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.”

Delays raise emission halt urgency

The inventors of the idea of using wedges to represent efforts that will grow to prevent a billion tonnes of CO2 emissions per year over 50 years made a game out of it. However, University of California, Irvine’s Steve Davis underlines that our ongoing failure to properly put the idea into action is very serious. Credit: Carbon Mitigation Initiative/Princeton University

We need to work towards completely cutting greenhouse gas emissions from energy generation for the goal of keeping global warming below 2°C to be realistic. So says Steve Davis at University of California, Irvine, who has updated a powerful method to make it easier to see what emission cuts are needed. That method originally just worked towards stopping emissions increasing, but Davis says that’s not enough today. “If you’ve been gaining weight and want to lose it, you don’t set a goal of eating just enough sweets to hold your weight constant for a few years, you set a goal of no sweets and set about losing weight right away,” Steve told me. “Why shouldn’t the same thing be true for carbon emissions?”

It’s hard to imagine how we can slow and stop emissions. In 2004, that drove scientists Stephen Pacala and Robert Socolow at Princeton University in New Jersey to come up with the idea of breaking the cuts needed into wedges. Each wedge is a unit of effort in stopping CO2 production, starting from a small beginning and becoming a massive impact. Over 50 years, each wedge of effort grows steadily from zero to a billion tons, or gigaton, of carbon emissions avoided per year. We can use the idea to decide how to cut out each wedge, assigning them to particular reduction efforts and technologies. Since their invention, wedges have been used to teach and make decisions about fighting climate change.

In their original study, the Princeton scientists just used the wedges  to bring our emissions to a stable level. At the time they found this would stop levels of the greenhouse gas in the air going above 500 parts per million (ppm). Reducing emissions from that level to zero would then have put a limit on climate change. However, accelerating emissions since their study have changed the starting point.

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.

Can we trust climate models?

Scientists use models like the Community Climate System Model (CCSM, shown here) to increase their understanding of the world’s climate patterns and learn how they may affect regions around the globe. Credit: PNNL

Computers crash, freeze, corrupt documents, and otherwise make us swear at them every day. At such moments I briefly blow my own fuse, and my computer becomes my enemy – until I remember it’s revolutionised how I work, communicate and access information. But knowing how easily they can go wrong – and how easily a small, overlooked, mistake in a piece of software can cause unexpected problems later – makes me cautious. That extends to writing this blog, when I often wonder just how much we can rely on the computer models used so widely by scientists studying global warming. So this year I’ve been asking researchers questions like: Why even use models? How can we trust that they’re accurate? How should we understand what they come up with?

These questions go deep into how science works, using evidence from what people see, or experiments we conduct, to build or knock down ideas. The best evidence is directly measured, in as much detail as possible. Today that’s available in some cases, but not all, and we can’t go back in time to get data over the long time periods that might be ideal. For example, this previously limited our understanding of global warming’s effect on tropical cyclones, Bruno Chatenoux from the Global Change and Vulnerability Unit at the United Nations Environment Program in Geneva, Switzerland told me in February. “Formal detection of trends in the existing records is challenged by data quality issues and record length,” he told me. “Model projections suffer less from this, but have other challenges, such as whether they are accurately representing all of the relevant physical processes.”

And while there are a lot of processes to represent, researchers have worked hard to establish them, underlined Xuefeng Cui from Beijing Normal University, China, in July. “Climate models have been developed by groups of scientists to include atmosphere, oceanography, land, biology, chemistry, physics, computing science for about 40 years,” he said. “They have a solid scientific foundation and model the climate system in reasonable resolution.”

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.

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.

Focus on uncertain climate cliff-edge invites disaster

Scott Barrett from the Earth Institute at Columbia University says existing climate negotiation strategies have failed. Credit: Earth Institute

Countries trying to agree climate deals based on avoiding dangerous ‘cliff-edge’ limits will not work. That’s according to Scott Barrett and Astrid Dannenberg from the Earth Institute at Columbia University in New York, who’ve modelled the negotiations in a simple game. They found that uncertainty about the threshold at which their actions hurt everyone made players ignore the deals they made almost every time.  “We found that if the threshold for catastrophic climate change were certain, Mother Nature would essentially enforce an agreement to avoid the threshold,” Scott told me. “The fear of falling off of a cliff disciplined everyone to do what was needed, collectively, to avoid falling off. When the threshold was uncertain, this effect collapsed. Uncertainty about the impact made no difference at all.” And with science unable to be completely certain where the limit is, Scott and Astrid think that how climate deals are put together must change.

Scott got the idea that knowing where the cliff-edge is important because of the two different ways climate can affect the world. The first is ‘gradual’, where small emissions add a little to greenhouse gas levels in the air and raise global temperatures slightly. The second is ‘abrupt and catastrophic’, where small emissions push part of the world’s climate over a limit into a new state. “The second kinds of change are more important to welfare,” he said. “The effects tend to be uniformly negative – think of 5 meters of sea level rise, or the possibility of warm temperatures releasing methane stored in tundra, causing a rapid rise in temperature. The effects also occur quickly, meaning that adaptation will be harder. For both reasons it seemed to me that countries would have a stronger reason to prevent this kind of climate change than the gradual kind.”

Warming cost estimates cheat our children

Economic calculations saying future generations are at least as important as we are make a strong argument for replacing fossil fuel electricity generation with renewable energy sources like wind. Credit: Caveman Chuck Coker/Flickr

The financial benefits of reducing CO2 emissions, and avoiding the climate change they would bring, is at least 2.6 times larger than the US government estimates. And, according to Laurie Johnson of the Natural Resources Defense Council in Washington, DC, and Chris Hope at the University of Cambridge, UK, they could be much higher. Undervaluing the damages, which play a part in how the US government makes decisions about climate issues, borders on insanity, Laurie told me. “What we have to ask ourselves is what our children are going to think of us,” she said. “We’re being very self-destructive, but also deeply unethical. We’re not even trying to minimise how much worse it’s going to get. They’ll look back at all this science and how everything is changing, and see how we treated the damages so trivially and did so little.”

In 2010 some of the top departments in the US government got together to publish the first estimates of the money value of benefits from CO2 cuts. The benefits come from avoiding losses through damage caused by climate change. Called the social cost of carbon (SCC), this value is important because it affects rules on CO2 emissions, such as those from cars and power stations. Using three models that linked climate and economics, the government departments decided that the SCC was $21 per metric tonne of CO2*. Thanks to its importance for future climate rules, Laurie had watched the value being calculated closely – and was worried about what she saw.

“One of the models includes infectious disease damage estimates that are highly questionable,” she told me. “The models also estimate net gains from agriculture from now up to 2300 globally. By contrast the insurance industries appear to be estimating $25 billion dollars for crop losses in the US this year. That’s just one year for one country, and their calculation is for more than two hundred years, all countries. It also estimates a couple of billion in extreme weather damages globally over that period. Last year, in the US alone, there was over $50 billion dollars’ worth of extreme weather damage. Overall, it’s a very problematic estimate.” While the faults are plain, correcting any of these areas with more accurate values is a big problem itself. So Laurie and Chris looked at two other areas that they also felt had been worked out badly, but were simpler to tackle.

Temperature rises could hamper developing world growth

Higher temperatures can lower productivity in non air-conditioned factories like this one owned by bead manufacturer Kazuya in Nairobi, Kenya, says MIT’s Ben Olken. Credit: Amy the Nurse/Flickr

Higher temperatures play a role in economic progress that brings bad news for poorer countries. Their development efforts may be slowed as the world warms further, suggest researchers at the Massachusetts Institute of Technology (MIT) and Northwestern University in Evanston, Illinois. Looking at over 50 years of weather data, MIT’s Ben Olken and his colleagues showed that every 1°C temperature increase shaves 1.3 percent off a poor country’s growth, over the course of a given year. That can have a big impact, considering the World Bank projects that developing countries’ economies will grow by 5.4 percent in 2012. “The key points of our study for thinking about climate change are that a) the impact seems to be larger for poorer countries and b) there is at least the possibility that the economic magnitude of the costs of higher temperatures for poorer countries could be quite large,” he told Simple Climate.

People have been asking whether temperature influences how rich a country is for centuries, with historian Ibn Khaldun discussing it in his book Muqaddimah in 1377. But researchers are still trying to tease out the various ways it can play a part even today. Getting a grip on this subject becomes more important as the world warms in response to human CO2 emissions, Ben noted. “Given the interest in global climate change, the link between temperature and economic growth is clearly important to understand,” he said. “While there are many studies that try to simulate these impacts, we thought it was very important to try to look, historically, at what actually happens when it gets warmer. When we thought of doing this, we were very surprised that nobody had really done it before.”

Ben, MIT’s Melissa Dell and Northwestern’s Ben Jones brought together temperature, rainfall and economic output data for 1950-2003 from 125 countries. In a paper published in the July edition of the American Economic Journal: Macroeconomics they compared temperature and rainfall changes against economic growth. By studying year-to-year changes they could avoid assumptions about what links exist and remove the effects of unchanging national factors. Looking at economic growth both in the same year as the weather data and up to ten years later allowed them to see how long any impacts lasted. While economic growth in poor countries was affected by temperature, there was little effect on growth in rich countries. Changes in rainfall have relatively mild effects on national growth in both rich and poor countries. Their data showed that these were permanent effects on growth, rather than temporary dips in output after which the countries continued the progress they were making before.

Developed countries duck warming responsibility

Beijing Normal University’s John Moore, Xuefeng Cui and their collegues assessed the relative impact on future warming if developed and developing countries follow the pledges to cut CO2 emissions they made at the UN climate change conference in Cancún, Mexico, in November 2010, shown here. Credit: UNclimatechange/Flickr

Disputes between leaders of rich and poor countries currently mean little comes from meetings where they’re meant to draw up plans to slow and stop climate change. But developed countries’ existing promises would achieve just 1/3 of any warming slowdown, even though we’re responsible for more than 2/3 of CO2 emissions before 2005. That’s according to a team of mainly Chinese researchers who have tried to settle these fights using “earth system” models, considering both natural and human factors. “Developed countries need to take more responsibility in climate mitigation by cutting more carbon emissions and helping developing countries to control carbon emission while maintaining economic development,” said Xuefeng Cui from Beijing Normal University (BNU).

At the United Nations’ Climate Change Conference in Cancún, Mexico, in November 2010, leaders agreed to try and limit the global temperature rise to 2°C higher than pre-industrial levels. They also agreed that doing this needs deep, but fair, cuts in the amount of warming-causing greenhouse gases humans emit. But they still argue about how to share those cuts. That prompted Cui and his team to make an unusual effort to use science to show what is fair.  “The arguments in the IPCC process demand some fact-based reasoning rather than just the ‘blame game’,” team member John Moore told Simple Climate. “Our study is the first interdisciplinary study by climate, social, economic, and ecological scientists and policy makers to look at the historical responsibilities and effect of future mitigation by applying state-of-art earth system models,” Xuefeng added.

Getting such a broad view meant that the team had to develop entirely new methods for their research, published online in the scientific journal Proceedings of the National Academy of Sciences of the USA on Monday. “Most scientists are interested in the real impacts rather than assigning responsibilities,” Moore said. “These are more abstract philosophical and moral points than they tend to consider.” It took a 37-strong team of scientists to develop the approach, and one of the two earth systems models, they used. Whole earth system models are needed to understand the effects plants, animals, land and oceans have on climate.