Analysis

Melting glaciers set to release more organic carbon as temperatures climb

  • 19 Jan 2015, 17:00
  • Robert McSweeney

Melting glacier | Shutterstock

Melting ice may affect more than sea levels, according to new research. As the earth warms, more of the carbon locked up in glaciers and ice sheets will be released into surrounding rivers and oceans.

This means that, as well as pushing up sea levels, melting ice could have unknown impacts on marine life.

Carbon release to increase by half

Glaciers and ice sheets cover around 11 per cent of Earth's land surface and hold around 70 per cent of its freshwater. These giant stores of ice also hold  organic carbon. Carbon accumulates in new snow and ice, and is released as the glacier melts.

A new study, published today in Nature Geoscience, finds the release of this carbon will speed up as the Earth warms due to climate change.

Around 15 million tonnes of extra organic carbon will be lost from melting glaciers over the next 35 years in the form of tiny dissolved particles, the researchers say. Ice also contains larger 'particulate' carbon, which are like bits of sediment that a river carries.

This extra organic carbon is 47 per cent more than we could expect without climate change, and equivalent to around half of what the Amazon river carries each year, the researchers say. 

Organic carbon provides food for tiny organisms at the bottom of the food web. So the extra carbon flowing into rivers and oceans may affect the plants and animals that live around the ice sheets, the researchers say. Adding organic carbon can also affect the chemistry of water, by making it more acidic, for example.

A research first

The research is the first to estimate the total amount of organic carbon held in ice across the world. Researchers collected measurements of organic carbon concentrations from more than 300 samples of glacier and ice sheets in four continents, as the map below shows.  

Hood Et Al (2015) Fig 1 Glacier DOC

Scientists collected organic carbon samples across four continents. Photos show examples of a) Alaska, b) Tibet, c) Dry Valley glaciers in Antarctica, and d) the Greenland Ice Sheet. Source: Hood et al. (2015)

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Scientists react: 2014 confirmed as hottest year on record

  • 16 Jan 2015, 17:13
  • Carbon Brief staff

Land & ocean percentiles 2014 | NOAA

NASA and the US National Oceanic and Atmospheric Administration (NOAA) have confirmed 2014 was the warmest year since records began in 1880. 

The 10 warmest years in the instrumental record, with the exception of 1998, have now occurred since 2000.

Carbon Brief rounds up the reaction from scientists…

Prof Jonathan Overpeck, co-director of the University of Arizona's Institute of the Environment,  said in USA Today:

"Humans are literally cooking their planet...It just shows that human emissions of greenhouse gases, mainly from the burning of fossil fuels, are taking over the Earth's climate system. The data are clear. The Earth is warming and humans are causing the bulk of this warming."

Overpeck said in the Huffington post:

"Perhaps more important than the global temperature story are the impacts of record regional heat. In places like California, the Southwest U.S. more generally, Australia and parts of Brazil, record heat is exacerbating drought and leading to more stress on our water supplies and forests."

"With continued global warming, we're going to see more and more of these unprecedented regional conditions, and with them will come more and more costs to humans and the things they value. 2014 shows that humans are indeed cooking their planet as they continue to combust fossil fuels."

Dr Radley Horton, a scientist from Columbia University, said in USA Today:

"What we have known for decades is that increasing greenhouse gas concentrations - due to human activities - have stacked the deck dramatically towards more record warm years, and fewer record cold years."

Prof Stefan Rahmstorf, head of earth system analysis at the Potsdam Institute for Climate Impact Research in Germany, said in the New York Times:

"Obviously, a single year, even if it is a record, cannot tell us much about climate trends. However, the fact that the warmest years on record are 2014, 2010 and 2005 clearly indicates that global warming has not 'stopped in 1998', as some like to falsely claim."

Dr Gavin Schmidt, director of Nasa's Goddard Institute of Space Studies, said in the New York Times:

"Why do we keep getting so many record-warm years? It's because the planet is warming. The basic issue is the long-term trend, and it is not going away."

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Explainer: How do scientists measure global temperature?

  • 16 Jan 2015, 11:40
  • Roz Pidcock

Every year around this time, there's a flurry of activity in the world's major meteorological agencies as they prepare to release official global temperature figures for the previous year.

This year, there's particular interest as it looks likely 2014 will be the hottest year on record.

First out the blocks with the official data was the Japan Meteorological Agency (JMA). Earlier this month, it confirmed 2014 had  taken the top spot with global temperatures 0.27 degrees Celsius above the long-term average. Today, it's the turn of NASA and the US National Oceanic and Atmospheric Administration, with the UK Met Office following suit next week.

Why so many records? While global temperature is a simple enough idea, measuring it is harder than you might think. We take a look at what goes into taking Earth's temperature.

The basics

To get a complete picture of Earth's temperature, scientists combine measurements from the air above land and the ocean surface collected by ships, buoys and sometimes satellites, too.

The temperature at each land and ocean station is compared daily to what is 'normal' for that location and time, typically the long-term average over a 30-year period. The differences are called an 'anomalies' and they help scientists evaluate how temperature is changing over time.

A 'positive' anomaly means the temperature is warmer than the long-term average, a 'negative' anomaly means it's cooler.

Daily anomalies are averaged together over a whole month. These are, in turn, used to work out temperature anomalies from season-to-season and year-to-year.

 

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Scientists issue stark warning as Earth passes into ‘danger zone’

  • 15 Jan 2015, 19:00
  • Robert McSweeney, Rosamund Pearce & Roz Pidcock

Human activity over the past century and a half has pushed the Earth into critical mode, say scientists. New research published today finds four out of nine 'planetary boundaries' have now been crossed. Biodiversity loss, fertiliser use, climate change and land use have all exceeded the point at which the risk of sliding into a "much less hospitable" world becomes high.

Passing any one of the nine critical boundaries risks disrupting the complex and delicate interactions that exist on Earth between the land, ocean, atmosphere, ice sheets and people, says the team of 18 researchers.

An early warning

The concept of planetary boundaries is to identify how much humans can develop and use the Earth's resources while staying safely within limits of what the planet can take.

In 2009, a collaboration of several top research institutions identified a set of nine processes that regulate the land, ocean and atmosphere systems on Earth. For each process they identified a boundary beyond which humans would cause "unacceptable environmental change".

You can see the boundaries in the figure below, which also shows the current status of each one.

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Global sea levels rising faster than previously thought, study shows

  • 14 Jan 2015, 18:00
  • Robert McSweeney

Sea level rise | Shutterstock

Scientists have a good idea of the different factors that contribute to sea level rise. But historical measurements of sea level change from the twentieth century don't seem to match up to sum of all these individual factors.

A new paper, published in Nature, offers an explanation to this puzzle. The study finds that the amount of sea level rise during the last century is lower than scientists previously thought.

But the implication of this finding is that the acceleration in sea level rise seen in recent decades is more rapid than scientists thought, the study says. And the researchers say that melting ice sheets are the reason.

Balancing the books

Several different components contribute to rising sea levels rise, including water expanding as it warms, melting glaciers and ice sheets, and changes to how much water is stored on land.

Scientists calculate global sea levels in two ways: by taking direct measurements of sea levels, and by using models and observations to estimate the contribution of each of these components and then adding them together.

But this has presented scientists with a problem: the figures from the two methods don't quite match for the twentieth century. In the latest  Assessment Report from the Intergovernmental Panel on Climate Change (IPCC), observed sea level rise is estimated at 1.5mm per year from 1900 to 1990, but only 1mm per year when researchers calculate it by adding together the individual contributions.

Scientists have sought the answer to this  enigma, and the new paper offers an answer. It says that there is no discrepancy, because historical observed measurements were overestimating sea level rise for much of the last century.

By eliminating the difference between the two types of measurements, lead author Dr Carling Hay at Harvard University tells Carbon Brief, they are able to close the sea level budget:

"To put it another way: the books are balanced."

 

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How small volcanic eruptions may have slowed surface temperature rise

  • 13 Jan 2015, 13:07
  • Robert McSweeney

Tungurahua eruption | Shutterstock

Yesterday, the Daily Mail reported on new research that suggests small volcanic eruptions have a bigger effect on the climate system than scientists previously thought.

The new study, just published in Geophysical Research Letters, shows the impact of 20th and 21st century volcanic eruptions can be detected in a number of climate variables, including sea surface temperature, rainfall, tropospheric temperatures and atmospheric water vapour.

This reinforces the findings of a paper Carbon Brief covered in November last year. Both studies could help explain why recent warming at the Earth's surface has been slower than in previous decades. Here's a repost of the original article we wrote back in November.

A cataclysmic event

In June 1991 Mount Pinatubo in the Philippines erupted, sending a cloud of ash, dust and sulphur dioxide 35 kilometers into the atmosphere.

That sulphur dioxide combined with oxygen and water to form sulphuric acid aerosols. These particles reflected sunlight and encouraged clouds to form, cooling parts of the world by up to 0.4°C for two years after the eruption.

Volcanic eruptions are rated from zero to eight on a scale of explosivity, measured by the amount of ash and debris they produce. The Pinatubo eruption was rated as a six, or 'colossal'.

While the world hasn't seen such a huge volcanic eruption since, on average there is one small eruption somewhere in the world every week. A new study, published in Geophysical Research Letters, finds that these smaller eruptions may together have a bigger impact on global climate than previously thought.

Pinatubo _ash _plume _910612

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Farming overtakes deforestation and land use as a driver of climate change

  • 12 Jan 2015, 17:11
  • Robert McSweeney

Rosamund Pearce, Carbon Brief

Greenhouse gas emissions from growing crops and raising livestock are now higher than from deforestation and land use change, a new study finds.

The research, published in Global Change Biology, estimates the contribution of agriculture, deforestation and land use change to global emissions. While the emissions of the sector as a whole are dropping, emissions from agriculture are still on the rise, the research says.

A smaller slice of a larger pie

The new study combines three global datasets of greenhouse gas emissions for the 'Agriculture, Forestry and Other Land Uses' (AFOLU) sector. It includes emissions from human activities, such as cutting down trees, clearing and burning biomass, and from raising and feeding livestock.

The data also include the carbon emissions that the sector removes from the atmosphere, such as from planting more trees.

Whether the actual emissions are of carbon dioxide, methane or nitrous oxide, the figures are all converted into figures of 'carbon dioxide equivalent', which makes them easier to compare.

As a whole, the sector takes up a decreasing share of total manmade emissions, the study finds. In the 1990s, AFOLU was responsible for around 29 per cent of our emissions, but this dropped to 24 per cent in the 2000s and then to 21 per cent in 2010.

There are two reasons for this: first, emissions from deforestation and land use change have fallen over the past two decades, and second, the overall total of manmade greenhouse gas emissions are growing.

The result is that AFOLU is responsible for a decreasing share of a growing global emissions pie.  You can see this is the infographic below, which shows the figures for one of the three datasets that the study uses.

Forest -pies -2

 Greenhouse gas emissions by sector for the 1990s, 2000s, and then 2010. Credit: Rosamund Pearce, Carbon Brief. Figures taken from Tuiello et al. (  2015) using the FAOSTAT dataset only.

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Long-term economic shocks imply taking strong, early action on climate change, study shows

  • 12 Jan 2015, 16:00
  • Mat Hope

Coastal erosion | Shutterstock

Policymakers need to take significant, early action to tackle climate change if they are to avoid lasting damage to the global economy, a new study suggests.

The paper, published in Nature Climate Change today, shows that poor countries are particularly vulnerable to long-term economic shocks associated with a warming world.The results bolster the sense of increasing urgency surrounding international climate negotiations.

UN secretary general Ban Ki-moon today called for politicians to "aim high" at this year's Paris negotiations. Writing in the  Guardian, he said that today's generation is the "last that can take steps to avoid the worst impacts of climate change".

Long-term economic shocks

The new research by two Stanford University academics models the impacts of rising temperatures on countries' economies. It says previous models underestimate the long-term economic shocks associated with climate change.

Models currently  struggle to quantify all the likely economic impacts of climate change. The Stanford University study tries to improve them by broadening the economic impacts they include.

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Scientists discuss how strongly a warming Arctic is implicated in extreme weather

  • 09 Jan 2015, 13:53
  • Robert McSweeney

Arctic sunset | Shutterstock

The possibility that a warming Arctic could be influencing extreme weather elsewhere in the world seemed to receive a boost this week.  A new paper presented further evidence linking diminishing Arctic sea ice to extreme cold winters elsewhere in the northern hemisphere.

Lead author, Prof Jennifer Francis from Rutgers University, tells us: "Our new results, together with other new studies in this field of research, are adding substantial evidence in support of the connection."

But not everyone is so sure. We asked a few scientists in the field how strong they consider the evidence linking Arctic sea ice and extreme weather to be. Here's what they told us.

Arctic amplification

The US, Canada, Japan and UK have all experienced very cold and snowy winters in recent years. In 2012, a paper by Francis and Dr Stephen Vavrus suggested that this extreme weather was a result of rapid warming in the Arctic.

Temperatures in the Arctic are increasing around twice as fast as the global average. As Arctic sea-ice diminishes, energy from the sun that would have been reflected away by sea-ice is instead absorbed by the ocean, a phenomenon known as Arctic amplification.

Francis and Vavrus suggested that warmer Arctic temperatures weaken the jet stream, a fast-flowing river of air high up in the atmosphere. The theory goes that a weaker jet stream becomes 'wavier' and leads to more persistent weather conditions, such as long cold spells in winter and heatwaves in summer.

The new paper by the same authors, published this week in Environmental Research Letters, offers further evidence to support the link.

Jet stream waviness

Francis and Vavrus' work triggered what has become a lively area of research. One of the difficulties with the theory proposed is that it's very hard to measure the 'waviness' of the jet stream directly. Instead, Francis and Vavrus use a number of metrics to measure it in other ways.

One method tries to see the mechanism in action by looking for evidence of temperature differences causing wind patterns to change and the jet stream to get wavier. Another way looks at whether these wavy jet stream patterns are occurring more frequently across the northern hemisphere.

Identifying these patterns of waviness is important because they lead to 'blocking', which causes cold weather patterns to hold on for longer. In the 2013-14 US winter, the prolonged spell of very cold weather caused 91 per cent of the Great Lakes to freeze over.

Francis says we're seeing more of this persistent extreme weather as the Arctic warms up:

"Occurrence of these events has increased during recent decades when Arctic amplification has emerged as a strong signal."

Arctic amplification is greatest in autumn and winter (see graph below), which is why it mainly results in persistent cold weather events, Francis explains.

Francis & Vavrus (2014) Fig 2a

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Warming oceans less able to store organic carbon, study suggests

  • 06 Jan 2015, 15:57
  • Robert McSweeney

Dr. Chris Marsay

The oceans' ability to store carbon may be reduced by global warming, a new study suggests. The research finds that warmer ocean temperatures limit how much organic carbon is being transported into the deep ocean.

This could cause a positive feedback loop, the authors suggest, with carbon storage in the oceans reducing as global temperatures rise further.

Reduced carbon storage

The Intergovernmental Panel on Climate Change estimates that since the 1970s, oceans have taken up more than 90 per cent of the heat trapped by greenhouse gases. A warming ocean has implications for sea level rise, but also for its ability to store organic carbon, a new study in Proceedings of the National Academy of Sciences finds.

The research measures how much carbon is being transported via the biological pump. This is the way carbon dioxide dissolved in the surface ocean is converted into organic carbon and sinks into the deep ocean where it can be stored for hundreds of years and beyond.

The researchers find that less organic carbon sinks to the deep ocean in warmer waters. This leaves more carbon dissolved in the surface ocean, which can then return to the atmosphere as carbon dioxide.

The findings suggest that as the oceans warm up as a result of manmade climate change, they would be less able to remove carbon dioxide from the atmosphere. As the study's lead author, Dr Chris Marsay, tells us:

"This would potentially result in reduced storage of carbon dioxide by the oceans, effectively acting as a positive feedback mechanism, with less atmospheric carbon dioxide being removed by the oceans."

Transporting carbon to the deep ocean

Microscopic plants called 'phytoplankton' take carbon dioxide from the ocean as they photosynthesize in the sunlit surface waters. This process converts carbon dioxide into organic carbon. Some of this phytoplankton will sink into the deeper ocean or be eaten by other organisms, which sink themselves when they die. This process is the 'biological pump'.

The study measures the amount of organic carbon sinking through the ocean. The researchers took measurements throughout the top 700m of ocean at four locations in the Atlantic, and combined their results with an earlier study from the Pacific.

When the researchers plotted their results, they found that the amount of organic carbon they collected was lower in areas where the water was warmer. The chart below shows how the ratio of sinking carbon to dissolving carbon drops as temperature increases.

Marsay Et Al . (2014) Fig 2b

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