Making climate models open source makes them even more useful

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MiMA: an open source way to model the climate.
Martin Jucker, Author provided

Martin Jucker, University of Melbourne

Designing climate experiments is all but impossible in the real world. We can’t, for instance, study the effects of clouds by taking away all the clouds for a set period of time and seeing what happens.

Instead, we have to design our experiments virtually, by developing computer models. Now, a new open-source set of climate models has allowed this research to become more collaborative, efficient and reliable.

Read more:
Why scientists adjust temperature records, and how you can too

Full climate models are designed to be as close to nature as possible. They are representations of the combined knowledge of climate science and are without a doubt the best tools to understand what the future might look like.

However, many research projects focus on small parts of the climate, such as sudden wind changes, the temperature in a given region, or ocean currents. For these studies, concentrating on a small detail in a full climate model is like trying to find a needle in the haystack.

It is therefore common practice in such cases to take away the haystack by using simpler climate models. Scientists usually write these models for specific projects. A quote commonly attributed to Albert Einstein maybe best summarises the process: “Everything should be made as simple as possible, but not simpler.”

Here’s an example. In a paper from last year I looked at the temperature and wind changes in the upper atmosphere close to the Equator. I didn’t need to know what happened in the ocean, and I didn’t need any chemistry, polar ice, or even clouds in my model. So I wrote a much simpler model without these ingredients. It’s called “MiMA” (Model of an idealised Moist Atmosphere), and is freely available on the web.


The drawbacks of simpler models

Of course, using simpler models comes with its own problems.

The main issue is that researchers have to be very clear what the limits are for each model. For instance, it would be hard to study thunderstorms with a model that doesn’t reproduce clouds.

The second issue is that whereas the scientific results may be published, the code itself is typically not. Everyone has to believe that the model does indeed do what the author claims, and to trust that there are no errors in the code.

The third issue with simpler models is that anyone else trying to duplicate or build on published work would have to rebuild a similar model themselves. But given that the two models will be written by two (or more) different people, it is highly unlikely that they will be exactly the same. Also, the time the first author spends on building their model is then spent a second time by a second author, to achieve at best the same result. This is very inefficient.

Open-source climate models

To remedy some (if not all) of these issues, some colleagues and I have built a framework of climate models called Isca. Isca contains models that are easy to obtain, completely free, documented, and come with software to make installation and running easier. All changes are documented and can be reverted. Therefore, it is easy for everyone to use exactly the same models.

The time it would take for everyone to build their own version of the same model can now be used to extend the existing models. More sets of eyes on one model means that errors can be quickly identified and corrected. The time saved could also be used to build new analysis software, which can extract new information from existing simulations.

As a result, the climate models and their resulting scientific experiments become both more flexible and reliable. All of this only works because the code is publicly available and because any changes are continuously tracked and documented.

An example is my own code, MiMA, which is part of Isca. I have been amazed at the breadth of research it is used for. I wrote it to look at the tropical upper atmosphere, but others have since used it to study the life cycle of weather systems, the Indian monsoon, the effect of volcanic eruptions on climate, and so on. And that’s only one year after its first publication.

Read more:
Climate models too complicated? Here’s one that everyone can use

Making models openly available in this way has another advantage. Using an accessible proof can counter the mistrust of climate science that is still prevalent in some quarters.

The burden of proof automatically falls on the sceptics. As all the code is there and all changes are trackable, it is up to them to point out errors. And if someone does find an error, even better! Correcting it is just another step to make the models even more reliable.

The ConversationGoing open source with scientific code has many more benefits than drawbacks. It allows collaboration between people who don’t even know one another. And, most importantly, it will make our climate models more flexible, more reliable and generally more useful.

Martin Jucker, Maritime Continent Research Fellow, University of Melbourne

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


The freak warm Arctic weather is unusual, but getting less so

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Research Vessel Lance in the middle of broken Arctic sea ice after a large warm winter storm in February 2015.
Nick Cobbing, Author provided

Amelie Meyer, Norwegian Polar Institute; Erik W. Kolstad, Uni Research; Mats Granskog, Norwegian Polar Institute, and Robert Graham, Norwegian Polar Institute

The Arctic has been unusually warm since the beginning of 2018. In the past week air temperatures have hovered around 20℃ above normal or even higher. On February 25, the Cape Morris Jesup weather station in northern Greenland recorded 6.1℃, despite the fact that at this time of year, when the sun is still below the horizon, temperatures are typically around -30℃.

Daily Arctic temperatures in 2018 (thick red line), for 1958-2002 (thin lines) and the average for 1958-2002 (thick white line).
Zack Labe

A surprising feature of this warming event was how far into (and beyond) the Arctic it has penetrated. Warm air migrated north from the Atlantic Ocean, over the North Pole and towards the Pacific Ocean, bringing above-freezing air temperatures to large areas of the Arctic Ocean for more than 24 hours.

We have not seen a warm intrusion from the Atlantic Ocean on this scale since at least 1980.

Air temperatures at 3pm on February 25, 2018, based on GFS forecast. The warm air incursion is clearly visible in green. of Maine

Is this unprecedented?

Warm events in the middle of the northern winter are not unheard of. Large winter storms can bring strong winds that pump warm air into the Arctic from lower latitudes.

For example, during the Norwegian explorer Fridtjof Nansen’s 1896 expedition aboard the icebreaker Fram, the crew observed temperatures of -3℃ on one midwinter’s day. More recently, in December 2015, an Arctic warming event brought temperatures of 2℃ to the North Pole, and the warm weather continued into early 2016.

Winter warming events at the North Pole. Number of days each winter when the air temperature exceeds a given threshold.
Graham et al., 2017

But, crucially, this type of event is becoming more common and longer in duration, with higher peak temperatures.

Record low sea ice extent

February 26 brought a new record low for sea ice extent: maximum sea ice extent on that day was 14.20 million square kilometres, which is 1.29 million km2 below the 1981-2010 average for that day. This follows several years with record low winter maximum sea ice extents in 2015, 2016 and 2017.

Arctic sea ice extent for January and February 2018 (orange line), compared with the 1980s average (purple line), 1990s average (cyan line), and 2000s average (blue line).
Zack Labe/JAXA AMSR2

The current warm conditions in the Arctic have implications for sea ice year-round. Sea ice grows in winter and melts in summer. The warm air temperatures will slow down sea ice growth, and strong winds will push it around, breaking it up in places – as happened north of Greenland earlier this week.

Open water where the ice is broken will release extra heat into the atmosphere. By the time the spring sun comes around, the sea ice pack is thinned and weakened, and may melt more easily.

Cold weather in Europe

While the Arctic has been hot, Europe has been bitterly cold this week: London recorded -6℃; Berlin reached -14℃; and the Alps plunged to -27℃. Rome received 5-15cm of snow on Monday, and up to 40cm of snow fell in Britain on Wednesday.

It might sound counter-intuitive, but this cold weather is directly linked to the recent warming event in the Arctic.

Temperature anomalies for February 25, 2018, showing a warm Arctic and cold Europe and parts of Russia. Browns and reds indicate above-average temperatures; blues indicate below-average temperatures.
Climate Re-analyzer/University of Maine

Normally, the cold air above the polar region is contained in the Arctic by a ring-like band of strong winds called the polar vortex. But in the middle of February this year, the polar vortex split into two vortices: one over Eurasia and the other over North America.

Between these two features, a strong high-pressure system gradually formed. As a result, warm air was pumped up into the Arctic on the west side of the high, while cold air was channelled southwards to the east of it. Hence the exceptionally warm air in the Arctic and the cold snap in Europe.

Illustration of the Arctic polar vortex and northern hemisphere weather patterns.
XNR Productions

Is the polar vortex changing?

The polar vortex is driven by the strong temperature differences between the warm mid-latitudes and the cold Arctic. With the Arctic warming more rapidly than the mid-latitudes, this temperature difference is decreasing and some scientists believe that the polar vortex is weakening.

Research suggests that the polar vortex has become “wavier” as a result of this weakening. A wavier jet stream would lead to more frequent cold outbreaks of polar air at lower latitudes, and at the same time cause warm air to intrude into the Arctic. However, other researchers have argued that “large uncertainties regarding the magnitude of such an influence remain”.

Generally speaking, warming at every latitude makes cold spells at low latitudes less likely, and warm intrusions at high latitudes more likely, unless the Arctic warming leads to a fundamental change in the dynamics of the atmosphere.

Read more:
Climate shenanigans at the ends of the Earth: why has sea ice gone haywire?

Since 1979, Arctic warming events have grown more frequent. However, climate projections indicate that there will be fewer Arctic storms in the latter part of this century, and thus fewer Arctic warming events.

The ConversationAs scientists, we were startled by the extent of this week’s Arctic warming, and will be working hard to understand the short- and long-term implications. All eyes will be on the upcoming maximum winter Arctic sea ice extent, which is likely to happen in the next few weeks and could possibly set a new record low.

Amelie Meyer, Postdoctoral Researcher, Physical Oceanography, Norwegian Polar Institute; Erik W. Kolstad, Research professor, Uni Research; Mats Granskog, Senior research scientist, Norwegian Polar Institute, and Robert Graham, Postdoctoral Researcher, Climate Modelling, Norwegian Polar Institute

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

Health Check: how can extreme heat lead to death?

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Our climate is going to get warmer, and we need to protect ourselves from heat-related illness.

David Shearman, University of Adelaide

Our climate is becoming hotter. This is our reality. Extreme heat is already responsible for hundreds of deaths every year. It’s a big environmental killer, and deaths from heatwaves in Australian cities are expected to double in the next 40 years.

Those most at risk are the elderly, people with chronic illness, those living in socioeconomic disadvantage, outdoor workers, and athletes who play their sport in brutally high temperatures. But extreme heat can affect anyone at any age.

So, what happens in our body during times of extreme heat? And how can it lead to fatal consequences?

Read more:
Australia’s ‘deadliest natural hazard’: what’s your heatwave plan?

How we lose and gain heat

Our core body temperature sits at around 37℃. If it rises or falls, a range of very efficient physiological mechanisms come into play. In good health, our body can usually cope well with deviations of about 3.5℃, but beyond that the body begins to show signs of distress.

In hot weather, the body maintains core temperature by losing heat in several ways. One is to transfer it to a cooler environment, such as surrounding air or water, through our skin. But if the surrounding temperature is the same or higher than the skin (greater than 35-37℃) the effectiveness of this mechanism is markedly reduced.

Blood vessels supplying blood to the skin dilate. This allows more warm blood to flow near the surface of the skin, where the heat can be lost to the air. That’s why some people’s skin looks redder in hot environments.

One way the body loses heat is by directly transferring it to a cooler environment.

Evaporation (or sweat) is another way to lose heat from the body. If there is enough airflow and humidity is low enough, we can lose large amounts of heat through sweat. But on humid days, the rate of evaporation is reduced, as the air cannot absorb so much if it is already saturated with water vapour.

We can also reduce our heat production by resting. About 80% of the energy produced by working muscles is heat, so any activity will increase the amount of heat the body has to lose. This is why athletes and outdoor manual workers are at particular risk when performing at high levels of physical activity.

Read more:
Health Check: do cold showers cool you down?

What happens if the body can’t lose heat

Heat stress describes a spectrum of heat-related disorders that occur when the body fails to lose heat to maintain core temperature. Heat stress ranges from heat cramps to heat exhaustion (pale, sweating, dizzy and fainting). If the core temperature rises above 40.5℃, it can lead to heatstroke, which is a medical emergency, can occur suddenly and often kills.

The hypothalamus works as the body’s thermostat.

Heatstroke is caused by a failure of the hypothalamus, the region of the brain that works as our thermostat and co-ordinates our physiological response to excessive heat. It’s what leads to mechanisms like sweating and rapid breathing, dilated veins and increased blood flow to the skin. So, when the hypothalamus fails, so does our ability to sweat and lose heat in other ways.

At temperatures higher than 41.5℃, convulsions are common. Irreversible brain damage can occur at temperatures above 42.5℃. Patients with heatstroke can show neurological signs such as lack of co-ordination, confusion, seizures and loss of consciousness.

Read more:
Health Check: how to exercise safely in the heat

When sweating stops, the skin may become hot and dry, heart rate and breathing increase and blood pressure is low. Cells and nerves in the body become damaged. Liver damage is also common, but may not manifest for several days. The kidneys stop working, normal blood clotting is impaired, the heart muscle can be damaged and skeletal muscles start breaking down.

Essentially, this is what we describe as multi-organ failure. People with heatstroke can die within a few hours, or several days or even weeks later from organ failure.

Protecting yourself

Heatstroke could be “exertional”, as with athletes, or “classic”, which occurs in patients with impaired thermostatic responses, as a result of age, illness or medications.

Heatstroke can be caused by exertion, such as with athletes putting their body through stress in extreme temperatures.

Much of the increase in deaths during hotter temperatures occurs in older patients with a chronic illness. This is because they may have a poorly functioning central nervous system that cannot orchestrate the physiological changes needed to lose heat.

Older hearts may not be able to cope with the changes in circulation needed for more blood flow to go to the skin. Some medications can also interfere with the mechanisms for heat loss.

People experiencing any of the warning signs of heat stress (headache, nausea, light-headedness and fatigue) need to alter their behaviour to reduce it.

The best way to do this is to find a cool spot indoors or in the shade, put on light clothing, avoid physical exertion, put a damp cloth on your skin, immerse yourself in cold water and stay well hydrated.

But for some people, like children who are too young to make changes to their environment (such as those left in cars), this is not possible. Also, for the elderly, perhaps those with chronic mental illness or on certain medications that impair their ability to respond to increasing core temperature, these signs may not be apparent or noticed.

Read more:
Strategies for coping with extremely hot weather

This means we need safeguards to ensure the vulnerable stay cool. This is especially a problem for elderly people who live alone.

So, as our climate warms up, we need to do all we can to minimise the consequences of an increasingly hot environment. That means we must adapt our behaviour, our understanding of the issues, our urban environments, our sporting events and our systems that look out for the vulnerable in our community.

The ConversationThis article was co-authored by Dr Mark Monaghan, an emergency physician, and Dr Liz Bashford, an anaesthetist, who are both members of Doctors for the Environment Australia.

David Shearman, Emeritus Professor of Medicine, University of Adelaide

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


Cape Town is almost out of water. Could Australian cities suffer the same fate?

Ian Wright, Western Sydney University

The world is watching the unfolding Cape Town water crisis with horror. On “Day Zero”, now predicted to be just ten weeks away, engineers will turn off the water supply. The South African city’s four million residents will have to queue at one of 200 water collection points.

Cape Town is the first major city to face such an extreme water crisis. There are so many unanswered questions. How will the sick or elderly people cope? How will people without a car collect their 25-litre daily ration? Pity those collecting water for a big family.

Read more:
Cape Town’s water crisis: driven by politics more than drought

The crisis is caused by a combination of factors. First of all, Cape Town has a very dry climate with annual rainfall of 515mm. Since 2015, it has been in a drought estimated to be a one-in-300-year event.

In recent years, the city’s population has grown rapidly – by 79% since 1995. Many have questioned what Cape Town has done to expand the city’s water supply to cater for the population growth and the lower rainfall.

Could this happen in Australia?

Australia’s largest cities have often struggled with drought. Water supplies may decline further due to climate change and uncertain future rainfall. With all capital cities expecting further population growth, this could cause water supply crises.

Read more:
This is what Australia’s growing cities need to do to avoid running dry

The situation in Cape Town has strong parallels with Perth in Australia. Perth is half the size of Cape Town, with two million residents, but has endured increasing water stress for nearly 50 years. From 1911 to 1974, the annual inflow to Perth’s water reservoirs averaged 338 gigalitres (GL) a year. Inflows have since shrunk by nearly 90% to just 42GL a year from 2010-2016.

To make matters worse, the Perth water storages also had to supply more people. Australia’s fourth-largest city had the fastest capital city population growth, 28.2%, from 2006-2016.

As a result, Perth became Australia’s first capital city unable to supply its residents from storage dams fed by rainfall and river flows. In 2015 the city faced a potentially disastrous situation. River inflows to Perth’s dams dwindled to 11.4GL for the year.

For its two million people, the inflows equated to only 15.6 litres per person per day! Yet in 2015/6 Perth residents consumed an average of nearly 350 litres each per day. This was the highest daily water consumption for Australia’s capitals. How was this achieved?

Tapping into desalination and groundwater

Perth has progressively sourced more and more of its supply from desalination and from groundwater extraction. This has been expensive and has been the topic of much debate. Perth is the only Australian capital to rely so heavily on desalination and groundwater for its water supply.

Volumes of water sourced for urban use in Australia’s major cities.
BOM, Water in Australia, p.52, National Water Account 2015, CC BY

Australia’s next most water-stressed capital is Adelaide. That city is supplementing its surface water storages with desalination and groundwater, as well as water “transferred” from the Murray River.

Australia’s other capital cities on the east coast have faced their own water supply crises. Their water storages dwindled to between 20% and 35% capacity in 2007. This triggered multiple actions to prevent a water crisis. Progressively tighter water restrictions were declared.

The major population centres (Brisbane/Gold Coast, Sydney, Melbourne and Adelaide) also built large desalination plants. The community reaction to the desalination plants was mixed. While some welcomed these, others question their costs and environmental impacts.

The desalination plants were expensive to build, consume vast quantities of electricity and are very expensive to run. They remain costly to maintain, even if they do not supply desalinated water. All residents pay higher water rates as a result of their existence.

Since then, rainfall in southeastern Australia has increased and water storages have refilled. The largest southeastern Australia desalination plants have been placed on “stand-by” mode. They will be switched on if and when the supply level drops.

Read more:
The role of water in Australia’s uncertain future

Investing in huge storage capacity

Many Australian cities also store very large volumes of water in very large water reservoirs. This allows them to continue to supply water through future extended periods of dry weather.

The three largest cities (Sydney, Melbourne and Brisbane) have built very large dams indeed. For example, Brisbane has 2,220,150 ML storage capacity for its 2.2 million residents. That amounts to just over one million litres per resident when storages are full.

The ConversationIn comparison, Cape Town’s four million residents have a full storage capacity of 900,000 ML. That’s 225,000 litres per resident. Cape Town is constructing a number of small desalination plants while anxiously waiting for the onset of the region’s formerly regular winter rains.

Ian Wright, Senior Lecturer in Environmental Science, Western Sydney University

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


Tornado – Vorticity


Australia’s climate in 2017: a warm year, with a wet start and finish

Linden Ashcroft, Australian Bureau of Meteorology; Blair Trewin, Australian Bureau of Meteorology, and Skie Tobin, Australian Bureau of Meteorology

The Bureau of Meterology’s Annual Climate Statement, released today, confirms that 2017 was Australia’s third-warmest year on record, and our maximum temperature was the second-warmest. Globally, 2017 is likely to be one of the world’s three warmest years on record, and the warmest year without an El Niño.

Read more: Explainer: El Niño and La Niña

But looking at the big picture can obscure some regional record-breaking features. Victoria experienced its driest June on record, and September saw New South Wales and the Murray–Darling Basin record their driest September since nationwide records begin in 1900. Sydney’s Observatory Hill had its driest September since records started there in 1858.

The southwest of Western Australia had its warmest maximum temperatures on record for June. Northern Australia also recorded its warmest dry season for maximum temperature.

A field in Moree, New South Wales. The state had its driest September on record.
Bureau of Meteorology, Author provided

This warm year occurred despite the fact that, unlike 2016, there was no strong El Niño or La Niña pattern in the Pacific Ocean for much of the year, and the Indian Ocean Dipole remained neutral.

Read more: What is the Indian Ocean Dipole?

Wet in the northwest, dry in the east

Australia’s average total rainfall in 2017 was 504mm, somewhat above average. But the annual average hides large swings from very dry months to damaging downpours, and large differences from the east to the west of the country.

The year began wet, particularly in the west. Tropical lows brought heavy rainfall across the Northern Territory, South Australia and Western Australia during January and February, and many places in Western Australia set new records for their wettest summer day. It was our fourth-wettest January on record nationally.

Severe Tropical Cyclone Debbie crossed the south Queensland coast in late March and tracked southwards delivering torrential rainfall along the east coast. Several locations received up to a metre of rainfall in two days, and major flooding occurred from Bowen, in Queensland, to Lismore, in New South Wales.

The west of Western Australia was dry for much of autumn and early winter. Winter rainfall was also low across southern Australia under the effect of a subtropical ridge stronger and further south than usual.

Heavy rain across much of Queensland and northern New South Wales during October meant that Bundaberg received more than 400% of its average rainfall for October in the first three weeks of the month.

In late December, Tropical Cyclone Hilda became the first cyclone to make landfall in the 2017-18 Australian cyclone season, bringing heavy rains around Broome.

Australia’s rainfall in 2017.
Bureau of Meteorology, Author provided

A hot start

It might not have always felt like it, but 2017 was much warmer than average. It was the third-warmest year on record for Australia, 0.95℃ above average, and the warmest on record for Queensland and New South Wales. Sea surface temperatures were also much warmer than average around Australia, although not as warm as 2016.

Australia’s average temperatures in 2017.
Bureau of Meteorology, Author provided

New South Wales experienced its warmest summer on record, and heatwaves affected much of eastern Australia during the first two months of the year. At the same time, rain kept summer temperatures below average in the west.

The high temperatures around eastern Australia continued into autumn, over both land and sea. Coral bleaching affected the Great Barrier Reef again, the first time mass bleaching events have occurred in consecutive years.

Warm days but chilly winter nights

As winter set in, the lack of rainfall and clouds led to warm sunny days. The southwest of Western Australia had its warmest maximum temperatures on record for June.

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

However the clear skies also meant frosty mornings across much of Victoria, southern New South Wales, South Australia and Tasmania. Canberra, which is known for its chilly nights, had its lowest winter mean minimum temperature since 1982. Some locations, including Sale in Victoria, and Deniliquin and West Wyalong in New South Wales, had their coldest night on record during the first few days of July.

Meanwhile, northern Australia recorded its warmest dry season on record for maximum temperature. The mean maximum temperature for northern Australia was 2℃ above average for the five months from May to September, beating the previous record set in 2013 by almost half a degree.

A warm finish

In September, northerly air flow brought the warm air over to the east of the country, with the month culminating in a week of exceptional heat. New South Wales recorded its first ever 40℃ in September – not once, but on two separate days – and some places beat their previous hottest September day on record by more than 3 degrees.

Late-season frosts in early November caused damage to crops in western Victoria, but the cold was soon replaced by prolonged heat thanks to a slow moving high pressure system parked over the Tasman Sea.

The northerly winds and sunny days meant that many places in Victoria and Tasmania had record runs of days warmer than 25℃, and nights warmer than 15℃. It was Tasmania’s warmest November on record, with temperatures more typical of late summer than late spring.

The long-lived weather system led to record-breaking November sea surface temperatures between Tasmania and New Zealand, which also had a very warm and dry November. The southeast of the country finished 2017 with our first heatwave of the summer in mid-December.

The bigger picture

Global mean temperature anomalies relative to 1961-1990, 1880–2017.
Bureau of Meteorology, Author provided

The World Meteorological Organization releases the final global mean temperature for 2017 in mid-January. This enables it to collect as many observations as possible from different countries. But the January to November global average can give a pretty good idea of where 2017 will sit: one of the world’s three warmest years on record.

The planet has seen plenty of extreme weather events over the past year, including hurricanes, flooding, and devastating bushfires.

The ConversationGlobal temperatures have increased by about one degree since 1900. Mean global temperatures have been above average every year since 1985, and all of the ten warmest years have occurred between 1998 and the present. Seven of Australia’s ten warmest years have now occurred since 2005.

Linden Ashcroft, Climatologist, Australian Bureau of Meteorology; Blair Trewin, Climate scientist, Australian Bureau of Meteorology, and Skie Tobin, Climatologist, Australian Bureau of Meteorology

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


2017: the year in extreme weather

Andrew King, University of Melbourne

Overall 2017 will be the warmest non-El Niño year on record globally, and over the past 12 months we have seen plenty of extreme weather, both here in Australia and across the world.

Here I’ll round up some of this year’s wild weather, and look forward to 2018 to see what’s around the corner.

Drought and flooding rains… again

It feels as if Australia has had all manner of extreme weather events in 2017.
We had severe heat at both the start and end of the year. Casting our minds back to last summer, both Sydney and Brisbane experienced their hottest summers on record, while parts of inland New South Wales and Queensland endured extended periods of very high temperatures.

Read more: We’ve learned a lot about heatwaves, but we’re still just warming up

More recently Australia had an unusually dry June and its warmest winter daytime temperatures on record. The record winter warmth was made substantially more likely by human-caused climate change.

The end of the year brought more than its fair share of extreme weather, especially in the southeast. Tasmania had by far its warmest November on record, beating the previous statewide record by more than half a degree. Melbourne had a topsy-turvy November with temperatures not hitting the 20℃ mark until the 9th, but a record 12 days above 30℃ after that.

November was rounded off by warnings for very severe weather that was forecast to strike Victoria. Melbourne missed the worst of the rains, although it still had a very wet weekend on December 2-3. Meanwhile, northern parts of the state were deluged, with many places recording two or three times the December average rainfall in just a couple of days.

Hurricane after hurricane after hurricane…

Elsewhere in the world there was plenty more headline-worthy weather.

The Atlantic Ocean had a particularly active hurricane season, with several intense systems. Hurricane Harvey struck Texas and its slow trajectory resulted in record-breaking rainfall over Houston and neighbouring areas.

Then Hurricanes Irma and Maria, both of which reached the strongest Category 5 status, brought severe weather to the Caribbean and southeastern United States just a couple of weeks apart. Island nations and territories in the region are still recovering from the devastation.

Around the same time, the Indian subcontinent experienced a particularly wet monsoon season. Flooding in India, Pakistan, Bangladesh, and Nepal killed more than 1,000 people and affected tens of millions more.

Other parts of the world experienced their own severe weather events. Whether it was summer heat in Europe or wildfires in California, 2017 dished up plenty of extremes.

In many cases, especially for heat extremes, we can rapidly identify a human influence and show that climate change is increasing the frequency and intensity of such events.

For other weather types, like the very active hurricane season and other extreme rain or drought events, it is harder (but not always impossible) to work out whether it bears the fingerprint of climate change.

What’s in store for 2018?

The main problem when trying to offer an outlook is that extreme weather is hard to predict, even on the scale of days or weeks in advance, let alone months.

For Australia, with a weak La Niña in the Pacific, there are few clear indications of what the rest of the summer’s weather will bring. There is a suggestion that we can expect a slightly wetter than average start to the year in parts of the southeast, along with warmer than average conditions for Victoria and Tasmania. Beyond that it is anyone’s guess.

Read more: Not just heat: even our spring frosts can bear the fingerprint of climate change

The La Niña is also likely to mean that 2018 won’t be a record hot year for the globe. But it’s a safe bet that despite the La Niña, 2018 will still end up among the warmest years on record, alongside every other year this century. Rising global average temperatures, along with our understanding of the effect of greenhouse gas emissions, are one of our clearest lines of evidence for human-caused climate change.

The ConversationSo it’s hard to say much about what extreme weather we’ll experience in 2018, other than to say that there’s likely to be plenty more weather news to wrap up in a year’s time.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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