Lawrence Livermore National Laboratory (LLNL) statistician Giuliana Pallotta and climate scientist Benjamin Santer created a statistical framework to comprehensively assess the significance of differences between simulated and observed natural variability in mid- to upper tropospheric temperature (TMT). The troposphere is the lowest region of the atmosphere, extending from the Earth's surface to a height of about 4 to 12 miles, depending on latitude and season.

The team found that in current and earlier generations of climate models, the natural decade-to-decade variability of tropospheric temperature is systematically too large relative to estimates of natural variability obtained from satellites. Such an overestimate of natural “climate noise” would make it more difficult to identify a human-caused tropospheric warming signal. The research appears in the Journal of Climate.

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