Analysis

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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Amazon rainforest is taking up a third less carbon than a decade ago

  • 18 Mar 2015, 18:05
  • Robert McSweeney

Amazon at dawn | P. van der Sleen

The amount of carbon that the Amazon rainforest is absorbing from the atmosphere and storing each year has fallen by around a third in the last decade, says a new 30-year study by almost 100 researchers.

This decline in the Amazon carbon sink amounts to one billion tonnes of carbon dioxide - equivalent to over twice the UK's annual emissions, the researchers say.

If this pattern exists in other forests around the world, deeper cuts in human-caused carbon dioxide emissions are needed to meet climate targets, the researchers say.

Three billion trees

The Amazon rainforest is the largest rainforest in the world. Spanning nine countries in South America, it's 25 times the size of the UK.

Using a process known as photosynthesis, the Amazon's three billion trees convert carbon dioxide, water and sunlight into the fuel they need to grow, locking up carbon in their trunks and branches.

As they grow, Amazon trees account for a quarter of the carbon dioxide absorbed by the land each year. Studies suggest that as human-caused carbon dioxide emissions increase, forests will absorb and store more carbon, assuming they have enough water and nutrients to grow.

But a new study, published today in Nature , suggests the Amazon has passed saturation point for how much extra carbon it can take up.

Diminishing carbon sink

A team of almost 500 people monitored trees in more than 300 sites across eight countries. Between 1983 and 2011, the researchers measured the trees in each plot, recording the number, size and density to calculate how much carbon each one stored.

The trees took up more carbon and grew more quickly during the 1990s, before levelling off since the year 2000. You can see this in the middle chart below.

Brienen Et Al (2015) Fig1

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Farming Africa’s wet savannahs would have a high climate cost, study warns

  • 17 Mar 2015, 14:10
  • Robert McSweeney

Irrigation in Zambia | Lyndon Estes

As the global population rises, some scientists have suggested that Africa's wet savannahs could be ideal for growing the extra crops needed to meet the growing demand for food and bioenergy.

But it isn't quite the solution it seems, according to new research. The idea that Africa can provide food and biofuels while keeping emissions low "does not add up", the researchers say.

The wet savannah

'Wet savannah' describes warm, tropical areas areas that are wet enough to support crops and aren't covered with dense forest. Africa is home to around half of the world's wet savannah. Much of it is found in the Guinea Savannah, which makes up around a third of sub-Saharan Africa

Searchinger Et Al (2015) Fig1

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Cyclone Pam: Untangling the complex science on tropical storms and climate change

  • 16 Mar 2015, 20:30
  • Roz Pidcock

Winds of up to 300 kilometres per hour tore through the South Pacific island nation of Vanuatu over the weekend, hitting the heavily populated capital of Port Vila on Saturday morning.

Aid agencies say Cyclone Pam could be one of the worst disasters ever to hit the region, the BBC reports. The death toll currently stands at eight and is expected to rise as rescuers reach the more remote islands.

Speaking at a disaster preparedness conference in Japan, Vanuatu's President Baldwin Lonsdale said he thought climate change was contributing to the rise in extreme weather.

With aid finally reaching the storm-stricken nation, Carbon Brief looks at how climate change is altering how often this part of the world bears the brunt of such a destructive force.

Screen Shot 2015-03-16 At 18.58.16

Wind speed in Cyclone Pam at 1900 GMT on 16th March 2015. Winds of more than 200 km per hour (red) are still being recorded as the cyclone continues its path from Vanuatu down the east coast of New Zealand. Images courtesy of Cameron Beccario via  earth.nullschool.net

Storm severity

A cyclone is a tropical storm. Tropical storms are given different names depending on which ocean they form in. They are called hurricanes in the north Atlantic and northeast Pacific, typhoons in the northwest Pacific, and cyclones in the Indian Ocean.

Vanuatu frequently experiences cyclones. The cyclone season runs from December to April when the weather in the region is hot and wet. Tropical storms  derive energy from the warmth of the ocean and convert it into wind strength.

While strong storms aren't unusual for the region, Cyclone Pam was exceptional. Prof Kevin Trenberth, expert in climate change and extreme weather at the US National Centre for Atmospheric Research, tells Carbon Brief:

"In the large area around Vanuatu the sea surface temperatures were one to two degrees Celsius above normal … So the atmosphere all around there has some 10 to 20% more moisture in it than a comparable storm in the 1970s would have had."

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