 Have you ever wondered how scientists measure CO2 and greenhouse emissions from local ecosystems here on Earth? Well, one way is a well-defined scientific method known as eddy covariance. Well, not that, Eddie. Eddie covariance is how we measure an ecosystem's breathing. It's the CO2 and other gases that are exchanged between soil, vegetation, and the air in an ecosystem. The data it provides helps scientists to develop models that forecast long-term trends in CO2 and greenhouse gases, much like the National Weather Service forecast the short-term weather. This data will allow policy makers to draft legislation to address pressing issues and improve people's quality of life. Eddie covariance quantifies gas fluxes or changes by directly measuring the movement of gases, like CO2, between an ecosystem and the atmosphere. To simplify it, let's look at both words. An eddy is a circular motion of air created by temperature fluctuations. At night, without the sun, the air is cool and relatively stable. With the rising of the sun, the earth and air temperature begins to climb. This constant night and day fluctuation creates the wind we feel and the eddies of air that scientists measure. Covariance has two parts, co, meaning together, and variance, meaning change. This means simultaneously measuring the differences between the concentration of a gas and the direction of the swirling wind. Eddie covariance is primarily measured by two pieces of high-tech gadgetry mounted on tripods and towers above areas of interest, like forests, lakes, or agricultural areas. The anemometer measures wind speed and direction. The infrared gas analyzer measures gas concentrations in the air. The data are collected simultaneously thousands of times per minute. Wind and gas concentration data go into a complex series of equations that, after several assumptions, yield estimates of the movement of gas into or out of an ecosystem. Two types of observations are primarily used to approximate the gas exchange. Imagine we place a box over the ecosystem. The gas moving in and out of the top of the box is calculated as fluctuations around the mean. The gas accumulated inside the box is calculated from the trend of gas concentration measurements in that area. When calculated over time, we can see trends that reveal how much CO2 and other gases are being reused by earth's organisms and how much is released into the atmosphere. To really simplify, the system works by measuring how many gas molecules pass through a defined volume over a specific time. For example, the system might capture a measurement of seven CO2 molecules being carried upward towards the atmosphere by an eddy. Then in the next moment, only five of those molecules are recorded traveling back down towards the ground. Then we know that the net flux over this specific time period is equal to two molecules of CO2 being emitted into the atmosphere. It isn't your everyday eddy that compiles this stuff. Eddy covariance data is collected by individual researchers and organizations around the globe, including the National Ecological Observatory Network. And what's really cool is that all these institutions contribute to an international database, FluxNet, to facilitate the use of eddy covariance data to contribute to global models at many times scales. Eddy covariance measurements are really important because they're the most conclusive method for measuring how much CO2 and other gases are taken in by photosynthesis, and also emitted into earth's atmosphere from things like respiration, geologic emissions, thawing permafrost, and human activity. Documenting these gas exchanges is important to understand trends in atmospheric concentrations. They allow for the development of accurate models to forecast greenhouse gas concentrations and other factors of climate change on our planet. So next time you think about how scientists measure CO2 and greenhouse emissions at a local level, just remember eddy. Eddy covariance and other data are freely available at neonscience.org.