Last month, one of your readers' letters was published under a title of "Don't fall for the climate change 'crisis'." In that letter, the writer urges us to "consider all sides" in the study of the climate. This letter is in that spirit.
In 2014 and 2015, I provided support to two climate-monitoring sites on the North Slope of Alaska operated by the Department of Energy. One of the instruments at those sites was called the Atmospherically Emitted Radiation Interferometer, or AERI. This instrument measured incoming heat energy from the sun while at the same time measuring how much heat energy the atmosphere reflected back. This is the energy balance the previous letter referred to. Further, the AERI instrument was sophisticated enough to distinguish between heat energy reflected by CO2, water vapor, methane and other gasses present in the atmosphere.
An 11-year study of data from the AERI on the North Slope, along with data from an identical AERI in Oklahoma, "specifically measured CO2's ability to trap energy near the surface." This study was peer-reviewed and published in the journal Nature on Feb. 25, 2015. According to one of the scientists, "We were able to isolate the distinct fingerprint of CO2 within the AERI spectrum and use that in our study." Further, "Data analysis for the two independent sites indicated the same trend: Atmospheric CO2 was responsible for a significant increase in radiative forcing [heating], about two-tenths of a Watt per square meter per decade in mid- and high-latitudes. The researchers attributed this trend to the 22 parts-per-million increase in atmospheric CO2 between 2000 and 2010."
You can read a summary of the paper at http://www.ssec.wisc.edu/news/articles/7145, unfiltered by non-scientists. As this relates to the previous reader's letter, yes, very modest increases in the global CO2 concentration do have a measurable, and significant, effect on warming of the planet as measured at the surface -- where we live.
I only lived in Alaska for 19 years so my personal observation of warming while there could be written off to minor swings. However, people I knew in their 60s said the climate was warming up there. Multi-year ice in the Arctic Ocean, the norm just a couple decades ago, is now nearly non-existent. Permafrost, ground that was frozen for centuries, is melting at an increasing rate, causing houses to sink and tilt. Roads are needing rebuilt, at taxpayer expense, as the ground under them melts. Vegetation and animals that in the early 1900s were never observed on the North Slope are now there. The evidence is clear: Increasing CO2 is causing the climate to warm. It will cost us dearly if we ignore these facts and take no action.