Climate measurement involves the systematic tracking of physical and chemical indicators over time to quantify shifts in the planet’s condition. The complexity of the Earth system requires scientists to use multiple, independent lines of evidence to build a comprehensive understanding of change. This multifaceted approach, spanning from atmospheric chemistry to deep-ocean physics, ensures that conclusions are robust and not dependent on any single data stream.
Tracking Atmospheric Composition
The foundation of climate change measurement begins with monitoring the gases that trap heat in the atmosphere. Scientists precisely track the concentration of greenhouse gases, primarily carbon dioxide (\(\text{CO}_2\)), methane, and nitrous oxide. The longest continuous record of atmospheric \(\text{CO}_2\) concentration is maintained at the Mauna Loa Observatory in Hawaii, beginning in 1958. This landmark data series, known as the Keeling Curve, reveals a steady, year-over-year increase in atmospheric \(\text{CO}_2\) concentration.
The curve also displays a distinct annual “zigzag” pattern, reflecting how atmospheric \(\text{CO}_2\) drops during the Northern Hemisphere’s summer growing season as plants absorb the gas, and rises again in the winter. Complementing these surface measurements are satellite-based instruments that provide a global view of greenhouse gas distribution. Missions like NASA’s Orbiting Carbon Observatory-2 (\(\text{OCO-2}\)) and the European TROPOMI use spectroscopy to measure the sunlight reflected off Earth, allowing scientists to determine the concentration of \(\text{CO}_2\) and methane across the entire planet.
Monitoring Global Temperature Shifts
Measuring the planet’s temperature involves calculating a global average from millions of separate data points collected across land and sea. Land-based thermometers at tens of thousands of weather stations provide air temperature readings near the surface. Sea surface temperatures are collected using ships, static moorings, and drifting buoys. These measurements are combined onto a global grid, with temperature anomalies calculated as the difference from a long-term reference period.
Using anomalies is preferred because it focuses on the rate of change rather than absolute temperature, which helps reduce errors from inconsistent measurement techniques and locations over time. The raw data must undergo homogenization, where scientists adjust historical records to remove non-climate-related biases, such as changes in instrument type or station relocation. Beyond the surface, the ocean’s massive capacity to store heat is tracked by autonomous devices known as Argo floats. These robotic devices profile the upper 2,000 meters of the ocean every 10 days, measuring temperature and salinity to quantify the deep ocean’s heat absorption, which accounts for over 90% of the Earth’s excess heat.
Quantifying Changes in Earth’s Water Systems
The physical effects of a warming climate are tracked primarily through changes in the cryosphere and ocean volume. Global sea level rise is monitored using two main techniques: coastal tide gauges and satellite altimetry. Tide gauges provide long-term local records, while satellite missions, such as the Jason series, use radar to precisely measure the height of the sea surface from space, giving a near-global measurement every ten days.
Scientists also track the loss of ice mass from glaciers and ice sheets. Gravimetric satellites, like the Gravity Recovery and Climate Experiment (\(\text{GRACE}\)), measure tiny shifts in the Earth’s gravity field caused by the movement of mass, allowing researchers to quantify the volume of ice lost. This ice loss, combined with the thermal expansion of seawater as it warms, accounts for the observed rise in sea level. Additionally, ocean acidification is monitored by the Global Ocean Acidification Observing Network (\(\text{GOA-ON}\)), which coordinates global measurements of seawater \(\text{pH}\) to track the ocean’s increasing acidity.
Utilizing Climate Proxies for Historical Context
To understand climate change over geological timescales, scientists rely on indirect evidence known as climate proxies. These preserved physical characteristics allow for the reconstruction of past climate conditions long before instrumental records existed. Ice cores drilled from ice sheets contain trapped air bubbles that preserve samples of the ancient atmosphere, including past concentrations of greenhouse gases.
The ice itself contains layers analyzed using oxygen isotope ratios to estimate historical temperatures. Tree rings, analyzed through dendrochronology, serve as another proxy, where the width and density of the annual rings reflect variations in temperature and moisture during the growing season. Sediment layers collected from the ocean floor or lake beds contain microfossils and chemical signatures that provide further evidence of past ocean temperatures and conditions. These proxy records establish the baseline data showing that the current rate of change far exceeds natural historical variability.