Atmospheric CO₂ at Mauna Loa (De-seasonalized Trend)

## What this measures

The Mauna Loa monthly CO₂ concentration with NOAA's estimate of the average seasonal cycle removed, in parts per million. What is left is the underlying rise.

## Why it matters

The seasonal swing is several times larger than one month's trend increase, so the raw series can fall for months while the trend keeps climbing. This version shows the trend directly and makes month-on-month changes readable.

## How to read it

Read the slope. The change over twelve months is the annual growth rate of atmospheric CO₂; an accelerating slope means the world is adding carbon faster than it did before.

## What it does not say

The seasonal adjustment is NOAA's model and is re-fitted as new data arrive, so recent values are revised. It shares every limit of the raw Mauna Loa series: one station, the background atmosphere, not emissions.

## Source

NOAA Global Monitoring Laboratory, Trends in Atmospheric Carbon Dioxide (co2_mm_mlo.csv, "deseasonalized" column), https://gml.noaa.gov/ccgg/trends/. Data from March 1958 to April 1974 were obtained by C. David Keeling of the Scripps Institution of Oceanography. Cite: Dr. Xin Lan, NOAA/GML and Dr. Ralph Keeling, Scripps Institution of Oceanography. US federal data, public domain.