The World Meteorological Organization warned Monday that levels of carbon dioxide topped 400 parts per million in the northern hemisphere in April, a landmark event it says highlights the growing peril of climate change.
The group said that the pollution levels show more proof of the relationship between burning fossil fuels like coal and rising amounts of greenhouse gases that warm the planet and lead to extreme weather.
The northern hemisphere has more manmade sources of carbon pollution than the southern hemisphere. However, the international climate group expects that average spring maximum levels of carbon will be recorded around the world in 2015 or 2016.
The amount of carbon in the air changes depending on the season, since plants absorb much of the gas in the summer. That leads to a glut in the spring, before plants can suck it up.
Carbon dioxide is considered the prime greenhouse gas released by human activities like burning fossil fuels. It was responsible for about 85 percent of the warming of the global climate from 2002 to 2012.
Global carbon levels have been rising since before the industrial revolution, when they were about 278 parts per million. The amount of the gas in the atmosphere has been rising by about 2 parts per million each year over the last decade.
President Obama has made it a priority to limit carbon pollution through two sets of controversial new power plant regulations that are considered the pillars of his second-term focus on the issue.
Energy industry groups have warned that one set of rules for new power plants, released last year, would effectively ban new plants from burning coal to produce electricity. That could lead to a massive surge in Americans’ energy prices, they say.
Another set of rules, set to be released next month, will place limits on the carbon emissions from currently operational plants. Those regulations are likely to be even more controversial than the previous rule for plants that have not yet been built.