The average concentration of carbon dioxide in the atmosphere hit record highs at all observation points in Japan in 2016, the Japan Meteorological Agency said Wednesday, underscoring the continuing upward trend in levels of the global warming-causing greenhouse gas.

Data collected in Japan show the CO2 concentration levels hit record highs every year since 1997 when the nation increased the number of observation points to three. The concentration increase last year was larger than the average growth over the past decade.

The record readings are believed to be due in part to a fall in CO2 absorption by forests due to factors related to an El Nino climate cycle spanning from the summer of 2014 to the spring of 2016.

The agency said levels of CO2 concentration rose 3.8 parts per million from a year earlier to 407.2 ppm in Ofunato, Iwate Prefecture, up 3.4 ppm to 404.9 ppm in Minamitori Island in the Ogasawara island chain and up 3.2 ppm to 407.1 ppm in Yonaguni Island, Okinawa Prefecture.

The Intergovernmental Panel on Climate Change has said in order to limit the global temperature increase to 2 C above preindustrial levels, it is necessary to keep CO2 concentration to below 450 ppm in 2100.

Global CO2 emission levels have largely remained the same but concentration of the greenhouse gas has been on the rise. Even if emissions are cut and abatement efforts are improved, it is estimated that it will take around 10 years for the concentration reduction measures to take effect.

The international climate accord agreed in Paris in 2015 aims to effectively reduce net greenhouse gas emissions to zero in the second half of this century. Japan, the world's fifth-largest emitter of greenhouse gasses, ratified the agreement last November.