Carbon release from ocean helped end the ice age

Fri, 02/13/2015 - 9:20am Jim Shelton, Yale Univ. New techniques are allowing scientists to understand how carbon dioxide, released from the deep ocean, helped to end the last ice age and create our current climate. An international team, including Yale paleoclimatologist Michael Henehan, studied the shells of ancient marine organisms that lived in surface waters of the southern Atlantic and eastern equatorial Pacific oceans thousands of years ago. The researchers determined that high concentrations of dissolved carbon dioxide in those waters coincided with rises in atmospheric carbon dioxide and global temperatures at the end of the last ice age. The findings give scientists valuable insights into how the ocean can affect the carbon cycle and climate change, say the researchers. A study describing the research appears in Nature. Joint lead authors of the study are Miguel Martínez-Botí of the Univ. of Southampton and Gianluca Marino of the Australian National Univ. The Univ. of Southampton led the effort. “This is an exciting time for research into past climates,” said Henehan, who is a postdoctoral associate in the Dept. of Geology and Geophysics. “Advances in technologies and improvements in our methods have allowed us in this study to show just how critical carbon dioxide release from the oceans was in kicking the Earth out of the last ice age and into the climate state we have today.” Henehan said Yale scientists are using the same technique to look even further back in time, investigating whether changes in atmospheric carbon dioxide played a role in the mass extinction of species at the end of the Cretaceous period. Source: Yale Univ.

Warming pushes Western US toward driest period in 1,000 years: Unprecedented Risk of Drought in 21st Century

Soil moisture 30 cm below ground projected through 2100 for high emissions scenario RCP 8.5. The soil moisture data are standardized to the Palmer Drought Severity Index and are deviations from the 20th century average. During the second half of the 21st century, the U.S. Southwest and Great Plains will face persistent drought worse than anything seen in times ancient or modern, with the drying conditions "driven primarily" by human-induced global warming, a new study predicts. The research says the drying would surpass in severity any of the decades-long "megadroughts" that occurred much earlier during the past 1,000 years -- one of which has been tied by some researchers to the decline of the Anasazi or Ancient Pueblo Peoples in the Colorado Plateau in the late 13th century. Many studies have already predicted that the Southwest could dry due to global warming, but this is the first to say that such drying could exceed the worst conditions of the distant past. The impacts today would be devastating, given the region's much larger population and use of resources. "We are the first to do this kind of quantitative comparison between the projections and the distant past, and the story is a bit bleak," said Jason E. Smerdon, a co-author and climate scientist at the Lamont-Doherty Earth Observatory, part of the Earth Institute at Columbia University. "Even when selecting for the worst megadrought-dominated period, the 21st century projections make the megadroughts seem like quaint walks through the Garden of Eden." "The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at," said lead author Benjamin I. Cook of the NASA Goddard Institute for Space Studies and the Lamont-Doherty Earth Observatory. "It all showed this really, really significant drying." The new study, "Unprecedented 21st-Century Drought Risk in the American Southwest and Central Plains," will be featured in the inaugural edition of the new online journal Science Advances, produced by the American Association for the Advancement of Science, which also publishes the leading journal Science. Today, 11 of the past 14 years have been drought years in much of the American West, including California, Nevada, New Mexico and Arizona and across the Southern Plains to Texas and Oklahoma, according to the U.S. Drought Monitor, a collaboration of U.S. government agencies. The current drought directly affects more than64 million people in the Southwest and Southern Plains, according to NASA, and many more are indirectly affected because of the impacts on agricultural regions. Shrinking water supplies have forced western states to impose water use restrictions; aquifers are being drawn down to unsustainable levels, and major surface reservoirs such as Lake Mead and Lake Powell are at historically low levels. This winter's snowpack in the Sierras, a major water source for Los Angeles and other cities, is less than a quarter of what authorities call a "normal" level, according to a February report from the Los Angeles Department of Water and Power. California water officials last year cut off the flow of water from the northern part of the state to the south, forcing farmers in the Central Valley to leave hundreds of thousands of acres unplanted. "Changes in precipitation, temperature and drought, and the consequences it has for our society -- which is critically dependent on our freshwater resources for food, electricity and industry -- are likely to be the most immediate climate impacts we experience as a result of greenhouse gas emissions," said Kevin Anchukaitis, a climate researcher at the Woods Hole Oceanographic Institution. Anchukaitis said the findings "require us to think rather immediately about how we could and would adapt." Much of our knowledge about past droughts comes from extensive study of tree rings conducted by Lamont-Doherty scientist Edward Cook (Benjamin's father) and others, who in 2009 created the North American Drought Atlas. The atlas recreates the history of drought over the previous 2,005 years, based on hundreds of tree-ring chronologies, gleaned in turn from tens of thousands of tree samples across the United States, Mexico and parts of Canada. For the current study, researchers used data from the atlas to represent past climate, and applied three different measures for drought -- two soil moisture measurements at varying depths, and a version of the Palmer Drought Severity Index, which gauges precipitation and evaporation and transpiration -- the net input of water into the land. While some have questioned how accurately the Palmer drought index truly reflects soil moisture, the researchers found it matched well with other measures, and that it "provides a bridge between the [climate] models and drought in observations," Cook said. The researchers applied 17 different climate models to analyze the future impact of rising average temperatures on the regions. And, they compared two different global warming scenarios -- one with "business as usual," projecting a continued rise in emissions of the greenhouse gases that contribute to global warming; and a second scenario in which emissions are moderated. By most of those measures, they came to the same conclusions. "The results … are extremely unfavorable for the continuation of agricultural and water resource management as they are currently practiced in the Great Plains and southwestern United States," said David Stahle, professor in the Department of Geosciences at the University of Arkansas and director of the Tree-Ring Laboratory there. Stahle was not involved in the study, though he worked on the North American Drought Atlas. Smerdon said he and his colleagues are confident in their results. The effects of CO2 on higher average temperature and the subsequent connection to drying in the Southwest and Great Plains emerge as a "strong signal" across the majority of the models, regardless of the drought metrics that are used, he said. And, he added, they are consistent with many previous studies. Anchukaitis said the paper "provides an elegant and convincing connection" between reconstructions of past climate and the models pointing to the risk of future drought. Toby R. Ault of Cornell University is a co-author of the study. Funding was provided by the NASA Modeling, Analysis and Prediction Program, NASA Strategic Science, and the U.S. National Science Foundation.

How Dry Will It Get? New Climate Change Predictions

 

Map of projected changes in global precipitation.
Credit: Scripps

Global warming's crystal ball is clearing as climate models improve, and scientists now predict that some regions will see a month's less rain and snow by 2100.

The new rain and snow estimates indicate that subtropical spots — such as the Mediterranean, the Amazon, Central America and Indonesia — will undergo the biggest precipitation shifts in the coming decades. The number of dry days in these zones will rise by as many as 30 days per year, according to the study, published today (March 13) in the journal Scientific Reports.

"Looking at changes in the number of dry days per year is a new way of understanding how climate change will affect us that goes beyond just annual or seasonal mean precipitation changes, and allows us to better adapt to and mitigate the impacts of local hydrological changes," said Suraj Polade, a climate scientist at Scripps Institution of Oceanography in San Diego and lead study author.

The findings also suggest a rising probability of droughts and floods in the near future as annual rainfall becomes more variable, the researchers said. [Weather vs. Climate Change: Test Yourself]

"Variability is going to play a big part in making things worse [as climate changes]," Polade told Live Science. "When you're increasing the variability of the climate, one year you can have a flood and the next year you can have a drought. You can also have an increase in extreme precipitation events, with a whole year's precipitation in just a few storms."

South Africa, Mexico and western Australia will go without rain for 15 to 20 more days per year, and California is likely to have five to 10 more dry days per year by the end of the century, the study found.

Some of the subtropical missing moisture will head north: The study predicts the Arctic will have 40 more wet days a year, but the South Pole will only get 10 more wet days per year.

Rerouting the weather

Why the shifts? Answers vary, but previous research has pointed the finger at changing storm tracks, particularly for tropical cyclones such as hurricanes and typhoons. Climate models suggest that midlatitude cyclones may shift north, while those that hit near the equator will likely stay their usual course.

There are also poleward shifts in the vast atmospheric patterns that control where rain falls. For example, the Hadley cell, the large-scale pattern of atmospheric circulation that transports heat from the tropics to the subtropics, has marched south during recent decades, moving the subtropical dry zone (a band that receives little rainfall) along with it. The northern and southern jet streams, which mark where cold and warm air meet, also seem to be creeping toward the poles. Their movement away from the equator suggests that the Earth's tropical zones are expanding, according to recent studies. The jet streams play an important role in moving moisture around the higher latitudes.

"We are looking at why this is happening," Polade said. "Earlier studies suggest that warmer regions will get wetter, while colder regions can get wetter or drier," he said. "The tropics are also getting wetter or drier, while the subtropics are drying."

The report relies on the latest global climate models (known as CMIP5), which predict future climate change under certain greenhouse-gas emissions scenarios. The study tested an increase in atmospheric carbon dioxide concentrations to 950 parts per million by 2100, more than twice the current level. The number means there would be 950 molecules of carbon dioxide in the air per every million air molecules. 

Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on Live Science.