Earth may temporarily pass dangerous 1.5℃ warming limit by 2024, major new report says


Pep Canadell, CSIRO and Rob Jackson, Stanford University

The Paris climate agreement seeks to limit global warming to 1.5℃ this century. A new report by the World Meteorological Organisation warns this limit may be exceeded by 2024 – and the risk is growing.

This first overshoot beyond 1.5℃ would be temporary, likely aided by a major climate anomaly such as an El Niño weather pattern. However, it casts new doubt on whether Earth’s climate can be permanently stabilised at 1.5℃ warming.

This finding is among those just published in a report titled United in Science. We contributed to the report, which was prepared by six leading science agencies, including the Global Carbon Project.

The report also found while greenhouse gas emissions declined slightly in 2020 due to the COVID-19 pandemic, they remained very high – which meant atmospheric carbon dioxide concentrations have continued to rise.

Woman holds a sign at a climate protest
The world may exceed the 1.5℃ warming threshold sooner than we expected.
Erik Anderson/AAP

Greenhouse gases rise as CO₂ emissions slow

Concentrations of the three main greenhouse gases – carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O), have all increased over the past decade. Current concentrations in the atmosphere are, respectively, 147%, 259% and 123% of those present before the industrial era began in 1750.

Concentrations measured at Hawaii’s Mauna Loa Observatory and at Australia’s Cape Grim station in Tasmania show concentrations continued to increase in 2019 and 2020. In particular, CO₂ concentrations reached 414.38 and 410.04 parts per million in July this year, respectively, at each station.

Atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂0) from WMO Global Atmosphere Watch.

Growth in CO₂ emissions from fossil fuel use slowed to around 1% per year in the past decade, down from 3% during the 2000s. An unprecedented decline is expected in 2020, due to the COVID-19 economic slowdown. Daily CO₂ fossil fuel emissions declined by 17% in early April at the peak of global confinement policies, compared with the previous year. But by early June they had recovered to a 5% decline.

We estimate a decline for 2020 of about 4-7% compared to 2019 levels, depending on how the pandemic plays out.

Although emissions will fall slightly, atmospheric CO₂ concentrations will still reach another record high this year. This is because we’re still adding large amounts of CO₂ to the atmosphere.

Global daily fossil CO₂ emissions to June 2020. Updated from Le Quéré et al. 2020, Nature Climate Change.

Warmest five years on record

The global average surface temperature from 2016 to 2020 will be among the warmest of any equivalent period on record, and about 0.24℃ warmer than the previous five years.

This five-year period is on the way to creating a new temperature record across much of the world, including Australia, southern Africa, much of Europe, the Middle East and northern Asia, areas of South America and parts of the United States.




Read more:
The world endured 2 extra heatwave days per decade since 1950 – but the worst is yet to come


Sea levels rose by 3.2 millimetres per year on average over the past 27 years. The growth is accelerating – sea level rose 4.8 millimetres annually over the past five years, compared to 4.1 millimetres annually for the five years before that.

The past five years have also seen many extreme events. These include record-breaking heatwaves in Europe, Cyclone Idai in Mozambique, major bushfires in Australia and elsewhere, prolonged drought in southern Africa and three North Atlantic hurricanes in 2017.

Left: Global average temperature anomalies (relative to pre-industrial) from 1854 to 2020 for five data sets. UK-MetOffice. Right: Average sea level for the period from 1993 to July 16, 2020. European Space Agency and Copernicus Marine Service.

1 in 4 chance of exceeding 1.5°C warming

Our report predicts a continuing warming trend. There is a high probability that, everywhere on the planet, average temperatures in the next five years will be above the 1981-2010 average. Arctic warming is expected to be more than twice that the global average.

There’s a one-in-four chance the global annual average temperature will exceed 1.5℃ above pre-industrial levels for at least one year over the next five years. The chance is relatively small, but still significant and growing. If a major climate anomaly, such as a strong El Niño, occurs in that period, the 1.5℃ threshold is more likely to be crossed. El Niño events generally bring warmer global temperatures.

Under the Paris Agreement, crossing the 1.5℃ threshold is measured over a 30-year average, not just one year. But every year above 1.5℃ warming would take us closer to exceeding the limit.

Global average model prediction of near surface air temperature relative to 1981–2010. Black line = observations, green = modelled, blue = forecast. Probability of global temperature exceeding 1.5℃ for a single month or year shown in brown insert and right axis. UK Met Office.

Arctic Ocean sea-ice disappearing

Satellite records between 1979 and 2019 show sea ice in the Arctic summer declined at about 13% per decade, and this year reached its lowest July levels on record.

In Antarctica, summer sea ice reached its lowest and second-lowest extent in 2017 and 2018, respectively, and 2018 was also the second-lowest winter extent.

Most simulations show that by 2050, the Arctic Ocean will practically be free of sea ice for the first time. The fate of Antarctic sea ice is less certain.

A polar bear on an ice floe
Summer sea ice in the Arctic is expected to virtually disappear by 2050.
Zaruba Ondrej/AP

Urgent action can change trends

Human activities emitted 42 billion tonnes of CO₂ in 2019 alone. Under the Paris Agreement, nations committed to reducing emissions by 2030.

But our report shows a shortfall of about 15 billion tonnes of CO₂ between these commitments, and pathways consistent with limiting warming to well below 2℃ (the less ambitious end of the Paris target). The gap increases to 32 billion tonnes for the more ambitious 1.5℃ goal.

Our report models a range of climate outcomes based on various socioeconomic and policy scenarios. It shows if emission reductions are large and sustained, we can still meet the Paris goals and avoid the most severe damage to the natural world, the economy and people. But worryingly, we also have time to make it far worse.




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The Conversation


Pep Canadell, Chief research scientist, Climate Science Centre, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO and Rob Jackson, Chair, Department of Earth System Science, and Chair of the Global Carbon Project, Stanford University

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

The world endured 2 extra heatwave days per decade since 1950 – but the worst is yet to come



Shutterstock

Sarah Perkins-Kirkpatrick, UNSW

The term “heatwave” is no stranger to Australians. Defined as when conditions are excessively hot for at least three days in a row, these extreme temperature events have always punctuated our climate.

With many of us in the thick of winter dreaming of warmer days, it’s important to remember how damaging heatwaves can be.

In 2009, the heatwave that preceded Black Saturday killed 374 people. The economic impact on Australia’s workforce from heatwaves is US$6.2 billion a year (almost AU$9 billion). And just last summer, extreme temperature records tumbled, contributing to Australia’s unprecedented bushfire season.

What are heatwaves?

Our new study – the first worldwide assessment of heatwaves at the regional scale – found heatwaves have become longer and more frequent since 1950. And worryingly, we found this trend has accelerated.

We also examined a new metric: “cumulative heat”. This measures how much extra heat a heatwave can contribute, and the new perspective is eye-opening.

What is ‘extra heat’?

In southeast Australia’s worst heatwave season in 2009, we endured an extra heat of 80℃. Let’s explore what that means.

For a day to qualify as being part of a heatwave, a recorded temperature should exceed an officially declared “heatwave threshold”.

And cumulative heat is generally when the temperature above that threshold across all heatwave days are added up.

Let’s say, for example, a particular location had a heatwave threshold of around 30℃. The “extra heat” on a day where temperatures reach 35℃ would be 5℃. If the heatwave lasted for three days, and all days reached 35℃, then the cumulative heat for that event would be 15℃.

Another decade, another heatwave day

We found almost every global region has experienced a significant increase in heatwave frequency since 1950. For example, southern Australia has experienced, on average, one extra heatwave day per decade since 1950.




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However, other regions have experienced much more rapid increases. The Mediterranean has seen approximately 2.5 more heatwave days per decade, while the Amazon rainforest has seen an extra 5.5 more heatwave days per decade since 1950.

The global average sits at approximately two extra heatwave days per decade.

The last 20 years saw the worst heatwave seasons

Since the 1950s, almost all regions experienced significant increases in the extra heat generated by heatwaves.

Over northern and southern Australia, the excess heat from heatwaves has increased by 2-3℃ per decade. This is similar to other regions, such as western North America, the Amazon and the global average.

Alaska, Brazil and West Asia, however, have cumulative heat trends of a massive 4-5℃ per decade. And, for the vast majority of the world, the worst seasons occurred in the last 20 years.

In the heatwave before Black Saturday, 374 people died.
Shutterstock

We also examined whether heatwaves were changing at a constant rate, or were speeding up or slowing down. With the exception of average intensity, we found heatwave trends have not only increased, but have accelerated since the 1950s.

Don’t be fooled by the maths

Interestingly, average heatwave intensity showed little – if any – changes since 1950. But before we all breathe a sigh of relief, this is not because climate change has stopped, or because heatwaves aren’t getting any warmer. It’s the result of a mathematical quirk.




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Since we’re seeing more heatwaves – which we found are also generally getting longer – there are more days to underpin the average intensity. While all heatwave days must exceed a relative extreme threshold, some days will exceed this threshold to a lesser extent than others. This brings the overall average down.

When we look at changes in cumulative heat, however, there’s just no denying it. Extra heat – not the average – experienced in almost all regions, is what can have adverse impacts on our health, infrastructure and ecosystems.

The Amazon has endured 5.5 more heatwave days per decade since 1950.
Shutterstock

Like nothing we’ve experienced before

While the devastating impacts of heatwaves are clear, it has been difficult to consistently measure changes in heatwaves across the globe. Previous studies have assessed regional heatwave trends, but data constraints and the spectrum of different heatwave metrics available have made it hard to compare regional changes in heatwaves.

Our study has closed this gap, and clearly shows heatwaves are on the rise. We are seeing more of them and they are generating more heat at an increasing pace.




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


While Australia may be no stranger to heatwaves in the past, those we see in the future under these accelerating trends will certainly be foreign.

For example, a 2014 study found that depending on where you are in Australia, anywhere between 15 and 50 extra heatwave days will occur by 2100 compared to the second half of the 20th century.

We can still abate those trends if we work collectively, effectively and urgently to reduce our greenhouse gas emissions.The Conversation

Sarah Perkins-Kirkpatrick, ARC Future Fellow, UNSW

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

Just how hot will it get this century? Latest climate models suggest it could be worse than we thought


Michael Grose, CSIRO and Julie Arblaster, Monash University

Climate scientists use mathematical models to project the Earth’s future under a warming world, but a group of the latest models have included unexpectedly high values for a measure called “climate sensitivity”.

Climate sensitivity refers to the relationship between changes in carbon dioxide in the atmosphere and warming.

The high values are an unwelcome surprise. If they’re right, it means a hotter future than previously expected – warming of up to 7℃ for Australia by 2100 if emissions continue to rise unabated.




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Our recent study analyses these climate models (named CMIP6), which were released at the end of last year, and what insights they give for Australia.

These models contain the latest improvements and innovations from some of the world’s leading climate modelling institutes, and will feed into the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report in 2021.

But the new climate sensitivity values raise the question of whether previous climate modelling has underestimated potential climate change and its effects, or whether the new models are overdoing things.

If the high estimate is right, this would require the world to make greater and more urgent emission cuts to meet any given warming target.

These higher climate sensitivity values point to the urgent need to cut our greenhouse gas emissions.
Shutterstock

What is climate sensitivity?

Climate sensitivity is one of the most important factors for climate change, strongly influencing our planning for adaptation and mitigation of greenhouse gas emissions.




Read more:
Explainer: what is climate sensitivity?


It’s a standardised measure of how much the climate responds when carbon dioxide concentrations in the atmosphere double. There are a few indices of climate sensitivity that the scientific community uses, and perhaps the most commonly used is “equilibrium climate sensitivity”.

We can estimate equilibrium climate sensitivity by raising carbon dioxide concentrations in models abruptly and then calculating the warming experienced after 150 years – when the atmosphere and ocean would return to a temperature balance.

In other words, giving the climate a “push” with more carbon emissions and waiting until it settles down into a new state.

The previous generation of models (CMIP5) had equilibrium climate sensitivity values between 2.1℃ to 4.7℃ global temperature change. The values for the latest models (CMIP6) are from 1.8℃ to 5.6℃.

This includes a cluster of models with sensitivity of 5℃ or more, a group of models within the previous range, and two models with very low values at around 2℃.

What this means for our future

Higher equilibrium climate sensitivity values mean a hotter future climate than previously expected, for any given scenario of future emissions.

We’ll see Australian temperature increase in a low and high emissions scenario projections (temperature relative to 1995-2014, range of models shown as coloured bands, observations as a black line).
Author provided

According to these new models, Australian warming could crack more than 7℃ by 2100 under a scenario where greenhouse gas emissions continue to increase through the century.

These higher temperature changes are not currently presented in the national climate projections, as they didn’t occur under the previous generation of models and emission scenarios.

So what does this mean in practice?

Higher climate sensitivity means increases to heat extremes. It would mean we’ll see greater flow-on changes to other climate features, such as extreme rainfall, sea level rise, extreme heatwaves and more, reducing our ability to adapt.




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Immediate phase out of fossil fuels could keep warming below 1.5°C


High equilibrium climate sensitivity would also mean we need to make bigger cuts to our greenhouse gas emissions for a given global warming target. The Paris Agreement aims to keep global warming well under 2℃ since pre-industrial times.

Should we be worried?

These are credible models, representing the new generation versions of top performing modelling systems, developed over decades at high-ranking research institutions globally. Their results cannot be rejected out of hand just because we don’t like the answer.

But – we shouldn’t jump on this piece of evidence, throw out all others and assume the results from a subset of new models is the final answer.




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Why 2℃ of global warming is much worse for Australia than 1.5℃


The weight and credibility of each piece of evidence must be carefully assessed by the research community, and by scientists putting together the upcoming IPCC assessment.

We’re only just starting to understand the reasons for the high sensitivity in these models, such as how clouds interact with particles in the air.

And there are other lines of evidence underpinning the IPCC estimate of equilibrium climate sensitivity.

These include the warming seen since the last ice age around 20,000 years ago; measurements of warming seen over recent decades from greenhouse gases already emitted; and understanding different climate feedbacks from field experiments and observed natural variability. These other lines of evidence may not support the new model results.




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Essentially, the jury is still out on the exact value of equilibrium climate sensitivity, high values can’t be ruled out, and the results from the new models need to be taken seriously.

In any case, the new values are a worrying possibility that no one wants, but one we must still grapple with. As researchers in one study conclude: “what scares us is not that the models’ [equilibrium climate sensitivity] is wrong […] but that it might be right”.The Conversation

Michael Grose, Climate Projections Scientist, CSIRO and Julie Arblaster, Associate Professor, Monash University

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

It’s official: the last five years were the warmest ever recorded


It’s official: the last five years were the warmest ever recorded

Blair Trewin, Australian Bureau of Meteorology and Pep Canadell, CSIRO

The World Meteorological Organisation today published a definitive climate report card showing concentrations of greenhouse gases continue to rise, and the last five years were the warmest on record.

The Statement on the State of the Global Climate also confirmed that the ongoing drought and recent bushfires in Australia were a globally significant climate event.

The report is an annual, comprehensive overview of the latest information from the world’s meteorological services and other key institutions. We are among the many authors who contributed.

It’s an important record of the magnitude and speed of changes to global climate, drawing on the latest data from across the fields of climate science.

A record year

Global average temperatures in 2019 were 1.1℃ above pre-industrial levels. Only 2016 was hotter, but that year came at the end of an extreme El Niño, which typically has a warming influence on global temperatures.

The last five years were the world’s five warmest on record. Areas which were especially warm, with temperatures in 2019 more than 2℃ above average, included parts of Australia, Alaska and northern Russia, eastern Europe and southern Africa. Central North America was the only significant land area with below-average temperatures.


CC BY-ND

Human-driven climate change is predominantly caused by increasing greenhouse gases in the atmosphere. Concentrations of carbon dioxide, methane and nitrous oxide, the three most potent greenhouse gases, have continued to grow and are now, respectively, 147%, 259% and 123% of pre-industrial levels, measured in the year 1750.

Global emissions of carbon dioxide from fossil fuels reached a record high of 36.6 billion tonnes, of which about half is absorbed by vegetation and oceans.

The Antarctic ozone hole was its smallest since 2002, after an unusually early spring breakdown of the Antarctic polar vortex following a sudden warming in the polar stratosphere.




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Many other indicators of large-scale climate change continued their long-term trends in 2019. These include the heat content of the global ocean – an important indicator because around 90% of warming generated by greenhouse gases from human activities is taken by the oceans.

In 2019, ocean heat content reached the highest levels since instrumental records began. Global mean sea level also reached new highs in 2019, while Arctic and Antarctic sea ice extent was well below average.

Glacial mass declined for the 32nd consecutive year. In Switzerland, for example, glacier loss over the past five years has exceeded 10%, the highest rate of decline in more than a century.


CC BY-ND

Australia’s fire and drought

The report confirms the ongoing drought in Australia and exceptional fire weather conditions late in the year were among the most significant global climate events last year.

2019 was Australia’s warmest and driest year since national records began – the first time both records have been broken in the same year.


CC BY-ND

In December, the monthly accumulated Forest Fire Danger Index – an indicator of severe fire weather – was the highest on record for any month in Queensland, New South Wales, South Australia and the ACT. Some fires burned for longer than two months.

In January and February 2019, a dry summer in Tasmania contributed to fires in the normally moist western and central parts of the island – the second time in four years that fires burnt regions where historically such events were extremely rare.




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The drought was strongly influenced by a very strong positive phase of the Indian Ocean Dipole – an oscillation of sea surface temperatures which affects the climate in Australia. A strong negative Southern Annular Mode – a climate driver which originates in Antarctica – brought westerly winds and dry conditions to the eastern states from September.

Australia was not the only nation affected by drought in 2019 – southern Africa, southeast Asia and central Chile were also significantly affected. In the Chilean capital Santiago, rainfall was more than 70% below average.

Heatwaves and cyclones

Two exceptional heatwaves affected Europe in the summer. France, Germany, Belgium, the Netherlands and the United Kingdom all had their highest recorded temperatures. Belgium and the Netherlands both reached 40℃ for the first time, and Paris reached a high of 42.6℃.

Australia had extreme heatwaves both early and late in the year, and in South America, temperatures exceeded 30℃ as far south as Tierra del Fuego.




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Tropical cyclones are amongst the most destructive weather phenomena in most years, and 2019 was no exception. The most severe cyclone impact was in Mozambique and Zimbabwe, when Cyclone Idai hit in mid-March, killing more than 900 people.

Hurricane Dorian, one of the strongest ever to affect land in the North Atlantic, caused massive destruction in the Bahamas, whilst Typhoon Hagibis led to exceptional flooding in Japan, and daily rainfall of more than 900 millimetres. The North Indian Ocean also had its most active cyclone season on record.

Looking to the future

Global climate projections show that under all scenarios, temperatures will continue to warm – and years such as 2019 will become the norm this decade.

The report is intended to inform decisions around the world on adaptation to, and mitigation of, climate change.The Conversation

Blair Trewin, Climate scientist, Australian Bureau of Meteorology and Pep Canadell, Chief research scientist, CSIRO Oceans and Atmosphere; and Executive Director, Global Carbon Project, CSIRO

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

Australia could see fewer cyclones, but more heat and fire risk in coming months


Jonathan Pollock, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Catherine Ganter, Australian Bureau of Meteorology, and Paul Gregory, Australian Bureau of Meteorology

Northern Australia is likely to see fewer cyclones than usual this season, but hot, dry weather will increase the risk of fire and heatwaves across eastern and southern Australia.

The Bureau of Meteorology today released its forecast for the tropical cyclone season, which officially runs from November 1 to April 30.




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Also published today is the October to April Severe Weather Outlook, which examines the risk of other weather extremes like flooding, heatwaves and bushfires.

Warmer oceans means more cyclones

On average, 11 tropical cyclones form each season in the Australian region. Around four of those cross the coast. The total number each season is roughly related to how much cooler or warmer than average the tropical oceans near Australia are during the cyclone season.

Map showing the average number of tropical cyclones through the Australian region and surrounding waters in ENSO-neutral years, using all years of data from the 1969-70 to 2017-18 tropical cyclone season.

One of the biggest drivers of change in ocean temperatures is the El Niño–Southern Oscillation, or ENSO. During La Niña phases of ENSO, the warmest waters in the equatorial Pacific build up in the western Pacific and to the north of Australia. That region then becomes the focus for more cloud, rainfall and tropical cyclones.

But during El Niño, the warmest water shifts towards the central Pacific and away from northern Australia. This decreases the likelihood of cyclones in our region.




Read more:
Explainer: El Niño and La Niña


And when ENSO is neutral, there is little push towards above or below average numbers of cyclones.

Temperatures in the tropical Pacific Ocean have been ENSO-neutral since April and are likely to stay neutral until at least February 2020. However, some tropical patterns are El Niño-like, including higher-than-average air pressure at Darwin. This may be related to the current record-strong positive Indian Ocean Dipole – another of Australia’s major climate drivers – and the cooler waters surrounding northern Australia.

The neutral ENSO phase alongside higher-than-average air pressure over northern Australia means we expect fewer-than-average tropical cyclones in the Australian region this season. The bureau’s Tropical Cyclone Season Outlook model predicts a 65% chance of fewer-than-average cyclones.

At least one tropical cyclone has crossed the Australian coast every season since reliable records began in the 1970s, so people across northern Australia need to be prepared every year. In ENSO-neutral cyclone seasons, this first cyclone crossing typically occurs in late December.




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Other severe weather

While cyclones are one of the key concerns during the coming months, the summer months also bring the threat of several other forms of severe weather, including bushfires, heatwaves and flooding rain.

With dry soils inland, and hence little moisture available to cool the air, and a forecast for clear skies and warmer days, there is an increased chance that heat will build up over central Australia during the spring and summer months. This increases the chance of heatwaves across eastern and southern Australia when that hot air is drawn towards the coast by passing weather systems.

Australian seasonal bushfire outlook, as of August 2019. Vast areas of Australia, particularly the east coast, have an above-normal fire potential this season.
Bushfire and Natural Hazards CRC/Australasian Fire and Emergency Service Authorities Council

Likewise, the dry landscape and the chance of extreme heat also raise the risk of more bushfires throughout similar parts of Australia, especially on windy days. And with fewer natural firebreaks such as full rivers and streams, even greater care is needed in some areas.

Widespread floods are less likely this season. This is because of forecast below-average rainfall and also because dry soils mean the first rains will soak into the ground rather than run across the landscape.

However, as we saw in northern Queensland in January and February this year, when up to 2 metres of rainfall fell in less than 10 days, localised flooding can occur in any wet season if a tropical low parks itself in one location for any length of time.




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Most of all, it’s always important to follow advice from emergency services on what to do before, during and after severe weather. Know your weather, know your risk and be prepared. You can stay up to date with the latest forecast and warnings on the bureau’s website and subscribe to receive climate information emails.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology; Andrew B. Watkins, Head of Long-range Forecasts, Australian Bureau of Meteorology; Catherine Ganter, Senior Climatologist, Australian Bureau of Meteorology, and Paul Gregory, BOM, Australian Bureau of Meteorology

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

How rising temperatures affect our health



The first half of 2019 is the equal hottest on record and summer is set to be a scorcher.
Chayathorn Lertpanyaroj/Shutterstock

Liz Hanna, Australian National University

This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.

Global warming is accelerating, driven by the continuing rise in greenhouse gas emissions. Australia’s climate has warmed by just over 1°C since 1910, with global temperatures on course for a 3-5°C rise this century.

Australia is ahead of the global temperature curve. Our average daily temperature is 21.8°C – that’s 13.7°C warmer than the global average of 8.1°C.

Heat extremes (days above 35°C and nights above 20°C) are now more frequent in Australia, occurring around 12% of the time compared to around 2% of the time between 1951 and 1980.

So what do high temperatures do to our bodies? And how much extra heat can people and our way of living tolerate?

More scorchers ahead

Australia’s summer of 2018-19 was 2.14°C warmer than the 1961–90 average, breaking the previous record set in 2012–13 by a large margin. It included an unprecedented sequence of five consecutive days with nationally averaged maximum temperatures above 40°C.




Read more:
The reality of living with 50℃ temperatures in our major cities


The first half of 2019 ranks as the equal second hottest since records began for the world, and also Australia.

The Bureau of Meteorology (BOM) has warned this summer will be another scorcher. Hot dry northerly winds tracking across drought-affected New South Wales and Queensland have the capacity to deliver blistering heat and extreme fire risks to the southern states, and little relief is in sight for those in drought.

Some rural Australians have already been exposed to 50°C days, and the major southern metro cities are set to do the same within the next decade or so.

How our bodies regulate heat

Like most mammals and birds, humans are endotherms (warm-blooded), meaning our optimal internal operating temperature (approximately 36.8°C +/− 0.5) is minimally influenced by ambient temperatures.

Quietly sitting indoors with the air temperature about 22°C, we passively generate that additional 15°C to keep our core temperature at about 37°C.

Even when the air temperature is 37°C, our metabolism continues to generate additional heat. This excess internal heat is shed into the environment through the evaporation of sweat from our skin.

Our optimal internal body temperature is 36.8°C.
Slaohome/Shutterstock

Temperature and humidity gradients between the skin surface and boundary layer of air determine the rate of heat exchange.

When the surrounding air is hot and humid, heat loss is slow, we store heat, and our temperatures rises.

That’s why hot, dry air is better tolerated than tropical, humid heat: dry air readily absorbs sweat.

A breeze appears refreshing by dislodging the boundary layer of saturated air in contact with the skin and allowing in drier air – thus speeding up evaporation and heat shedding.

What happens when we overheat?

Heat exposure becomes potentially lethal when the human body cannot lose sufficient heat to maintain a safe core temperature.

When our core temperature reaches 38.5°C, most would feel fatigued. And the cascade of symptoms escalate as the core temperature continues to rise beyond the safe functioning range for our critical organs: the heart, brain and kidneys.

Much like an egg in a microwave, protein within our body changes when exposed to heat.




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While some heat-acclimatised elite athletes, such as Tour de France cyclists, may tolerate 40°C for limited periods, this temperature is potentially lethal for most people.

As a pump, the heart’s role is to maintain an effective blood pressure. It fills the hot and dilated blood vessels throughout the body to get blood to vital organs.

Exposure to extreme heat places significant additional workload on the heart. It must increase the force of each contraction and the rate of contractions per minute (your heart rate).

If muscles are also working, they also need an increased blood flow.

If all this occurs at a time when profuse sweating has led to dehydration, and therefore lower blood volume, the heart must massively increase its work.

Dry air readily absorbs sweat, whereas humid air doesn’t, making it less tolerable.
Cliplab/Shutterstock

The heart is also a muscle, so it too needs extra blood supply when working hard. But when pumping hard and fast and its own demand for blood flow is not matched by its supply, it can fail. Many heat deaths are recorded as heart attacks.

High aerobic fitness levels offer some heat protection, yet athletes and fit young adults pushing themselves too hard also die in the heat.

Who is more at risk?

Older Australians are more vulnerable to heat stress. Age is commonly associated with poorer aerobic fitness and impaired ability to detect thirst and overheating.




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Obesity also increases this vulnerability. Fat acts as an insulating layer, as well as giving the heart a more extensive network of blood vessels to fill. The additional weight requires increased heat-generating muscular effort to move.

Certain medications can lower heat tolerance by interfering with our natural mechanisms necessary to cope with the heat. These include drugs that limit increases in heart rate, lower blood pressure by relaxing blood vessels, or interfere with sweating.

Core temperatures are increased by about half a degree during late stage pregnancy due to hormonal responses and increased metabolic rate. The growing foetus and placenta also demand additional blood flow. Exposure of the fetus to heat extremes can precipitate preterm birth and life-long health problems such as congential heart defects.

Won’t we just acclimatise?

Our bodies can acclimatise to hot temperatures, but this process has its limits. Some temperatures are simply too hot for the heart to cope with and for sweat rates to provide effective cooling, especially if we need to move or exercise.

We’re also limited by our kidneys’ capacity to conserve water and electrolytes, and the upper limit to the amount of water the human gut can absorb.

Profuse sweating leads to fluid and electrolyte deficits and the resulting electrolyte imbalance can interfere with the heart rhythm.

Mass death events are now occurring during heat waves in traditionally hot countries such as India and Pakistan. This is when heat extremes approaching 50°C exceed the human body’s capacity to maintain its safe core temperature range.




Read more:
Could we acclimatise to the hotter summers to come?


Heatwaves are hotter, more frequent and lasting longer. We can’t live life entirely indoors with air conditioning as we need to venture outdoors to commute, work, shop, and care for the vulnerable. People, animals and our social systems depend on this.

Besides, on a 50°C day, air conditioning units will struggle to remove 25°C from the ambient air.The Conversation

Liz Hanna, Honorary Senior Fellow, Australian National University

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

Why hot weather records continue to tumble worldwide


Andrew King, University of Melbourne

It sometimes feels like we get a lot of “record-breaking” weather. Whether it’s a heatwave in Europe or the “Angry Summer” in Australia, the past few years have seen temperature records tumble.

This is the case both locally – Sydney had its hottest year on record in 2016 – and globally, with the world’s hottest year in 2016 beating the record set only the year before.

Some of 2016’s heat was due to the strong El Niño. But much of it can be linked to climate change too.

We’re seeing more heat records and fewer cold records. In Australia there have been 12 times as many hot records as cold ones in the first 15 years of this century.

If we were living in a world without climate change, we would expect temperature records to be broken less often as the observational record grows longer. After all, if you only have five previous observations for annual temperatures then a record year isn’t too surprising, but after 100 years a new record is more notable.

In contrast, what we are seeing in the real world is more hot temperature records over time, rather than less. So if you think we’re seeing more record-breaking weather than we should, you’re right.

Why it’s happening

In my new open-access study published in the journal Earth’s Future, I outline a method for evaluating changes in the rate at which temperature records are being broken. I also use it to quantify the role of the human influence in this change.

To do it, I used climate models that represent the past and current climate with both human influences (greenhouse gas and aerosol emissions) and natural influences (solar and volcanic effects). I then compared these with models containing natural influences only.

Lots of hot records, fewer cold ones

Taking the example of global annual temperature records, we see far more record hot years in the models that include the human influences on the climate than in the ones without.

Crucially, only the models that include human influences can recreate the pattern of hot temperature records that were observed in reality over the past century or so.

Observed and model-simulated numbers of hot and cold global annual temperature records for 1861-2005. Observed numbers of record occurrences are shown as black circles with the model-simulated record numbers under human and natural influences (red box and whiskers) and natural influences only (orange box and whiskers) also shown. The central lines in the boxes represent the median; the boxes represent interquartile range.
Author provided

In contrast, when we look at cold records we don’t see the same difference. This is mainly because cold records were more likely to be broken early in the temperature series when there were fewer previous data. The earliest weather data comes from the late 19th century, when there was only a weak human effect on the climate relative to today. This means that there is less difference between my two groups of models.

In the models that include human influences on the climate, we see an increase in the number of global record hot years from the late 20th century onwards, whereas this increase isn’t seen in the model simulations without human influences. Major volcanic eruptions reduce the likelihood of record hot years globally in both groups of model simulations.

Projecting forward to 2100 under continued high greenhouse gas emissions, we see the chance of new global records continuing to rise, so that one in every two years, on average, would be a record-breaker.

Chance of record hot global annual temperatures in climate models with human and natural influences (red) and natural influences only (orange). Grey curve shows the statistical likelihood of a new hot record each year (100% in the first year, 50% in the second year, 33% in the third year, and so on). Grey vertical bars show the timing of major volcanic eruptions through the late-19th and 20th centuries.
Author provided

I also looked at specific events and how much climate change has increased the likelihood of a record being broken.

I used the examples of the record hot years of 2016 globally and 2014 in Central England. Both records were preceded by well over a century of temperature observations, so in a non-changing climate we would expect the chance of a record-breaking year to be less than 1%.

Instead, I found that the chance of setting a new record was increased by at least a factor of 30 relative to a stationary climate, for each of these records. This increased likelihood of record-breaking can be attributed to the human influence on the climate.

More records to come?

The fact that we’re setting so many new hot records, despite our lengthening observation record, is an indicator of climate change and it should be a concern to all of us.

The ConversationThe increased rate at which we are getting record hot temperatures is controlled by the speed of global warming, among other factors. To meet the Paris target of keeping global warming below 2℃ we will have to reduce our greenhouse gas emissions drastically. Besides keeping average global temperatures under control, this would also reduce the chance of temperature records continuing to tumble, both globally and locally.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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

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


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

Andrew King, University of Melbourne

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

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


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


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

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

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

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

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

Climate change and record warmth

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

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

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

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

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

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

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

More winter warmth to come

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

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

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

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

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


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

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

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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

Climate change to blame for Australia’s July heat


Andrew King, University of Melbourne

Winter hasn’t felt too wintry yet in much of Australia. Most of us have have had more sunshine, higher temperatures, and less rainfall than is normal for the time of year. In fact, Australia just had its warmest average daytime maximum temperatures for July since records began in 1910.

This July saw the warmest average maximum temperatures on record across Australia.
Bureau of Meteorology

The north and centre of the continent saw the biggest temperature anomalies as Western Australia, the Northern Territory and Queensland experienced record warm daytime July temperatures. Only the southwestern tip of Western Australia and western Tasmania had slightly below-average daytime temperatures.

Southern Australia was again very dry as the frontal systems that usually bring rain remained further south than usual.


Read more: Winter heatwaves are nice … as extreme weather events go.


For most of us, warm and dry winter conditions are quite pleasant. But with drought starting to rear its head and a severe bushfire season on the cards, some cooler wetter weather would be helpful to farmers and fire services across the country.

What caused the unusual warmth?

Often when we have warmer winter weather in Australia it is linked to El Niño conditions in the Pacific or a positive Indian Ocean Dipole. Both of these Pacific and Indian Ocean patterns tend to shift atmospheric pressure patterns in a way that brings more stable conditions and warmer, drier weather to Australia.

This year, however, neither El Niño nor the Indian Ocean Dipole is playing a role in the warm weather. The sea surface temperature patterns in the Pacific and Indian Oceans are close to average, so neither of these factors is driving Australia’s record warmth.

A clear human fingerprint

Another factor that might have influenced the July heat is human-caused climate change.

To assess the role of climate change in this event, I used climate model simulations and a standard event-attribution method. I first evaluated the climate models to gauge how well they capture the observed temperatures over Australia during July. I then computed the likelihood of unusually warm July average maximum temperatures across Australia in two groups of climate model simulations: one representing the world of today, and another representing a world without human influences on the climate.

I found a very clear signal that human-induced climate change has increased the likelihood of warm July temperatures such as the ones we’ve just experienced. My results suggest that climate change increased the chances of this record July warmth by at least a factor of 12.

July heat is on the rise

I also wanted to know if this kind of unusual July warmth over Australia will become more common in future.

I looked at climate model projections for the next century, and examined the chances of these warm conditions occurring in periods when global warming is at 1.5℃ and 2℃ above pre-industrial levels (we have had roughly 1℃ of global warming above these levels so far).

The 1.5℃ and 2℃ global warming targets were decided in the Paris Agreement, brokered in December 2015. Given that we are aiming to limit global warming to these levels it is vital that we have a good idea of the climate we’re likely to be living in at these levels of warming.

I found that even if we manage to limit global warming to 1.5℃ we can expect to experience such July heat (which is record-breaking by today’s standards) in about 28% of winters. At 2℃ of global warming, the chances of warm July temperatures like 2017 are 43% for any given year.

More Julys like this are on the way as the globe heats up.
Andrew King, Author provided

The ConversationGiven the benefits of fewer and less intense heat extremes over Australia at lower levels of global warming, there is a clear incentive to try and limit climate change as much as possible. If we can reduce our greenhouse gas emissions and hold global warming to the Paris target levels, we should be able to avoid the kind of unusual warmth we have seen this July becoming the new normal.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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