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More CO2 limits plants’ protein output

April 12, 2014 in Agriculture, Carbon Dioxide, Soil, Uncategorized, Vegetation changes, Warming

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The Mojave desert: As CO2levels rose, it took up unexpectedly large amountsofthe gas Image: Rennett Stowe via Wikimedia Commons

The Mojave desert: As CO2 levels rose, it took up unexpectedly large amounts of the gas
Image: Rennett Stowe via Wikimedia Commons

By Tim Radford

With increasing warmth drying more of the Earth, arid soils may absorb more carbon dioxide – but that in turn is likely to limit protein production.

LONDON, 12 April – As global temperatures rise, more than one third of the land surface may become more arid. Although there will be changes in rainfall patterns, heat – and the attendant evaporation of the soil – could extend ever drier conditions to more and more farmland and cities, according to research in the journal Climate Dynamics.

The new study – which excludes Antarctica – is led by Benjamin Cook, a climate scientist both with the University of Columbia’s Lamont-Doherty Earth Observatory and the US space agency Nasa. It is based on climate simulation, and forecasts that 12% of the land surface will be subjected to drought by 2100 just through changes in rainfall. Throw in the increased heat, though, and the drying effect will be spread to 30% of the land.

Even those regions that might be expected to get more rain will be at greater risk of drought. This would be very bad news for the wheat, corn and rice belts of the south-western US and south-eastern China.

“For agriculture, moisture in the soil is what really matters,” said Cook’s co-author, Jason Smerdon. The research confirms previous studies, and the more recent warnings from the Intergovernmental Panel on Climate Change, and other studies, have predicted that extremes of temperature will be bad news for farmers anyway, with yields  likely to be affected.

But nothing in climate research is simple. The extra warming will be a direct consequence of ever-higher levels of carbon dioxide in the atmosphere. A study in Nature Climate Change has just revealed that arid zones offer an unexpected source of what engineers call negative feedback.

Carbon sink

A 10-year experiment in the Mojave desert in the US has shown that as carbon dioxide levels increase, arid areas take up unexpectedly large amounts of the gas.

“They are a major sink for atmospheric carbon dioxide, so as CO2 levels go up, they’ll increase their uptake of CO2 from the atmosphere. They’ll help take up some of that excess CO2 going into the atmosphere. They can’t take it all up, but they’ll help,” says Dave Evans, a biologist at Washington State University.

All land surfaces absorb some carbon. Until now, most attention has been paid to the role of forests as major “sinks” of carbon. But the US experimenters marked out nine octagonal plots of the desert and blew air with current levels of CO2 over three of them, and air with 550 parts per million of CO2, the expected level by 2050, over another three. Three received no extra air at all.

Then the researchers excavated the soils to a depth of a metre to measure the absorbed carbon and were surprised by the gain in carbon during a relatively short exposure in the plots exposed to the extra carbon dioxide.

Arid and semi-arid soils account for a large proportion of the planet’s land surface: overall, they could increase carbon uptake to account for between 15% and 28% of the amount currently being absorbed by land surfaces.

Less protein

This sounds like good news, on balance. It may not be, as far as food supplies are concerned. In the same issue of Nature Climate Change a second study reports on experiments into the effects of elevated levels of carbon dioxide on wheat.

Carbon dioxide is seen as a fertiliser of plants and indeed, without it, there would be no plants. But Arnold Bloom, a plant scientist at the University of California Davis reports that, according to his experiments, elevated levels of carbon dioxide also inhibit the conversion of nitrate into protein in crops.

Wheat provides nearly one fourth of all protein in the global human diet. Other studies have shown the same effect with wheat – and also with rice, barley and potato tubers.

“When this decline is factored into the respective portion of dietary protein that humans derive from these various crops, it becomes clear that the overall protein available for human consumption may drop by about three per cent as atmospheric carbon dioxide reaches the levels anticipated to occur during the next few decades,” Bloom said. – Climate News Network

Farming on sand

March 10, 2014 in Black Carbon, Deforestation, Development Issues, Flooding, Food security, Glaciers, Himalayas, Land Use, Monsoon, Rainfall, Soil, Water

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It was once a rice paddy but now it's only sand Image: Kieran Cooke

It was once a rice paddy but now it’s only sand
Image: Kieran Cooke

By Kieran Cooke

The Brahmaputra river is one of the world’s mightiest rivers, with millions dependent on its waters. The river also brings misery, with flooding and erosion major problems: climate change is likely to bring more hardship. Kieran Cooke, one of the editors of the Climate News Network, has been in Assam in northeast India, meeting villagers living on the Brahmaputra’s banks.

Laupani village, Assam, 10 March – The holes are dug laboriously in the dusty, sandy soil. Krishna Maya Sharma stops her work to wipe the sweat from her lined face.

“In the old days we would plant paddy here and have enough to sell at market” says Krishna, a 42 year old mother of six children.

“Now the soil is so bad, sweet potato is the only thing that will grow. The rest of our land is ruined.”

Laupani is a village in the north of the tea state of Assam, spread along the banks of the Brahmaputra river. In the distance, the pink evening light shines on the snow capped ridges of the eastern Himalayas.

The Brahmaputra, its waters rising more than 5,000 metres up on the Tibetan Plateau and flowing for about 3,000 kilometres through China, India and Bangladesh before joining up with the Ganges and out into the Bay of Bengal, is one of the world’s major rivers, 10 kilometres wide in places.

Widespread flooding

According to a recent report by India’s Third Pole organisation, the Brahmaputra carries a volume of water exceeded only by the Amazon and Congo rivers – and greater than the combined flow of Europe’s 20 largest rivers.

The river is a lifeline to millions, delivering vital nutrients to the soils of the plains but its fast flowing waters also cause widespread misery to people like Krishna.

Floods are frequent. There is widespread erosion and massive amounts of sand washed out of the river’s banks are deposited on surrounding fields, making once verdant areas into what looks like an enormous beach. The floods also bring invasive plant species that colonise agricultural lands.

More than 40% of Assam’s geographical area is designated as being flood prone: more than 1.5 million people were displaced by floods in 2012, lives were lost and whole villages were washed away.

Sand accumulations

“The waters were so deep and stayed so long that the grass was destroyed and our cattle died because they had no fodder” says Krishna.

“The sand means our land is no good anymore – my husband has given up being a farmer and is working in construction. Many young men go away to try and find jobs, there is nothing for them here.”

Locals – the majority of whom are poor, subsistence farmers – say river flows are becoming more unpredictable, with erosion and what’s called sandcasting becoming worse.

In part the flooding caused by the Brahmaputra’s waters is a natural phenomenon which has been going on for centuries. As the river’s waters cascade down from the Tibetan Plateau and Himalayas, millions of tons of sediment is washed onto the alluvial plains of Assam and others states in India’s northeast.

Earthquake danger

There are other forces at work: the region is a highly seismic zone. In 1950 the Brahmaputra river basin suffered one of the most violent earthquakes ever recorded. The geology of the area was changed and the river level was raised dramatically, by between eight and 10 metres in places.

Climate change is another factor, with a combination of rising temperatures and accumulations of what’s known as black carbon or soot in the high Himalayas and on the Tibetan Plateau causing glaciers which feed into upper reaches of the Brahmaputra to melt.

Increasingly unpredictable rainfall patterns, with periods of intense downpours, are also contributing to more volatile river flows.

Professor Jogendra Nath Sarma is a locally based geologist who has been studying the Brahmaputra for years.

“Over time different rivers in the Brahmaputra basin have merged, braiding over a very wide area. Thousands of square kilometres of land has been eaten away. Rampant deforestation is another big contributor to land erosion. “

In the past, says Professor Sarma, people would migrate to higher ground during the flood season but now, due to population growth and large scale immigration, there is nowhere for them to go.

Doubtful future

The future does not look good. According to models produced by scientists at the Indian Institute of Technology in Guwahati, Assam’s capital, climate change will result in the Brahmaputra valley region experiencing more flood events.

The Institute says that not only will river peak flows increase: so will the incidence of pre-monsoon flooding, endangering key phases of the agricultural cycle.

Talk of climate change is not of great interest to Krishna, digging holes for her sweet potato plants. She has more immediate things to worry about.

“Life is getting harder. Every time the floods come, I wonder what will happen. But where else can we go?” – Climate News Network


 

 

 

 

Tree roots ‘are natural thermostat’

February 18, 2014 in Carbon Dioxide, Forests, Mountains, Palaeoclimatology, Soil

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In sight of the Carpathians: Mountain forests can cool - and warm - the Earth Image: Horia Varlan from Bucharest, Romania, via Wikimedia Commons

In sight of the Carpathians: Mountain forests can cool – and warm – the Earth
Image: Horia Varlan from Bucharest, Romania, via Wikimedia Commons

By Tim Radford

Trees can influence the climate in unexpected ways, and British researchers say their roots are an important way of helping rocks to weather and drawing carbon dioxide from the atmosphere.

LONDON, 18 February – Trees have become a source of continuous surprise. Only weeks after researchers demonstrated that old forest giants actually accumulate more carbon than younger, fast-growing trees, British scientists have discovered that the great arbiters of long-term global temperatures may not be the leaves of an oak, a pine or a eucalypt, but the roots.

The argument, put by a team from Oxford and Sheffield Universities in the journal Geophysical Research Letters, begins with temperature. Warmer climates mean more vigorous tree growth and more leaf litter, and more organic content in the soil. So the tree’s roots grow more vigorously, say Christopher Doughty of Oxford and colleagues.

They get into the bedrock, and break up it up into its constituent minerals. Once that happens, the rock starts to weather, combining with carbon dioxide. This weathering draws carbon dioxide out of the atmosphere, and in the process cools the planet down a little. So mountain ecosystems – mountain forests are usually wet, and on conspicuous layers of rock – are in effect part of the global thermostat, preventing catastrophic overheating.

The tree is more than just a sink for carbon, it is an agency for chemical weathering that removes carbon from the air and locks it up in carbonate rock.

That mountain weathering and forest growth are part of the climate system has never been in much doubt: the questions have always been about how big a forest’s role might be, and how to calculate its contribution.

Keeping climate stable

US scientists recently studied the rainy slopes of New Zealand’s Southern Alps to begin to put a value on mountain ecosystem processes. Dr Doughty and his colleagues measured tree roots at varying altitudes in the tropical rain forests of Peru, from the Amazon lowlands to 3,000 metres of altitude in the higher Andes.

They measured the growth to 30 cms below the surface every three months and did so for a period of years. They recorded the thickness of the soil’s organic layer, and they matched their observations with local temperatures, and began to calculate the rate at which tree roots might turn Andean granite into soil.

Then they scaled up the process, and extended it through long periods of time. Their conclusion: that forests served to moderate temperatures in a much hotter world 65 million years ago.

“This is a simple process driven by tree root growth and the decomposition of organic material. Yet it may contribute to the Earth’s long-term climate stability. It seems to act like a thermostat, drawing more carbon dioxide out of the atmosphere when it is warm and less when it is cooler”, Dr Doughty said.

If forests cool the Earth, however, they might also warm it up. A team from Yale University in the US has reported in Geophysical Research Letters that forest fires might have had an even greater impact on global warming during the Pliocene epoch about three million years ago than carbon dioxide.

Rapid rise expected

Nadine Unger, an atmospheric chemist, and a colleague have calculated that the release of volatile organic compounds, ozone and other products from blazing trees could have altered the planet’s radiation balance, by dumping enough aerosols into the atmosphere to outperform carbon dioxide as a planet-warmer.

In fact, the Pliocene was at least 2°C or 3°C warmer than the pre-industrial world. The Pliocene is of intense interest to climate scientists: they expect planetary temperatures to return to Pliocene levels before the end of the century, precisely because humans have cleared and burned the forests, and pumped colossal quantities of carbon dioxide into the atmosphere. The greater puzzle is why a rainy, forested and conspicuously human-free world should have been so much warmer.

“This discovery is important for better understanding climate change through Earth’s history, and has enormous implications for the impacts of deforestation and the role of forests in climate protection strategies”, Dr Unger said.

All this scholarship is concerned with the natural machinery of ancient climate change, and the Yale research was based on powerful computer simulations of long-vanished conditions that could not be replicated in a laboratory.

Meanwhile, ironically, forest scientists have had a chance to test the levels of volatile organic discharges from blazing forests because freakish weather conditions in Norway have seen unexpected wild fires in tracts of mountain forest. December was one of Norway’s warmest winter months ever. In one blaze, 430 residents were forced to evacuate. – Climate News Network

Fungus governs soil’s carbon content

January 28, 2014 in Carbon, Fungus, Soil, Vegetation changes

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By Tim Radford

The soil stores the greater part of the Earth’s carbon. Just how much it stores is determined largely by what sort of fungi live in the roots of plants and trees, researchers have found.

LONDON, 28 January – Most of the planet’s carbon is neither in the forests nor the atmosphere. It is in the soil under your feet. US scientists think that they have identified the mechanism that keeps most of this awesome treasury of carbon locked away in the soil – or surrenders much more of it back to the atmosphere. The answer is: a fungus.

This answer matters because what happens to soil carbon is critical to predicting the planet’s future climate, according to Colin Averill of the University of Texas at Austin.

He and colleagues from the Smithsonian Tropical Research Institute in Panama and Boston University in Massachusetts report in Nature that the storage of carbon in soils is influenced by the mycorrhizal fungi that live in symbiotic relationships with plants.

In a symbiotic relationship, creatures benefit from each other, and in this case the fungi extract nitrogen from the soil, and make it available to the roots of the growing plant. Plants take carbon from the air to make their tissues; when a tree falls, or a branch breaks, or a shrub dies, most of the carbon gets back into the atmosphere through decomposition. But some gets buried, and stays in the soil

Averill and colleagues decided to look at the respective roles of two kinds of mycorrhizal fungus: one group known as ecto- and ericoid mycorrhiza (EEM), and another called arbuscular mycorrhiza (AM). The first produce enzymes that degrade nitrogen.

Out-competing microbes

That means that whenever there is organic nitrogen in the soil, the fungi take the greater share: they compete with soil microbes for the soil nutrients.  So the scientists predicted that if the EEM type was dominant, then there would be greater proportions of carbon conserved in the soil.

They then looked at all the known data about soil carbon and nitrogen in various ecosystems: the boreal forests of the north; the temperate woodlands, the tropical forests and the grasslands.

An Amanita mushroom, the fruiting body of an ectomycorrhizal fungus associated with the roots of a Hemlock tree in Harvard Forest, US Image: Colin Averill

Amanita mushrooms, part of an ectomycorrhizal fungus in the roots of a Hemlock tree in Harvard Forest, US
Image: Colin Averill

Where the proportions of arbuscular mycorrhiza were highest, the levels of soil carbon tended to be lower. In an EEM world, there could be 70% more carbon stored in the soil. Unexpectedly, they found that the relationship was independent of, and mattered far more than, the effects of net primary production, temperature, rainfall and levels of soil clay. What mattered most was the type of fungus dwelling in the roots of the forest trees, or the savannah grasses.

“Natural fluxes of carbon between the land and atmosphere are enormous and play a crucial role in regulating the concentration of carbon dioxide in the atmosphere and in turn, the Earth’s climate”, said Averill.

“This analysis clearly establishes that the different types of symbiotic fungi exert major control on the global carbon cycle, which has not been fully appreciated or demonstrated until now.”

Complex relationships

The research, once again, is a reminder that climate models depend on an understanding of how the world works, and that there is still much more to understand about planetary workings. Fungi are mostly invisible. Ceps, morels, chanterelles, truffles and field mushrooms are edible prizes that pop up from the soil, but most of the fungal action is below the soil.

The biggest single creature on the planet is not the blue whale but a fungus that covers 10 square kilometers of soil in the Blue Mountains of Oregon, in the US.

The research is a reminder of a secret kingdom buried in the first metre or so of the world’s soils, a kingdom with profound influence on the machinery of the planetary carbon cycle.

“The research is not only relevant to models and predictions of future concentrations of atmospheric greenhouse gases, but also challenges the core foundation in modern biogeochemistry that climate exerts major control over soil carbon pools,” said Adrien Finzi, of Boston University, one of the authors. – Climate News Network

Rainy mountains speed CO2 removal

January 19, 2014 in Carbon Dioxide, Mountains, New Zealand, Rainfall, Soil

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The rainswept Southern Alps are young mountains and growing fast Image: Philip Capper from Wellington NZ via Wikimedia Commons

The rainswept Southern Alps are young mountains and growing fast, providing new rock for weathering
Image: Philip Capper from Wellington NZ via Wikimedia Commons

By Tim Radford

The speed at which soil is produced by rain falling on mountain slopes proves to be much faster than science had realised – with significant implications for carbon in the atmosphere.  

LONDON, 19 January – US scientists have measured the rate at which mountains make the raw material for molehills – and found that if the climate is rainy enough, soil gets made at an astonishing speed. And in the course of this natural conversion of rock to fertile farmland and forest loam, carbon is naturally removed from the atmosphere.

Isaac Larsen of the University of Washington in Seattle and colleagues from California and New Zealand took a closer look at rates of weathering on the western slopes of the Southern Alps in New Zealand. They report in Science that, according to their measurements, rock is being transformed into soil more than twice as fast as previously believed.

On the ridge tops of the NZ mountains, soil was being manufactured by chemical weathering (which is scientific shorthand for rain splashing on rock) at the rate of up to 2.5mm a year.

“A couple of millimeters a year sounds pretty slow to anyone but a geologist”, said David Montgomery, one of the authors. “Isaac measured two millimeters of soil production a year, so it would take just a dozen years to make an inch of soil. That’s shockingly fast for a geologist, because the conventional wisdom is it takes centuries.”

The research matters because – once again – it throws new light on one of the dark regions of the climate machine: how carbon dioxide is removed from the atmosphere, at what rate, and where it goes and where it all ends up.

Temperature drop

The Southern Alps of New Zealand are in geological terms young, and still going up in the world: they include some of the fastest-uplifting mountains on the planet. They are also among the rainiest: more than 10 metres of precipitation a year, on average.

Uplift – the process of mountain-building – provides fresh new rock for weathering to work on. Rainclouds arrive on the prevailing winds from the Tasman Sea, hit the mountain sides, rise, condense and release their burden on the western slopes, to generate colossal run-off, lots of silt and rock fragments and dissolved silica, and to nourish dense, vigorous forests at the bottom of the slope.

And along with all this trickling water and new soil is a steady delivery of carbon, removed from the atmosphere’s carbon dioxide.

The hypothesis that mountains play a role in chemical weathering, carbon dioxide removal and climate change is not new. Decades ago scientists argued that when the continent of India slammed into Asia and lifted up the Himalayas and the Tibetan plateau more than 50 million years ago, this process generated conditions for monsoon rainfall that accelerated the removal of carbon dioxide from the atmosphere at such a rate that global temperatures dropped dramatically and ushered in the Ice Ages.

Such an argument is difficult to clinch, but the latest research from NZ certainly lends support to the reasoning that new mountain chains are influential components in the climate machine.

Strenuous research

Larsen and colleagues calculate that the young, wet mountain chains of the world make up only 14% of the land area that drains into the ocean, but account for 62% of the sediment, 38% of the total dissolved solids and 60% of the dissolved silica delivered down the rivers and into estuaries and deltas and ultimately to the sea, where huge quantities of this run-off settle to become carbonate rock.

Mountains, in effect, are agencies that turn carbon dioxide from the air into limestone beneath the sea, and the evidence from the Southern Alps is that this happens more speedily than anyone first thought.

To complete the research, the scientists had repeatedly to take helicopter rides to the highest ridges, hike down to collect a burden of new soil, and then climb the steep mountain slopes again to await the return flight.

Back in Washington, they tested their soil samples for levels of beryllium-10, an isotope made at the Earth’s surface by cosmic rays, and therefore an indicator of the newness of the soil, and the rate at which it formed.

“I’ve worked in a lot of places,” said Larsen. “This was the most challenging fieldwork I have ever done.” – Climate News Network