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[music]

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Narrator: In order to understand the Earth’s climate,

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it’s critical we understand how warm the planet is, how its temperature changes over time

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and what factors can force those changes.

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The sun is the Earth’s primary source of heat, constantly bathing us with solar radiation.

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The land surface, cloud cover and our atmosphere

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help determine how much of that heat is reflected and how much is retained.

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Loeb: How that changes over time is really critical

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because in a climate system that’s in equilibrium

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those two should really balance and if they do

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then the temperatures will remain relatively constant with time.

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Now when you add greenhouse gases such as carbon dioxide,

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methane, you change that radiation balance

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at the top of the atmosphere, you reduce the amount of outgoing radiation

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and so that imbalance means more energy is in the system.

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Part of it goes into the ocean, is stored in the ocean,

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and part of it goes into actually warming the Earth.

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Narrator: One of NASA’s most important tools for measuring that heat

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is an instrument on board the Aqua, Terra, TRMM, and NPP satellites,

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called CERES, Clouds and the Earth’s Radiant Energy System.

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Parkinson: The CERES instrument has

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exactly three channels, but those three channels

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have been tuned to get really really important information

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about long wave radiation from the Earth’s system,

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the reflected short wave radiation from the sun, and then

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a window channel of radiation. So it’s got three channels that give us huge

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amounts of information about the radiation budget of the Earth.

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Narration: CERES observations complement data from another instrument on Aqua and Terra

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called MODIS. MODIS has a smaller footprint,

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but much higher resolution to its data, illuminating how the energy budget is affected

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by clouds, dust particles, oceans, and land cover.

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That energy budget can also be influenced by natural events

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such as the La Nina and El Nino weather patterns, the amount of ice and snow

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covering the Earth, and events that impact the Earth’s atmosphere like volcanoes.

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Researchers use CERES data and similar data sets

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from the past, to establish a long term trend that encompasses

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all those factors and the natural variation of the Earth’s radiation budget.

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Loeb: If you want to look at changes in the system

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that are significant that might be associated with

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actual global warming, you have to measure

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above that natural variablility, so you need a long record.

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Narration: The CERES instruments and their predecessors have been taking the Earth's temperature for almost 30 years,

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and this data can be used in conjunction with other measurements of the Earth's vital signs.

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Loeb: And so having the CERES measurements, the ocean

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heat storage measurements, measurements of sea level rise,

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measurements of land ice volume, all of those should give you

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a coherent picture of how things are changing