Essential Climate Variables

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When you visit the hospital, one of the first things that is done is checking your vital signs. These “vitals” are medical measurements that provide data about the body's basic functions and include heart rate, blood pressure, oxygen levels, etc. They are important because they give a quick picture of a patient’s overall health, aid in the detection and treatment of health problems, and guide future medical decisions.

Similarly, in our exploration of Earth's climate system, we need to select measurements that allow us to view the basic state of the climate and how it behaves, changes, and impacts our planet. This set of simple, but very important, parameters is known as Essential Climate Variables, or ECVs.

An ECV can be defined as a physical, chemical, or biological variable that holds a key importance in characterizing Earth's climate. ECVs are the variables that scientists believe are crucial to monitor because of their profound influence on the global climate system and their importance in understanding climate change. Moreover, these variables are pivotal in assisting decision-making processes related to climate change adaptation and mitigation.

There are three main criteria that make a particular measurement an ECV:

1. Relevance: The variable is critical for characterizing the climate system and its changes.
2. Feasibility: Observing or deriving the variable on a global scale is technically feasible using proven, scientifically understood methods.
3. Cost-effectiveness: Generating and archiving data on the variable is affordable. It mainly relies on coordinated observing systems using proven technology, taking advantage of historical datasets where possible.

While relevance and feasibility seem obvious, I want to emphasize that cost-effectiveness is also extremely important. ECVs require us to get as holistic of a view of the entire Earth system as possible – if we design a drone that can measure temperatures far higher than where planes fly, but the cost is $10 billion per craft, that doesn’t do us a tremendous amount of good in terms of sampling the entirety of the planet!

While we could probably think of some ECVs right off the top of our heads (surface temperature, anyone?), we delegate the organization of them to the Global Climate Observing System (GCOS). GCOS operates under the sponsorship of the World Meteorological Organization (WMO), the Intergovernmental Oceanographic Commission (IOC) of UNESCO, the United Nations Environment Program (UNEP), and the International Science Council (ISC). Phew, don't worry; there will not be a quiz on any of *those* acronyms!

So, what are some examples of ECVs?

We can consider that this list of ECVs provides the foundation for sharing climate data worldwide, both for current conditions and historical records. It is a Rosetta Stone that allows researchers from all around the world to speak the same climate language. However, I should emphasize that these variables – while we’ll use them a lot this semester – are not an “end-all be-all.” Scientists use a host of other data to track the climate system, too. We should just think of these 50 ECVs as a starting point for more complex climate studies. We also shouldn’t necessarily consider a single variable on this list to be more important than another; they all play a crucial role in different ways in understanding Earth's climate system as a whole.

Atmospheric

Atmospheric variables are probably the ones you are most familiar with. These even include those traditionally used to describe weather on your 6 PM news, like precipitation, wind, temperature -- even lightning. The atmospheric domain is divided into surface (near-ground) and upper air measurements (think about all the space above a tall skyscraper). Scientists are also concerned with air's chemical makeup. Pay special attention to the Earth’s “radiation budget,” which we'll discuss soon. This, in conjunction with the variables defined by atmospheric composition, is what is keenly important for understanding how our climate has changed and may change in the future.

Land

ECVs taken on land may seem diverse, but elements like river discharge and leaf area index are connected. Both contribute to energy and mass exchange on land surfaces. Other variables like soil carbon and fire disturbances relate to the global carbon cycle. Human activities can impact soil carbon levels, and fires, whether natural or human-caused, release significant carbon into the atmosphere. Of course, it goes without saying that we – as humans – live on the land’s surface, so these ECVs are of particular importance in our day-to-day lives. How much snow is on the ground can be pretty important in what we do on a dreary day in December!

Ocean

Lastly, in the ocean, things look a little different. Yes, we still look at temperature and currents (the ocean equivalent of wind), but we also look at ocean water composition, including salinity, acidity, oxygen levels, and tracers. Tiny organisms like phytoplankton help absorb carbon dioxide from the atmosphere and produce oxygen. By monitoring these ocean variables, we can learn a great deal about the evolution and vulnerabilities in specific ecosystems.

Defining ECVs is only half the story -- how do we go about measuring them? We really have two options, read on to learn about what each of these are.