Southeast Europe swelters through another heatwave with a human fingerprint



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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.


The ConversationYou 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.

Another attack on the Bureau, but top politicians have stopped listening to climate change denial


Michael J. I. Brown, Monash University

Has the Australian climate change debate changed? You could be forgiven for thinking the answer is no.

Just this week The Australian has run a series of articles attacking the Bureau of Meteorology’s weather observations. Meanwhile, the federal and Queensland governments continue to promote Adani’s planned coal mine, despite considerable environmental and economic obstacles. And Australia’s carbon dioxide emissions are rising again.

So far, so familiar. But something has changed.

Those at the top of Australian politics are no longer debating the existence of climate change and its causes. Instead, four years after the Coalition was first elected, the big political issues are rising power prices and the electricity market. What’s happening?


Read more: No, the Bureau of Meteorology is not fiddling its weather data.


A few years ago, rejection of climate science was part of the Australian political mainstream. In 2013, the then prime minister Tony Abbott repeated a common but flawed climate change denial argument:

Australia has had fires and floods since the beginning of time. We’ve had much bigger floods and fires than the ones we’ve recently experienced. You can hardly say they were the result of anthropic [sic] global warming.

Abbott’s statement dodges a key issue. While fires and floods have always occurred, climate change can still alter their frequency and severity. In 2013, government politicians and advisers, such as Dennis Jensen and Maurice Newman, weren’t shy about rejecting climate science either.

The atmosphere is different in 2017, and I’m not just talking about CO₂ levels. Tony Abbott is no longer prime minister, Dennis Jensen lost preselection and his seat, and Maurice Newman is no longer the prime minister’s business advisor.

Which Australian politician most vocally rejects climate science now? It isn’t the prime minister or members of the Coalition, but One Nation’s Malcolm Roberts. In Australia, open rejection of human-induced climate change has moved to the political fringe.

Roberts has declared climate change to be a “fraud” and a “scam”, and talked about climate records being “manipulated by NASA”. He is very much a conspiracy theorist on climate, as he is on other topics including banks, John F. Kennedy, and citizenship. His approach to evidence is frequently at odds with mainstream thought.

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This conspiratorial approach to climate change is turning up elsewhere too. I was startled by the author list of the Institute of Public Affairs’ new climate change book. Tony Heller (better known in climate circles by the pseudonym Steven Goddard) doesn’t just believe climate change is a “fraud” and a “scam”, but has also promoted conspiracy theories about the Sandy Hook school massacre. This is a country mile from sober science and policy analysis.

So where is the Australian political mainstream? It’s not denying recent climate change and its causes, but instead is now debating the policy responses. This is exemplified by political arguments about the electricity market, power prices, and the Finkel Review.


Read more: What I learned from debating science with trolls


While this is progress, it’s not without serious problems. The debate may have rightly moved on to policy rather than science, but arguments for “clean coal” power are at odds with coal’s high CO₂ emissions and the failure thus far of carbon capture. Even power companies show little interest in new coal-fired power plants to replace those that have closed.

The closure of the Hazelwood power station was politically controversial.
Jeremy Buckingham/flickr

History repeating?

Have those who rejected global warming and its causes changed their tune? In general, no. They still imagine that scientists are up to no good. The Australian’s latest attacks on the Bureau of Meteorology (BoM) illustrate this, especially as they are markedly similar to accusations made in the same newspaper three years ago.

This week, the newspaper’s environment editor Graham Lloyd wrote that the BoM was “caught tampering” with temperature logs, on the basis of measurements of cold temperatures on two July nights at Goulburn and Thredbo. For these nights, discrepant temperatures were in public BoM databases due to automated weather stations that stopped reporting data. The data points were flagged for BoM staff to verify, but in the meantime an amateur meteorologist contacted Lloyd and the Institute of Public Affairs’ Jennifer Marohasy.

In 2014, Lloyd cast doubt on the BoM’s climate record by attacking the process of “homogenisation,” with a particular emphasis on data from weather stations in Rutherglen, Amberley and Bourke. Homogenisation is used to produce a continuous temperature record from measurements that may suffer from artificial discontinuities, such as in the case of weather stations that have been upgraded or moved from, say, a post office to an airport.

The Tuggeranong Automatic Weather Station.
Bidgee/Wikimedia Commons

Lloyd’s articles from this week and 2014 are beat-ups, for similar reasons. The BoM’s ACORN-SAT long-term temperature record is compiled using daily measurements from 112 weather stations. Even Lloyd acknowledges that those 112 stations don’t include Goulburn and Thredbo. While Rutherglen, Amberley and Bourke do contribute to ACORN-SAT, homogenisation of their data (and that of other weather stations) does little to change the warming trend measured across Australia. Australia has warmed over the past century, and The Australian’s campaigns won’t change that.

In 2014, the government responded to The Australian’s campaign by commissioning the Technical Advisory Forum, which has since reviewed ACORN-SAT and found it to be a “well-maintained dataset”. Prime Minister Abbott also considered a taskforce to investigate BoM, but was dissuaded by the then environment minister Greg Hunt.

The ConversationHow will Malcolm Turnbull’s government respond to The Australian’s retread of basically the same campaign? Perhaps that will be the acid test for whether the climate debate really has changed.

Michael J. I. Brown, Associate professor, Monash University

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

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


Andrew King, University of Melbourne

This June was the seventh-warmest and second-driest on record for Australia. Parts of the southwest and southeast saw record dry conditions as frontal systems passed further south than normal and high pressure exerted its influence on the continent.

Australia’s second-driest June on record saw unusually dry conditions over most of the continent but more rain than average for Sydney and northeast New South Wales.
Bureau of Meteorology

While many of us will have enjoyed warm, dry weather, farmers in the south of the country will be concerned at the lack of winter rain for their crops. Winter is the dominant season for rainfall, especially in the southwest of the continent, so a return to wetter conditions would be welcome.

There are already indications of drought developing across the west coast of Western Australia and in other areas of the country.

Did climate change play a role?

To deduce whether climate change had an influence on this particular event, I used two sets of climate model simulations: one representing the world of today and another representing a world without human influences (that is, with pre-industrial greenhouse gas concentrations).

I compared the likelihood and magnitude of dry Junes in the two sets of simulations to determine the net effect of human-caused climate change.

I looked at the climate change influence on very dry Junes (such as the one we’ve just experienced) both for Australia as a whole, and for the southeast, which had its driest June on record. Both of these areas received well below half of their average June rainfall in June 2017.

Southeast Australia had its driest June on record this year.
Bureau of Meteorology

For Australia-wide June rainfall, I found a clear climate change signal towards drier conditions.

According to my analysis, climate change has increased the likelihood of very dry Junes by at least a third. The driest Junes now are about 12% drier than they would be in the absence of human greenhouse emissions.

When I looked at southeast Australia, however, I found that the influence of climate change is less clear.

My analysis suggested that climate change has probably increased the chance of dry conditions, although there is more uncertainty than for Australia as a whole.

That said, the driest Junes appear to be drier in the world of today than they would have been without climate change, by about 8% in the case of southeast Australia.

It’s not surprising that the result for southeast Australia is less distinct. Generally speaking, the smaller the area, the harder it is to detect an influence of climate change, as there is more year-to-year variability.

What can we expect in future?

The Paris Agreement aims to hold global warming well below 2℃ and preferably at around 1.5℃ above pre-industrial average temperatures. For context, we have had a little over 1℃ of global warming so far, so we’re more than two-thirds of the way to the 1.5℃ target already.

Under either a 1.5℃ or 2℃ global warming target, I project that dry Junes in Australia will become more frequent. For the southeast of the continent the picture is less clear, with high uncertainty in the change we might see.

Climate change is increasing the likelihood of dry Junes for Australia as a whole, but the signal is less clear over the southeast. The best estimate likelihoods are shown with 90% confidence intervals in parentheses.
Author provided

The trend towards drier Junes across Australia is related to the southward shift in the storm track, the prevailing westerly winds that bring frontal weather systems across southern Australia. June 2017 is a very clear example of this effect.

Scientists use the Southern Annular Mode (SAM) to describe the position of the storm track. It has been trending towards more “positive” conditions, reflecting a poleward movement in the frontal systems which typically causes them to pass to the south of the Australian landmass.

These positive SAM phases bring drier conditions to most of Australia, but wetter conditions to coastal New South Wales. This is precisely what we have seen in June 2017.

As the effects of climate change intensify in the coming years, scientists expect to see the frontal systems that bring vital rainfall to the south of Australia moving further and further south. This increases the chance of Australia experiencing more dry Junes like the one just passed. Increasing temperatures will cause greater evaporation when there is rainfall, further exacerbating drought conditions.


The ConversationYou can find full details of the methods used in this analysis here.

Andrew King, Climate Extremes Research Fellow, University of Melbourne

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

Why the climate is more sensitive to carbon dioxide than weather records suggest



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A new paper improves our estimate of the climate’s sensitivity to carbon dioxide.
NASA/Wikimedia Commons

Andrew Glikson, Australian National University

One of the key questions about climate change is the strength of the greenhouse effect. In scientific terms this is described as “climate sensitivity”. It’s defined as the amount Earth’s average temperature will ultimately rise in response to a doubling of atmospheric carbon dioxide levels.

Climate sensitivity has been hard to pin down accurately. Climate models give a range of 1.5-4.5℃ per doubling of CO₂, whereas historical weather observations suggest a smaller range of 1.5-3.0℃ per doubling of CO₂.

In a new study published in Science Advances, Cristian Proistosescu and Peter J. Huybers of Harvard University resolve this discrepancy, by showing that the models are likely to be right.

According to their statistical analysis, historical weather observations reveal only a portion of the planet’s full response to rising CO₂ levels. The true climate sensitivity will only become manifest on a time scale of centuries, due to effects that researchers call “slow climate feedbacks”.

Fast and slow

To understand this, it is important to know precisely what we mean when we talk about climate sensitivity. So-called “equilibrium climate sensitivity”, or slow climate feedbacks, refers to the ultimate consequence of climate response – in other words, the final effects and environmental consequences that a given greenhouse gas concentration will deliver.

These can include long-term climate feedback processes such as ice sheet disintegration with consequent changes in Earth’s surface reflection (albedo), changes to vegetation patterns, and the release of greenhouse gases such as methane from soils, tundra or ocean sediments. These processes can take place on time scales of centuries or more. As such they can only be predicted using climate models based on prehistoric data and paleoclimate evidence.

On the other hand, when greenhouse gas forcing rises at a rate as high as 2–3 parts per million (ppm) of CO₂ per year, as is the case during the past decade or so, the rate of slow feedback processes may be accelerated.

Measurements of atmosphere and marine changes made since the Industrial Revolution (when humans first began the mass release of greenhouse gases) capture mainly the direct warming effects of CO₂, as well as short-term feedbacks such as changes to water vapour and clouds.

A study led by climatologist James Hansen concluded that climate sensitivity is about 3℃ for a doubling of CO₂ when considering only short-term feedbacks. However, it’s potentially as high as 6℃ when considering a final equilibrium involving much of the West and East Antarctic ice melting, if and when global greenhouse levels transcend the 500-700ppm CO₂ range.

This illustrates the problem with using historical weather observations to estimate climate sensitivity – it assumes the response will be linear. In fact, there are factors in the future that can push the curve upwards and increase climate variability, including transient reversals that might interrupt long-term warming. Put simply, temperatures have not yet caught up with the rising greenhouse gas levels.

Prehistoric climate records for the Holocene (10,000-250 years ago), the end of the last ice age roughly 11,700 years ago, and earlier periods such as the Eemian (around 115,000-130,000 years ago) suggest equilibrium climate sensitivities as high as 7.1-8.7℃.

So far we have experienced about 1.1℃ of average global warming since the Industrial Revolution. Over this time atmospheric CO₂ levels have risen from 280ppm to 410ppm – and the equivalent of more than 450ppm after factoring in the effects of all the other greenhouse gases besides CO₂.

Estimate of climate forcing for 1750-2000.
Author provided

Crossing the threshold

Climate change is unlikely to proceed in a linear way. Instead, there is a range of potential thresholds, tipping points, and points of no return that can be crossed during either warming or transient short-lived cooling pauses followed by further warming.

The prehistoric records of the cycles between ice ages, namely intervening warmer “interglacial” periods, reveal several such events, such as the big freeze that suddenly took hold about 12,900 years ago, and the abrupt thaw about 8,200 years ago.

In the prehistoric record, sudden freezing events (called “stadial events”) consistently follow peak interglacial temperatures.

Such events could include the collapse of the Atlantic Mid-Ocean Circulation (AMOC), with consequent widespread freezing associated with influx of extensive ice melt from the Greenland and other polar ice sheets. The influx of cold ice-melt water would abort the warm salt-rich AMOC, leading to regional cooling such as is recorded following each temperature peak during previous interglacial periods.

Over the past few years cold water pools south of Greenland have indicated such cooling of the North Atlantic Ocean. The current rate of global warming could potentially trigger the AMOC to collapse.

A collapse of the AMOC, which climate “sceptics” would no doubt welcome as “evidence of global cooling”, would represent a highly disruptive transient event that would damage agriculture, particularly in the Northern Hemisphere. Because of the cumulative build-up of greenhouse gases in the atmosphere such a cool pause is bound to be followed by resumed heating, consistent with IPCC projections.

The growth in the cold water region south of Greenland, heralding a possible collapse of the Atlantic Mid-Ocean Circulation.
Author provided

Humanity’s release of greenhouse gases is unprecedented in speed and scale. But if we look far enough back in time we can get some clues as to what to expect. Around 56 million years ago, Earth experienced warming by 5-8℃ lasting several millennia, after a sudden release of methane-triggered feedbacks that caused the CO₂ level rise to around 1,800ppm.

The ConversationYet even that sudden rise of CO₂ levels was lower by a large factor than the current CO₂ rise rate of 2-3ppm per year. At this rate, unprecedented in Earth’s recorded history of the past 65 million years (with the exception of the consequences of asteroid impacts), the climate may be entering truly uncharted territory.

Andrew Glikson, Earth and paleo-climate scientist, Australian National University

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