Studies show global warming is likely to drive big changes in California's coastal waters

December 17, 2003

SANTA CRUZ, CA--Global warming could have profound effects on the wind-driven upwelling of deep ocean water along the California coast, according to recent studies by researchers at the University of California, Santa Cruz. The studies showed changes in both the intensity and the seasonal timing of the upwelling, which brings cold, nutrient-rich water into coastal ecosystems.

This seasonal upwelling supports California's diverse marine life and productive fisheries, but how changes in the upwelling will affect these and other aspects of coastal ecosystems remains uncertain. The researchers, led by professor of Earth sciences Lisa Sloan, used computer simulations of the regional climate to show that wind-driven upwelling along the California coast will likely intensify over the next 50 years as a result of increased concentrations of carbon dioxide in the atmosphere. In addition, the models showed the upwelling season extending later into the fall.

The first set of experiments was published in the August 14 issue of Geophysical Research Letters (GRL), and a second paper with additional findings will be published online this week by the Proceedings of the National Academy of Sciences (PNAS).

Previous studies by other researchers found that the intensity of upwelling along the California coast has been increasing over the past 30 years, leading some to speculate that the trend is a result of global warming, said Mark Snyder, lead author of the GRL paper. Snyder earned his Ph.D. this month working with Sloan.

"Some people think we may already be seeing the effects of climate change on the upwelling regime, so we thought we would use our climate models to see how increases in greenhouse gases would affect the winds that drive the upwelling," he said.

These winds are the result of differences in atmospheric pressure over the land and the ocean that develop because the land surface heats up faster than the ocean surface. Similarly, global warming could be expected to raise temperatures more over land than over the ocean, making the differences in atmospheric pressure even greater and creating stronger winds. Sloan's group set out to test this hypothesis using powerful computers to run complex models of the climate system.

The researchers used a high-resolution regional climate model, centered over California and driven by inputs from a global climate model with coarser resolution, to look at the effects of rising concentrations of carbon dioxide in the atmosphere. Concentrations of carbon dioxide, a greenhouse gas that traps heat in the atmosphere, are increasing due to emissions from the burning of fossil fuels.

The first set of experiments, published in the GRL paper, showed that with increasing carbon dioxide in the atmosphere, the intensity of upwelling is decreased in the early season (April to May) and is dramatically increased during the peak season (typically July to August). The results also showed the duration of the upwelling season extends further into the fall.

"The increase we saw in the upwelling intensity in the peak season supports some of the observational work showing a trend toward increased upwelling intensity in the present day," Snyder said.

The new results just published by PNAS reinforce these findings. In these experiments, the researchers included the effects on the climate system of changes in vegetation that are likely to occur with increased atmospheric carbon dioxide. The results showed the same general effects on upwelling as in the previous studies, only more pronounced, said postdoctoral researcher Noah Diffenbaugh, lead author of the PNAS paper.

"The interactions between vegetation and climate that are set in motion by increasing carbon dioxide concentrations enhance the effects on the upwelling regime," Diffenbaugh said.

The projected changes in vegetation result from warmer and dryer conditions created by global warming and lead to changes in the overall energy balance of the land surface, he said.

Diffenbaugh cautioned, however, that despite the complexity of the climate models, they still represent a simplified view of an extraordinarily complicated system of feedbacks and interactions. Nevertheless, as human activities continue to pour more carbon dioxide into the atmosphere, these studies show just how wide-ranging its effects may be.

"The regional climate model is certainly the best tool we have at the moment, and it shows us that elevated carbon dioxide is important not only for its direct effects on the climate, but also because it induces other changes that feed back into the climate system, and the magnitudes of those feedbacks appear to be substantial," Diffenbaugh said.

Researchers at UCSC and elsewhere are currently working to understand how changes in upwelling conditions will affect fisheries and the dynamics of coastal ecosystems. The new climate studies highlight the importance of those efforts, Snyder said.

University of California - Santa Cruz

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to