A Scientist's Life: Dan Cayan

Climate scientist describes the challenge of seeing climate in high definition

Dan Cayan is a climate researcher at Scripps Institution of Oceanography at UC San Diego and the U.S. Geological Survey. He focuses on regional climate variability and change with an emphasis on the climate of California and the western United States. In addition to his research, Cayan advises decision makers at local, state, and federal levels on climate issues. He has played a key role in a series of California climate change vulnerability and adaptation assessments and in directing the California-Nevada Applications Program, which conducts applied research and provides information to stakeholders. He entered the Scripps graduate program in 1972, was appointed as a staff research associate in 1977, and received a PhD in oceanography from Scripps/UCSD in 1990.

explorations now: Describe the focus of your research.

Dan Cayan: I’m a climate researcher and my emphasis is on regional climate and how it varies and how it may change. Over my career, I’ve looked at problems that are both very broad and regional in scale. My first work here was to look at how the oceans and the atmosphere communicate over the ocean surface and more recently I’ve gotten very focused on regional climate problems largely because there’s been such a demand to try to understand how climate variability and in particular climate change, will affect us in the future.

We are faced with substantial, and possibly massive changes in future decades. Understanding how these changes may unfold under different scenarios of intensity and rates of change will help to plan for impacts on a manifold of systems from coasts to energy, human health, forests, and agriculture. This drives us to explore observational records and various climate model simulations and apply results to the problems and topics that are facing resource managers, policymakers and other decision-makers. The goal is to provide them with information that is non-biased and includes a range of outcomes that might happen.

en: What drew you to climate research?

DC: Scripps is not only a multi-faceted oceanographic research environment, but also carries a strong earth science emphasis. A large part of my work has a terrestrial focus but I work on coastal ocean phenomena as well. I didn’t really understand the broad scope of this field when I arrived here. I came to Scripps as a fledgling graduate student studying physical oceanography and I sort of got into climate as I went along.

en: Why did you choose Scripps?

DC: I decided to come to Scripps because of the depth and the breadth of research and education that has been cultivated here.  Throughout the years I’ve been here, I’ve been repeatedly impressed by the breadth and quality of research by my colleagues.  Much of this research has a climate component because there are so many different aspects of ocean and terrestrial science, along with many social and human dimensions. So, there’s no lack of topics to be involved with. Scripps provides a great laboratory through which to explore these problems.

en: What are some of the tools you use in your research?

DC: We rely on a broad array of historical observations and different kinds of model simulations. Long-term observations such as mountain weather stations and the snow accumulated in Sierra Nevada meadows provide critical records to understand variations and changes in an important part of the California water supply. Extreme events occur pretty irregularly and rarely, so to capture analogues for high impact cases, we must include records over a time span of several decades. Thus, having samples that are quite granular so we can look at hour-by-hour evolution of the ocean, atmosphere, and coastal land area is quite critical.  

We also use datasets created by an array of numerical models, ranging from those that simulate the global climate system to those that represent the hydrology in an individual river basin. What happens here in California is not only affected by local conditions, but is strongly guided by phenomena happening over a semi-global landscape. So having models that are able to portray conditions within the region as well as those that depict the broader scale Pacific-North America and even global domain is really crucial in trying to sort through all this.

Over the last few decades, climate models have progressively developed and have become more realistic. There is now better representation of physical and chemical processes, higher spatial definition with more vertical levels in the atmosphere and ocean. In a complex topographic region like California, fine-scale model simulations are required to represent how marine weather influences along the coast grades to continental air masses in the interior, and how important elements such as precipitation are affected by mountains and valleys.

en: What are some of the issues in your field of research?

DC: There remain a number of basic science and engineering problems that must be solved to understand and monitor climate variability and change. An increasingly important emphasis in environmental fields, including climate sciences, is aimed at being socially relevant and helping to solve problems. This emphasis appears not only in regards to national and international climate change issues, but also to inform state and local decision-making. A major part of our recent research effort has been tied to the State of California’s attempts to conduct a comprehensive assessment of its climate profile, currently and in the future.  We are helping the State understand its unique blend of vulnerability to climate change.  

Because there is a lot of uncertainty, our approach is to construct and explore multiple scenarios of how climate-related changes could play out over the twenty-first century. This should help California and other regions to prepare, adapt and diminish their exposure to some very severe problems. Because of the increasing insight that comes from new observations and better models, and because likely impacts of climate change are diverse and costly, this kind of assessment needs to be continually updated. Building the capacity and support to sustain this enterprise is a major challenge for scientists as well as public agencies and private enterprise.  

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