Balancing Earth’s Energy Balance

Unlike weather forecasting and natural hazard monitoring, which rely upon near-real-time regional observations made on time scales from minutes to days, assessing the health of Earth’s entire climate system relies upon collection of data over the entire globe on time scales from years to decades. Will Earth continue its present warming trend and, if so, how rapidly will it warm?

Because the Sun powers our world’s climate system, to answer that question scientists must determine whether Earth’s energy budget is in balance. That is, over the course of a year, does the amount of solar energy entering the climate system equal the total amount of energy that is escaping back into space?

“Generally, the answer is yes, Earth’s energy budget is in balance and the climate system is stable,” explained Bruce Wielicki, Senior Scientist for Earth Science at NASA’s Langley Research Center, Hampton, Va. “But over the last 150 years, as humans have introduced increasing amounts of greenhouse gases and aerosol particles into the atmosphere, we have changed how our world reflects and absorbs solar energy as well as how it emits thermal energy (or heat).”

According to Wielicki, some of these changes result in more sunlight reflected back into space, thereby cooling the planet. On the other hand, some of the changes result in more solar energy getting trapped within Earth’s climate system, thereby warming the planet. Which changes will predominate in the future and how rapidly will the changes occur?

“We don’t know,” said Wielicki. “To answer that question we have to track a long list of variables all over the Earth over a long period of time.”

Then we have to spend time and brainpower analyzing all those data. Among the “variables” Terra tracks are cloud and aerosol concentrations in the sky, snow and ice cover on the surface, areas of expanding deserts and cities, and areas of human deforestation. Each of these variables plays a part in determining how much total energy gets absorbed into the climate system and how much gets reflected and emitted back to space.

To make matters more complicated, as each of these climate variables change they cause other variables to change. In one case study, scientists set out to determine how smoke from biomass burning across the Amazon region in South America affect clouds. Their hypothesis was that the sooty aerosol would modify the clouds by making them brighter white and longer lasting, thereby enhancing their ability to reflect sunlight and to cool the surface. Instead, much to their surprise, satellite data revealed that the smoke effectively chokes or limits cloud formation. Thus, more sunlight gets absorbed into the system and the net result is a regional warming, rather than the enhanced cooling scientists had expected. (Please read Clouds Are Cooler Than Smoke for more details.)

All working in concert, and together with the fifteen other NASA Earth Observing System (EOS) satellites currently in orbit, Terra data are helping scientists untangle the myriad cause-and-effect relationships at work within Earth’s climate system. And when scientists get to the bottom line on Earth’s radiant energy budget, Terra’s Clouds and Earth’s Radiant Energy System (CERES) instrument will help ensure they get it right.
 

At better than twice the accuracy of its predecessors, CERES makes daily global maps of how much sunlight and how much heat energy are escaping through the top of the atmosphere. Comparing CERES’ daily global maps of radiant energy flux with Terra’s other maps of changing variables allows scientists to more precisely measure the role each variable plays in how the whole system works.

“Terra is Earth science’s first great observatory,” said Wielicki. “It has provided the most comprehensive and the most accurate global view of the Earth’s climate yet on record. And it has pioneered the first comprehensive, multi-instrument approach to climate change research.”

It is important to note that Terra is not going it alone. The mission is part of an extended family that includes sixteen NASA Earth Observing System (EOS) satellites currently in operation.
 

Together, these EOS missions extend the legacy of global observations begun in the late 1970s by NASA’s Nimbus satellite and the series of increasingly advanced Earth-observing satellites launched through the 80s and 90s. And yet the data being collected today by Terra and its sister satellites show how NASA has made significant progress in measurement accuracy.

“The value of a climate record is directly proportional to the length of the record and to its accuracy,” said Wielicki. “There are no substitutes for these two data qualities.”

Ranson agreed, stating that Terra’s instruments brought new channels that provide data at better resolutions of time and space than previous satellites. Terra’s instruments are also better calibrated and collect data from multiple viewing angles, both of which result in data of sufficient quality for studies of the global climate system.

 How Terra Tracks Pollution