The concentration of greenhouse gases in the Earth's atmosphere hit another record high in 2014, a World Meteorological Organization (WMO) report said Monday.

The increase in gases such as carbon dioxide, methane and nitrous oxide is fueling climate change and making "the planet more dangerous and inhospitable for future generations," the WMO said. The WMO is the United Nations' weather agency.

The report found that concentrations of carbon dioxide — considered the most dangerous greenhouse gas because of its long life cycle — reached 397.7 ppm in 2014 and that in the Northern Hemisphere it "crossed the symbolically significant 400 ppm level" in the spring of 2014. PPM stands for parts per million.


“We can’t see (carbon dioxide). It is an invisible threat, but a very real one. It means hotter global temperatures, more extreme weather events like heat waves and floods, melting ice, rising sea levels and increased acidity of the oceans," WMO Secretary-General Michel Jarraud.


CO2 levels were around 280 ppm prior to the Industrial Revolution in the late 1800s, when large amounts of greenhouse gases began to be released by the burning of fossil fuels.


Carbon dioxide is invisible, odorless, and colorless, yet it's responsible for 63% of the warming attributable to all greenhouse gases, according to NOAA's Earth System Research Laboratory in Boulder, Colo.

Levels of carbon dioxide go up and down each year, reaching their highest levels in May and then going back down as plants absorb the gas.

Later this month in Paris, world leaders including President Obama will gather for a round of talks aimed at securing a plan to force a reduction in greenhouse gas emission's from the planet's worst polluters.

On Friday, Obama announced a rejection of an oil pipeline — Keystone XL — that would move energy products from Canada to Nebraska.

"Three weeks from now, I look forward to joining my fellow world leaders in Paris, where we've got to come together around an ambitious framework to protect the one planet that we've got while we still can," Obama said last week.

China and the United States emit more greenhouse gases than any other nations.

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