Atmospheric CO2 levels reach 400 ppm

The big weather/climate news this past week has been a measurement of CO2 in Earth's atmosphere of 400 ppm.  This measurement represents a daily average concentration and was taken at Mauna Loa, Hawaii.  This reporting station has the longest continuous record of CO2 measurements on Earth (see image on right, courtesy UC San Diego).  Climate scientists have long expected this day to come as unchecked, anthropogenic (human) burning of fossil fuels puts ever more carbon dioxide into the atmosphere.  The reading of 400 ppm is not meaningfully different from a climate standpoint compared to the 399 ppm measured in days prior.  Climate scientists also typically consider the annual average CO2 concentration as opposed to a single daily average, because atmospheric CO2 levels are typically highest in May - this is because plants are the main remover (or sink) of atmospheric CO2, and vegetation in the expansive Northern Hemisphere forests helps remove atmospheric CO2 during the summer months.

This 400 ppm observation is, however, very symbolic of a new normal in atmospheric CO2 concentrations and how humans and all other life will adapt.  CO2 levels this high are estimated to not have occurred on Earth for at least the past 3 million years, and certainly not during any time since humans first existed.  It's also estimated that, 3 million years ago, average planetary temperatures were about 5ºF higher and sea levels were 30 feet higher than they are now.  Why the difference?  There are other factors that control temperature and sea levels, and, the rate of increase in CO2 since the Industrial Revolution has been so rapid, that global temperature and sea level have not had enough time to fully respond.

What is clear is that climate change is a reality that mankind and all planetary life will have to adapt to in order to survive.  Even if humans can cut all CO2 emissions to zero, the excess CO2 that has built up over the past century will remain in the atmosphere for hundreds to thousands of years.  This is because CO2 is a very stable gas, meaning it does not break down easily, and the natural processes to remove CO2 work on very long time scales.  And at the moment, CO2 emissions continue to increase uncontrollably as world governments make little progress in agreeing to emissions reductions.  China is currently the biggest emitter of CO2, followed by the United States.  CO2 emission by the US are actually slowly decreasing, largely due to a gradual switch from coal to gas fired power generation and a steady improvement in automobile fuel economy, but emission from the US are still very high.  And, the rest of the developing world, such as south Asia, Africa, and Latin America, will likely have huge increases in CO2 emissions as their economies grow.  There is also little chance of coming up with a climate change silver bullet - both in ceasing CO2 emissions by developing alternative energy sources, and removing the excess CO2 that already resides in our atmosphere.  It is clear that climate change is no longer an issue of prevention, but an issue of triage, and has been for some time.