Probabilities reveal shape of climate change

Planners looking to prepare for floods, like this one in Venice, Italy, would like better local information on climate change – and now David Stainforth and his colleagues are helping deliver it. Image courtesy http://www.WorldIslandInfo.com, Allison Lince-Bentley, used under Flickr Creative Commons license.

If you want to plan for the future, or even for the present, knowing that our climate is changing, what’s the best way to do it? That’s a question that David Stainforth from the London School of Economics, Sandra Chapman from the University of Warwick and Nicholas Watkins from the British Antarctic Survey have puzzled over. And while David is co-founder of the climateprediction.net project that borrows spare time on peoples’ computers to run climate models, he doesn’t feel that models are always the best source of information.

“It’s clear to me that the detailed local information on how climate is changing, and what it will be like in 2050, can’t be had from climate models today,” David told me. “They’re just not that good. And yet I work a lot with the adaptation and impacts community, who are interested in what’s happening ‘here’, on a very local basis.” So together David, Sandra and Nicholas have turned to measured data, devising a simple way to pick the most important local climate changes from it.

Weather stations around the world monitor daily conditions, and combine to create a record containing occasional extremes, lots of ordinary days, and everything in between. Knowing how common these conditions are is important for people who want to prepare for future climate change. “For flood risks, you’re worried about going over certain rainfall amounts in a given time,” David explained. “Managers of overheating buildings are worried about what proportion of the time temperatures pass certain levels.”

Cave deposits reveal permafrost concern

University of Oxford’s Anton Vaks explores a cave, where he could find stalactites and stalagmites that reveal when the soil above was permafrost. Credit: University of Oxford

Stalagmite and stalactite deposits in Siberian and Mongolian caves have revealed the most accurate permafrost history yet, suggesting that a global 1.5°C temperature rise could trigger a widespread thaw. “The finding shows how vulnerable the permafrost is,” said Anton Vaks from the University of Oxford. “Russian gas facilities in north-western Siberia are located close to the boundary of the continuous permafrost and rely on it as hard ground. Thawing of the permafrost may cause damage both to Russia, as well as its gas trade partners, like the European Union. The melting permafrost may also release part of the organic carbon currently trapped in it as greenhouse gases, CO2 and methane, enhancing global warming.”

Anton first used cave deposits’ power to study climate history during his PhD to build a 350,000 year record for the northern margin of the Saharan-Arabian Desert. “Stalagmites and stalactites grow only when rain or snowmelt water seep into the cave through the ceiling,” Anton explained. “Therefore each layer of growth of stalagmites and stalactites records a humid event in the desert.” He realised that these deposits’ ability to track water flow could equally measure melting of previously permanently frozen soil known as permafrost. “Cave deposits cannot grow when the rock above the cave is frozen,” Anton said. “Thus, each growth layer in a stalagmite forms during warm periods, whereas growth breaks represent cold periods with permafrost. Past periods that were warmer than now are especially important, because they can show what may happen to the permafrost in the future warmer world.”

Extra stations bolster warming-extreme rainfall link

The highest daily rainfall in a year is increasing by around 7% per 1°C warming. Credit: Andrew Ciscel via Flickr

The most comprehensive review of changes to extreme rainfall yet has confirmed the link between extreme rainfall intensity and global atmospheric temperature, with annual rainfall highs intensifying by around 7% per 1°C warming. University of Adelaide’s Seth Westra and his teammates called on 8326 weather stations across the Earth’s surface with over 30 years’ data from the period between 1900 and 2009. “The real innovation in this study is the strength of the data set we used,” Seth told me.

As a flood engineer, Seth has conducted numerous flood risk studies using highest daily rainfall amounts over a year period for planning. But when trying to understand how these rainfall amounts are changing, he found that many studies did not present their information so engineers could use it easily. He therefore wanted to do a statistical study that could produce more precise estimates. And when he found out that Lisa Alexander at the University of New South Wales, Australia was bringing together measurements of temperature and rainfall extremes, he saw his opportunity.

Lisa is part of a team that has collected data from 11391 weather stations worldwide, a much larger record than previous studies had used. That’s partly to contribute to the Intergovernmental Panel on Climate Change’s fifth assessment report on global warming, due out in stages in late 2013 and 2014. But it meant the massive task of collecting the measurements needed to do the kind of study Seth planned was already being done. “You can imagine the sheer amount of work in getting data from dozens of meteorological agencies from around the world,” he said. “Trying to feed them all into one single repository is a lot of effort.”

With this data in hand, Seth, Lisa and Francis Zwiers from the University of Victoria, Canada, first selected only the 8326 stations with over 30 years’ worth of data. They then used two statistical tests to look at the annual extreme rainfall highs, which they published online last year in a paper in the Journal of Climate. In the first, they simply looked at whether rainfall extremes increase or decrease at each station over time, Seth explained.

Warming brings home the value of a meal

The 2012 Plant Hardiness Zone Map unveiled by the US Department of Agriculture this year shows average annual extreme minimum temperatures based on data from 1976-2005. In this version 2012 is modified to use the same colour code as 1990. Much of the US was one 5°F (2.8°C) half-zone colder in the 1990 Plant Hardiness Zone Map compared to the latest version. Credit: US Department of Agriculture/Friend of the Earth

Part one of two

Over the past few days I’ve been lucky enough to enjoy the kind of celebrations that would have been called feasting in the past. They’ve brought home how important food is as basic fuel, a source of pleasure and a reason for friends and family to get together. This year, that importance has drawn me increasingly to research into what climate change means for our food supply. What I’ve covered only begins to scrape the surface of the effects we can expect. However, these studies highlight how life could become yet harder for farmers, and what that could cost us all.

The warming world has already noticeably changed plant growing conditions, for example shifting the regions they are suited to grow in the US. In January, the US Department of Agriculture (USDA) redrew its map of planting zones to reflect warming seen since the 1990 version. Partly due to climate change, and partly due to new technology and better weather data, many places are now one 5°F (2.8°C) half-zone warmer. At around the same time, Chinese researchers found that the phases in the seasonal cycle of crop growth in their country had shifted between 1960 and 2008. Springtime events are now 6-15 days earlier and Autumn events 5-6 days later, they found.

2012’s record events put climate in mind

Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12. In the image, the areas classified as “probable melt” (light pink) correspond to those sites where at least one satellite detected surface melting. The areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected surface melting. The satellites are measuring different physical properties at different scales and are passing over Greenland at different times. As a whole, they provide a picture of an extreme melt event about which scientists are very confident. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

This has been another year of striking climate events and records – but they seem to be happening so much more often today that their effect on me has weakened. That’s pretty cold-hearted, I admit. ‘Extreme weather’ is having terrible effects on peoples’ lives all around the world. But the truth is that we can only handle so many problems before becoming too numbed and overwhelmed to act. And last year, Stefan Rahmstorf and coworkers at the Potsdam Institute for Climate Impact Research showed temperature records are much more likely today than in a stable climate. “I don’t think many people appreciate how much the odds for such extremes have increased due to global warming,” he told me at the time. “I certainly didn’t until we had performed this study.” So it’s hardly surprising if we begin to get complacent when records are flowing thick and fast. But when I actually faced up to what’s happened in the climate this year, it was intriguing how well you could see global warming’s fingerprint.

Warming’s most dramatic effects have long been obvious in the Arctic, and 2012 was no different. Images from three satellites showed that almost Greenland’s entire ice sheet surface was temporarily melted by July 12. That’s the largest area in over 30 years of satellite observations. Then, on September 16, sea ice in the Arctic reached a record annual minimum area of 1.32 million square miles, approximately half the size of the average annual minimum for 1979 to 2000. Just two weeks later, Antarctic sea ice covered its highest area on record at the peak of winter, at 7.49 million square miles. In case you think that’s a natural balance that shows the planet isn’t warming, it’s worth noticing the scale of the changes. The Antarctic record is 193,000 square miles higher than its average maximum area for the last 30 years. That’s much less than the 1.32 million square miles the Arctic lost compared to its long-term average.

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.

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.

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

Monsoon rains in India may fail more frequently as climate change proceeds into the 22^nd 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.”

Climate provides weak power to predict African violence

Two boys from the Local Defence Unit (LDU) in Kitgum, Northern Uganda, whose job is to protect the people at a refugee camp from attacks and kidnappings by the Lord’s Resistance Army, which has been responsible for much violence in East Africa in recent years. Credit: John & Mel Kots/Flickr

Rainfall and temperature changes are linked to conflict in East Africa, but have less power to predict violence than links to political, economic and geographical factors. That’s according to one of the most detailed studies into climate-violence relationships yet, done by John O’Loughlin from the University of Colorado, Boulder, and his team-mates. “Fears of climate wars across Africa are exaggerated,” John told me. “Any effect of climate change will likely be localized and subject to other conditions.”

One political argument made about our changing climate is that it will bring more violence, particularly in Africa. For example, in 2009, US President Barack Obama told the United Nations that a warming world represents an “urgent, serious, and growing threat” because “more frequent drought and crop failures breed hunger and conflict”. But, with a background of looking in detail at where violence happens and having studied African conflicts before the 1990s, John was concerned that the evidence didn’t back such statements. That’s even though other researchers have reported statistical links between climate and conflict. “I believe that previous studies were limited by data problems and also that the policy discussions were not connected to the research findings,” John explained.

John’s team described how they fixed this in a paper published in the research journal Proceedings of the National Academy of Sciences of the USA on Monday. Previous attempts to study climate-violence have either lacked detail, looking at data per country, per year, or have been too narrowly focussed to allow generalisations, they wrote. John added that this type of work needs detailed data on both conflicts and all the factors that might predict it. Collecting the information needed on conflicts as well as political, health, location and other possibly predictive data was the biggest challenge in the work, he said.

Warming weakens deep freeze on Arctic islands

Pictures from William D'Andrea's August 2012 expedition to Svalbard. There are 24 slides in this series - apologies for the poor formatting. Credit: The Earth Institute/Columbia University

Normally 6°C wouldn’t be very warm – but in the Norwegian islands of Svalbard it’s a sultry modern summer, unlike anything seen for at least 1,800 years. That’s what sediments taken from an Arctic lake have told William D’Andrea from Columbia University in New York and a US team. It’s even warmer than a medieval warm period when parts of the northern half of the planet were as hot as, or hotter, than today. And while the record they’ve made reflects just this one site, it adds to the picture showing how unique today’s climate is. It’s also another step towards understanding how climate has changed through history, William told me.

Climate dynamics are extremely complex, and cooling in some locations can happen at the same time as warming in others, or increased precipitation in some places along with drought in other places,” he said. “These are the fingerprints we are trying to map and understand by generating such reconstructions.”

The fingerprints slowly become clearer as scientists collect more historical records, often as tubes of ice drilled from glaciers, or of mud and rock drilled from sea and lake beds. The tubes, or cores, cut through layers of mud or ice built up year after year. Scientists can then use fossils and chemicals to date and work out what conditions were like when they were laid down.

Could pollution be stopping warming’s impact on rain?

A brown cloud of pollution over Phoenix, Arizona. Brown clouds of aerosol pollutant particles could be overwhelming the expected changes in rainfall arising from increasing greenhouse gas levels in the air. Credit: Flick/Flickr

Contrary to previous predictions and measurements, rain patterns have got more uniform as the world has warmed over the past 70 years. So say Michael Roderick and his teammates from Australian National University, Canberra, who’ve developed an ‘accounting system’ that looks closely at where and when rain fell. And the reason could be aerosols – clouds of pollutant particles – produced by humans. “The existing dogma is that increasing greenhouse gas concentrations in the atmosphere have raised rainfall variability,” Michael told me. “In that context, our results emphasise the importance of taking a whole system approach in trying to understand how something complex, like rainfall, is changing in different places.”

When scientists want to understand how climate has been changing over large areas, they usually look at maps of long-term average data that ignore patterns of change in time, Michael explained. When they want to look at how it’s changed over time, they usually either look at a single place or a worldwide average, which ignores patterns in where the changes are. But Michael, along with fellow scientists Fubao Sun and Graham Farquhar, wanted to find a way to link place and time.

To do this Fubao started from a common statistical test called Analysis of Variance or ANOVA. Normally it’s used to compare the effect of different “treatments” – such as a variety of temperatures – on the yield of a crop, for example. In such cases each treatment must be repeated more than once, giving different “replicates”, for the test to be valid. ANOVA can be used to give a value for variance – a measure that shows how spread out an experiment’s measurements are.