Analysis

World's plants and soils to switch from carbon sink to source by 2100, study shows

  • 24 Apr 2015, 15:40
  • Robert McSweeney

Autumn forest | Shutterstock

Every year, trees and plants across the world absorb a vast amount of carbon dioxide from the atmosphere.

But a new study suggests this massive carbon sink could instead become a source of carbon dioxide by the end of the century.

This means we might not be able to rely on plants soaking up our emissions for much longer, the lead author tells Carbon Brief.

Extra carbon dioxide

Through photosynthesis, plants convert carbon dioxide, water and sunlight into the fuel they need to grow, locking up carbon in their branches, stems and leaves in the process.

Research suggests that as human-caused carbon dioxide emissions accumulate in the atmosphere, plants will grow more quickly because the rate of photosynthesis speeds up. This is called 'carbon dioxide fertilisation'.

This argument is sometimes used in parts of the media to suggest that additional carbon dioxide is beneficial for the Earth as extra food for plants.

But research published this week in Nature Geoscience suggests that plants won't have enough nutrients to make full use of the extra carbon dioxide in the atmosphere.  So any benefits will be limited, say the authors.

Nutrient needs

Plants need the right mix of nutrients to grow. Two of the most important nutrients are nitrogen and phosphorus. But there isn't an endless supply in soils for plants to use, lead author Dr Will Wieder, from the National Centre for Atmospheric Research in Colorado, tells Carbon Brief:

"Many ecosystems appear to be co-limited, meaning that both nitrogen and phosphorus are important for plant growth. There are places where one element or the other may be slightly more limiting, but at the end of the day plants need both to build roots, leaves and wood. This is why many fertilizers used in gardens and farms come with both nitrogen and phosphorus."

While nitrogen is abundant in the air we breathe, most plants can only take it up from the soil. Nitrogen gets into the soil by being 'fixed' from the air by microbes and certain plants, such as soy, Wieder says. Phosphorus primarily originates from rocks, and reaches the soil when they are worn down by the weather.

Nutrients can come from a little further afield as well, Weider adds:

"Both nitrogen and phosphorus can be moved around and transported through the atmosphere as dust or air pollution. The subsequent deposition of nitrogen and phosphorus also can contribute new nutrients to an ecosystem."

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What do volcanic eruptions mean for the climate?

  • 23 Apr 2015, 15:35
  • Robert McSweeney & Roz Pidcock

Calbuco eruption | P.O. Calisto

Having lain dormant for over 40 years, the Calbuco volcano last night erupted twice within the space of a few hours. The blast sent a huge cloud of ash over southern Chile.

Carbon Brief has asked a number of experts what volcano eruptions mean for the climate, and whether or not we can expect this latest event to have global consequences.

Cooling effect

Volcanic eruptions can affect climate in two main ways.

First, they release the greenhouse gas carbon dioxide, contributing to warming of the atmosphere. But the effect is very small. Emissions from volcanoes since 1750 are thought to be at least 100 times smaller than those from fossil fuel burning.

Second, sulphur dioxide contained in the ash cloud can produce a cooling effect, explains Prof Jim McQuaid, professor of atmospheric composition at the University of Leeds:

"Sulphur dioxide is quickly converted into sulphate aerosol which then alongside the fine volcanic ash forms a partial barrier to incoming solar radiation"

You can see this in the NASA video below that maps movements of particles in the Earth's atmosphere. At around 2 minutes in you can see the impact of the volcanic eruption in Madagascar, just off the eastern coast of Africa.

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Tiny marine plants could amplify Arctic warming by 20%, new study finds

  • 20 Apr 2015, 20:00
  • Robert McSweeney

Temperatures in the Arctic are rising faster than the rest of the world. Now, new research suggests microscopic algae could speed up warming even further.

These miniscule floating plants, which do everything from storing carbon to supporting the ocean food web, could drive faster sea ice melt as the Earth heats up, the lead author tells Carbon Brief.

Microalgae are already showing signs of adapting to warmer oceans, says a second study. But this is no guarantee they'll be able to cope with future temperature increases, the researchers say.

Foundation for life

Microalgae, or phytoplankton , are tiny plants that float in the upper part of the ocean. Just like plants on land, they photosynthesise - using sunlight and carbon dioxide to generate energy for growth. In this way they take carbon dioxide out of atmosphere and help to buffer the impact of emissions from human activities.

The by-product of photosynthesis is oxygen, and microalgae are responsible for producing around half of the oxygen in the atmosphere. Microalgae are also the foundation of the food web, meaning they're ultimately the reason there's any life in the oceans at all.

As algae serve such an important purpose, scientists are trying to work out how their abundance and distribution could change in the future as the Earth warms.

Positive feedback

Temperatures in the Arctic are increasing around twice as fast as the global average. The intense warming, known as Arctic amplification, is largely caused by diminishing sea ice. Energy from the sun that would have been reflected away by sea ice is instead absorbed by the ocean.

Previous research has shown that shrinking sea ice has given a boost to algae abundance. But there's a downside to this accelerated growth. A new study, published in Proceedings of the National Academy of Sciences, suggests the increase in algae could intensify Arctic warming, and sea ice melt, in the future.

So how could algal blooms intensify sea ice decline? As the Arctic warms up and the sea ice melts, more sunlight can penetrate into the ocean surface, triggering more growth in the algae.

With more microalgae floating around in the surface waters of the ocean, they absorb an increasing amount of the sun's energy, which causes the water to warm up. A warmer ocean means more sea ice melts, boosting algal growth even further, and creating a positive feedback loop.

Ecosystem model

The researchers looked at how this feedback loop could play out in a changing climate. They linked their marine ecosystem model to a climate model and ran simulations where carbon dioxide levels increase by 1% per year until the total amount in the atmosphere is twice what it was in 1990.

You can see the results in the maps below. These show the difference in Arctic temperature and sea ice between model runs with and without the added impacts of microalgae.

Park Et Al (2015) Fig2

Projections of Arctic changes under a doubling of atmospheric carbon dioxide: A) annual average temperature, B) sea ice concentration, C) number of ice-free days, and D) concentration of chlorophyll. Source: Park et al. (2015).

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Darkening ice speeds up Greenland melt, new research suggests

  • 17 Apr 2015, 12:35
  • Robert McSweeney

Glacier in Greenland | Shutterstock

Scientists have noticed a curious thing happening as rising temperatures melt the Greenland ice sheet. The ice that's left is getting darker, making it more susceptible to further melting, according to new research presented at the  European Geosciences Union (EGU) conference in Vienna.

Scientists have identified three ways in which the gleaming white ice sheet is getting darker, each contributing to the normally-reflective ice sheet absorbing more of the sun's energy.

A darkening mood

Second only to the Antarctic ice sheet in terms of size, the Greenland ice sheet spans about 1.7 million square kilometres. This bright white sheet of ice reflects much of the sun's energy that hits it. This is called the albedo effect, derived from the Latin word 'albus', meaning 'white'. Albedo is measured as a percentage or fraction of the sun's energy that is reflected.

The albedo effect has a cooling effect on the planet. Ice on land and sea at both poles reflects away energy that would be absorbed had it landed on land and ocean instead.

But in recent years, scientists have found that the Greenland ice sheet is becoming darker. Darker ice absorbs more of the sun's energy instead of reflecting it away, causing the ice to warm up and melt further.

In an  EGU press conferenceProf Marco Tedesco, professor of Earth and Atmospheric Science at the City College of New York presented the graph below, showing that Greenland albedo has decreased significantly since the mid-nineties.

Tedesco _Fig1

Summer albedo over Greenland. Red line shows decreasing albedo (darkening) between 1996 and 2012. Dotted lines show the trend. Source: Tedesco et al. (2015)

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Britain’s fish ‘n’ chip favourites could dwindle as North Sea warms

  • 13 Apr 2015, 16:20
  • Robert McSweeney

Fish and chips | Shutterstock

The likes of haddock, plaice and lemon sole could find the North Sea a less comfortable place to live as the world's oceans warms up, according to a new study.

The findings suggest that some of our favourite fish species could become less common as they struggle to cope with warming conditions, the lead author tells Carbon Brief.

Close to our culinary hearts

The fishing industry in the North Sea is worth over $1 billion a year. Some of Britain's best-loved fish are caught there, such as haddock and cod, which are among the top five most-consumed fish in the UK.

But the findings of a new study, published in Nature Climate Change, suggest that warmer waters will make the North Sea less suitable for many of our mealtime favourites. And they may not be able to migrate to other areas, the researchers say.

North sea temperatures have risen by 1.3C over the last 30 years and are predicted to rise by a further 1.8C over the next 50 years. The study estimates how these rising temperatures will affect some of the most abundant North Sea fish species.

The researchers looked at eight bottom-dwelling fish, known as 'demersal' species: dab, haddock, hake, lemon sole, ling, long rough dab, plaice, and saithe. Lead author, Louise Rutterford, from the University of Exeter, explains why to Carbon Brief:

"North Sea demersal fish species are the ones that we Brits most associate with the North Sea and they are close to our culinary hearts. There is also great data available from the UK and international trawl surveys."

Abundance and distribution

Using 30 years of fisheries data from the North Sea and projections for climate change, the researchers developed models to estimate future abundance and distribution of the eight fish species by the middle of this century.

The models take into account factors such as sea temperatures at the surface and near the seabed, and salinity. They project future fish numbers and the latitudes and depths were the fish are most likely to be found.

Contrary to expectations, the study finds fish may not search out cooler, deeper waters or head north as the North Sea warms.

You can see this in the graphs below. They are arranged in a grid: each row showing a different fish species, and each column showing how fish distributions are expected to change in terms of latitude, temperature and depth. The results for fish abundance are shown in blue for present day and red for the middle of the century.

The results for lemon sole (fourth row down) in summer show lower fish abundance in future, but with their distribution staying much the same. Both near-bottom temperature (third column) and sea surface temperature (fourth column) show warmer conditions for future. However, the depth (first column) and latitude (second column) suggest the fish will be found in similar areas to the present day.

The results for dab  (top row) show a large reduction in summer abundance. Dab tend to live in shallow waters in the southern North Sea, says Rutterford, which is expected to experience the warmest summer temperatures. These temperatures may be higher than they can tolerate, Rutterford says.

Screen Shot 2015-04-13 At 12.02.24

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Guest post: What the latest science says about thawing permafrost

  • 13 Apr 2015, 10:30
  • Dr Christina Schädel

Greenland permafrost | Shutterstock

A guest post from Dr Christina Schädel, a research associate at the Ecosystem Dynamics Research Lab at Northern Arizona University.

Huge amounts of organic carbon are stored in frozen soils across the Arctic. Scientists are concerned that warming temperatures will thaw  permafrost , releasing carbon into the atmosphere. But questions still remain over how much carbon these soils hold, and how quickly it could be released.

In our new study, published last week in  Nature, we reviewed all the latest research to see what thawing permafrost could mean for climate change. We find that it is likely to be a gradual, long-lasting release of greenhouse gases over many decades rather than an abrupt pulse.

Frozen soils

In the Arctic, temperatures are so cold that soils stay frozen all year round, giving permafrost its name. These frozen soils cover about one quarter of the landmass in the northern hemisphere.

The soil holds a vast amount of carbon, accumulated from dead plants and animals over thousands of years. There is around twice as much carbon in permafrost than is currently in the Earth's atmosphere.

But global temperatures are now rising and these frozen soils are starting to thaw. Temperatures in the high latitudes of the northern hemisphere have risen by 0.6C per decade over the last 30 years. As the soils thaw, the microbes they contain are woken from their ice-induced hibernation. The microbes feed on the organic carbon, converting it into carbon dioxide and methane, which is released into the atmosphere.

Vicious cycle

Scientists are concerned that permafrost thaw and the subsequent release of carbon will fuel a positive feedback loop, which will accelerate climate change. Warmer conditions cause the release of carbon dioxide and methane from permafrost, which means more warming, which in turn causes more permafrost to thaw and so on.

Calling this cycle a 'positive' feedback might be misleading. It's more of a vicious cycle.

Our review looks at the research that has been conducted and published since the last  assessment report from the Intergovernmental Panel on Climate Change (IPCC). Our team of scientists from across Europe and North America combined data and model outputs to address three main questions: how much permafrost carbon exists, how fast will that carbon be released to the atmosphere, and will it be released as carbon dioxide or methane?

Carbon store

We gathered together estimates of carbon stored in permafrost from the most recent studies. The map below, for example, shows estimates from one  study of the amount of organic carbon held in the top three metres of permafrost soils. The reds and orange areas show the areas that contain the most carbon, which you can see across much of Siberia and Canada.

Hugelius Et Al 2014

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Western Canada’s glaciers could shrink by as much as 95% by 2100, study finds

  • 06 Apr 2015, 16:00
  • Robert McSweeney

Athabasca glacier | Shutterstock

The Canadian Rockies, which sit as a backdrop to many a stunning vista, could be almost entirely devoid of glaciers by the end of the century, a new study suggests.

Researchers modelled the impact of rising temperatures on glaciers across western Canada.

The results show widespread ice loss by 2050, and ice all but vanishing a few decades later.

Rising temperatures

Around 27,000 square kilometers of Western Canada is covered by glaciers, an area similar in size to the amount of ice in the Himalayas or the whole of South America.

For the new study, published in Nature Geoscience, the researchers developed a model to see how rising temperatures will affect the volume and area of glaciers in three regions in western Canada. These regions are shown in the map below: the coast (green sections), the interior (pink) and the Rockies (blue).Clarke Et Al Fig1

 

Map of study area in western Canada, including three subregions of the Coast (green), Interior (pink) and Rockies (blue). Present-day (2005) glacier extent is shown in white. Source: Clarke et al (2015)

 

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Natural variability could slow the pace of Arctic summer sea ice loss, study says

  • 30 Mar 2015, 20:00
  • Robert McSweeney

Arctic landscape | Shutterstock

Natural fluctuations in the oceans and atmosphere are currently conspiring to amplify the impact of manmade global warming on summer Arctic sea ice, according to a new paper.

Were these different cycles to weaken or reverse, they could instead dampen the warming effect in the Arctic, and slow the rate of Arctic sea ice loss, the author says.

But any change of pace would only be temporary, Dr Ed Hawkins, who leads an Arctic predictability project, tells Carbon Brief. We should expect the decline in sea ice to continue in the long-term, he says.

Declining summer sea ice

Scientists have been using satellites to measure Arctic sea ice since 1979. As one measure of the Arctic's health, scientists record its smallest extent each year, which it usually hits at the end of summer. You can see the long-term decrease in September sea ice in the graph below, with the eight smallest summer extents all recorded in the last eight years.

Monthly _ice _NH_09

Average September Arctic sea ice extent from full satellite record (1979-2014), Source:  NSIDC

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Antarctic ice shelf thinning is accelerating, reveals new study

  • 26 Mar 2015, 19:30
  • Robert McSweeney

Antarctic ice shelf | Shutterstock

A new study reveals ice shelves in the western part of Antarctica are melting much faster than a decade ago. Satellite data from three separate missions shows melting of these vast, floating ice shelves has increased by 70% in the last decade.

If current warming trends continue, the researchers say the ice could thin so much that these icy 'gatekeepers' risk collapsing, unlocking parts of the ice sheet to faster ice loss.

Floating sheets of ice

Ice shelves form where a glacier on land reaches the coast and flows into the ocean. They surround 75% of the Antarctic continent. If the ocean is cold enough, the ice doesn't melt but instead forms a floating sheet of ice that extends over the ocean.

Ice Shelf Diagram

Ice shelf diagram. Credit: Professor Helen Fricker, Scripps Institution of Oceanography, UC San Diego.

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Arctic sea ice hits lowest winter peak on record

  • 20 Mar 2015, 12:15
  • Robert McSweeney and Sophie Yeo

Arctic | Shutterstock

The latest satellite data shows the winter maximum extent of Arctic sea ice this year is the lowest recorded since measurements began in 1979. Provisional data from the National Snow and Ice Data Center (NSIDC) in the US shows 2015 has broken the previous record set in 2011 by 130,000 square kilometers.

Warm air temperatures in the Arctic have been a key reason why less ice has formed this winter, the NSIDC says.

It's around this time of year when the freeze-up of Arctic sea ice through the winter hits a peak, and signals the start of the melt season in spring and summer.

Using satellites, scientists can mark this point every year, recording when the Arctic sea ice hit its largest extent and the size it reached.

For 2015, the NSIDC thinks this point was on 25 February, when sea ice covered 14.54 million sq km. At 1.1 million sq km smaller than the 1981-2010 average, this year has set a new record for the lowest winter peak.

Arctic Sea Ice Winter Extent _NSIDC

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