Analysis

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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2014 was the UK’s hottest year on record, confirms the Met Office

  • 05 Jan 2015, 14:16
  • Robert McSweeney

CC 2.0: Andrew Bowden

Last year was the warmest for the UK since records began in 1910, according to provisional full-year data from the UK Met Office. 2014 was also the UK's fourth wettest on record, the agency says.

Record-breaking year

Met Office figures released today show the average temperature in the UK during 2014 was 9.9 degrees Celsius, putting it 1.1 degrees above the long-term average from 1981 to 2010.

This means 2014 was hotter than the previous warmest year of 2006 by 0.2 degrees.

The latest data also shows that eight of the UK's ten hottest years have occurred since 2002, the Met Office says.

The announcement confirms the Met Office's early figures released in December, which suggested that 2014 could be record-breaking.

Consistently warm

The Met Office provisional data shows that the year was consistently warm, rather than having a particularly hot spell that pushed average temperatures up for the year. Every month apart from August was above the long-term average.

2014 was a warm year across the whole of the UK, as the map below shows. It was the hottest year on record for every region of the UK except for Northern Ireland, for which 2014 was the joint-third warmest year.

2014_17_Mean Temp _Anomaly _1981-2010

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The year in climate science

  • 31 Dec 2014, 09:30
  • Robert McSweeney

Rajendra Pachauri on Sky News

2014 has seen much to talk about in the world of climate science, from devastating flooding to record-breaking temperatures. The year has seen a mountain of climate change reports from the IPCC, polar sea ice debate, and an El Niño that's more undecided than a scientist in a cardigan shop.

We take look back over how climate science hit the news this year.

Debate over winter flooding

The winter going into 2014 was  one of the most exceptional periods of rainfall in England and Wales in at least 248 years, when records began. When the flooding hit, the media was awash with debate on whether climate change was the culprit. Inevitably, some of the stories got things a bit mixed up.

The Times suggested a recent academic study found "the increase in the number of floods in Britain is due to urban expansion and population growth rather than the early impacts of climate change". Except, as the study's authors  explained to us, it did nothing of the sort.

The  Mail on Sunday reported that Met Office scientists were arguing amongst themselves on the contribution of climate change to the floods. The Met Office  swiftly dismissed the claims, saying "this is not the case and there is no disagreement."

We thought it best to get an expert in, so Dr Peter Stott from the Met Office wrote us a  guest blog on how scientists work out the human influence on extreme weather events.

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Five bits of research that shaped climate science in 2014

  • 26 Dec 2014, 10:25
  • Roz Pidcock

Climate science never stops developing. Over the course of the year we've covered a myriad of scientific studies, some of which have made the news, and others which have been more quietly received. Here's our pick of the papers that have shaped scientific discussion about climate change in 2014.

1. Pacific winds drive surface warming slowdown

In February,  a paper by Matthew England and colleagues helped shed light on why surface temperatures have risen  more slowly over the last 15 years or so than in previous decades, even though we're emitting greenhouse gases  faster than ever before.

England et al (1).png

Colours show temperature trends in the Pacific during 1992-2011 at the sea surface. Trade winds blowing east to west are shown by the blue arrow. Thin arrows indicate a strengthening circulation, with more water transported to deeper layers. Source: England et al. (2014)

few pieces of research last year pointed towards the tropical Pacific as holding the key. The England paper added a layer of detail by describing the process that could be at play.

Trade winds have been  particularly strong since about 2000, which is driving heat deeper into the oceans and bringing cooler water up. This has made earth's average surface temperature  0.1 to 0.2 degrees cooler than it would otherwise be, the scientists estimate.

While scientists suggest there could be an  additional role for the Atlantic in driving the hiatus, evidence for the Pacific Ocean mechanism seems to be  winning out at the moment.

For more on how the ocean deeps influence what we feel up here on earth's surface, here's our  top to bottom look at the oceans and climate change.

England, M. et al. (2014) Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus. Nature.  doi:10.1038/nclimate2106

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25 inspirational texts about climate change

  • 25 Dec 2014, 12:10
  • Simon Evans

Did Santa bring any of these this Christmas?

We asked 25 thinkers, writers and journalists a simple question: What books or readings inspired you to get involved in climate change-related work?

We were expecting to get back a list of books - and we did. But we also got some interesting insights into why people work on this issue, why they started, and why they carry on.

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Pacific winds change the speed of global warming, says new study

  • 22 Dec 2014, 16:00
  • Robert McSweeney

Coral reef | Shutterstock

The strength of the trade winds that cross the Pacific can affect how quickly the planet warns, new research suggests.  By analysing the chemical makeup of corals in the tropical Pacific, researchers have found that changing wind patterns affected how quickly the Earth warmed during the last century.

The study adds "another piece of evidence" that strong Pacific winds are contributing to the recent slowdown in global surface temperature rise, says an accompanying News and Views.

Trade winds over the ocean

The trade winds are the typical east-to-west winds that blow across the tropics, which you can see in the diagram below. They are driven by warm air rising along the equator and the rotation of the Earth.

Edu 1.3-image

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First look at new NASA satellite map reveals global carbon dioxide hotspots

  • 18 Dec 2014, 20:10
  • Roz Pidcock

NASA space scientists today unveiled a new satellite map showing carbon dioxide levels in the atmosphere right across the globe.

The map is the first two months of data from the new Orbiting Carbon Observatory-2 (OCO-2) mission, launched in July this year.

The team from NASA's Jet Propulsion Laboratory, Colorado State University and California Institute of Technology presented their findings at AGU conference in San Francisco today.

PIA18934

The map shows an average global concentration of 400 parts per million (ppm) with hotspots of high carbon dioxide in the Southern Hemisphere above southern Africa and Brazil. The scientists attribute this to springtime burning of savannas and forests to clear land for farming. 

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What do squirrels, beavers and reindeer have to do with methane emissions?

  • 18 Dec 2014, 15:44
  • Robert McSweeney

Arctic squirrel | Shutterstock

It's not just humans that are causing climate change. Squirrels and beavers have both been implicated in recent days as research reveals their contribution to the release of methane, a powerful greenhouse gas.

Obviously the Internet loves a good rodent story. But could it really be the case that these toothy animals are paving the way to climate catastrophe?

It's unlikely, an expert tells us, but that's not to say they should be overlooked.

Global methane emissions

Methane is a powerful greenhouse gas, around 25 times more effective at trapping heat than carbon dioxide over the course of a century. About a fifth of the global warming linked to human activity is as a result of methane emissions, scientists estimate.

The sources of methane emissions are shown in the figure below. Total emissions from human activities, such as farming livestock and burning fossil fuels, are similar to natural sources, the largest of which is from decomposing vegetation in wetlands.

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Deforestation in the tropics affects climate around the world, study finds

  • 18 Dec 2014, 10:00
  • Robert McSweeney

"The effects of tropical deforestation on climate go well beyond carbon," says Professor Deborah Lawrence, "[it] causes warming locally, regionally, and globally, and it changes rainfall by altering the movement of heat and water."

These are the conclusions of a worldwide study into the deforestation of tropical rainforests, which shows that cutting down trees can have immediate impacts on the climate and put agricultural productivity at risk.

Rainforests are more than just a carbon store

Deforestation and land use change account for approximately 11 per cent of global carbon dioxide emissions. But the new research finds that cutting down trees doesn't only affect the carbon they lock up.

The research, published in Nature Climate Change, reviews academic studies on deforestation of tropical rainforests in the Amazon basin, central Africa, and southeast Asia. Many of the studies use climate models to simulate what happens if you remove these forests completely, and they suggest that deforestation in the tropics can affect the climate on the other side of the world.

The map below shows how far-reaching some of these potential impacts are. The triangles show areas where rainfall is expected to decrease because of tropical deforestation, and the circles show areas of increase. The colours indicate the link to where the deforestation occurs.

So the models suggest deforestation in the Amazon, for example, can reduce rainfall over the US Midwest and even in northeast China. Deforestation in central Africa can cause a drop in rainfall in southern Europe, and loss of trees in southeast Asian can bring wetter conditions in southern Europe and the Arabian Peninsula.

Lawrence & Vandecar (2014) Fig1

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