Mega-droughts, droughts that last two decades or longer, are tipped to increase, finds a new research.

The finding came after an analysis of geological records from the Eemian Period – 129,000 to 116,000 years ago – which offered a proxy of what we could expect in a hotter, drier world.

The research (Hamish McGowan, Micheline Campbell, John Nikolaus Callow, Andrew Lowry, Henri Wong, Evidence of wet-dry cycles and mega-droughts in the Eemian climate of southeast Australia, Scientific Reports, 2020; 10 (1) DOI: 10.1038/s41598-020-75071-z) was led by scientists from the University of Queensland (UQ).

UQ’s Professor Hamish McGowan said the findings suggested climate change would lead to increased water scarcity, reduced winter snow cover, more frequent bushfires and wind erosion.

The scientists engaged in paleoclimatology, the study of past climates, to see what the world will look like as a result of global warming over the next 20 to 50 years.

“We found that, in the past, a similar amount of warming has been associated with mega-drought conditions all over south eastern Australia,” Professor McGowan said.

Professor McGowan said: “These drier conditions prevailed for centuries, sometimes for more than 1000 years, with El Niño events most likely increasing their severity.”

“The Eemian Period is the most recent in Earth’s history when global temperatures were similar, or possibly slightly warmer than present,” Professor McGowan said.

“The ‘warmth’ of that period was in response to orbital forcing, the effect on climate of slow changes in the tilt of the Earth’s axis and shape of the Earth’s orbit around the sun.

Professor McGowan said: “In modern times, heating is being caused by high concentrations of greenhouse gases, though this period is still a good analogue for our current-to-near-future climate predictions.”

The scientists worked with the New South Wales Parks and Wildlife service to identify stalagmites in the Yarrangobilly Caves in the northern section of Kosciuszko National Park.

Small samples of the calcium carbonate powder contained within the stalagmites were collected, then analyzed and dated at UQ.

That analysis allowed the researchers to identify periods of significantly reduced precipitation during the Eemian Period.

“They’re alarming findings, in a long list of alarming findings that climate scientists have released over the last few decades,” Professor McGowan said.

“We hope that this new research allows for new insights to our future climate and the risks it may bring, such as drought and associated bushfires.

“But, importantly, if humans continue to warm the planet, this is the future we may all be looking at.”

The study report said:

The Eemian or peak of the Last Interglacial is the most recent geologic period when global temperatures were similar to present, but in response to orbital forcing rather than greenhouse gas loading of the atmosphere. While this makes the Eemian an imperfect analogue for near-future climate due to anthropogenic global warming, the latitudinal temperature distribution was similar to the present. Eemian global mean temperature was zero—2 °C warmer than present, mean global sea surface temperatures (SSTs) were indistinguishable from current SSTs, though sea level was around 6–9 m higher from meltwater inflows from the Greenland and Antarctic ice sheets. Therefore, understanding the climate of the Eemian may provide valuable insight to future climate and its variability.

It said:

While often thought of as a period of relative climate stability, climate variability during the Eemian was likely greater than in the Holocene. This has been attributed to meltwater outflows disturbing the Atlantic meridional overturning circulation (AMOC) and a general global cooling trend toward glacial inception. The resulting changes in sea surface salinity and temperature are believed to have driven regional changes in atmospheric circulation leading to periods of widespread aridity across Europe6, and onset of abrupt cold periods as SSTs cooled by several degrees Celsius.

In State of the Planet (Earth Institute, Columbia University), Kevin Krajick wrote on April 16, 2020:

With the western United States and northern Mexico suffering an ever-lengthening string of dry years starting in 2000, scientists have been warning for some time that climate change may be pushing the region toward an extreme long-term drought worse than any in recorded history. A new study says the time has arrived: a megadrought as bad or worse than anything even from known prehistory is very likely in progress, and warming climate is playing a key role. The study, based on modern weather observations, 1,200 years of tree-ring data and dozens of climate models, appears this week in the leading journal Science.

“Earlier studies were largely model projections of the future,” said lead author Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “We’re no longer looking at projections, but at where we are now. We now have enough observations of current drought and tree-ring records of past drought to say that we’re on the same trajectory as the worst prehistoric droughts.”

Reliable modern observations date only to about 1900, but tree rings have allowed scientists to infer yearly soil moisture for centuries before humans began influencing climate. Among other things, previous research has tied catastrophic naturally driven droughts recorded in tree rings to upheavals among indigenous Medieval-era civilizations in the Southwest. The new study is the most up-to-date and comprehensive long-term analysis. It covers an area stretching across nine U.S. states from Oregon and Montana down through California and New Mexico, and part of northern Mexico.

Using rings from many thousands of trees, the researchers charted dozens of droughts across the region, starting in 800 AD. Four stand out as so-called megadroughts, with extreme aridity lasting decades: the late 800s, mid-1100s, the 1200s, and the late 1500s. After 1600, there were other droughts, but none on this scale. (“Climate-Driven Megadrought Is Emerging in Western U.S., Says Study”).


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