Climate change to profoundly affect the Midwest, new report says

University of Michigan News Service: Climate change will lead to more frequent and more intense Midwest heat waves while degrading air and water quality and threatening public health. Intense rainstorms and floods will become more common, and existing risks to the Great Lakes will be exacerbated.

Those are some of the conclusions contained in the Midwest chapter of a draft report released last week by the federal government that assesses the key impacts of climate change on every region in the country and analyzes its likely effects on human health, water, energy, transportation, agriculture, forests, ecosystems and biodiversity.

...University of Michigan aquatic ecologist Donald Scavia was a lead convening author of the Midwest chapter. Dan Brown of the School of Natural Resources and Environment was a lead convening author of the chapter on changes in land use and land cover. Rosina Bierbaum of SNRE and the School of Public Health was a lead convening author of the chapter on climate change adaptation. Missy Stults, a research assistant with Bierbaum and a doctoral student at the A. Alfred Taubman College of Architecture and Urban Planning, was a contributing author on the adaptation chapter.

... The report stresses that climate change is already affecting Americans, that many of its impacts are expected to intensify in coming decades, and that the changes are primarily driven by human activity. "Climate change impacts in the Midwest are expected to be as diverse as the landscape itself. Impacts are already being felt in the forests, in agriculture, in the Great Lakes and in our urban centers," said Scavia, director of the Graham Sustainability Institute and special counsel to the U-M president on sustainability issues.

In the Midwest, extreme rainfall events and floods have become more common over the last century, and those trends are expected to continue, causing erosion, declining water quality and negative impacts on transportation, agriculture, human health and infrastructure, according to the report....

The Boone River in Iowa, shot by Tim Kiser (Malepheasant), Wikimedia Commons, under the Creative Commons Attribution-Share Alike 2.5 Generic license

Global warming has increased monthly heat records by a factor of five

A press release from the Potsdam Institute for Climate Impacts Research: Monthly temperature extremes have become much more frequent, as measurements from around the world indicate. On average, there are now five times as many record-breaking hot months worldwide than could be expected without long-term global warming, shows a study now published in Climatic Change. In parts of Europe, Africa and southern Asia the number of monthly records has increased even by a factor of ten. 80 percent of observed monthly records would not have occurred without human influence on climate, concludes the authors-team of the Potsdam Institute for Climate Impact Research (PIK) and the Complutense University of Madrid.

“The last decade brought unprecedented heat waves; for instance in the US in 2012, in Russia in 2010, in Australia in 2009, and in Europe in 2003,” lead-author Dim Coumou says. “Heat extremes are causing many deaths, major forest fires, and harvest losses – societies and ecosystems are not adapted to ever new record-breaking temperatures.” The new study relies on 131 years of monthly temperature data for more than 12.000 grid points around the world, provided by NASA. Comprehensive analysis reveals the increase in records.

The researchers developed a robust statistical model that explains the surge in the number of records to be a consequence of the long-term global warming trend. That surge has been particularly steep over the last 40 years, due to a steep global-warming trend over this period. Superimposed on this long-term rise, the data show the effect of natural variability, with especially high numbers of heat records during years with El Niño events. This natural variability, however, does not explain the overall development of record events, found the researchers.

If global warming continues, the study projects that the number of new monthly records will be 12 times as high in 30 years as it would be without climate change. “Now this doesn’t mean there will be 12 times more hot summers in Europe than today – it actually is worse,“ Coumou points out. For the new records set in the 2040s will not just be hot by today’s standards. “To count as new records, they actually have to beat heat records set in the 2020s and 2030s, which will already be hotter than anything we have experienced to date,” explains Coumou. “And this is just the global average – in some continental regions, the increase in new records will be even greater.”....

Record-breaking hot months have become much more frequent. (For full graphic see Fig. 4 in the study) Graphic: PIK

Temperatures to rise by six degrees in Middle East countries

Laurence Caramel in the Guardian (UK): Countries in the Middle East and north Africa will be among those hardest hit by global warming, unless the upward trend for greenhouse gas emissions can be checked, the World Bank warned last month at the Doha climate change conference.

There will be lower rainfall, higher temperatures and continuing desertification, said Rachel Kyte, World Bank vice-president for sustainable development, during her presentation of the report on Adaptation to a Changing Climate in the Arab Countries.

According to the forecasts, average temperatures could rise by 3C between now and 2050. But night temperatures in city centres could increase by double that figure. The report notes that over the last three decades 50 million people have been affected by climate disasters. Severe flooding is now a recurrent event. But the increasing scarcity of water resources is the biggest challenge for countries in the region, which already have some of the lowest per capita reserves in the world.

Kuwait and Qatar depend on desalination plants for almost 40% of their needs. With demand for water forecast to increase by 60% over the next 30 years, due to population growth and changing ways of life, the World Bank fears there is a high risk of shortages and conflict. Measures to adapt to climate change are still limited, even if a regional strategy for reducing the risks of natural disasters has been adopted.

The lack of reliable data is a stumbling block for any preventive measures. The launch of a research centre, announced by Qatar last month, could help remedy this situation. Funded by the Qatar Foundation, in partnership with the Potsdam Institute, the centre will focus on the impact of climate change on countries in the Gulf....

A natural arch in Jebel Kharaz, Jordan, shot by Etan J. Tal, Wikimedia Commons, under the Creative Commons Attribution 3.0 Unported license

Fear of 'catastrophic' sea-level rise as ice sheets melt faster than predicted

Steve Connor in the Independent (UK): Glaciologists fear they may have seriously underestimated the potential for melting ice sheets to contribute to catastrophic sea-level rises in coming decades which could see increases of a metre or more by 2100.

The ice sheets of Greenland and Antarctica contain about 99.5 per cent of the Earth's glacier ice and could raise sea levels by 65 metres if they melted completely – although experts think this is highly unlikely in the foreseeable future. However, a survey of the world's top 26 glaciologists found most believe melting of the ice sheets could be more rapid and severe than previously estimated. They believe that melting of the ice sheets alone this century would be likely to raise the average global sea level by 29cm, the poll found, but there is a five per cent chance of it increasing even further by a catastrophic 84cm.

This would take the total sea-level increase to well over a metre if other factors such as the thermal expansion of oceans and runoff from mountain glaciers are taken into account. "Our analysis shows the biggest uncertainty when it comes to sea levels is the contribution from the ice sheets," said Professor Jonathan Bamber of Bristol University, lead author of the study published in the journal Nature Climate Change.

"It shows glaciologists believe there is a one-in-20 chance of sea levels rising by a metre or more by 2100, and a metre rise in sea level is really very serious. "The impacts of sea-level rise of this magnitude are potentially severe, implying a conceivable risk of the forced displacement of up to 187 million people within this century."...

The 1872 Baltic sea flood in southern Lolland, Denmark. Xylography from Illustreret Tidende

Delayed action raises costs of climate change, study says

EurActiv: An agreement by almost 200 nations to curb rising greenhouse gas emissions from 2020 will be far more costly than taking action now to tackle climate change, a new report says. Quick measures to cut emissions would give a far better chance of keeping global warming within an agreed UN limit of 2o Celsius above pre-industrial times to avert more floods, heatwaves, droughts and rising sea levels.

"If you delay action by 10, 20 years you significantly reduce the chances of meeting the 2o target," said Keywan Riahi, one of the authors of the report at the International Institute for Applied Systems Analysis in Austria.

"It was generally known that costs increase when you delay action. It was not clear how quickly they change," he told Reuters on Wednesday (2 January) of the findings in the science journal Nature Climate Change based on 500 computer-generated scenarios.

It said the timing of cuts in greenhouse gases was more important than other uncertainties - about things like how the climate system works, future energy demand, carbon prices or new energy technologies. The study indicated that an immediate global price of €15 a tonne on emissions of carbon dioxide (CO2), the main greenhouse gas, would give a roughly 60% chance of limiting warming to below 2o.

Wait until 2020 and the carbon price would have to be around €75 a tonne to retain that 60% chance, Riahi told Reuters of the study made with other experts in Switzerland, New Zealand, Australia and Germany. And a delay of action until 2030 might put the 2o limit - which some of the more pessimistic scientists say is already unattainable - completely out of reach, whatever the carbon price....

At Disneyland, the hat worn by Mickey Mouse in "The Sorcerer's Apprentice," shot by Fabi1994 at de.wikipedia, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Supercomputers used to help predict future extreme climate changes in the US

RedOrbit: With the recent history of extreme droughts and super storms, many are wondering what the future holds for the climate of the eastern United States. New research from the University of Tennessee, Knoxville, has taken the guesswork out of it. The results of this study, published in a recent issue of Environmental Research Letters, show that the region will be hotter and wetter in the future.

The research team consisting of Joshua Fu, a civil and environmental engineering professor, and Yang Gao, a graduate research assistant created a “climate crystal ball,” a set of precise scales of cities that predict high-resolution climate changes almost 50 years into the future.

The researchers combined high-resolution topography, land use information and climate modeling using the power of UT’s Kraken and Oak Ridge National Laboratory’s (ORNL) Jaguar, now called the Titan, which is the fastest supercomputer in the world. They used dynamic downscaling – which allowed the researchers to develop climate scales as small as four square kilometers – to develop climate model results.

“Instead of studying regions, which is not useful when examining extreme weather, dynamical downscaling allows us to study small areas such as cities with a fine resolution,” said Fu, who is also a professor within the UT-ORNL Bredesen Center for Interdisciplinary Research and Graduate Education.

...The team found that heat waves would become more severe throughout the eastern portion of the country by comparing present climate to future predictions, with the Northeast and Midwest experiencing a greater increase in heat waves than the Southeast. The Southeast will almost equalize the temperatures between the future North and current South according to the model....

Heat shimmering from an air strip, USAF photo

IPCC underestimates climate risks

Glenn Scherer in the Daily Climate: Across two decades and thousands of pages of reports, the world's most authoritative voice on climate science has consistently understated the rate and intensity of climate change and the danger those impacts represent, say a growing number of studies on the topic.

This conservative bias, say some scientists, could have significant political implications, as reports from the group – the U.N. Intergovernmental Panel on Climate Change – influence policy and planning decisions worldwide, from national governments down to local town councils.

As the latest round of United Nations climate talks in Doha wrap up this week, climate experts warn that the IPCC's failure to adequately project the threats that rising global carbon emissions represent has serious consequences: The IPCC’s overly conservative reading of the science, they say, means governments and the public could be blindsided by the rapid onset of the flooding, extreme storms, drought, and other impacts associated with catastrophic global warming.

"We're underestimating the fact that climate change is rearing its head," said Kevin Trenberth, head of the climate analysis section at the National Center for Atmospheric Research (NCAR) and a lead author of key sections of the 2001 and 2007 IPCC reports. "And we're underestimating the role of humans, and this means we're underestimating what it means for the future and what we should be planning for."...

Photo by Ian Muttoo, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license

Climate models project increase in US wildfire risk

NASA: Scientists using NASA satellite data and climate models have projected drier conditions likely will cause increased fire activity across the United States in coming decades. Other findings about U.S. wildfires, including their amount of carbon emissions and how the length and strength of fire seasons are expected to change under future climate conditions, were also presented Tuesday at the annual meeting of the American Geophysical Union in San Francisco.

Doug Morton of NASA's Goddard Space Flight Center in Greenbelt, Md., presented the new analysis of future U.S. fire activity. The analysis was based on current fire trends and predicted greenhouse gas emissions.  "Climate models project an increase in fire risk across the U.S. by 2050, based on a trend toward drier conditions that favor fire activity and an increase in the frequency of extreme events," Morton said.

The analysis by Morton and colleagues used climate projections, prepared for the Fifth Assessment Report of the United Nations Intergovernmental Panel on Climate Change, to examine how dryness, and therefore fire activity, is expected to change.

The researchers calculated results for low and high greenhouse gas emissions scenarios. In both cases, results suggest more fire seasons that are longer and stronger across all regions of the U.S. in the next 30-50 years. Specifically, high fire years like 2012 would likely occur two to four times per decade by mid-century, instead of once per decade under current climate conditions.

Through August of this year, the U.S. burned area topped 2.5 million hectares (6.17 million acres), according to a fire emissions database that incorporates burned area estimates produced from observations by the Moderate Resolution Imaging Spectroradiometer instruments on NASA's Aqua and Terra satellites. That is short of the record 3.2 million hectares (7.90 million acres) burned in 2011, but exceeds the area burned during 12 of the 15 years since record keeping began in 1997. This and other satellite records, along with more refined climate and emissions models, are allowing scientists to tease out new information about fire trends....

'Black swan' storms: extreme cyclones linked to warming seas

Becky Oskin in Our Amazing Planet: A "black swan" cyclone may sound like the latest comic book hero, but this "extreme of the extremes" is the result of climate models that suggest global warming will make future hurricanes more intense.

The rare monster tropical cyclones (the term for hurricanes, typhoons and other tropical storms) could inundate coastal areas with storm surges greater than 15 feet (4.6 meters), and could even surpass 30 feet (9 m) in some regions of the world. The research was described here yesterday (Dec. 3) at the annual meeting of the American Geophysical Union.

By simulating thousands of possible future storms, researchers identified the outliers that could hit coastal areas in the future but that wouldn't show up in predictions based solely on historical records, said Ning Lin, a professor at Princeton University. The scientists relied on the same model the National Weather Service uses to predict hurricane activity for a given season.

...Even though Hurricane Sandy broke several records and generated tremendous storm surge, the superstorm was not a black swan, Lin said. The simulated storm surges calculated by the model for New York, at up to 16 feet, top the record set by Hurricane Sandy, at 14 feet (4.3 m) — part of which was the high tide at the time....

The Brooklyn waterfront during Hurricane Sandy, shot by lookcatalog, Wikimedia Commons via Flickr,  under the Creative Commons Attribution 2.0 Generic license

Physicist happens upon rain data breakthrough

NASA: A physicist and researcher who set out to develop a formula to protect Apollo sites on the moon from rocket exhaust may have happened upon a way to improve weather forecasting on Earth.

Working in his backyard during rain showers and storms, John Lane, a physicist at NASA's Kennedy Space Center in Florida, found that the laser and reflector he was developing to track lunar dust also could determine accurately the size of raindrops, something weather radar and other meteorological systems estimate, but don't measure.

The special quantity measured by the laser system is called the "second moment of the size distribution," which results in the average cross-section area of raindrops passing through the laser beam.

"It's not often that you're studying lunar dust and it ends up producing benefits in weather forecasting," said Phil Metzger, a physicist who leads the Granular Mechanics and Regolith Operations Lab, part of the Surface Systems Office at Kennedy.

Lane said the additional piece of information would be useful in filling out the complex computer calculations used to determine the current conditions and forecast the weather. "We may be able to refine (computer weather) models to make them more accurate," Lane said. "Weather radar data analysis makes assumptions about raindrop size, so I think this could improve the overall drop size distribution estimates."...

John Lane looks over data recorded from his laser system as he refines his process and formula to calibrate measurements of raindrops. Photo credit: NASA/Jim Grossmann

Pledges to fight global warming inadequate, US off track

Reuters: Major nations' policies are inadequate to limit global warming and the United States is off track even in carrying out its weak pledge to limit greenhouse gas emissions, a scientific scorecard showed on Friday.

The Climate Action Tracker report, issued on the sidelines of talks among almost 200 countries in Doha about climate change, said a toughening of policies was still possible to avert damaging floods, heat waves and rising seas.

Major emitters China, the United States, the European Union and Russia all got "inadequate" ratings for their plans to help limit global warming to an agreed U.N. ceiling of below 2 degrees Celsius (3.6F) above pre-industrial times, it said.

Adding up all national pledges and taking account of rising emissions, the world was headed for a warming of about 3.3 degrees Celsius (6F), it said.

"We are off track and the United States is not likely to meet its pledge," said Niklas Hoehne of research group Ecofys, which compiles the tracker with Climate Analytics and the Potsdam Institute for Climate Impact Research....

Flag shot by Jnn13, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Sea levels rising more quickly than predicted, warn scientists

Emily Beament in the Independent (UK): Sea levels are rising faster than predicted as a result of climate change, scientists said today. Satellite measurements show sea levels rose 3.2mm a year between 1993 and 2011, 60% above the 2mm estimate in central projections made by the Intergovernmental Panel on Climate Change (IPCC) in its most recent review of climate science.

A study published in the Institute of Physics (IOP) journal Environmental Research Letters said it was "very unlikely" the higher rate of sea level rise is due to natural variability such as temporary ice discharge from ice sheets.

Lead author Stefan Rahmstorf said: "This study shows once again that the IPCC is far from alarmist, but in fact has underestimated the problem of climate change. That applies not just for sea level rise but also to extreme events and the Arctic sea loss."

The researchers also warn that the rate of annual sea level rise may increase as global temperatures go up, a suggestion backed up by past sea level data and which leads to larger projections of future sea level rise than the IPCC predicts.

And they said the concern that the IPCC's estimates for future sea level rise are low is supported by the fact ice sheets in Greenland and Antarctica are increasingly losing mass, while the panel's projections assume that Antarctica will gain enough ice to compensate for losses from Greenland....

Scientists pioneer method to predict environmental collapse

Terra Daily via SPX: Scientists at the University of Southampton are pioneering a technique to predict when an ecosystem is likely to collapse, which may also have potential for foretelling crises in agriculture, fisheries or even social systems.

The researchers have applied a mathematical model to a real world situation, the environmental collapse of a lake in China, to help prove a theory which suggests an ecosystem 'flickers', or fluctuates dramatically between healthy and unhealthy states, shortly before its eventual collapse.

Head of Geography at Southampton, Professor John Dearing explains: "We wanted to prove that this 'flickering' occurs just ahead of a dramatic change in a system - be it a social, ecological or climatic one - and that this method could potentially be used to predict future critical changes in other impacted systems in the world around us."

A team led by Dr Rong Wang extracted core samples from sediment at the bottom of Lake Erhai in Yunnan province, China and charted the levels and variation of fossilised algae (diatoms) over a 125-year period. Analysis of the core sample data showed the algae communities remained relatively stable up until about 30 years before the lake's collapse into a turbid or polluted state.

However, the core samples for these last three decades showed much fluctuation, indicating there had been numerous dramatic changes in the types and concentrations of algae present in the water - evidence of the 'flickering' before the lake's final definitive change of state. Rong Wang comments: "By using the algae as a measure of the lake's health, we have shown that its eco-system 'wobbled' before making a critical transition - in this instance, to a turbid state....

Géza Maróti's plan of Atlantis mock-up, around 1941 -- public domain

Climate change report warns of dramatically warmer world this century

The World Bank: Like summer’s satellite image of the melting Greenland ice sheet, a new report suggests time may be running out to temper the rising risks of climate change. "Turn Down the Heat: Why a 4°C Warmer World Must be Avoided," warns we’re on track for a 4°C warmer world marked by extreme heat-waves, declining global food stocks, loss of ecosystems and biodiversity, and life-threatening sea level rise.

Moreover, adverse effects of a warming climate are “tilted against many of the world's poorest regions” and likely to undermine development efforts and global development goals, says the study by the Potsdam Institute for Climate Impact Research and Climate Analytics, on behalf of the World Bank. The report, urges "further mitigation action as the best insurance against an uncertain future."

"A 4°C warmer world can, and must be, avoided – we need to hold warming below 2°C," said World Bank Group President Jim Yong Kim. "Lack of action on climate change threatens to make the world our children inherit a completely different world than we are living in today. Climate change is one of the single biggest challenges facing development, and we need to assume the moral responsibility to take action on behalf of future generations, especially the poorest."

The report, reviewed by some of the world’s top scientists, is being released ahead of the next comprehensive studies by the Intergovernmental Panel on Climate Change (IPCC) in 2013/14, and follows the Bank’s own Strategic Framework for Development and Climate Change in 2008 and the World Development Report on climate change in 2010. "Turn Down the Heat" combines a synthesis of recent scientific literature with new analysis of likely impacts and risks, focusing on developing countries. It chronicles already observed climate change and impacts, such as heat waves and other extreme events, and offers projections for the 21st century for droughts, heat waves, sea level rise, food, water, ecosystems and human health....

$1.24 billion needed to rescue Saigon from flooding

Vietnam Net Bridge: By 2070, there will be nearly 10,000 hectares, 257,000 people, 1,494 km of roads and many production facilities, industrial parks being flooded due to high tides and the sea level rise, according to a workshop assessing the risk of climate change on human health in HCM City on November 13.

At this workshop, experts said that climate change has made the appearance of diseases affecting human health. They also demonstrated that climate change affects flooding, especially in big cities like Ho Chi Minh City.  In particular, Mr. Bui Chi Nam, from the Southern Institute of Hydrometeorology and Environment showed a flooding script in Ho Chi Minh City to 2070 (excluding the impact of rain).

Nam said that flooding in Ho Chi Minh City is caused by many effects, including rain, high tides plus the rise of upstream water. Skipping the rain factor, only high tides and the sea level rise have affected the city's flooding. He said that by 2070, there will be nearly 10,000 hectares in the city to be flooded, especially in the districts of Can Gio, Nha Be, Binh Chanh, Thu Duc and District 12.

Based on research data, Nam proved that by 2070, flooding caused by high tides and sea level rise under the impact of climate change will seriously affect land use planning, water resources, infrastructure, manufacturing facilities, industrial areas and people in HCM City....

The Saigon River winding through Ho Chi Minh City, shot by nft, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported licencse

Climate change: taking a toll on coffee?

Eryn Brown in the Los Angeles Times: .... [R]esearchers demonstrated this week that the beloved cup of joe may be at dire risk from climate change. Writing in the journal PLoS One on Wednesday, research botanist Aaron Davis of the Royal Botanic Gardens, Kew  in London and colleagues reported that climate warming could drive wild varieties of Coffea arabica to extinction by 2080.

Using a computer model, the group analyzed different warming scenarios, focusing on 20-year time spans around 2020, 2050 and 2080. In the best-case scenario for 2080, the African habitats they studied — in Ethiopia, the Sudan and Kenya — would experience a 65% reduction in suitable localities for planting.  In the worst-case scenario, suitable localities declined nearly 100%.  “Our modeling shows a profoundly negative trend for the future distribution of indigenous Arabica coffee under the influence of accelerated global climate change,” the study authors wrote.

Arabica is the prized plant that produces 70% of the more than $15 billion worth of coffee sold around the world each year.  Mostly it is cultivated on farms, which grow varieties descended from a small number of plants that were carried out of Ethiopia in the 1600s and 1700s, Davis told National Geographic this week. 

The lack of genetic diversity in cultivated Arabica plants is a cause for concern for the industry, Davis said, noting that "Arabica's history is punctuated by problems with diseases, pests, and productivity problems — and growers have always gone back to the wild and used genetic diversity to address them.”  By interbreeding wild plants with resistance to pests or climate extremes with the cultivated varieties, they could maintain healthy crops....

Coffee arabica berries, shot by Mette Nielsen, Wikimedia Commons,  under the Creative Commons Attribution-Share Alike 3.0 Unported license

Future warming likely to be on high side of climate projections, analysis finds

NCAR-UCAR Atmos News: Climate model projections showing a greater rise in global temperature are likely to prove more accurate than those showing a lesser rise, according to a new analysis by scientists at the National Center for Atmospheric Research (NCAR). The findings, published in this week’s issue of Science, could provide a breakthrough in the longstanding quest to narrow the range of global warming expected in coming decades and beyond.

NCAR scientists John Fasullo and Kevin Trenberth, who co-authored the study, reached their conclusions by analyzing how well sophisticated climate models reproduce observed relative humidity in the tropics and subtropics. The climate models that most accurately captured these complex moisture processes and associated clouds, which have a major influence on global climate, were also the ones that showed the greatest amounts of warming as society emits more greenhouse gas into the atmosphere.

“There is a striking relationship between how well climate models simulate relative humidity in key areas and how much warming they show in response to increasing carbon dioxide,” Fasullo says. “Given how fundamental these processes are to clouds and the overall global climate, our findings indicate that warming is likely to be on the high side of current projections.”

...The most common benchmark for comparing model projections is equilibrium climate sensitivity (ECS), or the amount of warming that eventually occurs in a model when carbon dioxide is doubled over preindustrial values. At current rates of global emission, that doubling will occur well before 2100.

For more than 30 years, ECS in the leading models has averaged around 5 degrees Fahrenheit (3 degrees Celsius).  This provides the best estimate of global temperature increase expected by the late 21st century compared to late 19th century values, assuming that society continues to emit significant amounts of carbon dioxide. However, the ECS within individual models is as low as 3 degrees F and as high as 8 degrees F, leaving a wide range of uncertainty that has proven difficult to narrow over the past three decades....

Computer models that more accurately depict dry conditions in a key part of the subtropical atmosphere are also more likely to predict greater climate warming from increased greenhouse gases. In this graphic, each star indicates one of 16 leading global climate models. The left axis ("warming") corresponds to equilibrium climate sensitivity (ECS) in degrees C, which is the amount of warming produced by each model when carbon dioxide concentrations in the atmosphere are doubled over preindustrial values. The bottom axis shows May-to-August relative humidity for a portion of the upper atmosphere between about 20,000 to 30,000 feet in height and between about 10° and 25° latitude south in the southern subtropics. (©UCAR. Image by Carlye Calvin, based on Fasullo and Trenberth, Science, 2012.)