A little-known index is key to understanding how the Earth's climate continues to build up heat in the air and oceans, resulting in sweeping changes across the globe.

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Adapted from a NOAA Earth System Research Laboratory report; Chart: Axios Visuals

Why it matters: Known as the Annual Greenhouse Gas Index, or AGGI, which NOAA produces, it clearly shows that despite numerous agreements and goals for cutting greenhouse gas emissions, the ability of the atmosphere to trap extra heat keeps growing.

Details: This year the AGGI rose to a value of 1.43, meaning that the increase in the atmosphere’s heat-trapping capacity attributable to human activity has risen 43% since 1990. James Butler, who directs NOAA's air monitoring program, tells Axios the growth in the AGGI is accelerating.

  • "It’s a measure of what we’ve already committed towards causing climate to change,” Butler says. "Since 1990, we’ve added 43% more long-lived greenhouse gases than in the previous 240 years.”

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Photo illustration: Sarah Grillo/Axios. Photo: Roy Rochlin/Getty Images and BRENDAN SMIALOWSKI/AFP via Getty Images

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Bolton's hidden aftershocks

Photo illustration: Sarah Grillo/Axios. Photo: Justin Sullivan/Getty Images

The news media has largely moved on, but foreign government officials remain fixated on John Bolton's memoir, "The Room Where It Happened."

Why it matters: Bolton's detailed inside-the-Oval revelations have raised the blood pressure of allies who were already stressed about President Trump's unreliability.