The data in the left-hand CO2 widget, which I've recently updated, derives from the Scripps Institution of Oceanography in La Jolla, California.
“This web site serves both as a tribute to Charles David Keeling, who was the first person to document the rise in Carbon Dioxide concentration, and provides access to products of the Scripps CO2 Program based at the Scripps Institution of Oceanography in La Jolla, California.”
“The Mauna Loa atmospheric CO2 measurements constitute the longest continuous record of atmospheric CO2 concentrations available in the world,” according to the Scripps Institution.
The site makes available data on the steady increase of carbon dioxide (CO2) levels in the atmosphere.
This data is available from three different sampling stations, including one in the Mauna Loa Observatory in Hawaii. This is a pristine area from where the data is likely to be a reliable regional indicator of CO2 levels in the lower atmosphere.
It would be nice to be a “skeptic” and harbor the warm and cuddly thought that higher CO2 levels are simply better for outdoor plants, but if you work for the Royal Society in England, or the National Academy of Sciences in the U.S., you might have concluded that this kind of manmade "carbon forcing" has a scarily disruptive effect on the earth's climate, and the ability of six billion people to successfully live within it.
These scientists fear that if left unchecked, CO2 levels exceeding 400-500 parts per million or higher will cause nonlinear effects, in other words, not gradual ones but rapid climate change within a few decades or so.
There is presently a lot of flaming and disinformation on the Web and elsewhere about climate change. If you want to read more reasoned discussions by scientists, try realclimate.org.