It used to seem like a big deal when we first got close to going above 400 parts per million (ppm) in CO2 concentration, if only for a short time because of seasonal variations, and only in the Northern Hemisphere where landmass is concentrated. Now it looks like we're going to live permanently above this level on a global basis, according to the World Meteorological Organization.
In 2014, we were just on the threshold of this sad milestone: Atmospheric concentrations of CO2 – the most important long-lived greenhouse gas – reached 397.7 ppm during that year. Only in the Northern hemisphere did CO2 concentrations cross the symbolically significant 400 ppm level in the spring of 2014, when CO2 is most abundant on a seasonal basis.
But in the spring of 2015, the global average concentration of CO2 crossed the 400 ppm barrier. That's 43% more than pre-industrial levels!
Just between 1990 and 2014, there was a 36% increase in radiative forcing – the warming effect on our climate – because of long-lived greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from industrial, agricultural and domestic activities.
Another report by the Met Office and Climatic Research Unit at Britain’s University of East Anglia reported that the Earth’s average temperature has crossed another sad milestone: We're now averaging 1-degree C (1.8 F) of warming, with temperatures over the first nine months of 2015 exceeding normal levels by 1.02 degrees C. The report further says that 2015 is likely to beat 2014 as the warmest year on record.
“Every year we report a new record in greenhouse gas concentrations,” said WMO Secretary-General Michel Jarraud. “Every year we say that time is running out. We have to act NOW to slash greenhouse gas emissions if we are to have a chance to keep the increase in temperatures to manageable levels. We will soon be living with globally averaged CO2 levels above 400 parts per million as a permanent reality,” Said Mr Jarraud.
“We can’t see CO2. It is an invisible threat, but a very real one. It means hotter global temperatures, more extreme weather events like heatwaves and floods, melting ice, rising sea levels and increased acidity of the oceans. This is happening now and we are moving into unchartered territory at a frightening speed. Carbon dioxide remains in the atmosphere for hundreds of years and in the ocean for even longer. Past, present and future emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are non-negotiable,” said Mr Jarraud.