How Earth’s lower atmosphere is rising due to climate change

Global temperatures are rising and so, it seems, is part of the sky.

Atmosphere readings collected by weather balloons in the Northern Hemisphere over the last 40 years reveal that climate change is pushing the upper boundary of the troposphere — the slice of sky closest to the ground — steadily upward at a rate of 50 to 60 meters per decade, researchers report November 5 in Science Advances.

Temperature is the driving force behind this change, says Jane Liu, an environmental scientist at the University of Toronto. The troposphere varies in height around the world, reaching as high as 20 kilometers in the tropics and as low as seven kilometers near the poles. During the year, the upper boundary of the troposphere — called the tropopause — naturally rises and falls with the seasons as air expands in the heat and contracts in the cold. But as greenhouse gases trap more and more heat in the atmosphere, the troposphere is expanding higher into the atmosphere (SN: 10/26/21).

Liu and her colleagues found that the tropopause rose an average of about 200 meters in height from 1980 to 2020. Nearly all weather occurs in the troposphere, but it’s unlikely that this shift will have on a big effect on weather, the researchers say. Still, this research is an important reminder of the impact of climate change on our world, Liu says.

“We see signs of global warming around us, in retreating glaciers and rising sea levels,” she says. “Now, we see it in the height of the troposphere.”

The troposphere (seen here in orange) is the lowest layer of Earth’s atmosphere and where nearly all weather occurs. Over the last 40 years, the boundary between the troposphere and the neighboring stratosphere (pink) has risen as a result of climate change.

IMAGE SCIENCE & ANALYSIS LABORATORY/NASA JOHNSON SPACE CENTER

Abstract

Tropopause height (H) is a sensitive diagnostic for anthropogenic climate change. Previous studies showed increases in H over 1980–2000 but were inconsistent in projecting H trends after 2000. While H generally responds to temperature changes in the troposphere and stratosphere, the relative importance of these two contributions is uncertain. Here, we use radiosonde balloon observations in the Northern Hemisphere (NH) over 20°N to 80°N to reveal a continuous rise of H over 1980–2020. Over 2001–2020, H increases at 50 to 60 m/decade, which is comparable to the trend over 1980–2000. The GPS radio occultation measurements from satellites and homogenized radiosonde records are in good agreement with those results. The continuous rise of the tropopause in the NH after 2000 results primarily from tropospheric warming. A large trend in H remains after major natural forcings for H are removed, providing further observational evidence for anthropogenic climate change

RESULTS

Long-term variability in tropopause height in the NH over 20°N to 80°N from 1980 to 2020

Over the entire study period from 1980 to 2020, a continuous rise of H in the NH over 20°N to 80°N is evident in the natural variability–removed IGRA2 radiosonde time series (Fig. 1A). Positive trends in H prevail in IGRA2 over most subperiods longer than 10 years (fig. S3A). Similarly, the corresponding H in gridded RAOBCORE or RICH data also increases monotonously with a faster rate (70 to 80 m/decade) than that in IGRA2 (50 to 60 m/decade) (Table 1A). These differences may be due to that H for RAOBCORE and RICH is determined based on a monthly mean temperature profile, while for IGRA2, H is determined based on single profiles, and the resulting H values are then averaged for monthly means. In addition, the vertical resolution of the RAOBCORE and RICH data is somewhat coarser than that of IGRA2 (see Materials and Methods). The correlation coefficient between the monthly anomalies of H in IGRA2 and RAOBCORE (or RICH) data is 0.87 (or 0.89) over 1980–2020. In the original IGRA2 data in which the signals of natural variability are not filtered out, the mean H increases from 12.2 km in 1980 to 12.4 km in 2020 in absolute altitude. The increasing trend in H over 1980–2020 is estimated to be 49.7 ± 3.6 m/decade in the original IGRA2 data and 44.0 ± 2.5 m/decade in the natural variability–removed IGRA2 data.