Japan's Meteorological Agency says levels of carbon dioxide hit record highs at all observation points across the country last year. CO2 is known to be a major global warming gas.

The agency has been monitoring CO2 levels at three land locations: Ofunato City in Iwate Prefecture; the western-most island of Yonaguni in Okinawa Prefecture; and the eastern-most island of Minamitorishima in the Ogasawara Island chain.

The whole-year average was 425 ppm in Ofunato, 424.4 ppm on Yonaguni and 421.8 ppm on Minamitorishima.

All figures were up from the all-time highs recorded the year before.

CO2 concentrations in Japan have been steadily rising since the agency began taking data in Ofunato in 1987.

The agency also monitors CO2 levels about six kilometers above the sea southeast of Japan. The last year's average of CO2 levels also hit the highest on record at 420.6 ppm.

At a sea surface area on the Pacific Ocean, the average of CO2 stood a 422.9 ppm last year, also the highest-ever.

The agency says CO2 levels continue rising despite measures to reduce greenhouse gas emissions, and that efforts to mitigate global warming should continue.