Did climate change kill off the Neanderthals? Not likely…

The reasons why the Neanderthals died off remain a mystery. One of the major theories says that they were the victims of major climate changes, but new evidence suggests that this is an unlikely scenario.

In an age where climate change driven by our own hand is poised to cause catastrophic changes to human life, it seems fitting to work out if shifting climates also doomed our evolutionary cousins, the Neanderthals.

The question of why the Neanderthals died out has been the source of fierce debate since the first bones were discovered in the early 19^th century. Some scientists turned the finger of blame inwards, suggesting that early humans killed them off, either directly, through violence and the spread of new diseases, or indirectly by gradually out-competing them.

Others have accused changing climates. According to them, Neanderthals were adapted to cold environments and, being less flexible than humans, they were unable to cope with a warming post-Ice Age world.

Now, Chronis Tzedakis from the University of Leeds has found compelling evidence that the Neanderthals extinction was unlikely to have coincided with the extreme shifts in climate at the end of the last Ice Age.

While their findings don’t rule out the climate change model completely, they strongly suggest that it wasn’t a major factor in the Neanderthals’ downfall.

Bleached corals recover in the wake of hurricanes

Hurricanes can physically cool coral reefs but they can also save them, by cooling the surrounding ocean and reversing the effects of bleaching.

In 2005, corals in the large reef off the coast of Florida were saved by four hurricanes. Tropical storms seem to be unlikely heroes for any living thing. Indeed, coral reefs directly in the way of a hurricane, or even up to 90km from its centre, suffer serious physical damage. But Derek Manzello from the National Oceanic and Atmospheric Administation has found that corals just outside the storm’s path reap an unexpected benefit.

Hurricanes can significantly cool large stretches of ocean as they pass overhead, by drawing up cooler water from the sea floor. And this cooling effect, sometimes as much as 5°C, provides corals with valuable respite from the effects of climate change.

Rising temperatures, dying corals

As the globe warms, the temperature of its oceans rises and that causes serious problems for corals. Their wellbeing depends on a group of algae called zooxanthellae that live among their limestone homes and provide them with energy from photosynthesis. At high temperatures, the corals eject the majority of these algae, leaving them colourless and starving.

These ‘bleached’ corals are living on borrowed time. If conditions don’t improve, they fail to recover their algae and eventually die. But if the water starts to cool again, they bounce back, and Manzello found that hurricanes can help them to do this.

Together with scientists from the Universities of Miami and the US Virgin Islands, he measured the extent of bleaching in reefs off Florida and the US Virgin Islands over the course of 2005.

By September, both reefs were suffering from equal amounts of bleaching. But while the situation continued to worsen in the storm-free Virgin Islands, the advent of four hurricanes in Florida turned the tide in the reefs’ favour.

Hurricanes vs bleaching

The storms – Dennis, Rita, Wilma and the infamous Katrina – each left behind an imprint of cooler water and the seas within 400km of their paths cooled by up to 3.2°C and stayed that way for up to 40 days. Two weeks after the fourth hurricane, Wilma, had passed, the corals had almost completely recovered.

Manzello’s study shows that the benefits of hurricanes on coral reefs can sometimes outweigh the localised physical wear and tear they cause. The question now is whether this is an isolated incident or a common occurrence.

Manzello isn’t sure. Based on the numbers of bleaching events and hurricane landfalls in Florida since the 19^th century, the odds of both happening at the same time (as in 2005) is about one in seven. But the actual probability is likely to be higher especially since the same factors that cause bleaching, such as warmer water, also encourage the growth of hurricanes.

Even so, it would be extremely foolish to expect hurricanes to bail corals out completely – only conservation projects and addressing rising temperatures can do that.

Reference: Manzello, Brandt, Smith, Lirma, Hendee & Nemeth. 2007. Hurricanes benefit bleached corals. PNAS doi.10.1073/pnas.0701194104.

Related posts on corals:
Hope for corals – swapping algae improves tolerance to global warming
Corals survive acid oceans by switching to soft-bodied mode

Related posts on the hidden effects of climate change: Icebergs are hotspots for life
Human nitrogen emissions indirectly capture carbon by fertilising forests
When the heat is on, male dragons become females
Climate change responsible for decline of Costa Rican amphibians and reptiles

Icebergs are hotspots for life

Icebergs are hotspots for Antarctic life. The water around them teems with nutrients, plankton and animals – a mobile community dragged along by the drifting ice. Together, they enrich over a third of Antarctic waters.

Say the word iceberg, and most people are likely to free-associate it with ‘Titanic’. Thanks to James Cameron (and, well, history too), the iceberg now has a reputation as an cold murderous force of nature, sinking both ships and Leonardo DiCaprio. But a new study shows that icebergs are not harbingers of death but hotspots of life.

In the late 1980s, about 200,000 icebergs roamed across the Southern Ocean. They range in size from puny ‘growlers’, less than a metre long, to massive blocks of ice, larger than some small countries.

They may be inert frozen lumps, but icebergs are secretly in the business of nutrient-trafficking. As the ice around Antarctica melts in the face of global warming, some parts break free from the parent continent and strike out on their own. As they melt, they release stored minerals into the water around them, and these turn them into mobile homes for a variety of life.

A tale of two icebergs

Kenneth L. Smith Jr, from the Monterey Bay Aquarium Research Institute, and other scientists from San Diego discovered the true extent of these icy ecosystems by studying two icebergs floating in the Antarctic Weddell Sea.

Even the smaller of the two, W-86, has a surface area larger than 17 football pitches. The larger one, A-52 was over a thousand times bigger, with a surface area of 300 km² and extending 230 metres into the freezing waters.

Smith and crew identified the duo through satellite imaging, and tracked them down by boat. Their ship spiralled around the blocks of ice collecting water samples as it went, from a dangerously close distance of a few hundred feet to a safer five miles away.

Hotspots for life

The skies above the two icebergs were patrolled by seabirds, including Cape petrels and Antarctic fulmars. Below the water, Smith explored the icebergs’ undersides with a remote-operated vehicle and found them teeming with life.

Below W-86, he saw a lattice-like surface, and the ridges of these were home to diatoms (right). These single-celled algae are part of the phytoplankton, microscopic creatures that make their energy from the sun and form the basis of the ocean’s food web. In between these diatom-covered ridges, baby icefish and segmented worms swam among the lattice’s nooks and crannies.

A-52 was even more varied, with large caves extending deep into the iceberg’s core. The team found diatoms here too, along with Antarctic krill (below), small shimp-like animals with a taste for diatoms. Among these were various invertebrates – comb jellies, colonial jellyfish-like animals called siphonophores, and predatory torpedo-shaped worms called chaetognaths.

Further out, the area immediately around the iceberg was void. But just beyond that, the ice was encircled by another halo of phytoplankton. These creatures, along with the diatoms on the ice itself, were thriving on the nutrients released by the melting ice, such as iron.

When Smith exposed diatoms to tiny mineral-rich particles filtered from his collected water samples, they grew slowly and steadily, while other diatoms cultured in normal water did not.

These drifting islands of ice were dragging entire communities along with them. As they drift and melt, they release small amounts of important nutrients. That triggers the growth of creatures at the bottom of the food chain and provides the foundations for larger animals like krill and seabirds. A-52 alone enriched a massive ring of water about the size of the Isle of Man.

To estimate the effect of other icebergs, Smith used satellites to count the number of bergs in a sample area. Within this space, the satellites spotted almost a thousand individual icebergs that, together, covered less than 0.5% of the ocean’s surface. But even this small amount was enough to enrich over 39% of the Southern Ocean!

Icebergs and climate change

By providing support for phytoplankton, the icebergs were also inadvertently helping to mitigate the effects of climate change. Just like land plants, phytoplankton make their own energy through photosynthesis. And just like land plants, they absorb carbon dioxide to do so. By eating the phytoplankton and excreting the remains, krill cause carbon to fall down into the ocean depths in a rain of droppings.

So even as their parent continent melts and releases carbon into the atmosphere, icebergs serve to draw planet-warming carbon away from the air and transfer it to the deepest sea. Smith believes that climate modellers need to take this into account to better predict the effects of melting Antarctic ice.

The disappearing ice can reveal underlying rock which absorbs more heat, hastens melting and releases even more trapped carbon – this is known as ‘positive feedback’. But as the ice melts, icebergs break off and these help to suck in carbon from the atmosphere – this is ‘negative feedback’. The next task is to understand how these two processed balance out.

Reference: Smith Jr, Robison, Helly, Kaufmann, Ruhl, Shaw, Twining and Vernet. 2007. Free-drifting icebergs: hot spots of chemical and biological enrichment in the Weddell Sea. Science doi.10.1126/science.1142834.

Other posts on ecology:
Shark-hunting harms animals at bottom of the food chain
The fox and the island – an Aleutian fable
Parasites can change the balance of entire communities
Human nitrogen emissions indirectly capture carbon by fertilising forests

Human nitrogen emissions indirectly capture carbon by fertilising forests

Human activity has greatly increased the levels of active nitrogen in the environment. By acting as a fertiliser and speeding the growth of forests, this extra nitrogen has indirectly locked up more carbon dioxide in the world’s trees.

There is no doubt that of all the elements in the entire periodic table, carbon is currently hogging the limelight. As it cycles through our environment, the policy decisions and economic futures of entire countries hang in the balance.

For all its media-whoring, you might be forgiven for forgetting that carbon is not the only element we are belching into the environment. Over the last century, we have greatly overwhelmed the natural nitrogen cycle too.

Nitrogen – the neglected element

Through the manufacture of nitrogen-based fertilisers and the exhausts of our cars, power plants and factories, we have more than doubled the natural levels of active nitrogen in the atmosphere.

Nitrogen is a valuable commodity in many parts of the world, and restricts the growth of local plant life. As such, the recent man-made influx has led to large increases in plant growth. In some cases like algal blooms that choke rivers and lakes, it’s too much of a good thing. But there is a silver lining.

Federico Magnani from the University of Bologna, together with an international team of scientists, have found that the changes in the nitrogen cycle may have been inadvertently fertilising our forests.

Carbon and nitrogen

The world’s forests act as massive carbon sinks, delaying the global warming effects of carbon dioxide by trapping it in prisons of wood and leaves. And larger forests mean more trapped carbon. The temperate forests of the Northern Hemisphere alone could store a massive 600 megatonnes of carbon every year.

The carbon and nitrogen cycles dance around each other in complex ways. When nitrogen levels increase, forests respond by channelling growth from roots to leaves and trunks. These above-ground organs are more enduring than roots and retain sequestered carbon for a longer time. More leaves also means increased photosynthesis, which serves to draw more carbon dioxide in from the air.

The extra nitrogen also delays the decay of leaf litter, further halting the release of organic carbon into the atmosphere.

Magnani’s colleagues are not the first group to try and look at the interplay between nitrogen levels and carbon capture. But other studies have found it difficult or impossible to account for the effects of nitrogen alone.

Carbon balance

A forest’s carbon balance – the amount of carbon trapped versus the amount released – depends on a variety of factors, including its age, logging, fires, and more. Some of these are easy to account for at a small scale. For example, when logging or fires kill off patches of forest, they become net sources of carbon as they start to regrow.

But after a couple of decades or so, the mature forest turns into a carbon sink, and the amount it stores outweighs the amount it releases. Clearly, a forest’s carbon balance changes as it matures, but real forests consist of patches of vegetation are very different ages.

To look at the overall picture, Magnani’s group took direct measurements of the carbon balance over a long period of time, from a network of forest sites in Western Europe and the USA. This allowed them to account for short-term sources of variation. And by using direct measurements, they have surpassed the models and simulations of previous studies.

The group found that carbon balance corresponds well with nitrogen levels in the area. In fact, the prowess of some forests at carbon capture seem to be overwhelmingly driven by their extra nitrogen boost. Our effects on the nitrogen cycle may have been acting like an unexpected carbon offset scheme.

Practicalities

So should we start pumping nitrogen in our forests to trap more carbon dioxide? Certainly, Magnani’s results suggest that small extra amounts of nitrogen can cause unexpectedly large levels of carbon capture. But his view and those of other commentators is a resounding “Not yet”.

There are still many questions left to be answered, particularly about the exact relationship between nitrogen addition and carbon levels. There is some evidence that some temperate forests are suffering from nitrogen saturation. Could adding more nitrogen damage them, or prevent them from returning to a situation where nitrogen is limited and not free-flowing?

And what of the other risks and benefits? The extra wood from the faster-growing trees could find a use as a replacement for concrete, a notoriously eco-unfriendly building material. But additional nitrogen could affect other animals and plants in the local environment. Would biodiversity suffer if certain species monopolise the newfound nitrogen bonuses?

As future research addresses these questions, those involved in forest management would do well to heed the importance of the world’s forests in sequestering carbon dioxide. There are other ways of increasing forest coverage besides mass-fertilisation, and the most obvious one is safeguarding the forests that we already have!

Reference: Magnani, Mencuccini, Borghetti, Berbigier, Berninger, Delzon, Grelle, Hari, Jarvis, Kolari, Kowalski, Lankreijer, Law, Lindroth, Loustau, Manca, Moncrieff, Rayment, Tedeschi, Valentini & Grace. 2007. The human footprint in the carbon cycle of temperate and boreal forests. Nature 447: 848-850.

Technorati Tags: carbon cycle, nitrogen cycle, nitrogen emissions, forests, carbon sequestration, science

When the heat is on, male dragons become females

It seems almost fashionable now to blame everything on climate change, but the most unusual claim yet is that it could lead to sex-changing lizards.

For humans and other mammals, sex is neatly determined by the X and Y chromosomes. If you have a Y you are male, and without it you are female. Reptiles however, use a variety of strategies, and the mammalian X/Y system is just one of them.

In some species, the female is the one with different chromosomes, in this case Z and W, and the male has two Zs. And some reptiles ignore sex chromosomes altogether. For them, an individual’s sex is determined by the temperature that their eggs were incubated at.

Scientists had long believed that these strategies were mutually exclusive with each species choosing one of the other.

But Alexander Quinn and colleagues form the University of Canberra have found that an Australian lizard, the central bearded dragon (Pogona vitticeps) flouts this rule. It has become the first animal known to use two separate methods to determine the sex of individuals.

The dragon uses the Z/W system, where the males carry two Z chromosomes and the females have a Z and a W. But Quinn found that these genes are only the dominant influence on gender if eggs are incubated between 20 and 32 degrees Celsius.

At higher temperatures, males ignore their genetic heritage and become females instead. When Quinn incubated broods of eggs between 34 and 37 degrees Celsius, the hatchlings were almost invariably female. And as predicted, about half of these sisters were genetically male. For dragons at least, when the heat is on, the men turn into women

Quinn believes that the key to the manliness of boy dragons lies in a temperature-sensitive protein produced by the Z chromosome. The protein’s activity needs to surpass a certain threshold before a dragon can become male. For that, there need to be two copies of Z, and the temperature must be just right.

Reptiles that use temperature to assign gender must have fine-tuned their systems over time to cope with an ever-changing environment. But Quinn fears that the current pace of climate change may be too rapid for these animals to adapt to.

If temperatures rise far enough to bias an entire species over to a single gender, extinction would be all but inevitable. These warnings have been sounded before, and Quinn’s work suggests that they should be shouted a little bit louder.

More about animal sex and reproduction: 
Virgin birth by Komodo dragons
Butterflies evolve resistance to male-killing bacteria in record time 
Chimerism, or How a marmoset’s sperm is really his brother’s
Aphids get superpowers through sex

More on the effects of climate change: 
Icebergs are hotspots for life
Climate change responsible for decline of Costa Rican amphibians and reptiles
Hope for corals – swapping algae improves tolerance to global warming
Corals survive acid oceans by switching to soft-bodied mode

 

 

Reference: Quinn, Georges, Sarre, Guarino, Ezaz & Graves. 2007. Temperature sex reversal implies sex gene dosage in a reptile. Science 316: 411.

Technorati Tags: bearded dragon, sex determination, temperature sex, temperature lizards, science

Climate change responsible for decline of Costa Rican amphibians and reptiles

Amphibians around the world are facing extinction from habitat loss and a killer fungus. Now, climate change joins their list of enemies. In Costa Rica, warmer and wetter days have led to a loss of rainforest leaf litter that has sent amphibian and reptile populations crashing.

Miners used to take canaries into unfamiliar shafts to act as early warning systems for the presence of poisons. Today, climate scientists have their own canaries – amphibians.

Amphibians – the frogs, toads and salamanders – are particularly susceptible to environmental changes because of their fondness for water, and their porous absorbing skins. They are usually the first to feel the impact of environmental changes.

And feel it they have. They are one of the most threatened groups of animals and one in three species currently faces extinction. The beautiful golden toad (right) was one of the first casualties and disappeared for good in 1989. Even though they are less glamorous than tigers, pandas or polar bears, amphibians are a top priority for conservationists.

The usual factors – introduced predators and vanishing habitats – are partially to blame, but many populations have plummeted in parts of the world untouched by pesky humans.

More recently, a large number of these deaths have been pinned on a fatal fungal disease called chytridiomycosis. Hapless individuals become infected when they swim in water used by diseased peers, and fungal spores attach to their skins. The disease had decimated amphibians across the Americans.

The extent of the damage may be even worse than we think. We have very little long-term data on the population sizes of many amphibian species, particularly in the tropics, where the greatest diversity exists. One of the few sites to buck the trend of ignorance is La Selva Biological Station in Costa Rica, which has been monitoring amphibian populations since the 1950s.

Steven Whitfield and colleagues from Florida International University used the La Selva data to analyse the populations of a species living among the leaf litter that covers the local rainforest floor. The team ran their census of about 30 species of amphibians, as well as many reptiles (lizards and snakes).

To their astonishment, the populations of these species had plummeted by 75% in 35 years. This massive decline is worrying for many reasons, the least of which is that La Selva sits within a protected area. Habitat destruction is non-existent here, so something else must be happening.

Nor is chytridiomycosis to blame. The fungus doesn’t tolerate high temperatures and only grows in temperate regions or mountainous ones. La Selva is neither. The killer fungus marks its presence with rapid falls in amphibian numbers within months, but these declines took place over decades.

And most tellingly of all, the reptiles suffered population losses as great as those of the amphibians. With their dry, scaly skins, reptiles lack the amphibian vulnerability to chemicals and chytridiomycosis. Something else is afoot.

Whitfield believes that climate change is the answer. Over the past 35 years, La Selva has experienced wetter and warmer days. Temperatures have gone up by one degree Celsius, which slows the growth of local trees, and reduces the volume of leaves that they shed. The number of dry days has halved, and with more rainfall, the leaves that do fall decay faster.

So these combined climate changes have conspired to reduce the levels of leaf litter in the forest, robbing amphibians and reptiles alike of their homes. Even in this protected area, habitat destruction is going on right under our feet.

The climate change idea explains another odd finding. Whitfield saw that amphibian and reptile numbers had not declined in nearby abandoned cacao plantations. That’s because cacao trees shed their leaves throughout the year and provide a continual supply of new leaf litter.

The picture for the world’s amphibians seemed bleak enough, but it seems that we have been ignoring a larger simmering danger in the face of the immediate threat of chytridiomycosis. It is telling that all but one of the disappearing species in this study are listed as ‘least concern’ by the World Conservation Union (IUCN). Whitfield’s study should be a call to action for conservationists.

Reference: Whitfield, Bell, Phillippi, Sasa, Bolanos, Chaves, Savage & Donnelly. 2007. Amphibian and reptile declines over 35 years at La Selva, Costa Rica. PNAS doi.0611256104.

Technorati Tags: reptiles, amphibians, amphibian extinction, Costa Rica, amphibian conservation, amphibian climate change, chytridiomycosis, science

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Carbon offset schemes worsen global warming if trees are planted in the wrong places

Many carbon offset schemes rely on planting new trees to counteract rising carbon dioxide levels and the climate change they cause. But new research shows that these schemes only work if trees are planted in the tropics. Plant elsewhere, and you’ll only be adding to global warming.

Plant a tree and save the planet. If it sounds too good to be true, it’s usually because it is.

It is now crystal clear that modern global warming is a man-made phenomenon. But with this acceptance comes guilt, and the quest to find ways of mitigating our energy-hungry lifestyles

On the surface, carbon offset schemes appear to offer a win-win solution. People can assuage their guilt over yet another business flight, or drive to the shops, by paying for trees to be planted or investing in renewable technology.

Trees act as carbon sinks, sucking the gas in from the air and shunting the carbon atoms across into the plants’ own molecules. So plant enough trees, and the emissions you are responsible for will effectively be negated. You can whistle a jaunty tune and slap a carbon-neutral sticker on your car.

That’s the theory anyway. But Govindasamy Bala and colleagues form the Lawrence Livermore National Laboratory have found that it’s not just what you plant that matters, it’s where.

They ran complex simulations of how the planet’s climate would change if trees in different parts of the world were removed or restored. Unexpectedly, they found that overall, deforestation cools the planet down, and adding new trees in some regions may actually fuel global warming.

In a simulation where all the world’s trees were removed, the global temperature fell by about 0.3 degrees Celsius.

Why should this be? After all, trees soak up carbon dioxide and store carbon in their bodies – this keeps the planet cool. They release water vapour into the air, which forms clouds that reflect solar radiation away form the earth, again resulting in cooling.

But forests are also dark and by absorbing the energy from sunlight, they heat the planet too. According to Bala’s simulation, this heating effect outweighs the cooling ones.

When Bala looked at the effect of deforestation in specific areas, a clearer picture emerged. The tropical rainforests are doing their bit in fighting global warming by forming clouds and absorbing carbon dioxide. Their loss led to a rise in global temperature.

In contrast, the temperate and polar forests aren’t pulling their weight. These verdant slackers heat the planet themselves by absorbing solar radiation. Without them, the underlying snow would reflect more of the sun’s energy into space and we’d get a cooler planet.

These experiments suggest that tree-planting will only help to restrain global warming as planned if it happens in the tropics. In other parts of the world, it could even do more harm than good. When it comes to carbon offset schemes, the devil’s in the details.

Bala and his co-workers are modest on their work and are quick to point out that it is based on a single simulation. And they are careful to quickly stem the inevitable backlash from anti-environmental groups, who may well perversely suggest that this data warrants declaring war on trees.

Forests clearly have value beyond their influence on temperature. They harbour a great richness of life, keep the soil together and stop the oceans from acidifying by storing carbon dioxide – the list goes on. Deforestation is clearly not a solution to global warming, but wanton re-forestation won’t do any good idea.

Bala’s study gives pause for thought to those of us who seek to placate our environmental consciences by paying into carbon offset schemes.

At the very least, the details of any schemes should be checked carefully. Even better, serious thought should be given to preventive measures, like reducing car or plane use, rather than cures.

 

Reference: Bala, Caldeira, Wickett, Phillips, Lobell, Delire & Mirin. 2007. Combined climate and carbon-cycle effects of large-scale deforestation. PNAS 104: 6550-6555.

Technorati Tags: carbon+offset, climate+change, global+warming, deforestation, trees, environment, science

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Corals survive acid oceans by switching to soft-bodied mode

Biologists fear that the world’s beautiful coral reefs may be early victims of climate change, succumbing to the increasing acidity of the planet’s oceans. But new research provides a small glimmer of hope, by showing that corals may be able to weather the upcoming storm by shifting to a temporary soft-bodied lifestyle.

Climate change is not just about surface warming and glacial melting. The carbon dioxide that human activity is pumping into the atmosphere also dissolves in the world’s oceans, slowly increasing their acidity over time. And that spells trouble for corals.

Corals may seem like immobile rock, but these hard fortresses are home to soft-bodied animals. These creatures – the coral polyps – build their mighty reefs of calcium carbonate using carbonate ions drawn from the surrounding water.

But as the water’s pH levels fall, these ions become depleted and the corals start to run out of their chemical mortar. The upshot is that in acid water, corals find it hard to build their homes.

Scientists have predicted that if carbon dioxide levels double, the reef-building powers of the world’s corals could fall by up to 80%. If they can’t rebuild quickly enough to match natural processes of decay and erosion, the reefs will start to vanish.

Now, Maoz Fine and Dan Tchernov from the Interuniversity Institute of Marine Science, Israel, have found that they have a way of coping with homelessness.

They grew some fragments form two European coral species under normal Mediterrenean conditions, and others in water slightly more acidic, by a mere 0.7 pH units.

Those that spent a month in the acidic tank were quickly transformed. The skeleton dissolved and the colony split apart. The exposed and solitary polyps, looking like little sea anemones, still remained attached to rocky surfaces. When the going gets tough, the tough clearly go soft.

Even without their protective skeletons, they survived for over a year and seemed to be going about business as usual. They thrived, they reproduced normally and they still kept the symbiotic algae that allow them to produce energy through photosynthesis.

And when they were put back in normal conditions, they readily gave up their independence and re-formed both colonies and hard shells.

Fine and Tchernov’s findings suggest that corals may be able to survive upcoming climate changes by adopting soft-bodied, free-living lifestyles. And there is evidence that they have used this trick before.

The hard shells of coral reefs fossilise easily, but the fossil record still has large gaps where no reefs are found. These may represent periods of time when corals were biding their time in their soft-bodied phase instead.

But while this new discovery is cause for hope, it should not be cause for complacency. Even though the corals themselves may persist in another guise, the vast diversity of species that depend on them may go for good if their reefs disappear.

More about corals: 
Bleached corals recover in the wake of hurricanes
Hope for corals – swapping algae improves tolerance to global warming

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles

Reference:  Fine and Tchenov. 2007. Scleractinian coral species survive and recover from decalcification. Science 315: 1811.

Technorati Tags: corals, climate+change, environment, science, coral+reefs, ocean+acidication, science,

Opinion: How biofuels could cut carbon emissions, produce energy and restore dead land

A new way of producing biofuels could not only curb carbon emissions and produce renewable energy, but also restore unusable agricultural land and improve biodiversity. But only if this winning breakthrough find its way onto the political agenda.

The twenty-first century is having a troubled infancy. Six years in and it is facing the twin perils of climate change and a looming energy crisis. Solutions to both are in high demand and many research dollars and pounds are being channelled into developing environmentally-friendly, renewable resources.

Biofuels – the product of living things – certainly fit the bill, being both renewable and biodegradable. But there is always a catch. Currently, biofuels are a matter of harvesting single crops grown on fertile soils such as corn or sugarcane or waste products such as straw.

In George Bush’s State of the Union address of January 2007, corn-based biofuels played a major role in reducing the USA’s dependence on oil. But it is highly unlikely that these fuels will make a large dent in America’s energy demands.

The fuel-bearing plants need land to grow on, and the choice becomes either using up current agricultural land that provides much-needed food for growing populations, or to clear natural land and damage the ecosystems they nourish.

Any new crops must also be irrigated and treated with potentially polluting fertilisers and pesticides. And the water, chemicals and eventual crops must be transported with fossil-fuel-burning vehicles.

At first glance, biofuels seem to create more problems than they solve. In an ideal world, we would source biofuels from crops grown on used land with no other agricultural value, with a minimum of chemical help.

But such a world may be just round the corner, thanks to scientists from the University of Minnesota. David Tilman, Jason Hill and Clarence Lehman have discovered that the key to low maintenance biofuels is diversity.

The trio cultivated plants in 152 plots on agriculturally degraded soil (see left; photo taken by David Tilman), with low levels of the nitrogen that crop plants need to thrive on. They were irrigated once when the crops were planted, and left untouched by fertilisers.

They found that plots which cultivated a variety of plants produced far more energy than those with a single species, with the most productive ones containing 16 different species.

These so-called ‘low-input, high-diversity’ or LIHD plots contained a mix of humble woody plants, legumes and grasses, such as wild lupine, goldenrod, and switchgrass.. They produced over three times as much energy as monocultures of single species.

Tilman found that every hectare of the LIHD plots yielded 68 gigajoules of energy a year but because they were so low maintenance, they only needed 4 gigajoules to pay off the energy debt of production, harvesting and transport. At processing plants, the fuels can be converted into gasoline, diesel and electricity.

In this way, each hectare of LIHD plots produce over 50% more usable energy on abandoned soil than other crops do with fertile soils.

Part of the LIHD crops’ success lay in the fact that legumes can seed impoverished soils with valuable nitrogen. Over the decade the experiment ran for, nitrogen levels in the LIHD plots increased by a quarter.

The biological diversity in each plot also warded against diseases and marauding species, never allowing a single invader to gain a proper foothold. This greatly reduced the need for pesticides and chemical protections.

Providing an alternative to fossil fuels is just one way in which LIHD biofuels could help to curb carbon emissions – they also act as carbon sinks. Monocultured crops such as corn and soybean produce less greenhouse gases than petroleum-based petrol and diesel, but they are still carbon-positive – their production leads to a net increase in carbon dioxide.

In contast, LIHD biofuels are carbon-negative, removing carbon dioxide from the atmosphere and storing it in both the soil and the growing roots of the plants themselves.

This stored CO₂ outweighs the total amount emitted during production and transportation by more than ten times and every hectare of crop captures about 4 tonnes of carbon dioxide every year. Compared to corn-based biofuels, the greenhouse gas reductions achieved by LIHD fuels were 6-16 times greater.

The world currently has at least 500 million hectares of agriculturally abandoned land that serves no fruitful purpose, and could be used to sow LIHD crops. The resulting biofuel harvest could replace 13% of the world’s petroleum consumption and 19% of its electricity needs.

LIHD biofuels are an environmentalist’s dream, and could provide a very rare win-win situation for the world’s energy providers. They represent a way of providing renewable energy while reducing carbon emissions, conserving biodiversity and both using and renewing otherwise degraded land.

It is an opportunity that scientists need to explore further and the world’s policy-makers need to start taking seriously.

 

Reference: Tilman, Hill & Lehman. 2006. Science 314: 1598-1600

Technorati Tags: Biofuels, LIHD, carbon emissions, renewable resources, science

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Climate change – one degree till the point of no return

The world is beginning to take the problem of climate change very seriously, and it should. New data from NASA shows that the world is within a degree of the hottest temperature in the last million years. Hit this target, and the disastrous effects of global warming will become irreversible. We are nearing the point of no return.

When it comes to temperature, one degree Celsius seems like nothing. If the temperature outside changed by a single degree, almost none of us would notice and if it rose by this much, almost none of us would complain.

But according to new research, this single degree now separates us form the point of no return, when the threat and problems of climate change become irreversible.

Around the world, scientists, politicians and the public alike are starting to realise that climate change is a very real and very serious problem. Reports of record temperature levels seem to be an increasingly common fixture in the British press.

But the world’s entire climate is connected. To get a proper picture of the impact of climate change, it is useful to look at the global situation.

This is what James Hansen and colleagues at NASA’s Goddard Institute for Space Studies did in September of this year. They looked at global changes in the world’s temperature over the last century, using a wealth of measurements from land stations, ships and satellites.

Their results show an unmistakeable pattern of increasing temperatures, particularly during the turn of the century.

Compared to climate in 1951-1980, the world in the first five years of the 21st century is warmer almost everywhere, although more so over land than sea, and at high northern latitudes in particular.

Over the last century, the global temperature has risen by 0.8C in the last century, and 0.6C of that was in the last three decades. On average, 2005 was the warmest year on record, largely because of aberrantly high temperatures in the Arctic.

Wasting time

As ever, climate sceptics are not convinced. Some have suggested that these higher average temperatures are invalid and biased because of measurements taken in typically hotter urban centres. But studies in some of the world’s remotest regions are clearly saying otherwise.

Glaciers are retreating and the ice on rivers and lakes is breaking up earlier. Even the open ocean is heating up, and if that were not enough, the largest temperature rises have been found in remote locations in the northern hemisphere. Global climate change is very real and is happening faster than ever.

This is not the first time that Hansen has sounded the alarm. In 1988, he published a model for global temperature change and presented it to the US Congress.

Unfortunately, he was heavily criticised in some quarters, most notably by Michael Crichton in his lamentable novel, State of Fear, which asserted that Hansen’s data was out by 300%.

The result was unproductive time-wasting at a critical juncture. As the window of opportunity shrank, Crichton, firmly leaning towards fiction over science, was invited to provide testimony to the US Senate and was even granted an audience with the President.

Hansen’s new analysis soundly trashes Crichton’s criticisms and shows that his earlier model of the ‘most plausible’ warming scenario has come to pass some 20 years later.

Looking into the past; staring into the future

The recent data all well and good, but variations over a short time could be one-off incidents, becoming mere blips when longer time-scales are considered. To account for this, Hansen compared our current temperature with that of prehistoric times, by looking at fossil shells.

Shelled animals deposit different amounts of minerals into their shells depending on the surrounding temperatures, so fossilised marine shell-wearers can tell us how hot it was in prehistoric times to within a degree’s accuracy. .

The results are astonishing. Because of our unremitting greenhouse gas emissions, the Earth is now within one degree Celsius of the hottest temperature it has experienced in the last millions years.

The situation is especially stark in the Western Equatorial Pacific region, an crucial area that regulates much of the world’s atmosphere and oceanic weather. Drastic changes here will not go unnoticed elsewhere.

They can even affect the rate at which the polar ice caps melt, as sub-tropical Pacific waters intermingle with Antarctic currents. Temperature rises in this region have not been matched by rises in the Eastern Pacific, and this difference may be driving more frequent El Nino events, like those in 1993 and 1998.

At the current rate, global temperatures are increasing by 0.2C every ten years. By 2056, the world will be a degree higher, and Hansen’s analysis shows that this is the turning points where things go from bad to irreversibly catastrophic.

If we halt climate change so that future warming occurs at under 0.1C per decade, things still don’t look rosy. Sea levels will still rise by about a metre every century, spelling problems for the world’s substantial coastal populations, such as Bangladesh and many island nations.

But these problems are completely dwarfed by the terrifying potential of what could happen if we let greenhouse gas emissions continue unabated.

What happens if we do nothing

In this worst-case scenario, CO2 emissions continue to grow at 2% a year and other greenhouse gases such as methane and nitrogen oxide continue to rise.

As a result, Earth becomes 2-3 degrees hotter by the turn of the next century, reaching a level not seen for 3 million years.

Much of the polar ice caps will melt. As they do, less sunlight will be reflected, ice streams will flow faster, and the structural integrity of ice shelves will collapse, accelerating the process in what scientists call ‘positive feedback loops’.

The influx of meltwater will raise sea levels by several metres each century, driving coastlines 25-35 metres higher than they are today, and completely altering the face of the globe.

The world’s animals and plants will undergo mass migrations in range, habitats will fragment and the carefully balanced ecosystems of today will be sundered. Extinction will claim some 60% of today’s species, and if the planet’s history is to be believed, a rise of 5C could kill 90%.

The message to our generation is clear – global warming is real and is following a path that we can accurately model. For anyone under the age of 40, the point of no return will probably happen within our lifetimes if nothing is done.

In as little as another decade, a lack of action could render the challenge of climate change insurmountable. Everyone from Governments to individuals must do their part and they must do it now.

Hansen, Sato, Ruedy, Lo, Lea & Medina-Elizade. 2006. PNAS 103: 14288-14293 .

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Hope for corals – swapping algae improves tolerance to global warming

Corals are under severe threat from climate change as higher temperatures cause them to lose the algae that provide them with energy. But salvation may come in the form of a newly discovered ability of corals to swap their algal partners with strains that can take the heat.

Among all of the world’s animals, the two which have built the largest settlements could not be more different. The champions, humans, are intelligent and mobile, rapidly adapting to new conditions with technology and ever-changing strategies. In contrast, the runners-up, corals, seem unchanging and immobile, spending their lives ensconced in their impressive but stationary reefs. But it now seems that corals may have to adapt quickly in the face of looming extinction, ironically, brought about by humans.

Corals are hugely successful animals. Their reefs have endured across millions of years and today, they cover an area of 280,000 square kilometres, larger than the entire United Kingdom. Their success depends on a partnership with a group of algae called zooxanthellae. Over a million of these lodgers can live in a single cubic centimetre of coral, and they provide their landlords with both colour and energy through photosynthesis.

Despite their benefits, the algae are expensive to maintain. During periods of environmental stress, the corals eject them to make ends meet, losing their colour in the process. These ‘bleached’ corals (below) are free to regain their partners at easier times, but if conditions don’t improve, they die.

This is the doom that they now face as global warming threatens to send oceanic temperatures soaring to record levels. The existence of the corals and the biological riches they support is under severe threat. But new research from by Ray Berkelmans and colleagues at the Australian Institute of Marine Science shows that some corals may be able to buy themselves some extra time by swapping their algal partners.

There are 8 different lineages of zooxanthellae (labelled A to H) and it is becoming increasingly clear that how a coral reacts to its environment depends on which of these groups it harbours. In particular, corals with group D algae seem to be particularly good at dealing with high temperatures, and this might prove to be their salvation.

Berkelmans tested this idea by transplanting 22 colonies of the stony coral (Acropora millipora) from a cool inshore reef on the eastern coast of Australia, to a warmer bay about 400 miles away. The colonies contained group C algae, and within half a year, they had all bleached and seven had died. But a few months later, about half of them had recovered and regained their colour. Every single survivor had replaced their partners with those from group D.

Further experiments revealed that the corals’ ability to tolerate temperature was based almost entirely on their choice of partners, with their own biochemistry had no detectable effect. In this partnership, the algae proved to be the weakest link. The key difference between the various groups lies in the membranes of their chloroplasts – their in-house photosynthesis factories. Those that can take the heat have membranes that are stable across a larger range of temperatures.

It isn’t clear from this study alone whether the ability to evict less hardy tenants is widespread among coral species, or even among other populations of stony coral. Even if it is, it may not be enough. Berkelmans found that corals that made the swap could tolerate temperatures about 1-1.5°C higher. With the temperatures of the world’s oceans set to increase beyond that, the corals are living on borrowed time.

We can only hope that this newly discovered ability of corals to rapidly adapt to environmental change gives us enough time to curb carbon emissions and halt climate change.

More about corals: 
Bleached corals recover in the wake of hurricanes
Corals survive acid oceans by switching to soft-bodied mode

More about the effects of climate change: 
Icebergs are hotspots for life
When the heat is on, male dragons become female
Climate change responsible for decline of Costa Rican amphibians and reptiles
Reference: Berkelmans & van Oppen. 2006. Proc Biol Sci 273: 2305-2312.

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