2,000 year water temperature high underlines Arctic threat

Bathymetric map of the Norwegian-Greenland Sea and Arctic Ocean (base map: http://www.ibcao.org). White shading marks average summer sea ice cover. White arrows mark ice drift directions. Red arrows mark the transport path of warm Atlantic water entering the Arctic where it submerges under the cold, ice-covered surface layer. The yellow spot marks the site the sediment core used in the study was taken from. Image courtesy of Robert Spielhagen (IFM-GEOMAR, Kiel)

The water flowing from the Atlantic Ocean into the Arctic through the Fram Strait is warmer today than any time in the past 2,000 years. That’s what microscopic seabed deposits have told Robert Spielhagen of the Academy of Sciences, Humanities, and Literature in Mainz, Germany, and his colleagues. The scientists have shown that the average temperature of water flowing into the Arctic since 1890 is 2ºC higher than it has been on average in the previous two millennia. This sends a stark message about the prospects for the Northern polar region. “I am afraid that my children – now 14 and 17 years old – will be able to see a summer ice-free Arctic Ocean,” Spielhagen told Simple Climate.

On August 4, 2007 Spielhagen and his co-workers extracted the key deposits when they drilled a 46 cm long cylinder of rock from the sea bed. Such “sediment cores” had previously been used to look at temperature changes as far as 12,000 years into the past, but could only provide measurements for periods of a few hundred years at a time. That’s down to how much sediment settles to the sea bed, with too little deposition for high-resolution temperature measurements occurring where cores have been taken before. By contrast, Spielhagen’s team was able to give temperatures on a scale of 2-3 decades at a time. “We took our core in a place where a lot of fine-grained particles settle, due to diminished bottom currents,” he explained. “We were the first to find such a spot.”

Rain-soaked plants trudge downhill

Historical photo of vegetation of California from the early 20th century. This image is part of a US Forest Service effort to document the flora of the state in the 1920’s and 1930’s. Credit: Marian Koshland Library, UC Berkeley

Californian plants have responded to climate change in a surprising way, data collected under the direction of a forester born almost exactly 121 years ago have helped show. Albert Everett Wieslander headed surveys in the 1920s and 1930s covering 28 million hectares, over most of the state’s natural environment outside of deserts and larger agricultural areas. The data was originally intended to provide 220 detailed vegetation maps, but publication was halted by the Second World War after just 23 maps were released. Then in 2005 a digitized version of the raw data, now known as the Wieslander Vegetation Type Mapping (VTM) collection, was made available online.

Now, Solomon Dobrowski, from the University of Montana’s Department of Forest Management and his colleagues have compared this record with modern studies of plant populations for Northern California. “We used their survey plots,” Dobrowski told Simple Climate. “Basically they’d delineate a fixed area on the ground as roughly 800 square metres in size and they would document the types of trees and shrubs and other plants they found within that location.”

Prior studies of how plants are reacting to climate change have shown them moving to habitats in pursuit of their preferred temperatures as the planet warms. This typically means that they move towards the poles, or up mountainsides to higher altitudes. However, what Dobrowksi’s team found from their comparison, and published in top journal Science yesterday, at first glance seems to almost directly disagree with this. “I was mildly incredulous when my graduate student Shawn Crimmins first approached me and said that things are moving downhill,” Dobrowski admitted. “I asked him to go back and revisit his analysis and make certain that it was right. When he came back and said yes, we’ve dotted our i’s and crossed our t’s, I realised we had to revisit our assumptions about what was going on.”

Ice melt poses dual sea rise and water access threat

Ice from Arctic Canada, like this small unnamed valley glacier and the Kaskawulsh glacier in the background in Saint Elias Mountains, Yukon Territory, will be among the largest contributors to sea level rise as ice caps and glaciers across the world melt in the 21st century. Credit: Christian Schoof.

Around one-fifth of the total volume of ice held in ice caps and glaciers will melt by 2100, adding around 12 cm to sea levels and threatening very low-lying coastal regions. That’s according to the latest simulations from Valentina Radić of the University of British Columbia, Canada and her US-based colleague Regine Hock from the University of Alaska, Fairbanks. “The problem will be floods and storm surges which also will be higher if the sea level is higher than today,” Radić told Simple Climate. She and Hock used detailed glacier measurements to model how the world’s ice will respond to predicted temperature changes. Their results, published in leading journal Nature Geoscience last Sunday, also show that Europe and New Zealand look set to lose around three-quarters of their glacier volume, impacting water supplies.

So far, there have been few predictions of what will happen to the world’s ice this century, and there has been large disagreement among those that have been produced. The resulting sea-level rise predictions range from a minimum of 5 cm to an extreme maximum of 36 cm. The issue, Radić explained, is that there are surprisingly few measurements of glaciers to begin predictions from. “The World Glacier Inventory today covers approximately 40 percent of the total ice area,” she said. “For the remaining 60 percent we still do not know how many glaciers there are, what is their surface area, elevation range, and so on.”

Worse still, less than one percent of the world’s glaciers have been measured for mass balance – the difference between the mass a glacier gains through the accumulation of snow, and what it loses – over the long term. “Observations of glacier mass balance are extremely important for the modellers,” Radić explained. “To reassure ourselves that the models are performing well, we need to validate their results with the ‘real world’. A lack of these observations presents a major obstacle for modelling of future glacier volume changes.”

Greenhouse gases break temperature-rainfall link

Downpours like this one in Varanisi, India, in 1944, are set to become more common on average worldwide as the planet warms - although less so than simple physics alone suggests, and in a pattern that will mean that some areas will see decreasing precipitation. Credit: The National Archives UK

Global warming is set to increase the amount of rain and snow the world gets – but researchers from the UK and Germany have confirmed this week that the proportion of water in the atmosphere becoming precipitation will decrease. “Warmer air can take up more water than colder air,” Potsdam Institute for Climate Impact Research’s Katja Frieler told Simple Climate. She underlines that global climate models – which are also closely related to models used to predict weather – show a 7 percent increase in atmospheric water vapour content per degree of global warming.

“The interesting point is that the increase in global mean precipitation is much lower,” Frieler explained, “in the range of 1 to 3 percent per degree of warming.” The difference between increases in water vapour and precipitation stems from the “energy budget” of the troposphere – the level of the atmosphere closest to the Earth’s surface. Climate modellers like Frieler treat the troposphere as a “box” where incoming and outgoing energy fluxes balance relatively quickly. When water vapour condenses to become rain it releases energy as heat. This is an energy input into the tropospheric box, which is balanced by an increased energy outflow from the troposphere. As the troposphere’s temperature rises, longwave radiation provides that increased energy outflow, allowing more precipitation.

The troposphere is the layer of the atmosphere nearest Earth. Credit: NASA

However, the reason the planet is warming in the first place is because greenhouse gases trap energy from longwave radiation that would otherwise be released into space as heat. Likewise, “black carbon” soot absorbs shortwave radiation, which usually comes direct from the sun. This extra energy is what is raising global temperatures and therefore increasing water vapour content in the atmosphere. Some of the gases absorbing and trapping the energy are in the troposphere “box”. Rather than even greater outward flows compensating for this additional energy input to the troposphere, Frieler’s research shows it is being offset in a different way. “Model simulations have shown that much of this extra energy is balanced by a decrease in precipitation,” she explained. The more greenhouse gases and soot there are, the weaker the link between water vapour content in the atmosphere and precipitation, Frieler added.

Dust research polishes climate models

Dust particles in the atmosphere range from about one ten-thousandth of a millimetre to five hundredths of a millimetre in diameter. The size of dust particles determines how they affect climate and weather, influencing the amount of solar energy in the global atmosphere as well as the formation of clouds and precipitation in more dust-prone regions. The NASA satellite image in this illustration shows a 1992 dust storm over the Red Sea and Saudi Arabia. Credit: University Corporation for Atmospheric Research

Dust particles in the atmosphere contribute greatly to the uncertainties remaining in today’s climate models, but principles seen in breaking glass can further reduce those uncertainties. That’s according to Jasper Kok at the US National Center for Atmospheric Research, in Boulder, Colorado, who says that these principles can accurately predict atmospheric dust particles’ size.

Some dust particles reflect solar energy and cool the planet, while others trap energy as heat, depending on their size and other characteristics. How glass breaks is an important comparison because Kok studied mineral dust particles, which are usually emitted by wind-blown sand shattering dirt and sending fragments into the air. Kok suspected that this process, known as “sandblasting”, would cause fractures to develop in the same way that they do in other brittle materials. Regardless of their size, when such brittle materials fracture they all produce fragments with similar size ranges – and Kok found that this also held true in sandblasting. “As small as they are, conglomerates of dust particles in soils behave the same way on impact as a glass dropped on a kitchen floor,” Kok said. “Knowing this pattern can help us put together a clearer picture of what our future climate will look like.”