KVIG Informative

Carbon dioxide makes up less than half a percent of Earth’s atmosphere. That tiny fraction is the main reason the planet has warmed as fast as it has over the past century.

The greenhouse effect itself is not the problem. NASA describes it as the reason Earth is habitable at all: certain gases in the atmosphere trap heat radiating up from the surface, keeping the planet’s average temperature around 59 degrees Fahrenheit instead of far below freezing. Without any greenhouse gases, scientists say Earth’s surface temperature would drop dramatically, and life as it exists today would not be possible.

How the Trapping Actually Works Sunlight passes through the atmosphere and warms Earth’s surface. The surface then radiates that energy back out as infrared heat, and greenhouse gases, including carbon dioxide, methane, water vapor, and nitrous oxide, absorb a portion of that outgoing infrared radiation and re-release it in all directions, including back down toward the surface. Roughly half of that re-released energy returns to Earth as additional heat, according to Columbia University’s Climate School. Carbon dioxide specifically absorbs energy across a range of wavelengths that overlaps directly with the infrared energy Earth’s surface gives off, which is what makes it such an effective heat-trapping gas at a molecular level.

What’s Actually Changed Before the Industrial Revolution began around 1750, atmospheric carbon dioxide sat at 280 parts per million or lower, and ice core records show it never exceeded roughly 300 parts per million during any ice age cycle over the past million years, according to NOAA’s Global Monitoring Laboratory. NASA’s Mauna Loa Observatory in Hawaii has tracked carbon dioxide levels directly since 1958, and that record now shows concentrations that have climbed well past any level found in the deep ice-core record. NOAA’s own analysis finds that carbon dioxide alone accounts for about 80 percent of the total additional heating caused by all human-produced greenhouse gases since 1990.

Scientists trace the source of that added carbon dioxide directly to human activity, primarily the burning of fossil fuels like coal, oil, and natural gas, along with land-clearing for agriculture and industry. The mechanism was not discovered recently. Physicist Eunice Foote first demonstrated in 1856 that carbon dioxide and water vapor trap heat radiation, and Swedish scientist Svante Arrhenius published the first prediction in 1896 that rising atmospheric carbon dioxide could meaningfully raise Earth’s surface temperature, more than a century before the warming trend became apparent in everyday weather.

NASA scientists have also tested and ruled out the most obvious alternative explanation. If the sun itself were driving the current warming trend, both the lower atmosphere and the upper atmosphere would be expected to warm together. Instead, satellite measurements show the troposphere warming while the stratosphere cools, a pattern NASA describes as consistent specifically with a greenhouse-gas-driven mechanism and inconsistent with warming caused by the sun. Ice cores from Greenland, Antarctica, and tropical glaciers, along with tree rings, coral reefs, and ocean sediment layers, provide independent physical evidence confirming that Earth’s climate has always responded to changes in greenhouse gas concentration, and that the current rate of change is roughly ten times faster than the average warming rate that followed past ice ages.

None of this mechanism is new or in dispute among the scientists who study it directly. What makes the current moment distinct in Earth’s climate history isn’t the existence of the greenhouse effect, which has kept the planet livable for billions of years. It’s the speed at which one species has changed the concentration of the gases that control it, and how quickly the planet’s systems, from ice sheets to ocean currents to desert ecosystems, are now being asked to respond.