Questions on CO2 and climate change
A Jan. 5 letter asked two good questions about CO2 and warming trends. Both are easily answered.
One question was how human-generated emissions, which account for only 3 percent of CO2 emissions, can possibly affect the climate? The reason is that emissions from human activity, unlike natural emissions, are cumulative. A few percent per year over many years results in a large increase in CO2. Natural emissions are normally in a perpetual cycle where CO2 goes in and out of the ocean, the air, vegetation, etc.
There is no net increase, just a change in form for the carbon that has been part of the biosphere for 100 million years. CO2 that comes from fossil fuels are a net increase to the naturally cycling CO2. The ocean and vegetation cannot absorb all of this new CO2 so it grows slowly over time in the atmosphere.
As to CO2 levels measured at Mauna Loa and reconciling the decrease in levels with global warming: Scientists never use the data from a single point because that point can be affected by local geology, human activity or other things. Rather, they take the average over a very large number of points across the entire globe and use that to assess the globally averaged CO2 content of the atmosphere. When that is done, it clearly shows a steady increase in CO2. You can see the globally averaged data yourself at the NOAA website.