Evidence suggests more mega-droughts are coming

Mega-droughts—droughts that last two decades or longer—are tipped to increase thanks to climate change, according to University of Queensland-led research.

Credit: University of Queensland

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 revelation 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.

"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. "These drier conditions prevailed for centuries, sometimes for more than 1000 years, with El Nino events most likely increasing their severity."

The team 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.

"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. In modern times, heating is being caused by high concentrations of greenhouse gasses, though this period is still a good analog for our current-to-near-future climate predictions."

Researchers 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 team 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 was published in Scientific Reports.

Source: University of Queensland [October 30, 2020]

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Habitat loss is bad news for species – especially for top predators

Scientists at Linkoping University, Sweden, have simulated what happens in ecosystems when the habitats of different species disappear. When plants and animals lose their habitats, predator species at the top of the food chain die out first. The results have been published in Ecology Letters, and may provide information for and strengthen initiatives to preserve biodiversity.

Credit: Nagel Photography/Shutterstock

One of the most serious threats against biodiversity is habitat loss. Humans cause severe changes in the landscapes when converting or removing natural land to be used for construction or food production. In addition, climate change is also causing some regions to become uninhabitable for some species. Researchers at Linkoping University have developed a mathematical method to investigate how large ecosystems are affected when habitat disappears.

"We can reach two important conclusions from our study. The first is that initiatives to preserve biological diversity must preserve habitat and not only focus on a particular species. It is very important to consider the interactions between the ecosystem's species by looking at the food web—which animals and plants are eaten by which other animals. The second conclusion is that the order in which habitats disappear has a profound significance," says Anna Eklof, senior lecturer in the Department of Physics, Chemistry and Biology (IFM) at Linkoping University.

The LiU researchers use modeling and computer simulations to study ecological networks, which describe how the various species in an ecosystem interact. The article, published in Ecology Letters, combines two mathematical models: a classical and a new one. The model described in the article distinguishes between suitable habitats in which species can live, and other areas in which they cannot. Suitable habitat patches are distributed across the landscape, with different plant and animal species spread across them. The species are connected to each other in a food web, a network that describes how they feed on each other. A hare eats several types of plants, the hare and several other prey species can become food for foxes, and the fox is one of the predators at the top of the food web.

The survival of an animal in a particular habitat depends on having the correct prey animals or plants in the same habitat patch. The model developed by the researchers also considers how effectively species can move between the habitat patches. In the real world, the habitat patches are often separated by inhospitable regions, such as a road with heavy traffic, that can prevent plants and animals from moving between them. If dispersal between different habitat patches becomes more difficult, probability increases that a species becomes extinct in the ecological network—which in turn influences the survival of other species.

 

The researchers have used the model to analyze a large number of simulated networks involving several hundreds of species. They also tested the model on a dataset of measurements describing the food web of the Serengeti National Park in Tanzania. In order to investigate how ecosystems are affected by habitat loss, the researchers ranked the habitat patches in order of how important they are for species at the bottom of the food chain. They then simulated three different ways in which habitat loss can occur: with the least important habitat patches removed first, the most important ones first, or removing them in a random order. The destruction of habitat in a random order is similar to what happens when humans construct roads or buildings without considering how valuable the region is for different species.

"In our model, the species at the upper levels of the food chain die out first when habitat patches are lost. What surprised us was that the damage to the ecosystem was almost the same when patches were lost in a random order as when the most valuable patches were lost first," says research fellow Gyorgy Barabas.

The researchers emphasize that it is important to classify how significant various habitats patches are when considering initiatives to preserve ecosystems, and to give priority to the most valuable ones. The resilience of the ecosystem to species extinctions can also be improved by, for example, strengthening connections between patches. By taking such matters into consideration when determining how land is used, humans can protect ecosystems and prevent species from becoming extinct—particularly species that are high up in the food chain.

Author: Karin Soderlund Leifler | Source: Linkoping University [October 28, 2020]

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Leaving more big fish in the sea reduces CO2 emissions

An international team of scientists has found leaving more big fish in the sea reduces the amount of carbon dioxide (CO2) released into the Earth's atmosphere.

Leaving more big fish in the sea--especially where fishing is not economically profitable in the
Central Pacific, South Atlantic, and North Indian Oceans --reduces the amount of
carbon dioxide (CO2) released into the Earth's atmosphere [Credit: Enric Sala]

When a fish dies in the ocean it sinks to the depths, sequestrating all the carbon it contains with it. This is a form of 'blue carbon'--carbon captured and stored by the world's ocean and coastal ecosystems.

"But when a fish is caught, the carbon it contains is partly emitted into the atmosphere as CO2 a few days or weeks after," said Gael Mariani, a PhD student at the University of Montpellier in France.

Mr Mariani led a world-first study showing how ocean fisheries have released at least 730 million metric tons of CO2 into the atmosphere since 1950. An estimated 20.4 million metric tons of CO2 was emitted in 2014--equivalent to the annual emissions of 4.5 million cars.

Co-author Professor David Mouillot from the ARC Centre of Excellence for Coral Reef Studies at James Cook University (CoralCoE at JCU) and the University of Montpellier said the carbon footprint of fisheries is 25 percent higher than previous industry estimates.

"Fishing boats produce greenhouse gases by consuming fuel," Prof Mouillot said. "And now we know that extracting fish releases additional CO2 that would otherwise remain captive in the ocean."

Large fish such as tuna, sharks, mackerel and swordfish are about 10 to 15 percent carbon.

"When these fish die, they sink rapidly," Prof Mouillot said. "As a result, most of the carbon they contain is sequestered at the bottom of the sea for thousands or even millions of years. They are therefore carbon sinks--the size of which has never been estimated before."

He says this natural phenomenon--a blue carbon pump--has been increasingly and greatly disrupted by industrial fishing.

The authors also say the phenomenon has not only been overlooked until now, but it happens in areas where fishing is not economically profitable: in the Central Pacific, South Atlantic, and North Indian Oceans.

"Fishing boats sometimes go to very remote areas--with enormous fuel consumption--even though the fish caught in these areas are not profitable and fishing is only viable thanks to subsidies," Mr Mariani said.

For the authors of the study, the new data strongly supports more reasoned fishing.

"The annihilation of the blue carbon pump represented by large fish suggests new protection and management measures must be put in place, so that more large fish can remain a carbon sink and no longer become an additional CO2 source," Mr Mariani said. "And in doing so we further reduce CO2 emissions by burning less fuel."

"We need to fish better," Prof Mouillot said.

The study is published in Science Advances.

Source: ARC Centre of Excellence for Coral Reef Studies [October 28, 2020]

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Coastal Greenland reshaped as ice sheet mass loss accelerates

Ice loss from the Greenland Ice Sheet has accelerated significantly over the past two decades, transforming the shape of the ice sheet edge and therefore coastal Greenland, according to scientific research led by Twila Moon, deputy lead scientist of the National Snow and Ice Data Center. These changes to the ice sheet could have far-reaching impacts on ecosystems and communities, as the flow of water under the ice sheet as well as nutrient and sediment flow are altered. 

Greenland Ice Sheet [Credit: Hannes Grobe, Alfred Wegener Institute
for Polar and Marine Research]

"The speed of ice loss in Greenland is stunning," said Moon. "We can now see many signs of a transformed landscape from space. And as the ice sheet edge responds to rapid ice loss, the character and behavior of the system as a whole is changing, with the potential to influence ecosystems and people who depend on them."

The researchers compiled data from NASA, the United States Geological Survey, and other satellites from 1985 to 2015 to compare ice edge position, ice sheet surface elevation, and glacier flow over three decades. Advancements in satellite technology allowed them to observe the changes to the ice sheet in much greater detail than was possible in the past. Much of the data used was from the NASA Inter-mission Time Series of Land Ice Velocity and Elevation (ITS_LIVE) project, which facilitates ice sheet, ice shelf, and glacier research by providing a global record of land ice velocity and elevation derived from nearly three decades of satellite observations.

Using these comparisons, the researchers developed a few key findings. The most consistent trend, found across the entire ice sheet, is widespread ice edge retreat. While there is a range of behavior among glaciers across the ice sheet, there is a noticeable lack of sustained ocean-connected glacier advance. Out of 225 ocean-connected glaciers that were measured, none have substantially advanced while 200 have retreated, particularly since 2000. This is notable even in regions dominated by slower-moving glaciers and cooler ocean water, such as the northern and northeastern regions of the ice sheet. In addition, while the vast majority of glaciers are retreating, ice flow response on those glaciers, such as speeding up or slowing down, is affected in large part by topography and upstream factors. This includes the slope of the landscape and the presence and shape of bedrock and sediments underneath the glacier. Therefore, even glaciers within the same regional or local area can behave differently.

As the researchers examined changes in the Greenland Ice Sheet, they found that zones of fast glacier flow are narrowing, ice is being rerouted, and in some cases, the flow of new ice to glaciers is slowed, stranding glaciers in place. These processes could have a variety of downstream impacts, such as altering how water moves under the ice sheet, which could affect the availability of water to communities and animals, altering where nutrients and sediment enter the ocean, exposing new land areas, opening new fjord waters, and altering ecosystems and physical landscapes.

"As the Arctic ocean and atmosphere warm, we can clearly see the flow of ice into the ocean accelerate and the ice edge retreat," said Alex Gardner, a research scientist at NASA's Jet Propulsion Laboratory and co-author of the study. "When we look more closely, however, we can see the complexity of how individual glaciers respond, owing to differences in the properties of the ocean water that reach the glacier front, the bedrock and till that lie below, and in how meltwater runoff is routed beneath. Understanding the complexity of individual glacier response is critical to improving projections of ice sheet change and the associated sea level rise that will arrive at our shores."

Results of the research were published in the American Geophysical Union's Journal of Geophysical Research: Earth Surface.

Source: University of Colorado at Boulder [October 27, 2020]

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Hidden losses deep in the Amazon rainforest

Few places on Earth are as rich in biodiversity and removed from human influence as the world's largest rainforest -- the Amazon. Scientists at Louisiana State University (LSU) have been conducting research within the pristine rainforest for decades. However, they began to notice that some of the animals, specifically birds that forage on and near the forest floor, had become very difficult to find.

New research shows animal patterns are changing in the absence of landscape change, which signals
a sobering warning that simply preserving forests will not maintain rainforest biodiversity
[Credit: Vitek Jirinec, LSU]

"What we think is happening is an erosion of biodiversity, a loss of some of the richness in a place where we would hope biodiversity can be maintained," said LSU School of Renewable Natural Resources Professor Philip Stouffer, who is the lead author of a new study published in Ecology Letters.

Stouffer began leading field research deep within the Amazon rainforest, north of Manaus, Brazil, when he was a post-doctoral researcher with the Smithsonian in 1991. With support from the National Science Foundation, he continued to oversee bird monitoring at the Biological Dynamics of Forest Fragments Project until 2016. However, around 2008, he and his graduate students noticed that they could seldom find some bird species that they had observed in previous years.

Stouffer and his students devised a research plan to collect new data that would be directly comparable to historical samples from the early 1980s. LSU graduate students Vitek Jirinec and Cameron Rutt collaborated with Stouffer to synthesize the results, aided by the computational modeling expertise from co-author LSU Department of Oceanography & Coastal Sciences Assistant Professor Stephen Midway. The team analyzed the vast dataset that spanned more than 35 years and covered 55 sites to investigate what Stouffer and his graduate students had observed in the field.

"It's a very robust dataset from a variety of places collected over many years. It's not just some fluke. It looks like there's a real pattern and it looks like it could be linked to things we know are happening with global climate change that are affecting even this pristine place," Midway said.

This downward trend signals a shifting baseline that could have gone undetected.

"Our nostalgia was correct--certain birds are much less common than they used to be," Stouffer said. "If animal patterns are changing in the absence of landscape change, it signals a sobering warning that simply preserving forests will not maintain rainforest biodiversity."

Winners and losers

In general, the birds that have experienced the most dramatic declines live on or near the forest floor where they forage on arthropods, mostly insects. However, there is some variation among species winners and losers in the rainforest.

The iconic voice of the Amazon rainforest, the Musician Wren, is one of the birds that researchers
have discovered is on the decline in pristine, remote parts of the Amazon
[Credit: Philip Stouffer, LSU]

For example, the Wing-banded Antbird , or Myrmornis torquata, is one of the species that has declined since the 1980s. It is also one of the species that forages insects on the forest floor by searching under leaves and other debris. Also declining is the Musician Wren , or Cyphorinus arada, a seldom-seen bird with one of the iconic voices of the Amazon.

Conversely, the White-plumed Antbird , or Pithys albifrons, has not declined and remains common. Its foraging strategy may be the key to its resilience. The White-plumed Antbird follows swarms of marauding ants that churn up other insects hidden on the forest floor. The antbird jockeys for an advantageous position ahead of the ant swarm and preys upon the fleeing insects. The White-plumed Antbird is not tied to one location in the rainforest. It travels and eats a variety of prey surfaced by the swarms of ants.

The scientists also found that frugivores, or birds that also eat fruit, are increasing in abundance. This suggests that omnivorous birds with more flexible diets can adjust to changing environmental conditions.

More research is needed to better understand the hidden losses and shifting baseline that are happening in the Amazon rainforest and other parts of the planet. "The idea that things are changing, even in the most pristine parts of our planet yet we don't even know it, illustrates the need for us to pay more attention," Stouffer said.

Source: Louisiana State University [October 26, 2020]

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The uncertain future of the oceans

The ocean plays a key role in the current climate change, as it absorbs a considerable part of the atmospheric carbon dioxide emitted by mankind. On the one hand, this slows down the heating of the climate, and on the other hand, the dissolution of CO2 in seawater leads to acidification of the oceans. This has far-reaching consequences for many marine organisms and thus also for the oceanic carbon cycle. One of the most important mechanisms in this cycle, is called the biological carbon pump. Part of the biomass that phytoplankton forms in the surface ocean through photosynthesis sinks to the depths in the form of small carbonaceous particles. As a result, the carbon is stored for a long time in the deep sea. The ocean thus acts as a carbon sink in the climate system. How strongly this biological pump acts varies greatly from region to region and depends on the composition of species in the ecosystem.

One of the mesocosm experiments evaluated in the current study took place
in 2010 in Kongsfjord, Spitsbergen [Credit: Kerstin Nachtigall]

The study, which has now been published in the journal Nature Climate Change, is one of the most comprehensive studies so far on the effects of ocean acidification on marine ecosystems. Scientists at the GEOMAR Helmholtz Centre for Ocean Research in Kiel have now been able to show for the first time that ocean acidification influences the carbon content of sinking organic material, and thus the biological pump. Surprisingly, the observed changes were highly variable. The carbon content of sinking particles increased or decreased significantly with increasing CO2, depending on the composition of species and the structure of the food web. Since the underlying data cover a wide range of ocean regions, this seems to be a global phenomenon. These findings allow a completely new assessment of the effects of ocean acidification.

Dr. Jan Taucher, marine biologist and main author of the study, says: "Interestingly, we found that bacterial and animal plankton, such as small crustaceans, play a key role in how the carbon cycle and biological pump respond to ocean acidification. Until now, it has been widely held that biogeochemical changes are mainly driven by reactions of phytoplankton. Therefore, even modern Earth system models do not take into account the interactions we observe between the marine food web and the carbon cycle. Our findings thus help to make climate models more realistic and improve climate projections".

Up to now, most of the knowledge on this topic has been based on idealized laboratory experiments, which only represent ecological interactions and the dynamics of the complex marine food web in a highly simplified way. This makes it difficult to transfer such results to real ocean conditions and project them into the future. In order to gain a more realistic insight, the study summarizes several field experiments that were conducted with large-volume test facilities, so-called mesocosms, in different ocean regions, from arctic to subtropical waters.

Mesocosms are, so to speak, oversized test tubes in the ocean, in which changes in environmental conditions in a closed but otherwise natural ecosystem can be studied. For the present study, a large amount of data from five mesocosm experiments was synthesized to provide a more precise picture of plankton communities and biogeochemical processes within the ecosystem. A total of over ten thousand data points were included in the analysis.

The newly gained knowledge can now be used to implement the complex ecological interactions in Earth system models, thus contributing to further improve climate projections.

Source: GEOMAR Helmholtz Centre for Ocean Research Kiel [October 26, 2020]

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