Space agencies pinpoint polar ice sheet damage

The midnight sun casts a golden glow on an iceberg and its reflection in Disko Bay, Greenland, where ice sheet mass loss was five times higher in 2011 than it was in 1992. Much of Greenland’s annual mass loss occurs through 'calving' of icebergs such as this. Credit: Ian Joughin.

The midnight sun casts a golden glow on an iceberg and its reflection in Disko Bay, Greenland, where ice sheet mass loss was five times higher in 2011 than it was in 1992. Much of Greenland’s annual mass loss occurs through ‘calving’ of icebergs such as this. Credit: Ian Joughin.

47 scientists from 26 key laboratories across the world. 10 satellite missions flown over a period of 20 years, whose data adds up to 51 years’ worth. This giant effort looks to have squashed stubborn uncertainty surrounding one key climate question: How quickly are ice sheets resting on land masses at the North and South Poles shrinking? The international team has now found that Greenland’s mass loss is five times as fast as it was in 1992. Overall loss rates in Antarctica are roughly constant in this period, though the east of the continent is actually gaining ice. Over the past 20 years, the polar ice sheets have added 11 mm to sea level rise across the world, one-fifth of the total rise seen in that time.

“Our new estimates are the most reliable to date and they provide the clearest evidence yet of polar ice sheet losses,” said Andrew Shepherd from the University of Leeds, UK, co-leader of the project. “They also end 20 years of uncertainty concerning changes in the mass of the Antarctic and Greenland ice sheets and they’re intended to become the benchmark dataset for climate scientists to use from now on.”

Until the early 1990s, climate researchers expected that mass lost by ice sheets in Greenland as the planet warmed would be balanced by that gained by Antarctica. But measurements showed that both melting and ‘calving’ of icebergs could be speeding up at both poles. This meant the UN’s Intergovernmental Panel on Climate Change (IPCC) couldn’t put an upper limit on what ice sheets might add to sea levels in its last major report on global warming in 2007. And the overall picture has been confused, as efforts to measure whether ice sheets are shrinking or growing have given differing results. Since 1998, there have been 29 different estimates of changes in ice sheet mass. “Taken all of the past studies together, the recent global sea level contribution due to Antarctica and Greenland may have been anywhere between a 2 mm per year rise and a 0.4 mm per year fall,” Andrew told a press conference yesterday. At a workshop in 2010, the IPCC said it was concerned that no further progress would be made by its next report, due in 2014. Read the rest of this entry »

Carbon conundrum could push firmer emission action

Measuring CO2 emitted by  soil in tropical forests from tree debris with a particular chemical signature, with a wire mesh tent excluding other tree debris. Climate change could enhance tree growth in tropical forests, and the resulting increase in litterfall could stimulate soil micro-organisms leading to a release of stored soil carbon. Such uncertainties in the carbon cycle aren't well captured by climate models. Credit: Dr. Emma Sayer

Measuring CO2 emitted by soil in tropical forests from tree debris with a particular chemical signature, with a wire mesh tent excluding other tree debris. Climate change could enhance tree growth in tropical forests, and the resulting increase in litterfall could stimulate soil micro-organisms leading to a release of stored soil carbon. Such uncertainties in the carbon cycle aren’t well captured by climate models. Credit: Dr. Emma Sayer

Rather than sucking up ever more of the greenhouse gas CO2 as the world warms, plants and soil could begin releasing it instead. This hasn’t been included in climate models, and means their predictions of the temperature rise following us burning more fossil fuels might be too low.  That’s what US researchers have found after linking two models, one simulating climate and the other the ‘carbon cycle’ moving through living creatures and the environment. “That means that to keep concentrations of CO2 in the atmosphere at ’safe’ levels, we might have to reduce our emissions more aggressively than we currently realise,” said Paul Higgins from the American Meteorological Society in Washington DC.

Plants take up CO2 to power their growth through photosynthesis. Many climate models that consider the carbon cycle assume that more CO2 in the air will speed their growth, and mean they absorb the gas faster. But when Paul looked at what plants actually did during his master’s degree at Stanford University, California, more than a decade ago he found this ‘CO2 fertilisation’ didn’t always happen. “Carbon cycle models did tend to make an optimistic assumption about CO2 enrichment that was not entirely consistent with what the experiments were suggesting,” he told me.

That thought stayed in Paul’s mind as he continued his research, which brought him to John Harte’s labs at University of California, Berkeley, in 2003. There he found that plants faced limits on how readily they can move to places where conditions suit them best as climate changes. That can also affect how much CO2 they store overall, he noted. “Over the next couple of years, I kept going back to that and thinking ‘Why don’t we think about CO2 enrichment in the context of this work as well?’”

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Australians overestimate climate change rejection

CSIRO's Zoe Leviston has run a survey that found Australians' actual opinions on climate change are very different from what they estimate other people think. Credit: CSIRO

CSIRO’s Zoe Leviston has run a survey that found Australians’ actual opinions on climate change are very different from what they estimate other people think. Credit: CSIRO

People in Australia overestimate how many of their fellow citizens don’t think climate change is happening, but still think their own opinion is the most common. That’s according to a survey run by Zoe Leviston from Australia’s national science agency, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), in Perth and her teammates. Roughly one person in 20 surveyed fell in the ‘not happening’ group, but on average people thought that one person in five did. That’s partly down to a well-known effect called ‘false consensus bias’, where we tend to think more people agree with us than really do. However, how politicians and the media in Australia discuss climate change could be making the effect stronger than usual.

“There is a mis-estimation of community sentiment,” Zoe told me. “Our perception of what others think is a dynamic process, and if we have these misperceptions, they can actually reinforce our own patterns of thinking. Other research has shown that people can be hesitant to speak out if they think their opinion is on the decline, because they think that they risk social censure. It’s important to communicate accurately what the consensus is, otherwise you can needlessly propagate this myth of widespread denial.”

As part of a major CSIRO research program, known as the Climate Adaptation Flagship, Zoe surveyed more than 5,000 Australians in both 2010 and 2011, 1,355 of whom completed both surveys. Among other questions, they were asked which of four statements best described their view. They could choose: climate change is not happening; don’t know whether it’s happening or not; it’s happening but natural fluctuations; or it’s happening and caused by humans.

But Zoe and her fellow CSIRO scientist Iain Walker wanted to look beyond this basic opinion. “In Australia the media and political debate surrounding climate change have often rested on these competing claims about what Australians support and what they think,” Zoe said. “We knew that people are very bad estimators of what others are thinking, so we decided to ask about that as well.” So straight after the first question, Zoe and Iain asked what proportion of Australians would choose each of the four answers. Read the rest of this entry »

Monsoon instability raises food questions for India

A street in Calcutta floods during monsoon season. After some decades of increasing rainfall, climate change could bring drier monsoons,  said Jacob Schewe from the Potsdam Institute for Climate Impact Research. Credit: Mark E Dyer/Flickr

A street in Calcutta floods during monsoon season. After some decades of increasing rainfall, climate change could bring drier monsoons, said Jacob Schewe from the Potsdam Institute for Climate Impact Research. Credit: Mark E Dyer/Flickr

Monsoon rains in India may fail more frequently as climate change proceeds into the 22nd century, German researchers said this week. That danger could be critical for farming in what is set to become the world’s most highly populated country by 2030, and would follow an already expected wetter period. “Previous studies showed that Indian monsoon rainfall would increase more or less linearly with global warming over the next century,” said Jacob Schewe from the Potsdam Institute for Climate Impact Research. “The monsoon can respond to climate change in a more complicated way. We’ve seen that it matters to look further into the future.”

In South Asia, summer monsoon rains fall as winds blow from the southwest Indian Ocean over the continent between June and September. They end when the wind direction reverses in September or October. What Indian monsoon rain seasons will do as the world warms is an important and difficult question that many researchers are trying to answer. Though more rainfall has been predicted, recent years haven’t matched that expectation. While factors like pollution have an effect, changes climate scientists already know a major climate pattern plays a very important part in monsoons.

“There is a coupling between the El Niño Southern Oscillation and the monsoon that’s been observed for a long time,” Jacob told me. In years when El Niño occurs, an air movement pattern called the Walker circulation pattern gets shifted eastward. That brings high pressure over India and weakens the monsoon. While some changes in El Niño are already happening, the Walker circulation is expected to weaken, but not for some time yet. That could mean scientists’ climate models don’t pick up its effects. “People have looked at monsoon changes but not many studies have looked beyond 2100,” Jacob said. “You really have to consider longer timescales – beyond 2100 – to assess the full range of consequences for the monsoon.” Read the rest of this entry »

Butterfly effect limits climate models

National Center for Atmospheric Research's Clara Deser. Credit: NCAR

National Center for Atmospheric Research’s Clara Deser. Credit: NCAR

Natural chaos in our climate system creates uncertainty in predictions that can’t be removed, no matter how good scientists’ models get. Clara Deser from the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado and her colleagues have shown these effects can be as strong as human-caused warming. “Over multiple decades intrinsic climate variability on a local and regional scale can be on a par with climate change due to greenhouse gas emissions,” she told me. “You’re not going to just see the result of the greenhouse gas increases – you’re going to see both. This simple message has been missing from the climate change literature.”

Climate scientists are working hard to improve the accuracy of their models’ predictions – perhaps so hard they haven’t yet looked at what their limits are. “We’ve been focussed on identifying how greenhouse gas changes and the like can affect the climate system,” Clara said.  “The uncertainties in climate projections have all been lumped together. There hasn’t been a set of runs that were designed the way that we have done them to really address this point.”

Anyone who’s had to run outside to rescue drying clothes from a rain shower knows that weather can be variable from day to day. Climate patterns also vary from year-to-year, like El Niño or the North Atlantic Oscillation, and some chaotic climate processes work over decades. Wanting to reduce model uncertainty, Clara previously tried to answer a series of detailed questions about these kinds of natural variability. Her team’s answers showed that they accounted for at least half of the disagreement between different climate model predictions. When she told this to two fellow climate scientists, Reto Knutti, from the Swiss Federal Institute of Technology, Zurich and Massachusetts Institute of Technology’s Susan Solomon, they were surprised. “They said, ‘Something very simple and illustrative is needed to get this important message across,’” Clara recalled.
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