Charles David Keeling’s rigorous work reshaped humanity’s understanding of its influence on the planet. He continuously measured atmospheric carbon dioxide (CO2), an effort that led to the “Keeling Curve.” This graph provides clear evidence of increasing CO2 levels in the Earth’s atmosphere. His meticulous approach to data collection and analysis laid a foundation for modern climate science.
The Keeling Curve: A Landmark Discovery
The Keeling Curve illustrates the ongoing measurement of atmospheric CO2 concentration over an extended period. It shows two distinct features: an annual seasonal oscillation and a consistent upward trend in CO2 levels. The seasonal fluctuation, around 6 parts per million (ppm) each year, reflects the natural cycle of plant growth and decay. CO2 levels decrease during spring and summer in the Northern Hemisphere as plants absorb carbon dioxide through photosynthesis, and then rise in autumn and winter as vegetation decays and releases CO2 back into the atmosphere.
Beneath this annual zigzag, the curve reveals a steady increase in atmospheric CO2 concentrations year after year. For example, average concentrations rose from approximately 316 ppm in 1959 to about 370 ppm in 2000, reaching around 425 ppm by 2024. This upward trajectory demonstrates a continuous accumulation of CO2 in the atmosphere. The Keeling Curve provided the first clear, continuous, and long-term instrumental record of rising atmospheric CO2, shifting climate science to an evidence-based understanding of carbon dioxide accumulation.
Pioneering Atmospheric CO2 Measurement
The meticulous measurements that form the Keeling Curve began at the Mauna Loa Observatory in Hawaii. This remote location, situated at an elevation of about 3,400 meters (11,135 feet) on an active volcano, was chosen to minimize interference from local vegetation or urban pollution, ensuring representative air samples. An inversion layer further helps to suppress local pollutants from lower elevations. The first reading from Mauna Loa, taken on March 29, 1958, measured atmospheric CO2 at 313 ppm.
Keeling developed a rigorous methodology for consistent and accurate measurements over decades. He used an infrared gas analyzer for continuous CO2 measurements in air samples. This involved precise instrument calibration and systematic collection of air samples, using specialized “Keeling flasks.” Data integrity was important, with measurements frequently calibrated against World Meteorological Organization (WMO) standards, ensuring accuracy better than 0.2 ppm. This dedication to data quality and scientific integrity made the Keeling Curve highly credible and a benchmark for subsequent atmospheric measurements.
Global Impact and Enduring Legacy
The Keeling Curve has become an important piece of evidence for understanding human-caused climate change. It clearly demonstrates the link between the burning of fossil fuels and the increasing concentration of CO2 in the atmosphere. This data has informed major international scientific assessments, such as those conducted by the Intergovernmental Panel on Climate Change (IPCC), and has influenced global climate policy discussions.
Keeling’s work spurred further research into the global carbon cycle and atmospheric chemistry. His early findings about the seasonal CO2 oscillations and the steady annual increase in CO2 levels helped to illuminate how the Earth’s biosphere and human activities interact with atmospheric carbon. The Keeling Curve continues to be a symbol of climate science, representing the impact of human activities on the environment. Following Charles David Keeling’s passing in 2005, his son, Ralph Keeling, took over the Scripps CO2 Group, ensuring the unbroken continuation of this important long-term record.