The Human Contribution To Atmosphere Circulation Changes
- The Human Contribution To Atmosphere Circulation Changes
by Staff Writers
Virginia Key FL (SPX) May 05, 2006
A new study published in this week's issue of Nature is the first to
show that human activity is altering the circulation of the tropical
atmosphere and ocean through global warming.
Scientists widely agree that the climate has warmed over the past
century and that human activities, such as burning fossil fuels,
have significantly contributed to this global warming.
This study tapped historical records that date back to the mid-19th
century as well as simple theory and state-of-the-art computer model
simulations to detect and attribute these climate changes.
The conclusion was that the principal loop of winds that drives
climate and ocean behavior across the tropical Pacific is slowing
down and causing the climate to drift towards a more El Niño-like
state. This could have important implications for the frequency and
intensity of future El Niño events and biological productivity in
In their paper, titled "Weakening of Tropical Pacific Atmospheric
Circulation Due to Anthropogenic Forcing," the researchers identify
a 3.5 percent weakening that has occurred since the mid-1800s in
this air system known as the Walker circulation. They also cite
evidence that it may weaken another 10 percent by 2100.
"There is an indication that the slowdown may be intensifying," said
Dr. Gabriel A. Vecchi, lead author from NOAA's Geophysical Fluid
Dynamics Laboratory. "The trend since World War II is larger than
that over the entire record, and the long-term trend is larger than
what is expected from natural climate variability. This is why we
employed a very long observational record to be able to accurately
detect and attribute these changes."
The study does send mixed signals on the future of El Niño/La
Niña. "While we can't predict with certainty how the frequency or
intensity of El Niño-related weather events will respond to global
warming, our study does suggest that the climate as a whole is
slowly moving towards a more El Niño-like state," said Dr. Brian
Soden, a co-author from the University of Miami Rosenstiel School of
Marine and Atmospheric Science.
"Additionally, this slowdown has modified the structure and
circulation of the tropical Pacific Ocean, which is a source of
nutrients to one of the most biologically productive regions of the
world's oceans. This has implications to the well-being and
proliferation of marine life in tropical oceans."
"The Walker circulation is fundamental to climate throughout the
globe: its variations are closely linked to those of the El
Niño/Southern Oscillation and monsoonal circulations over adjacent
continents, and variations in its intensity and structure affect
climate all over the globe," wrote Vecchi, Soden, and their co-
authors Andrew T. Wittenberg, Isaac M. Held, Ants Leetmaa, and
Matthew J. Harrison, also from the NOAA Geophysical Fluid Dynamics
Laboratory in Princeton, N.J. The Walker circulation spans almost
half the circumference of the Earth.
This study found a weakening of the Walker circulation in historical
observations that corresponds closely to what theoretical and
modeling studies expect from an increase in greenhouse gases. This
agreement provides increased confidence in model projections of
future climate change in the tropics.
Rosenstiel School is part of the University of Miami and, since its
founding in the 1940s, has grown into one of the world's premier
marine and atmospheric research institutions.
An Envisat image of La Nina in February 2006.