The Planet's CO2 Levels Are Continuing to Climb The Mauna Loa Observatory says last month, already record levels were at 414.8 parts per million. This is a peak not seen for millions of years. It is also 3.5 parts per million higher than the Hawaii complex recorded a year ago. In May, levels of the gas are typically at their highest. When the fall season hits, they then drop due to plants absorbing CO2. Carbon dioxide has been named the biggest culprit for the Earth's global warming issue. The National Oceanic and Atmospheric Administration over 60% of global warming from greenhouse gases is from CO2. Over the past two decades, its rise had led to Earth's overall temperature increasing two-thirds of a degree.