While climate scientists agree the earth is warming, and human activity is a significant contributor to climate change, many are still working to understand the relationships between naturally occurring climate variability and global warming and how those relationships affect weather patterns and extreme weather events locally and regionally around the world.
Portland State University geography professor and climate scientist Paul Loikith and Judah Detzer, a graduate student and research analyst, are collaborating with researchers at the University of California, Los Angeles (UCLA), to better understand how natural climate variability and climate change are evolving across the continent of South America.
Specifically, Loikith and Detzer explore how major climate drivers such as the El Niño Southern Oscillation, the Antarctic Polar Vortex, and the Atlantic Multidecadal Oscillation influence observed weather patterns throughout South America. It's the research they'll use to create a spatial and temporal picture of average, natural climate variability over the continent. That work, in turn, will inform researchers at UCLA analyzing South American climate trends. Led by Roberto Mechoso, the UCLA researchers ask if those trends are outside the range of natural variability and trying to determine whether trends in the observational record are attributable to identifiable anthropogenic forcings such as well-mixed greenhouse gases, land-use changes, and black carbon aerosols.
"To our knowledge, this is the first study to holistically and systematically examine natural climate variability and the evolution of climate change over the entire continent of South America and then to ask if we can attribute variations from the norm to specific human activities driving observed climate trends," said Loikith.
According to Loikith, who heads the Climate Science Laboratory at PSU, understanding average natural climate variability over time requires combing through and making sense of an enormous cache of reanalysis data: an aggregation of historical, place-based meteorological data recorded at locations throughout the continent multiple times a day over many years, as well as observational data. In the lab, graduate student Judah Detzer develops algorithms that sort through the reanalysis data and additional data from observations and climate models, producing maps that illustrate how natural phenomena such as an El Niño affect temperature, precipitation, and atmospheric pressure throughout all South America. Once the data have been analyzed, aggregated, and adjusted to account for uncertainties, Detzer and Loikith can use their findings to make generalizations about natural climate variability anywhere on the continent.
"In our approach to the research, we're looking at top-down mechanisms that drive climate at large scales—things like El Niño," Loikith said. "We're also analyzing climate and weather from the bottom up, looking at regional and local-scale data for things like temperature, wind, precipitation, atmospheric pressure, and other factors that drive variability regionally and may affect local climate and weather. And, when we put these pieces together, we'll have a more comprehensive understanding of natural climate variability, and that will inform the efforts of our partners at UCLA who are exploring whether they can identify if specific human activities are contributing to observed variation and trends in climate over the continent."
Once we understand the fundamental mechanisms for climate and weather variability over South America, Loikith noted, climate scientists will be able to ask other complex questions such as: are the current state-of-the-art climate models used to project future climate under a range of anthropogenic forcings producing reliable data? And will certain types of weather patterns and weather extremes become more prominent in South America as the planet continues to warm?
"That's the end goal we're working towards," Loikith said. "We want to get to a place with our understanding of natural climate variability over South America and with our climate models where we have a baseline to measure climate change against and methods to systematically detect, attribute, and understand the anthropogenic factors contributing to changes in climate and weather patterns."