Although it had been assumed, data now firmly link warming to CO2 rise from human activities
For the first time, scientists have shown a direct link between rising levels of carbon dioxide — or CO2 — in Earth’s atmosphere and an increase in how much solar energy warms the ground. The finding supports a key theory about what’s behind the recent worldwide warming of Earth’s climate. It links a measurable share of that warming to human activities that release CO2. These include the burning of fossil fuels (coal, oil and gas) for heating, power and transportation.
CO2 is known as a greenhouse gas. By that, scientists mean that this gas allows the sun’s visible light to pass through. But when that light hits Earth’s surface, it can be transformed to heat (infrared light). CO2 now traps that heat (like a greenhouse window) and holds much of it within the lower atmosphere — right down to Earth’s surface.
Daniel Feldman is a climate scientist at Lawrence Berkeley National Laboratory. It’s a Department of Energy research center in Berkeley, Calif. He and his colleagues sought to uncover how large the effect of recent increases in CO2 have been on Earth’s near-surface warming. To do that, they monitored the sunlight hitting two sites on cloudless days. One was in Alaska, the other in Oklahoma.
CO2 absorbs some wavelengths of the infrared light now being radiated from Earth’s surface. Then it releases very specific wavelengths of this infrared light. This infrared radiation goes in all directions — including back to Earth’s surface.
Knowing this, the researchers could look at the wavelengths of infrared light and, like a fingerprint, link it to what share was from a CO2 buildup in the air, and what share was due to other things, such as water vapor.
Feldman’s group reviewed more than 10 years of near-daily observations of sunlight and temperature for the two locations. After sifting through these data, the team showed that a rise in CO2 levels of 22 parts per million in air boosted the amount of the sun’s heat on the ground by 0.2 watts per square meter. That’s an increase of about 10 percent.
The researchers say their results agree with predictions of CO2-driven warming created by computer models. Those models have been used to forecast future climate conditions. Feldman’s team reported its findings online February 25. They appear in the journal Nature.
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carbon dioxide A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter (including fossil fuels like oil or gas) is burned. Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
climate The weather conditions prevailing in an area in general or over a long period.
computer model A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.
fossil fuels Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed in the Earth over millions of years from the decayed remains of bacteria, plant or animals.
global warming The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.
greenhouse A light-filled structure, often with windows serving as walls and ceiling materials, in which plants are grown. It provides a controlled environment in which set amounts of water, humidity and nutrients can be applied — and pests can be prevented entry.
greenhouse gas A gas that contributes to the greenhouse effect by absorbing heat. Carbon dioxide is one example of a greenhouse gas.
infrared light A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X rays, radio waves and microwaves. It tends to record a heat signature of an object or environment.
parts per million (billion or trillion) Frequently abbreviated as ppm (or ppb or ppt), it is a measure of the number of units of some material that it mixed into another. The units should be the same (or equivalent) for both materials. The term is used to describing extremely small concentrations of one chemical dissolved in another. For example, a solution of 300 parts per billion of sodium in water would mean that there are 300 sodium atoms for every billion water molecules.
radiation (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
solar Having to do with the sun, including the light and energy it gives off.
watt A measure of the rate of energy use, flux (or flow) or production. It is equivalent to one joule per second. It describes the rate of energy converted from one form to another (or moved) per unit of time. For instance, a kilowatt is 1,000 watts; household energy use is typically measured and quantified in terms of kilowatt-hours, or the number of watts used per hour.
wavelength The distance between one peak and the next in a series of waves, or the distance between one trough and the next. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
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Original Journal Source: D.R. Feldman et al. Observational determination of surface radiative forcing by CO2 from 2000 to 2010. Nature. Published online February 25, 2015. doi: 10.1038/nature14240.