Analysis

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.

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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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What happens if we overshoot the two degree target for limiting global warming?

  • 10 Dec 2014, 12:30
  • Roz Pidcock

Two degrees is the internationally-agreed target for limiting global warming, and has a  long history in climate policy circles. Ambition that we can still achieve it is running high as climate negotiators gather in Lima to lay the groundwork for a potential global deal in 2015.

But against this optimistic backdrop, greenhouse gas emissions have continued to rise. With each passing year the scale of the task looms ever larger. There are very real questions about  whether or not the world will be able to stay below the two degree limit.

So what happens if we fail to meet the two degree target? What would it mean to resign ourselves to a post-two degree world? And if not two degrees, then what?

As temperatures rise, so do the risks

Two degrees above pre-industrial temperature has been agreed by countries as an appropriate threshold beyond which climate change risks become unacceptably high.

Global temperature has risen 0.85 degrees Celsius since 1880, according to the latest report from the Intergovernmental Panel on Climate Change (IPCC).

We could be due another couple of tenths on top of that as past emissions take a decade or so to reach their full effect warming. Together with current and expected emissions we're essentially already committed to about one degree of warming, scientists estimate.

Extended RCPs

Extension of the IPCC's emissions scenarios to 2300. RCP2.6 limits warming to two degrees above pre-industrial levels (blue), RCP4.5 levels out as about three degrees (green). In RCP8.5, temperatures exceed four degrees by 2100 and continue to rise. Meehl et al., (2013)

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Two degrees: Will we avoid dangerous climate change?

  • 09 Dec 2014, 11:30
  • Simon Evans

Limiting warming to no more than two degrees has become the internationally accepted target for climate policy, as we saw in  the first blog of our series of pieces looking at the two degrees limit.

Scientists think the risks of climate change increase as temperatures rise. Two degrees isn't a 'safe' level of climate change, but nor is it a red line with only chaos beyond, as we'll see in part three.

It is a readily understood and useful marker of how we're doing at limiting dangerous climate change that has helped focus minds on the scale of the challenge. It's also what the world's governments have committed to achieving.

So will we manage to limit warming to two degrees above pre-industrial? We take a look at what it will take to stay below two degrees, how things are going so far, how experts say we should proceed and what we'd need to do if we wanted to follow their advice.

1. What we would need to do to stay below two degrees

The world has already warmed by 0.85 degrees celsius above the pre-industrial average and if emissions stay high we're on course for more like three to five degrees by 2100,  according to the latest Intergovernmental Panel on Climate Change (IPCC) reports.

Broadly speaking, however, scientists say it is still theoretically possible to limit warming to two degrees as long as we stick within a fixed  carbon budget. This is the total amount we can emit from the beginning of the industrial revolution until the day we stop adding carbon to the atmosphere.

So how big is the budget? It is likely that we'll stay below two degrees as long as we emit no more than about 2,900 billion tonnes of carbon dioxide, the IPCC  says. 'Likely' here means a 66 per cent chance.

We've already emitted 1,900 billion tonnes, leaving a remaining budget of just 1,000 billion tonnes that we can emit between now and forever. At current rates we'll  use that quota up within 21 years.

If we're willing to accept a higher risk of breaching the two degree target then our budget would be a bit bigger. It might last 33 years at current emissions rates, instead of 21 years.

If the earth is  less sensitive to emissions than we thought, that would increase the budget too: we could emit more carbon and still stay below two degrees. But at current rates we would burn through that extra allowance in  about a decade.

Whether climate sensitivity is lower than thought or not, we don't have many years left to significantly cut emissions.

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European summer heatwaves ten times more likely with climate change

  • 08 Dec 2014, 16:00
  • Robert McSweeney

CC 2.0: Andrew Bowden

Climate change is raising the odds of summer heatwaves in Europe by a factor of 10, according to new research from the Met Office. Over the past 10 to 15 years, the likelihood of a 'very hot' summer has risen - from once every 50 years to once every five years.

As the frequency of heatwaves increases, so do risks to human health. Improving resilience to high temperatures is critical to avoiding deaths caused by extended periods of hot weather, the authors say.

A record heatwave

The summer of 2003 was the hottest ever recorded for central and western Europe, with average temperatures in many countries as much as five degrees higher than usual.

Studies show at least 70,000 people died as a result of the extreme high temperatures. In August alone, France recorded over 15,000 more deaths than expected for that time of year, a 37 per cent rise in the death rate. The same month also saw almost 2,000 extra deaths across England and Wales.

To see how climate change is affecting the likelihood of heatwaves and other extreme events, researchers carry out attribution studies. These identify the fingerprints of human influence on observed changes in temperature, rainfall, and other climate parameters.

The heatwave was the first extreme weather event to be attributed to the human influence on the climate, with research suggesting it was made more than twice as likely because of climate change.

Now a new study, published in Nature Climate Change, finds that recent warming means a similar heatwave is even more likely. The increasing impact of humans on the climate means the risk of 'extremely hot' summers is now ten times greater than when the 2003 European heatwave struck.

Very hot summers every five years

In the new study, Met Office researchers ran their climate models twice: first with both natural climate fluctuations and manmade warming included, and secondly with only natural influences on the climate. They compared the results to see how rising temperatures have altered the odds of heatwaves in Europe.

You can see in the left-hand chart below how close the model simulations that include manmade warming (black line) are to actual recorded summer temperatures (red line). By contrast, modelled summer temperatures from a world where there's no human influence on the climate don't match up well with what scientists are seeing.

This shows summer temperatures can't be explained by natural variability alone, and climate change is playing a role, the paper explains.

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2014 on course to be the hottest year on record

  • 03 Dec 2014, 15:00
  • Robert McSweeney & Rosamund Pearce

UK Met Office

2014 is expected to be the among the hottest years since records began for the UK and the world, and may well prove to be the hottest, according to data from the World Meteorological Organisation (WMO) and the UK Met Office.

Rising temperatures are already contributing to greater risks of extreme weather, scientists warn.

A very warm and wet year for the UK

Met Office figures released today show the mean UK temperature for 2014 is 1.6 degrees Celsius above the long-term average. Currently 2006 is the warmest year since records began in 1910, but 2014 looks likely to replace it.

In England, where temperature records stretch back further, 2014 will be one of the warmest in the 350-year Central England Temperature (CET) record , the longest instrumental record in the world.

This year has also been a very wet one for the UK, and is on course to be the fourth wettest on record. A rainy December could even put 2014 over the annual record of 1337 mm set in 2000, says the Met Office.

A record-breaking year for the world

Globally, it seems likely that 2014 will be the hottest since records began in 1850. Average air temperature over the land and sea surface for 2014 so far is 0.57°C above the 1961-90 average. The previous high of 0.55°C warmer is held jointly by 2005 and 2010.

The ranking of hottest years is shown in the chart below. The red bars show years since the turn of the century, and show that for the most part the hottest years on record have occurred in the past decade or so.

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