Analysis

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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Why aren't climate models better at predicting Arctic sea ice loss?

  • 17 Dec 2014, 01:20
  • Roz Pidcock

Climate models generally do a poor job of capturing how rising temperatures in the Arctic are affecting sea ice. Most underestimate the rapid pace at which sea ice is diminishing.

Why is that?

Scientists at the huge science conference hosted by the American Geophysical Union (AGU) taking place now in San Francisco have been discussing why it is so difficult to capture what's happening to Arctic sea ice in climate models, and how we can make the most reliable forecasts possible with the tools available.

A policy-making tool

Arctic sea ice extent has been declining by about  four per cent per decade, with the seasonal low at the end of summer shrinking particularly quickly.Screen Shot 2014-12-15 At 23.02.08 

Decadal trend in Arctic sea ice extent since 1979 (left) Map of changes in sea ice concentration across the Arctic (right) Source:  IPCC 5th Assessment Report (Sep 2013)

Reliable forecasts of how warming will affect sea ice are important for decision making, Professor Julienne Stroeve from the US National Snow and Ice Data Centre told the AGU conference. This includes questions like when the Arctic is likely to be sea ice free in summer.

But only a quarter of models simulate a rate of sea ice loss comparable with that observed by satellites since 1979, according to the  Intergovernmental Panel on Climate Change (IPCC).

So where are they going wrong?

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New satellite maps reveal hidden intricacies of Greenland ice loss and sea level rise

  • 15 Dec 2014, 20:00
  • Roz Pidcock

Jakobshavn Icebergs | B. Csatho

Greenland lost enough ice between 2003 and 2009 to raise sea levels by more than four millimetres, according to new research that maps the vast ice sheet in unprecedented detail.

Scientists have used satellites to measure ice loss at nearly 100,000 locations, concluding that the Greenland ice sheet is far more complicated that it's often assumed to be. And that means projections of how much we can expect sea levels to rise need updating.

Between 2003 and 2009, Greenland lost about 243 billion tonnes of ice a year, adding 0.68 millimetres to sea levels annually, the research finds. Almost half the ice lost came from Southeast Greenland.

Castho Et Al 2014_Fig3

Annual total ice loss from the Greenland ice sheet between 2003 and 2009. Source: Csatho et al., (2014)

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New paper raises question of tropical forest carbon storage

  • 15 Dec 2014, 16:00
  • Robert McSweeney

Tropical rainforest | P. Groenendijk

The world's forests provide a huge carbon sink, absorbing around a third of manmade carbon emissions, and helping to moderate global temperature rise.

A new study argues that the speed of tree growth in tropical rainforests isn't keeping pace with rising carbon dioxide levels in the atmosphere, and so it may be "too optimistic" to expect this buffering effect to keep pace with rising emissions.

But another scientist tells us the finding needs to be examined carefully, and it could be difficulties in taking measurements in tropical rainforests that are leading to the result.

Rainforests are an important carbon store

As part of the Earth's natural carbon cycle, vast amounts of carbon dioxide are taken out of the atmosphere and absorbed by the land each year. Tropical rainforests, the extremely productive forest ecosystems found gathered around the equator, are responsible for much of that exchange.

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

Experiments scientists have carried out in temperate forests and greenhouses suggest that when there's more carbon dioxide in the air, trees can grow more quickly because their photosynthesis rate speeds up. This process is called 'carbon dioxide fertilisation'.

Scientists expect that as manmade carbon dioxide emissions increase, forests will absorb and store more carbon.

But a new study, published in Nature Geoscience, suggests that tropical rainforests might not be absorbing more carbon as emissions rise. Despite a 35 per cent increase in atmospheric carbon dioxide over the last 150 years, the study suggests that trees in the tropics aren't growing any quicker.

Studying tree rings

The researchers studied over a thousand trees of different ages, covering 12 different species and three different parts of the tropics. They chose areas of old-growth forests in Thailand, Cameroon and Bolivia that were undisturbed by deforestation or human settlements.

They analysed tall 'canopy' trees, which are the most common type in tropical forests and typically reach around 30 metres in height, and also smaller 'understorey' trees that grow to around 10 metres tall.

Examining tree rings can show how quickly a tree has grown from year to year. As a tree grows, it puts on extra layers of wood around its trunk, creating a new ring each year. The more a tree has grows in a year, the more wood it adds, and the wider the tree ring is.

800px -Tree _rings

Tree rings. Source: Creative Commons 2.5: Arnoldius

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