we know today.

Rick Stuart-Smith, Research Fellow, University of Tasmania; Christopher Brown, Research Fellow, Australian Rivers Institute, Griffith University; Daniela Ceccarelli, Adjunct Senior Research, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Graham Edgar, Senior Marine Ecologist, Institute for Marine and Antarctic Studies, University of Tasmania

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

Southeast Europe swelters through another heatwave with a human fingerprint

File 20170809 3360 1sy8t74 — Searching for respite from the heat in one of Rome’s fountains.
Max Roxxi/Reuters

Andrew King, University of Melbourne

Parts of Europe are having a devastatingly hot summer. Already we’ve seen heat records topple in western Europe in June, and now a heatwave nicknamed “Lucifer” is bringing stifling conditions to areas of southern and eastern Europe.

Several countries are grappling with the effects of this extreme heat, which include wildfires and water restrictions.

Temperatures have soared past 40℃ in parts of Italy, Greece and the Balkans, with the extreme heat spreading north into the Czech Republic and southern Poland.

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Some areas are having their hottest temperatures since 2007 when severe heat also brought dangerous conditions to the southeast of the continent.

The heat is associated with a high pressure system over southeast Europe, while the jet stream guides weather systems over Britain and northern Europe. In 2007 this type of split weather pattern across Europe persisted for weeks, bringing heavy rains and flooding to England with scorching temperatures for Greece and the Balkans.

Europe is a very well-studied region for heatwaves. There are two main reasons for this: first, it has abundant weather observations and this allows us to evaluate our climate models and quantify the effects of climate change with a high degree of confidence. Second, many leading climate science groups are located in Europe and are funded primarily to improve understanding of climate change influences over the region.

The first study to link a specific extreme weather event to climate change examined the record hot European summer of 2003. Since then, multiple studies have assessed the role of human influences in European extreme weather. Broadly speaking, we expect hotter summers and more frequent and intense heatwaves in this part of the world.

We also know that climate change increased deaths in the 2003 heatwaves and that climate change-related deaths are projected to rise in the future.

Climate change’s role in this heatwave

To understand the role of climate change in the latest European heatwave, I looked at changes in the hottest summer days over southeast Europe – a region that incorporates Italy, Greece and the Balkans.

I calculated the frequency of extremely hot summer days in a set of climate model simulations, under four different scenarios: a natural world without human influences, the world of today (with about 1℃ of global warming), a 1.5℃ global warming world, and a 2℃ warmer world. I chose the 1.5℃ and 2℃ benchmarks because they correspond to the targets described in the Paris Agreement.

As the heatwave is ongoing, we don’t yet know exactly how much hotter than average this event will turn out to be. To account for this uncertainty I used multiple thresholds based on historically very hot summer days. These thresholds correspond to an historical 1-in-10-year hottest day, a 1-in-20-year hottest day, and a new record for the region exceeding the observed 2007 value.

While we don’t know exactly where the 2017 event will end up, we do know that it will exceed the 1-in-10 year threshold and it may well breach the higher thresholds too.

A clear human fingerprint

Whatever threshold I used, I found that climate change has greatly increased the likelihood of extremely hot summer days. The chance of extreme hot summer days, like this event, has increased by at least fourfold because of human-caused climate change.

Climate change is increasing the frequency of hot summer days in southeast Europe. Likelihoods of the hottest summer days exceeding the historical 1-in-10 year threshold, one-in-20 year threshold and the current record are shown for four scenarios: a natural world, the current world, a 1.5℃ world, and a 2℃ world. Best estimate likelihoods are shown with 90% confidence intervals in parentheses.
Author provided

My analysis shows that under natural conditions the kind of extreme heat we’re seeing over southeast Europe would be rare. In contrast, in the current world and possible future worlds at the Paris Agreement thresholds for global warming, heatwaves like this would not be particularly unusual at all.

There is also a benefit to limiting global warming to 1.5℃ rather than 2℃ as this reduces the relative frequency of these extreme heat events.

As this event comes to an end we know that Europe can expect more heatwaves like this one. We can, however, prevent such extreme heat from becoming the new normal by keeping global warming at or below the levels agreed upon in Paris.

You can find out more about the methods used here.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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

Severe heatwaves show the need to adapt livestock management for climate

Image 20170227 27378 u8yry6 — Cows don’t do well in the heat.
Shutterstock

Elisabeth Vogel, University of Melbourne; Christin Meyer, Potsdam Institute for Climate Impact Research, and Richard Eckard, University of Melbourne

Climate change and extreme weather events are already impacting our food, from meat and vegetables, right through to wine. In our series on the Climate and Food, we’re looking at what this means for the food chain.

During the recent heatwave in New South Wales, which saw record-breaking temperatures for two days in a row, 40 dairy cows died in Shoalhaven, a city just south of Sydney.

Climate change doubled the likelihood of this kind of record-breaking heatwave. And even the higher minimum temperatures we’ve recently experienced may soon be the “new normal” for this time of the year.

Farmers that already find it difficult to make a profit will need to adapt to these changing conditions, ensuring they mitigate the effects on their livestock. This could take the form of more shade and shelter, but also the selection of different breeds to suit the conditions.

What’s happening?

Cattle are vulnerable to changes in rainfall patterns (variability and extremes), temperature (average and extremes), humidity, and evaporation. These climactic changes can affect livestock directly, and also indirectly through pasture growth, forage crop quantity and quality, the production and price of feed-grain as well as spatial changes in disease and pest distribution.

The greatest risks stem from extreme events such as heatwaves and droughts, as they are less predictable and much more difficult to adapt to than gradual changes.

Dairy cows are particularly affected by heatwaves, which can not only reduce milk production, but, as the NSW heatwave illustrated, cause illness or death. Further, the effects on milk production and the protein content of the milk can last for several weeks.

Similar to humans, instances of high relative air humidity and little wind worsen the negative effects of high temperatures on livestock. When this occurs, the animals cannot easily offload excess heat through transpiration. This is compounded when there is little or no cloud cover, as the cattle are exposed to more solar radiation.

Milk production is also impacted by night-time temperatures and the timing of the heatwave. When night-time temperatures are high, cows cannot offload excess heat. If a heatwave occurs after the cows’ peak of lactation, milk production is less likely to recover and the impact is even worse.

The response of cattle to heat stress also depends on the breed. This can differ as a result of, among other things, differences in metabolic rate, sweating rate, coat texture and colour. Researchers have even identified a “slick hair gene”, responsible for producing cattle with shorter, slicker hair that reduces their vulnerability to direct radiative heat. The full benefits of the slick gene still require more research as a strategy for animals to cope in future climates.

Sheep are generally less affected by high temperatures than dairy cows. However, heatwaves with temperatures beyond 40℃ can cause heat stress. Hot days may have short-term impacts on rams’ fertility, and recently shorn sheep are at risk of sunburn if they are exposed to direct sunlight.

Factors that are unique to each individual animal, such as previous heat exposure and overall health and age, also play a role in how vulnerable they are to heat.

Mitigation

In the short run, farmers can mitigate the worst of these issues by providing high-quality water and shade (such as from trees, buildings, and shade cloth) in the heat, warm shelter in the cold, and by adjusting feed. During heatwaves, farmers can also adjust milking procedures and milk their cows very early in the morning or late at night. To provide immediate cooling they can also use sprinklers or misting systems. But care is needed to avoid simply increasing humidity around the animals.

A more long-term option is to selectively choose breeds that are better adapted to higher temperatures (such as breeds with lighter coat colour or Bos indicus types or crosses). Unfortunately, breeds adapted to warmer climates, such as the Brahman, tend not to be high milk producers or to do as well in feedlots as the traditional British beef breeds, so there will be a hit to productivity.

As the impact of climate change isn’t solely on the animals themselves, farmers will also have to adjust their work patterns and other aspects of their operations. To cope with heat, farmers themselves may need to consider working more during the cooler hours of the day. Farming both crops and livestock together can also provide a buffer against the impact of an extreme event. The combined production of wheat and wool is a typical example of spreading of risk on farm.

But for these strategies to really be effective, farmers need more information.

This includes accurate and timely forecasts of weather (temperature, rainfall, solar radiation) and heat (such as the temperature humidity index, THI) at daily, weekly and seasonal scales. Armed with this data, farmers and livestock managers can effectively plan and implement protection measures ahead of time.

A wide range of agricultural, climate and weather services exist. For example, the Bureau of Meteorology weather forecasts, seasonal outlooks of rainfall and temperature, and the current water balance and soil moisture information. There’s also the the Cool Cows website, the Dairy Forecast Service and the Cattle heat load toolbox.

We also need more research into improving our understanding of the climate system, to develop risk management plans for industries by regions, and more accurate and reliable forecasts, so that farmers and livestock managers can make management decisions and ensure the wellbeing of themselves and their animals.

Elisabeth Vogel, PhD Student, University of Melbourne; Christin Meyer, PhD student, Potsdam Institute for Climate Impact Research, and Richard Eckard, Professor & Director, Primary Industries Climate Challenges Centre, University of Melbourne

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

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What’s in a name

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Sea temperatures the culprit

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Climate change’s role in this heatwave

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