Researchers confirm role of massive flood in climate change

Climate modelers at the Goddard Institute for Space Studies (GISS) have succeeded in reproducing the climate changes caused by a massive freshwater pulse into the North Atlantic that occurred at the beginning of the current warm period 8,000 years ago. Their work is the first to consistently model the event and the first time that the model results have been validated by comparison to the record of climate proxies that scientists regularly use to study the Earth's past.

"We only have one example of how the climate reacts to changes, the past," said Gavin A. Schmidt, a GISS researcher and co-author on the study. "If we're going to accurately simulate the Earth's future, we need to be able to replicate past events. This was a real test of the model's skill."

The study was led by Allegra LeGrande, a graduate student in the department of earth and environmental sciences at Columbia University. The results appear in a paper being published in this week's edition of the journal Proceedings of the National Academy of Sciences (PNAS).

The group used an atmosphere-ocean coupled climate model known as GISS Model E-R to simulate the climate impact of a massive freshwater flood into the North Atlantic that happened about 8,200 years ago after the end of the last Ice Age. As retreating glaciers opened a route for two ancient meltwater lakes known as Agassiz and Ojibway to suddenly and catastrophically drain from the middle of the North American continent.

At approximately the same time, climate records show that the Earth experienced its last abrupt climate shift. Scientists believe that the massive freshwater pulse interfered with the ocean's overturning circulation, which distributes heat around the globe. According to the record of what are known as climate proxies, average air temperatures apparently dropped fell as much as several degrees in some areas of the Northern Hemisphere.

Climate researchers use these proxies--chemical signals locked in minerals and ice bubbles as well as pollen and other biological indicators--as indirect measures of temperature and precipitation patterns in the distant past. Because GISS Model E-R incorporates the response of these proxies in its output, the authors of the PNAS study were able to compare their results directly to the historical record.

The researchers prodded their model with a freshwater pulse equal to between 25 and 50 times the flow of the Amazon River in 12 model runs that took more than a year to complete. Although the simulations largely agreed with proxy records from North Atlantic sediment cores and Greenland ice cores, the team's results showed that the flood had much milder effects around the globe than many people fear--including the dramatic shifts in climate depicted in the 2004 movie 'The Day After Tomorrow'.

According to the model, temperatures in the North Atlantic and Greenland showed the largest decrease, with slightly less cooling over parts of North America and Europe. The rest of the northern hemisphere, however, showed very little effect, and temperatures in the southern hemisphere remained largely unchanged. Moreover, ocean circulation, which initially dropped by half after simulated flood, appeared to rebound within 50 to 150 years.

"This was probably the closest thing to a 'Day After Tomorrow' scenario that we could model," said LeGrande. "The flood we looked at was even larger than anything that could happen today. Still, it's important for us to study because the real thing occurred during a period when conditions were not that much different from the present day."

The GISS climate model is also being used for the latest simulations by the Intergovernmental Panel on Climate Change (IPCC) to simulate the Earth's present and future climate. "Hopefully, successful simulations of the past such as this will increase confidence in the validity of model projections," said Schmidt.

Source: The Earth Institute at Columbia University

Related stories:

Ice Age lesson predicts a faster rise in sea level
If the lessons being learned by scientists about the demise of the last great North American ice sheet are correct, estimates of global sea level rise from a melting Greenland ice sheet may be seriously underestimated.
New clues to air circulation in the atmosphere
Air circulates above the Earth in four distinct cells, with two either side of the equator, says new research. The new observational study describes how air rises and falls in the atmosphere above the Earth's surface, creating the world's weather.
New research suggests Burmese pythons will find little suitable habitat outside South Florida
Burmese Pythons – one of the largest snakes in the world – may have chosen Florida as a vacation destination, but are unlikely to expand further, according to a study released August 13 by researchers at the City University of New York (CUNY), published in the online, open access journal PLoS ONE. Although the United States Geological Survey (USGS) earlier this year released 'climate maps' indicating that the pythons could potentially inhabit up to thirty two states in the continental U.S., new research indicates that the snakes are unlikely to expand out of south Florida.
Bugs put the heat in chili peppers
If you're a fan of habañero salsa or like to order Thai food spiced to five stars, you owe a lot to bugs, both the crawling kind and ones you can see only with a microscope. New research shows they are the ones responsible for the heat in chili peppers.
Climate change and species distributions
Scientists have long pointed to physical changes in the Earth and its atmosphere, such as melting polar ice caps, sea level rise and violent storms, as indicators of global climate change. But changes in climate can wreak havoc in more subtle ways, such as the loss of habitat for plant and animal species. In a series of talks at the Ecological Society of America (ESA) 93rd Annual Meeting, climate change scientists will discuss how temperature-induced habitat loss can spell disaster for many living things.
More kidney stone disease projected due to global warming
Global warming is likely to increase the proportion of the population affected by kidney stones by expanding the higher-risk region known as the "kidney-stone belt" into neighboring states, researchers at UT Southwestern Medical Center and UT Dallas have found.
Scattered nature of Wisconsin's woodlands could complicate forests' response to climate change
If a warmer Wisconsin climate causes some northern tree species to disappear in the future, it's easy to imagine that southern species will just expand their range northward as soon as the conditions suit them.
Scientists integrate data in three dimensions to study climate effects on young fish
From the surface, the two areas of ocean off the coasts of northern New Jersey and Long Island, New York look the same. But to NOAA scientists, the four-square-mile patches could not be more different as they view real-time underwater images and environmental data to try to figure out what lives there and how climate change is affecting marine life, especially very young fish.

News discussion:

Space & Earth science news