Carbon dioxide concentrations have been measured at the Mauna Loa Observatory since 1958. Photo: – John Game CC BY

Average CO2 level exceeds 410 ppm for first time

Since 1990, there has been a 40 per cent increase in total radiative forcing – the warming effect on our climate  due to long-lived greenhouse gases.

The University of California reports that the average concentration of carbon dioxide in the atmosphere was 410.31 parts per million (ppm) for the month of April 2018, according to the Keeling Curve measurement series made at the Mauna Loa Observatory in Hawaii. This marks the first time in the history of the Mauna Loa record that a monthly average has exceeded 410 parts per million. It also represents a 30 per cent increase in carbon dioxide concentration in the global atmosphere since the Keeling Curve began in 1958. In March, Scripps Institution of Oceanography at the University of California San Diego observed the 60th anniversary of the data series, the first measurements of which were 315 ppm.

Last autumn the World Meteorological Organization (WMO) reported that concentrations of carbon dioxide in the atmosphere surged at record-breaking speed in 2016 to the highest level in 800,000 years. The abrupt changes in the atmosphere witnessed in the past 70 years are without precedent. Globally averaged concentrations of carbon dioxide reached 403.3 parts per million in 2016, up from 400.00 ppm in 2015 due to a combination of human activities and a strong El Niño event. Concentrations of carbon dioxide are now 145 per cent of pre-industrial (before 1750) levels, according to WMO.

Rapidly increasing atmospheric levels of carbon dioxide and other greenhouse gases have the potential to initiate unprecedented changes in climate systems, leading to “severe ecological and economic disruptions,” said WMO.
Since 1990, there has been a 40 per cent increase in total radiative forcing – the warming effect on our climate – due to all long-lived greenhouse gases, and a 2.5 per cent increase from 2015 to 2016 alone, according to figures from the US National Oceanic and Atmospheric Administration quoted by WMO.

“Without rapid cuts in carbon dioxide and other greenhouse gas emissions, we will be heading for dangerous temperature increases by the end of this century, well above the target set by the Paris climate change agreement,” said WMO Secretary-General Petteri Taalas. “Future generations will inherit a much more inhospitable planet,” he said. “Carbon dioxide remains in the atmosphere for hundreds of years and in the oceans for even longer. The laws of physics mean that we face a much hotter, more extreme climate in the future. The last time the Earth experienced a comparable concentration of carbon dioxide was 3–5 million years ago, the temperature was 2–3°C warmer and sea level was 10–20 meters higher than now.”

Carbon dioxide is by far the most important anthropogenic long-lived greenhouse gas. Globally averaged concentrations for carbon dioxide reached 403.3 parts per million in 2016, up from 400.00 ppm in 2015. This record annual increase of 3.3 ppm was partly due to the strong 2015/2016 El Niño, which triggered droughts in tropical regions and reduced the capacity of “sinks” like forests, vegetation and the oceans to absorb carbon dioxide.

Concentrations of carbon dioxide are now 145 per cent of pre-industrial (before 1750) levels. The rate of increase of atmospheric carbon dioxide over the past 70 years is nearly 100 times larger than that at the end of the last ice age. As far as direct and proxy observations can tell, such abrupt changes in the atmospheric levels of carbon dioxide have never before been seen.

Over the last 800,000 years, pre-industrial atmospheric carbon dioxide content remained below 280 ppm, but it has now risen to the 2016 global average of 403.3 ppm. From the most-recent high-resolution reconstructions from ice cores, it is possible to observe that changes in CO2 have never been as fast as in the past 150 years. The natural ice-age changes in CO2 have always preceded corresponding temperature changes. Geological records show that the current levels of CO2 correspond to an “equilibrium” climate last observed in the mid-Pliocene (3–5 million years ago), a climate that was 2–3°C warmer, where the Greenland and West Antarctic ice sheets melted and even some of the East Antarctic ice was lost, leading to sea levels that were 10–20 m higher than those today.

Methane (CH4) is the second most important long-lived greenhouse gas and contributes about 17 per cent of radiative forcing. Approximately 40 per cent of methane is emitted into the atmosphere by natural sources (e.g., wetlands and termites), and about 60 per cent comes from human activities like cattle breeding, rice agriculture, fossil fuel exploitation, landfills and biomass burning. Atmospheric methane reached a new high of about 1,853 parts per billion (ppb) in 2016 and is now 257 per cent of the pre-industrial level.

Nitrous oxide (N2O) is emitted into the atmosphere from both natural (about 60%) and anthropogenic sources (approximately 40%), including oceans, soil, biomass burning, fertilizer use, and various industrial processes. Its atmospheric concentration in 2016 was 328.9 parts per billion. This is 122 per cent of pre-industrial levels. It also plays an important role in the destruction of the stratospheric ozone layer which protects us from the harmful ultraviolet rays of the sun. It accounts for about 6 per cent of radiative forcing by long-lived greenhouse gases.

The Washington Post reports that planetary carbon dioxide levels have been this high or even higher in the planet’s history – but not for a long time. Scientists are also concerned that the rate of change now is far faster than what Earth has previously been used to. In the mid-Pliocene warm period more than 3 million years ago, CO2 levels were also around 400 parts per million – but Earth’s sea level is known to have been 20 metres or more higher, and the planet was still warmer than now. As a recent federal climate science report noted, the 400 parts per million carbon dioxide level in the Pliocene “was sustained over long periods of time, whereas today the global CO2 concentration is increasing rapidly”. In other words, Earth’s movement toward Pliocene-like conditions may play out in the decades and centuries ahead of us. Even farther back, in the Miocene era between 14 million and 23 million years ago, carbon dioxide concentrations in the atmosphere are believed to have reached 500 parts per million. Antarctica lost tens of metres of ice then, probably corresponding to a sea level rise once again on the scale of that seen in the Pliocene.

Compiled by Reinhold Pape



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