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.

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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.

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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.

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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.

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.

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A rare natural phenomenon brings severe drought to Australia. Climate change is making it more common

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Nicky Wright, Australian National University; Bethany Ellis, Australian National University, and Nerilie Abram, Australian National University

Weather-wise, 2019 was a crazy way to end a decade. Fires spread through much of southeast Australia, fuelled by dry vegetation from the ongoing drought and fanned by hot, windy fire weather.

On the other side of the Indian Ocean, torrential rainfall and flooding devastated parts of eastern Africa. Communities there now face a locust plague and food shortages.

These intense events can partly be blamed on the extreme positive Indian Ocean Dipole, a climate phenomenon that unfolded in the second half of 2019.

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The Indian Ocean Dipole refers to the difference in sea surface temperature on either side of the Indian Ocean, which alters rainfall patterns in Australia and other nations in the region. The dipole is a lesser-known relative of the Pacific Ocean’s El Niño.

Climate drivers, such as the Indian Ocean Dipole, are an entirely natural phenomenon, but climate change is modifying the behaviour of these climate modes.

In research published today in Nature, we reconstructed Indian Ocean Dipole variability over the last millennium. We found “extreme positive” Indian Ocean Dipole events like last year’s are historically very rare, but becoming more common due to human-caused climate change. This is big news for a planet already struggling to contain global warming.

So what does this new side-effect of climate change mean for the future?

The Indian Ocean brings drought and flooding rain

First, let’s explore what a “positive” and “negative” Indian Ocean Dipole means.

During a “positive” Indian Ocean Dipole event, waters in the eastern Indian Ocean become cooler than normal, while waters in the western Indian Ocean become warmer than normal.

Warmer water causes rising warm, moist air, bringing intense rainfall and flooding to east Africa. At the same time, atmospheric moisture is reduced over the cool waters of the eastern Indian Ocean. This turns off one of Australia’s important rainfall sources.

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In fact, over the past century, positive Indian Ocean Dipoles have led to the worst droughts and bushfires in southeast Australia.

The Indian Ocean Dipole also has a negative phase, which is important to bring drought-breaking rain to Australia. But the positive phase is much stronger and has more intense climate impacts.

We’ve experienced extreme positive Indian Ocean Dipole events before. Reliable instrumental records of the phenomenon began in 1958, and since then a string of very strong positive Indian Ocean Dipoles have occurred in 1961, 1994, 1997 and now 2019.

The Dipole Mode Index is used to track variability of the Indian Ocean Dipole.
Author provided

But this instrumental record is very short, and it’s tainted by the external influence of climate change.

This means it’s impossible to tell from instrumental records alone how extreme Indian Ocean Dipoles can be, and whether human-caused climate change is influencing the phenomenon.

Diving into the past with corals

To uncover just how the Indian Ocean Dipole has changed, we looked back through the last millennium using natural records: “cores” taken from nine coral skeletons (one modern, eight fossilised).

These coral samples were collected just off of Sumatra, Indonesia, so they’re perfectly located for us to reconstruct the distinct ocean cooling that characterises positive Indian Ocean Dipole events.

Scientists drilling into corals to study past climate. Corals are like trees, and grow a band for every year they live.
Jason Turl, Author provided

Corals grow a lot like trees. For every year they live they produce a growth band, and individual corals can live for more than 100 years. Measuring the oxygen in these growth bands gives us a detailed history of the water temperature the coral grew in, and the amount of rainfall over the reef.

In other words, the signature of extreme events like past positive Indian Ocean Dipoles is written in the coral skeleton.

Altogether, our coral-based reconstruction of the Indian Ocean Dipole spans 500 years between 1240 and 2019. There are gaps in the timeline, but we have the best picture so far of how exactly the Indian Ocean Dipole has varied in the past.

How unusual was the 2019 Indian Ocean Dipole event?

Extreme events like the 2019 Indian Ocean Dipole have historically been very rare.

We found only ten extreme positive Indian Ocean Dipole events in the entire record. Four occurred in the past 60 years, but only six occurred in the remaining 440 years before then. This adds more weight to evidence that positive Indian Ocean Dipole events have been occurring more often in recent decades, and becoming more intense.

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But another finding from the reconstruction surprised – and worried – us. Events like 2019 aren’t the worst of what the Indian Ocean Dipole can throw at us.

Of the extreme events we found in our reconstruction, one of them, in 1675, was much stronger than anything we’ve seen in observations from the last 60 years.

The 1675 event was around 30–40% stronger than what we saw in 1997 (around the same magnitude as 2019). Historical accounts from Asia show this event was disastrous, and the severe drought it caused led to crop failures, widespread famine and mortality, and incited war.

The wiggles that make up 500 years of reconstructed Indian Ocean Dipole variability. The red triangles show when extreme positive events occurred.
Author provided

As far as we can tell, this event shows just how extreme Indian Ocean Dipole variability can be, even without any additional prompting from external forces like human-caused climate change.

Why should we care?

Indian Ocean Dipole variability will continue to episodically bring extreme climate conditions to our region.

Drilling through fossilised coral layers to look into the past.
Nerilie Abram, Author provided

But previous studies, as well as ours, have shown human-caused climate change has shortened the gaps between these episodes, and this trend will continue. This is because climate change is causing the western side of the Indian Ocean to warm faster than in the east, making it easier for positive Indian Ocean Dipole events to establish.

In other words, drought-causing positive Indian Ocean Dipole events will become more frequent as our climate continues to warm.

In fact, climate model projections indicate extreme positive Indian Ocean Dipole events will occur three times more often this century than last, if high greenhouse gas emissions continue.

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This means events like last year will almost certainly unfold again soon, and we’re upping the odds of even worse events that, through the fossil coral data, we now know are possible.

Knowing we haven’t yet seen the worst of the Indian Ocean Dipole is important in planning for future climate risks. Future extremes from the Indian Ocean will act on top of long-term warming, giving a double-whammy effect to their impacts in Australia, like the record-breaking heat and drought of 2019.

But perhaps most importantly, rapidly cutting greenhouse gas emissions will limit how often positive Indian Ocean Dipole events occur in future.

Nicky Wright, Research Fellow, Australian National University; Bethany Ellis, PhD Candidate, Australian National University, and Nerilie Abram, Professor; ARC Future Fellow; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University

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