Category Archives: Publication Stories

New NOAA study finds natural climate cycles and

human activities are drivers of change

Scientists in the Gulf of Mexico now have a better understanding of how naturally-occurring climate cycles–as well as human activities–can trigger widespread ecosystem changes that ripple through the Gulf food web and the communities dependent on it, thanks to a new study published Saturday in the journal Global Change Biology.

A team of NOAA oceanographers spent three years reviewing over 100 indicators derived from environmental, fishery, and economic data, including sea surface temperature, currents, atmospheric patterns, fishing effort, harvest, and revenues. Through extensive analysis, they found a major ecosystem reorganization that appeared to be timed with a naturally-occurring climate shift that occurred around 1995.

The climate phenomenon is known as the Atlantic Multidecadal Oscillation (AMO), a climate signal in the North Atlantic Ocean that switches between cool and warm phases, each lasting for 20-40 years at a time. The AMO, which was in a cool phase between 1965 until 1995 and has been in a warm phase since, influences global ocean and weather conditions in the northern hemisphere such as hurricane activity in the Atlantic ocean and the severity and frequency of droughts.

However, the AMO is not as extensively studied as other climate phenomena, such as El Nino, and this study is the first to investigate what scientists hope will be many future studies examining how the AMO influences ecosystem-scale change in the Gulf. Scientists hope this work will spur interest in further studying this phenomenon and its implications for the marine environment in this region.

“These major ecosystem shifts have probably gone unrecognized to date because they are not apparent when considering single species or individual components of the ecosystem,” said lead investigator Dr. Mandy Karnauskas of NOAA’s Southeast Fisheries Science Center. “Only when we put a lot of things together — including currents, hypoxia, fish abundances, fishing effort, and more — does a strong climate signal emerge.”

Additionally, scientists observed shifts in many species around the late 1970s coincident with the advent of the U.S. Magnuson-Stevens Fishery Conservation and Management Act– a policy designed to set rules for international fishing in U.S. waters, make the expansion of certain fisheries more favorable for economic development, and ensure the long-term sustainability of the nation’s fish stocks.

Other human influences that are not as pronounced–or easily distinguishable–include coastal development, agricultural runoff, oil spills, and fishing. Natural phenomena like coastal storms and hurricanes play a role as well.

The scientists expect their study to be useful to resource managers throughout the Gulf region. While managers cannot control Earth’s natural climate cycles, they may need to consider how to alter management strategies in light of them, in order to effectively meet their mandates.

Karnauskas’ team included other scientists from NOAA Fisheries as well as NOAA’s Atlantic Oceanographic and Meteorological Laboratory, the University of Miami, and the University of Texas.

Click on the thumbnail to the left to download the full study.

Originally Published in March 2015 by Shannon Jones

How do hurricanes form, survive, and intensify? Hurricane scientists have long believed upper ocean temperatures are the key factor. AOML’s Dr. Joe Cione reveals a new theory, after observing 62 Atlantic hurricanes of a span of 32 years, suggesting this common theory may not be all that accurate. If his theory holds, it could have the potential to significantly improve hurricane intensity forecasts for the nation.

Dr. Cione found that in addition to ocean temperature, the near-surface air temperature and moisture around the hurricane are also essential energy requirements for sustaining a hurricane. These two variables often play an even more important role than ocean temperature.

This study assessed sea surface conditions in tropical systems, by monitoring the difference between dewpoint temperature and the sea surface temperature within the hurricane environment. When the dewpoint temperature was higher than the hurricane’s inner core’s sea surface temperature, the storms internal energy would decrease and weaken the hurricane.

Contrary to long held assumptions, results from this study show hurricanes can, and occasionally do, maintain intensity even when sea surface temperatures are at or below a threshold of 26^°C.  In six percent of the cases Dr. Cione studied, ocean surface temperatures of 26^°C or higher were not required for a hurricane to survive.

For hurricanes south of 29°N, near-surface atmospheric moisture was found to be the most important factor in maintaining a hurricane. In deep tropic storms between 10^°N – 20^°N, atmospheric environment in and around a storm was found to be the primary factor responsible for determining how much surface energy was drawn up out of the ocean and into the hurricane environment.

Dr. Cione’s research has potential to greatly impact intensity hurricane forecast models, which traditionally focus on ocean surface temperature. With this study showing the importance of moisture and atmospheric temperature for hurricane growth, scientists can now investigate how these factors impact hurricane intensity prediction.

Originally Published in February 2015 by Shannon Jones