Study provides new insights on drought predictions in East Africa

Wood Hole Oceanographic Institution: With more than 40 million people living under exceptional drought conditions in East Africa, the ability to make accurate predictions of drought has never been more important. In the aftermath of widespread famine and a humanitarian crisis caused by the 2010-2011 drought in the Horn of Africa—possibly the worst drought in 60 years— researchers are striving to determine whether drying trends will continue.

While it is clear that El Niño can affect precipitation in this region of East Africa, very little is known about the drivers of long-term shifts in rainfall. However, new research described in the journal Nature helps explain the mechanisms at work behind historical patterns of aridity in Eastern Africa over many decades, and the findings may help improve future predictions of drought and food security in the region.

“The problem is, instrumental records of temperature and rainfall, especially in East Africa, don't go far enough in time to study climate variability over decades or more, since they are generally limited to the 20th century,” explains first author Jessica Tierney, a geologist at the Woods Hole Oceanographic Institution (WHOI). Tierney and her colleagues at WHOI and the Lamont-Doherty Earth Observatory of Columbia University used what is known as the paleoclimate record, which provides information on climate in the geologic past, to study East African climate change over a span of 700 years.

The paleoclimate record in East Africa consists of indicators of moisture balance—including pollen, water isotopes, charcoal, and evidence for run-off events – measured in lake sediment cores. Tierney and her colleagues synthesized these data, revealing a clear pattern wherein the easternmost sector of East Africa was relatively dry in medieval times (from 1300 to 1400 a.d.), wet during the “Little Ice Age” from approximately 1600 to 1800 a.d., and then drier again toward the present time.

Climate model simulations analyzed as part of the study revealed that the relationship between sea surface temperatures and atmospheric convection in the Indian Ocean changes rainfall in East Africa. Specifically, wet conditions in coastal East Africa are associated with cool sea surface temperatures in the eastern Indian Ocean and warm sea surface temperatures in the western Indian Ocean, which cause ascending atmospheric circulation over East Africa and enhanced rainfall. The opposite situation—cold sea surface temperatures in the western Indian Ocean and warmer in the East—causes drought. Such variations in sea-surface temperatures likely caused the historical fluctuations in rainfall seen in the paleorecord...

Climate model simulations analyzed as part of the study revealed that the relationship between sea surface temperatures and atmospheric convection in the Indian Ocean changes rainfall in East Africa. Specifically, wet conditions in coastal East Africa are associated with cool sea surface temperatures in the eastern Indian Ocean and warm sea surface temperatures in the western Indian Ocean, which cause ascending atmospheric circulation over East Africa and enhanced rainfall. The opposite situation—cold sea surface temperatures in the western Indian Ocean and warmer in the East—causes drought. Such variations in sea-surface temperatures likely caused the historical fluctuations in rainfall seen in the paleorecord.(Courtesy Jessica Tierney, et al, 2013)

New planning tool for climate adaptation in cities

The Swedish Meteorological and Hydrological Institute: A changing climate places great pressure on society, and creates many new challenges. To make city planning easier, a planning tool has been developed to support climate adaptation of cities and regions in Europe. The European research project SUDPLAN, co-ordinated by SMHI, has developed a planning tool for climate adaptation of European cities and regions for intensive precipitation, hydrological conditions and the air environment.

“Already today we are beginning to notice climate-related problems in cities, such as flooding. As the climate changes even more, these difficulties will increase. This is why a tool is needed to facilitate planning ahead of decisions regarding investments in infrastructure, for instance, and to ensure that projects are adapted to the altered conditions we will be facing in the future,” says Lars Gidhagen, researcher in air quality at SMHI and co-ordinator of SUDPLAN.

The planning tool SUDPLAN makes information available for the period 1961-2100, from a number of climate scenarios scaled down across Europe, complete with hydrological simulations and results from an air pollution model.

“An altered climate means that cities will be exposed to new strains such as higher temperatures, more torrential rain and altered air pollution levels which affect our health. By taking into account the climate impact when planning development in relation to waterways, dimensioning surface water networks and planning traffic routes, we can already to some extent plan for good health, comfort, safety and quality of life,” Gidhagen explains.

Using the tool, city planners anywhere in Europe can themselves generate more detailed future information by entering local precipitation data, flow data from watercourses or emissions of air pollutants. The projections can use several different climate scenarios to run the same future simulation. Similarities and differences in the various scenario results produce information about the uncertainty in the conditions we can expect to face in the future. The planning tool also contains functionality for advanced visualisation, and for linking downscaled data to users’ own local models....

High water in Koblenz, shot by Holger Weinandt, under the Creative Commons Attribution-Share Alike 3.0 Germany license

Climate model is first to study climate effects of Arctic hurricanes

EurekAlert: Though it seems like an oxymoron, Arctic hurricanes happen, complete with a central "eye," extreme low barometric pressure and towering 30-foot waves that can sink small ships and coat metal platforms with thick ice, threatening oil and gas exploration. Now climate scientists at the University of Massachusetts Amherst and in England report the first conclusive evidence that Arctic hurricanes, also known as polar lows, play a significant role in driving ocean water circulation and climate.

Results point to potentially cooler conditions in Europe and North America in the 21st century than other models predict.

Geoscientist Alan Condron at UMass Amherst and Ian Renfrew at the University of East Anglia, U.K., write in the current issue of Nature Geoscience that every year thousands of these strong cyclones or polar lows occur over Arctic regions in the North Atlantic, but none are simulated by the latest climate prediction models, which makes it difficult to reliably forecast climate change in Europe and North America over the next couple of decades.

"Before polar lows were first seen by satellites, sailors frequently returned from the Arctic seas with stories of encounters with fierce storms that seemed to appear out of nowhere," says Condron, a physical oceanographer. "Because of their small size, these storms were often missing from their weather charts, but they are still capable of producing hurricane-force winds and waves over 11 meters high (36 feet)."

He and Renfrew say that despite the fact that literally thousands of polar lows occur over the Arctic region of the North Atlantic ocean every year, none are simulated by even the most sophisticated climate models. To understand the importance of these storms on climate, Condron and Renfrew therefore turned to a new, state-of-the-art climate model to simulate the high wind speeds associated with these "missing" storms.

"By using higher resolution modeling we can more accurately simulate the high wind speeds and influence of polar lows on the ocean," Condron says. "The lower-resolution models currently used to make climate predictions very much miss the level of detail required to accurately simulate these storms."....

This photo-like image of a subtropical storm was acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite on November 1, 2006. Located 900 miles off the coast of Oregon in the northwestern Pacific, this storm system looks like a hurricane, but it is located far from any of the typical hurricane formation areas. The storm originally formed from a cold-cored extratropical storm, but after sending two days over anomalously warm water, it developed a warm center and the hurricane characteristics of a cloud-free eye and an eyewall of thunderstorms circling the eye. Though the storm was strong enough to be named had it formed in one of the hurricane sectors, it is outside the regions which hurricane monitoring organizations administer, so the authority to give it a full name is not well defined. As of November 2, 2006, the Central Pacific Hurricane Center in Honolulu had not issued any information on the storm nor even applied it with a name. It was known merely as Storm 91C by the U.S. Navy.

Canopy structure more important to climate than leaf nitrogen levels

Terra Daily via SPX: Claims that forest leaves rich in nitrogen may aid in reflecting infrared radiation - helping cool the atmosphere - have been challenged by new research that shows that the structure of tree canopies is a more important factor in infrared reflection. Recent studies have noticed a strong positive correlation between the concentration of nitrogen in forests and infrared reflectance measured from aircraft and satellites.

Some scientists have suggested this demonstrates a previously overlooked role for nitrogen in regulating the earth's climate system.

However, a new paper in Proceedings of the National Academy of Sciences, shows that the apparent relationship between leaves' nitrogen levels and infrared reflection is spurious and it is in fact the structure of forest canopies (the spatial arrangement of the leaves) that determines their ability to reflect infrared light.

The authors, including Professor Philip Lewis and Dr Mathias Disney (UCL Geography), show that the richer in nitrogen individual leaves are the worse at reflecting infrared radiation they become.

However, the complex arrangements of trees with radically different arrangements of leaves within a forest can act to mask this effect, making it appear as if higher levels of leaf nitrogen are leading to increased infrared reflection....

A tree canopy in Sri Lanka's Sinharaja Forest Reserve, shot by Chamal N, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported 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....

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.)