Global temperatures are rising and so, it seems, is the lowest part of the sky.
Weather balloons collect a range of measurements as they ascend into the sky. Those in the Northern Hemisphere show that the upper boundary of the troposphere — the slice of sky closest to the ground — has been climbing. Over the past 40 years, it’s moved steadily upward. Its rate of climb has been some 50 to 60 meters (165 to 200 feet) per decade. Troposphere temperatures have been driving this rise, says Jane Liu. She works at the University of Toronto in Canada. The troposphere varies in height around the world, the environmental scientist notes. It reaches up to 20 kilometers (12.4 miles) in the tropics. It can be as low as 7 kilometers (4.3 miles) near the poles. The upper boundary of the troposphere — known as the tropopause — naturally rises and falls with the seasons. The reason: Air expands as it warms and contracts as it cools.
Lately, greenhouse gases have been trapping more and more heat in the air. The troposphere has responded to this climate change by expanding.
Liu is part of a team that found this tropopause has risen an average of about 200 meters between 1980 and 2020. Nearly all weather occurs in this part of the atmosphere. Still, the researchers say, it’s unlikely this expansion will have much effect on the weather.
A rising tropopause does, however, offer yet one more clue to how climate change is altering our world. “We see signs of global warming around us, in retreating glaciers and rising sea levels,” says Liu. “Now, we see it in the height of the troposphere.”
atmosphere: The envelope of gases surrounding Earth, another planet or a moon.
average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
Climate change: Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.
glacier: A slow-moving river of ice hundreds or thousands of meters deep. Glaciers are found in mountain valleys and also form parts of ice sheets.
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 gases: Gases that contribute to the greenhouse effect by absorbing heat. Carbon dioxide and methane are two examples of such gases.
Poles: (in Earth science and astronomy) The cold regions of the planet that exist farthest from the equator; the upper and lower ends of the virtual axis around which a celestial object rotates.
Sea level: The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.
Tropics: The region near Earth’s equator. Temperatures here are generally warm to hot, year-round.
tropopause: A boundary between the two lower layers of Earth's atmosphere, the troposphere and the stratosphere. That boundary layer varies with latitude, running from a height of about 6 kilometers (4 miles) over the poles to 18 kilometers (11 miles) over the equator.
troposphere: The lowest level of Earth's atmosphere. It runs from the planet's surface to a height of 8 to 14 kilometers (5 to 9 miles), depending on the latitude. It's the region where the air is thickest and where most weather occurs. Air currents moving through this region often flow not only horizontally, but often vertically (up and down).
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