Much of the early methane rise can be attributed to the spreading of northern peatlands

The surprising increase in methane concentrations millennia ago, identified in continental glacier studies, has puzzled researchers for a long time. According to a strong theory, this would have resulted from the commencement of rice cultivation in East Asia. However, a study conducted at the University of Helsinki’s Department of Environmental Sciences and the Department of Geosciences and Geography shows that the massive expanse of the northern peatlands occurred around 5000 years ago, coincident with rising atmospheric methane levels.

After water vapour and carbon dioxide, methane is the most significant greenhouse gas, resulting in about one fifth of atmospheric warming caused by humans. Methane emissions are mainly created by peatlands, animal husbandry, rice cultivation, landfill sites, fossil fuel production and biomass combustion.

Northern peatlands are immense sources of methane, but previous studies have argued them to have been established almost immediately after the Ice Age ended. Consequently, they could not explain the increase of methane, dated to have commenced thousands of years later, since the methane emissions of peatlands decrease as they age.

William Ruddiman, Professor Emeritus in environmental sciences at the University of Virginia, has presented a widely published theory according to which humanity started to affect the climate thousands of years ago, not just since the start of the industrial revolution. According to the theory, rice cultivation, commenced in East Asia already over 5,000 years ago, caused the declining methane amounts to again increase, which contributed to preventing the next ice age.

The timeframe of the spread of peatlands matches the increase in methane levels

The new study, conducted under the supervision of Professor Atte Korhola, explains the emergence of the peatlands in the northern hemisphere, and their development history, in a new way. The researchers compiled an extensive radiocarbon dating database concerning the bottom peat in peatlands. Based on over 3,000 dates, their statistical and location information-based analysis, it was identified that the expansion of northern peatlands significantly accelerated about 5,000 years ago. At the same time, the methane content in the atmosphere started to increase.

Peatland expansion resulted in the emergence of millions of square kilometres of young peatlands of the mineretrophic fen type, and they puffed large amounts of methane gas in to the air as the organic matter rotted. According to the study, the early increase in methane levels was mainly caused by natural reasons, and human operations are not necessarily required to explain it.

The expansion of peatlands was triggered by the climate turning moister and cooler, which caused the groundwater levels to rise, while accelerating peat build-up and growth. A similar methane peak may also emerge in the future if precipitation in the arctic areas increases as forecasted.

Heat and moisture from Himalayas could be a key cause of the South Asian monsoon

Harvard climate scientists suggest that the Tibetan Plateau-thought to be the primary source of heat that drives the South Asian monsoon-may have far less of an effect than the Himalayas and other surrounding mountains. As the monsoon brings needed rainfall and water to billions of people each year, understanding its proper origin, especially in the context of global climate change, is crucial for the future sustainability of the region.

The researchers say the their findings, published in the January 14th issue of Nature, have broad implications for how the Asian climate may have responded to mountain uplift in the past, and for how it might respond to surface changes in the coming decades.

Often called the “roof of the world,” the Tibetan Plateau is a vast area of 2.5 million square kilometers with an average elevation of more than 4,500 meters. Scientists have long theorized that the massive release of heat from the surface of the plateau-with air being heated to higher temperatures over the plateau than air at the same height over lower-level surfaces nearby-has been a major contributor to the strength of the monsoon.

“The South Asian monsoon supplies water to billions of people, many of whom live in developing nations and agricultural societies that are highly vulnerable to variations in this water supply,” explains co-author Zhiming Kuang, Assistant Professor of Climate Science in Harvard’s School of Engineering and Applied Sciences (SEAS) and Department of Earth and Planetary Sciences (EPS).

While the heating by the plateau does enhance rainfall along its southern edge, Kuang and his colleague William Boos, Daly Postdoctoral Fellow in EPS and an environmental fellow at the Harvard University Center for the Environment (HUCE), used an atmospheric circulation model to show that the large-scale South Asian summer monsoon circulation remains unaffected when the plateau is removed.

It turns out that the narrow geography of the Himalayas and other nearby mountain ranges can, in fact, produce an equally strong monsoon by insulating warm, moist air over continental India from the cold dry extratropics, the area between the subtropics and polar regions.

“Because heat from the plateau has been seen as the main contributor to the power of the monsoon, much attention has been given to changes in the plateau’s albedo, or its reflectivity level of the sun’s radiation,” says Kuang.

For example, a decrease in snow cover over the Tibetan Plateau resulting from an increase in global temperatures can affect reflectivity, and hence, the level of heat. The revised theory, emphasizing the important role the mountains play in trapping warm and moist air, suggests that climate scientists should pay as much attention to changes over the Indian subcontinent due to, for example, land use.

How the region’s natural environment is modified through activities such as building, mining, and agriculture, Zhang explains, can influence albedo and moisture, thus altering the temperature/humidity of the boundary layer air.

By considering the influence of both the plateau and the mountains on the strength of the monsoon, the Harvard researchers expect a clearer picture will emerge about the potential changes in the South Asian water supply in the coming decades.

“Ultimately, our revised view has implications for future projections of how the South Asian monsoon might be altered in a warmer world and can be used to infer aspects about the earth’s climate history,” says Boos.

Melting tundra creating vast river of waste into Arctic Ocean

Sofia Hjalmarsson is a postgraduate student at the Department of Chemistry, University of Gothenburg, Sweden -  University of Gothenburg
Sofia Hjalmarsson is a postgraduate student at the Department of Chemistry, University of Gothenburg, Sweden – University of Gothenburg

The increase in temperature in the Arctic has already caused the sea-ice there to melt. According to research conducted by the University of Gothenburg, Sweden, if the Arctic tundra also melts, vast amounts of organic material will be carried by the rivers straight into the Arctic Ocean, resulting in additional emissions of carbon dioxide.

Several Russian rivers enter the Arctic Ocean particularly in the Laptev Sea north of Siberia. One of the main rivers flowing into the Laptev Sea is the Lena, which in terms of its drainage basin and length is one of the ten largest rivers in the world. The river water carries organic carbon from the tundra, and research from the University of Gothenburg shows that this adds a considerable amount of carbon dioxide to the atmosphere when it is degraded in the coastal waters.

Increased temperatures


The increase in temperature in the Arctic, which has already made an impact in the form of reduced sea-ice cover during the summer, may also cause the permafrost to melt.

“Large amounts of organic carbon are currently stored within the permafrost and if this is released and gets carried by the rivers out into the coastal waters, then it will result in an increased release of carbon dioxide to the atmosphere,” says Sofia Hjalmarsson, native of Falkenberg and postgraduate student at the Department of Chemistry.

Study of two areas

In her thesis, Sofia Hjalmarsson has studied the carbon system in two different geographical areas: partly in the Baltic Sea, the Kattegat and the Skagerrak, and partly in the coastal waters north of Siberia (the Laptev Sea, the East Siberian Sea and the Chukchi Sea). The two areas have in common the fact that they receive large volumes of river water containing organic carbon and nutrients, mainly nitrogen.

Bering Strait influenced ice age climate patterns worldwide

Closed Bering Strait and global climate. Scientists are unraveling a chain of events that led to large-scale warmings and coolings across the Northern Hemisphere during past ice ages. As ice sheets expanded, water levels dropped in the narrow Bering Strait (left) and cut off the flow of relatively fresh water from the northern Pacific through the Arctic into the saltier Atlantic. This altered ocean currents, increasing the flow of Atlantic water northward from the tropics and producing warming in the north Atlantic (right, shown in dark red) that melted ice sheets and affected climate patterns and sea levels across much of the world. (Courtesy Nature, modified by UCAR.)
Closed Bering Strait and global climate. Scientists are unraveling a chain of events that led to large-scale warmings and coolings across the Northern Hemisphere during past ice ages. As ice sheets expanded, water levels dropped in the narrow Bering Strait (left) and cut off the flow of relatively fresh water from the northern Pacific through the Arctic into the saltier Atlantic. This altered ocean currents, increasing the flow of Atlantic water northward from the tropics and producing warming in the north Atlantic (right, shown in dark red) that melted ice sheets and affected climate patterns and sea levels across much of the world. (Courtesy Nature, modified by UCAR.)

In a vivid example of how a small geographic feature can have far-reaching impacts on climate, new research shows that water levels in the Bering Strait helped drive global climate patterns during ice age episodes dating back more than 100,000 years.

The international study, led by scientists at the National Center for Atmospheric Research (NCAR), found that the repeated opening and closing of the narrow strait due to fluctuating sea levels affected currents that transported heat and salinity in the Atlantic and Pacific oceans. As a result, summer temperatures in parts of North America and Greenland oscillated between warmer and colder phases, causing ice sheets to alternate between expansion and retreat and affecting sea levels worldwide.

While the findings do not directly bear on current global warming, they highlight the complexity of Earth’s climate system and the fact that seemingly insignificant changes can lead to dramatic tipping points for climate patterns, especially in and around the Arctic.

“The global climate is sensitive to impacts that may seem minor,” says NCAR scientist Aixue Hu, the lead author. “Even small processes, if they are in the right location, can amplify changes in climate around the world.”

The study is being published this week in Nature Geoscience. Funded by the Department of Energy and the National Science Foundation, NCAR’s sponsor, it used the latest generation of supercomputers to study past climate at a level of detail that would have been impossible just a few years ago.

New clues to an ice age mystery

Hu and his colleagues set out to solve a key mystery of the last glacial period: Why, starting about 116,000 years ago, did northern ice sheets repeatedly advance and retreat for about the next 70,000 years? The enormous ice sheets held so much water that sea levels rose and dropped by as much as about 100 feet (30 meters) during these intervals.

In other cases, scientists have associated such major oscillations in climate with fluctuations in Earth’s orbit around the Sun. But in the time period that the research team looked at, the orbital pattern did not correspond with the geologic movement of the ice sheets and associated sea level changes.

The study team considered an alternative possibility: that changes in the Bering Strait, the main gateway in the Northern Hemisphere between the Atlantic and Pacific oceans, might have affected ocean currents across much of the globe. Although small-the strait is currently about 50 miles (80 kilometers) wide between Russia and the westernmost islands of Alaska-it allows water to circulate from the relatively fresh north Pacific to the saltier north Atlantic via the Arctic Ocean. This flow is instrumental to regulating the strength of a current known as the meridional overturning circulation, a key driver of heat from the tropics to the poles.

Supercomputers reveal a pattern of warming and cooling

Using the NCAR-based Community Climate System Model, a powerful computer tool for studying worldwide climate, the researchers compared the responses of ice age climate to conditions in the Bering Strait. They ran the model on new supercomputers at NCAR and the Department of Energy’s Oak Ridge National Laboratory, enabling them to focus on smaller-scale geographic features that, until recently, could not be captured in long-term simulations of global climate.

The simulations accounted for the changes in sea level, revealing a recurring pattern-each time playing out over several thousand years-in which the reopening and closing of the strait had a far-reaching impact on ocean currents and ice sheets.

  • As the climate cooled because of changes in Earth’s orbit, northern ice sheets expanded. This caused sea levels to drop worldwide, forming a land bridge from Asia to North America and nearly closing the Bering Strait.

  • With the flow of relatively fresh water from the Pacific to the Atlantic choked off, the Atlantic grew more saline. The saltier and heavier water led to an intensification of the Atlantic’s meridional overturning circulation, a current of rising and sinking water that, like a conveyor belt, pumps warmer water northward from the tropics.

  • This circulation warmed Greenland and parts of North America by about 3 degrees Fahrenheit (1.5 degrees Celsius)-enough to reverse the advance of ice sheets in those regions and reduce their height by almost 400 feet (112 meters) every thousand years. Although the Pacific cooled by an equivalent amount, it did not have vast ice sheets that could be affected by the change in climate.

  • Over thousands of years, the Greenland and North American ice sheets melted enough to raise sea levels and reopen the Bering Strait.

  • The new inflow of fresher water from the Pacific weakened the meridional overturning circulation, allowing North America and Greenland to cool over time. The ice sheets resumed their advance, sea levels dropped, the Bering Strait again mostly closed, and the entire cycle was repeated.


The combination of the ocean circulation and the size of the ice sheets-which exerted a cooling effect by reflecting sunlight back into space-affected climate throughout the world. The computer simulations showed that North America and Eurasia warmed significantly during the times when the Bering Strait was open, with the tropical and subtropical Indian and Pacific Oceans, as well as Antarctica, warming slightly.

Learning from the past

The pattern was finally broken about 34,000 years ago, the point in Earth’s 95,000-year orbital cycle at which the planet was so far from the Sun at certain times of year that the ice sheets continued to grow even when the Bering Strait closed. When the orbital cycle brought Earth closer to the Sun in the northern winter, the ice sheets retreated sufficiently about 10,000 years ago to reopen the strait. This helped lead to a relatively stable climate, nurturing the rise of civilization.

“This kind of study is critical for teasing out the nuances of our climate system,” says NCAR scientist Gerald Meehl, a co-author of the paper. “If we can improve our understanding of the forces that affected climate in the past, we can better anticipate how our climate may change in the future.”

Study probes mystery of loop current in eastern Gulf of Mexico

A study released by the Minerals Management Service today examines the circulation in the Eastern Gulf of Mexico (GOM) and sheds new light on the behavior of the Loop Current (LC) and Loop Current Eddies (LCEs), the relation between the upper- and lower-layer currents, and the variability of water mass characteristics in deepwater.

When the LC and the LCE are present in the Gulf near oil and gas activities, operators may have to curtail or amend their operations due to the strength of the current or eddy.

“The observations from this study will help MMS and other scientists better understand the Loop Current and improve our forecasting of its behavior in the Gulf of Mexico,” said Dr. Alexis Lugo-Fernandez, the MMS physical oceanographer responsible for the study. “This is important because oil and gas activities in the deepwater Gulf are affected by the presence of the Loop Current and the Loop Current Eddies.”

Prepared under a cooperative agreement by Louisiana State University’s Coastal Marine Institute, Observation of the Deepwater Manifestation of the Loop Current and Loop Current Rings in the Eastern Gulf of Mexico chronicled the deployment in the Eastern Gulf of a deepwater mooring cable measuring more than 11,800 feet for two years. The study supplements information gathered from a previous three year deployment.

The mooring data suggest the LC and LCEs that dominate upper-layer circulation in the Eastern GOM also influence the deeper currents in the Eastern GOM.

Dr. Lugo-Fernandez noted that a method to transmit significant energy in the form of heat to deep water in the GOM during the 2005 hurricane season was observed during this study. As sea levels rise near the center of tropical storms, the resulting higher pressure causes a small but measurable increase in temperature at all water depths. He explained that “Simply due to the large number of storm occurrences within the GOM, these findings represent an important process for transmitting energy to the deepwater.”

Coal from mass extinction era linked to lung cancer mystery

Coal from China's Xuan Wei County, widely used for cooking and heating, may contribute to unusually high rates of lung cancer among women in the region. -  US Department of Energy
Coal from China’s Xuan Wei County, widely used for cooking and heating, may contribute to unusually high rates of lung cancer among women in the region. – US Department of Energy

The volcanic eruptions thought responsible for Earth’s largest mass extinction – which killed more than 70 percent of plants and animals 250 million years ago – is still taking lives today. That’s the conclusion of a new study showing, for the first time, that the high silica content of coal in one region of China may be interacting with volatile substances in the coal to cause unusually high rates of lung cancer. The study, which helps solve this cancer mystery, appears in ACS’ Environmental Science & Technology, a semi-monthly publication.

David Large and colleagues note that parts of China’s Xuan Wei County in Yunnan Province have the world’s highest incidence of lung cancer in nonsmoking women – 20 times higher than the rest of China. Women in the region heat their homes and cook on open coal-burning stoves that are not vented to the outside. Scientists believe that indoor emissions from burning coal cause cancer, but are unclear why the lung cancer rates in this region are so much higher than other areas. Earlier studies show a strong link between certain volatile substances, called PAHs, in coal smoke and lung cancer in the region.

The scientists found that coal used in parts of Xuan Wei County had about 10 times more silica, a suspected carcinogen, than U.S. coal. Silica may work in conjunction with PAHs to make the coal more carcinogenic, they indicate. The scientists also found that this high-silica coal was formed 250 million years ago, at a time when massive volcanic eruptions worked to deposit silica in the peat that formed Xuan Wei’s coal.