Climate Dynamics and the Decline of Elephants and Their Precursors

Elephants and their forebears were pushed into wipeout by waves of extreme global environmental change, rather than overhunting by early humans, according to new research.

The study, published in Nature Ecology & Evolution, challenges claims that early human hunters slaughtered prehistoric elephants, mammoths and mastodonts to extinction over millennia. Instead, its findings indicate the extinction of the last mammoths and mastodonts at the end of the last Ice Age marked the end of progressive climate-driven global decline among elephants over millions of years.

Although elephants today are restricted to just three endangered species in the African and Asian tropics, these are survivors of a once far more diverse and widespread group of giant herbivores, known as the proboscideans, which also include the now completely extinct mastodonts, stegodonts and deinotheres. Only 700,000 years ago, England was home to three types of elephants: two giant species of mammoths and the equally prodigious straight-tusked elephant.

An international group of palaeontologists from the universities of Alcalá, Bristol, and Helsinki, piloted the most detailed analysis to date on the rise and fall of elephants and their predecessors, which examined how 185 different species adapted, spanning 60 million years of evolution that began in North Africa. To probe into this rich evolutionary history, the team surveyed museum fossil collections across the globe, from London’s Natural History Museum to Moscow’s Paleontological Institute. By investigating traits such as body size, skull shape and the chewing surface of their teeth, the team discovered that all proboscideans fell within one of eight sets of adaptive strategies.

“Remarkably for 30 million years, the entire first half of proboscidean evolution, only two of the eight groups evolved,” said Dr Zhang Hanwen, study coauthor and Honorary Research Associate at the University of Bristol’s School of Earth Sciences.

“Most proboscideans over this time were nondescript herbivores ranging from the size of a pug to that of a boar. A few species got as big as a hippo, yet these lineages were evolutionary dead-ends. They all bore little resemblance to elephants.”

The course of proboscidean evolution changed dramatically some 20 million years ago, as the Afro-Arabian plate collided into the Eurasian continent. Arabia provided crucial migration corridor for the diversifying mastodont-grade species to explore new habitats in Eurasia, and then into North America via the Bering Land Bridge.

“The immediate impact of proboscidean dispersals beyond Africa was quantified for the very first time in our study,” said lead author Dr Juan Cantalapiedra, Senior Research Fellow at the University of Alcalá in Spain.

“Those archaic North African species were slow-evolving with little diversification, yet we calculated that once out of Africa proboscideans evolved 25 times faster, giving rise to a myriad of disparate forms, whose specialisations permitted niche partition between several proboscidean species in the same habitats. One case in point being the massive, flattened lower tusks of the ‘shovel-tuskers’. Such coexistence of giant herbivores was unlike anything in today’s ecosystems.”

By 3 million years ago the elephants and stegodonts of Africa and eastern Asia seemingly emerged victorious in this unremitting evolutionary ratchet. However, environmental disruption connected to the coming Ice Ages hit them hard, with surviving species forced to adapt to the new, more austere habitats. The most extreme example was the woolly mammoth, with thick, shaggy hair and big tusks for retrieving vegetation covered under thick snow.

The team’s analyses identified final proboscidean extinction peaks starting at around 2.4 million years ago, 160,000 and 75,000 years ago for Africa, Eurasia and the Americas, respectively.

“It is important to note that these ages do not demarcate the precise timing of extinctions, but rather indicate the points in time at which proboscideans on the respective continents became subject to higher extinction risk,” said Dr Cantalapiedra.

Unexpectedly, the results do not correlate with the expansion of early humans and their enhanced capabilities to hunt down megaherbivores.

Sources: University of Bristol

Pine Island Glacier Reaching Tipping Point

Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level.

Pine Island Glacier is a region of fast-flowing ice draining an area of West Antarctica approximately two thirds the size of the UK. The glacier is a particular cause for concern as it is losing more ice than any other glacier in Antarctica.

Currently, Pine Island Glacier together with its neighbouring Thwaites glacier are responsible for about 10% of the ongoing increase in global sea level.

Scientists have argued for some time that this region of Antarctica could reach a tipping point and undergo an irreversible retreat from which it could not recover. Such a retreat, once started, could lead to the collapse of the entire West Antarctic Ice Sheet, which contains enough ice to raise global sea level by over three metres.

While the general possibility of such a tipping point within ice sheets has been raised before, showing that Pine Island Glacier has the potential to enter unstable retreat is a very different question.

Now, researchers from Northumbria University have shown, for the first time, that this is indeed the case.

Their findings are published in leading journal, The Cryosphere.

Using a state-of-the-art ice flow model developed by Northumbria’s glaciology research group, the team have developed methods that allow tipping points within ice sheets to be identified.

For Pine Island Glacier, their study shows that the glacier has at least three distinct tipping points. The third and final event, triggered by ocean temperatures increasing by 1.2C, leads to an irreversible retreat of the entire glacier.

Sources: Phys.org

Arctic Permafrost Releases More Carbon Dioxide Than Once Believed

Rising global temperatures are causing frozen Arctic soil— permafrost—in the northern hemisphere to thaw and release CO2 that has been stored within it for thousands of years. The amount of carbon stored in permafrost is estimated to be four times greater than the combined amount of CO2 emitted by modern humans.

Research results from an international team, which includes a researcher from the University of Copenhagen among others, suggests that the newly discovered phenomenon will release even larger quantities of CO2 than once supposed from organic matter in permafrost—a pool of carbon previously thought to be bound tightly and safely sequestered by iron.

The amount of stored carbon that is bound to iron and gets converted to CO2 when released is estimated to be somewhere between two and five times the amount of carbon released annually through anthropogenic fossil fuel emissions.

Iron doesn’t bind organic carbon after all

Researchers have long been aware that microorganisms play a key role in the release of CO2 as permafrost melts. Microorganisms activated as soil thaws convert dead plants and other organic material into greenhouse gases like methane, nitrous oxide and carbon dioxide.

What is new, is that the mineral iron was believed to bind carbon even as permafrost thawed. The new result demonstrates that bacteria incapacitate iron’s carbon trapping ability, resulting in the release of vast amounts of CO2. This is an entirely new discovery.

“What we see is that bacteria simply use iron minerals as a food source. As they feed, the bonds which had trapped carbon are destroyed and it is released into the atmosphere as greenhouse gas,” explains Associate Professor Carsten W. Müller of the University of Copenhagen’s Department of Geosciences and Natural Resource Management. He elaborates:

“Frozen soil has a high oxygen content, which keeps iron minerals stable and allows carbon to bind to them. But as soon as the ice melts and turns to water, oxygen levels drop and the iron becomes unstable. At the same time, the melted ice permits access to bacteria. As a whole, this is what releases stored carbon as CO2,” explains Müller.

The study has just been published in Nature Communications.

Absent from climate models

Although the researchers have only studied a single bog area in Abisko, northern Sweden, they have compared their results with data from other parts the northern hemisphere and expect their new results to also be valid in other areas of permafrost worldwide.

“This means that we have a large new source of CO2 emissions that needs to be included in climate models and more closely examined,” says Carsten W. Müller.

Even though carbon stored in permafrost has a major impact on our climate, researchers know very little about the mechanisms that determine whether carbon in soil is converted into greenhouse gases.

“The majority of climate research in the Arctic focuses on the amount of stored carbon and how sensitive it is to climate change. There is a great deal less of a focus on the deeper mechanisms which trap carbon in soil,” says Carsten W. Müller.

Researchers remain uncertain about how much extra carbon from soil could potentially be released through this newly discovered mechanism. Closer investigation is needed.

Source: University of Copenhagen

Green New Deal Polling

Green New Deal Polling:

Green New Deal Very General Summary: The proposal would achieve net-zero greenhouse-gas emissions by creating millions of green jobs and investing in a new, clean-energy infrastructure.

Research shows that age strongly predicts support for the Green New Deal, even controlling for several variables like party, ideology, and race. One wonders if this is because young people, unlike older generations, must contemplate living through the worst effects of climate change a few decades down the line.

Polling Question: “Would you support or oppose a Green New Deal to end fossil fuel use in the United States and have the government create clean energy jobs? The plan would be paid for by raising taxes, including a tax on carbon emissions.”

Reference: Millennials as ages 18–37, Generation X as 38–53, baby boomers as 54–72, and Silent as 72 or older.

Note: “Data For Progress” who conducted the poll is a progressive think tank.

#GreenNewDeal #ClimateChange