Despite some recent regional reductions in greenhouse gas emissions in the United States and other industrial nations, the total concentration of greenhouse gases in the atmosphere continues its upward march at an unprecedented rate, the World Meteorological Organization announced today.
Compared to the preindustrial era of the 1750s, the Earth's atmosphere is now choked with 142 percent more carbon dioxide, 253 percent more methane and 121 percent more nitrous oxide, the WMO reported in the release of its annual bulletin on greenhouse gas. Last year, the warming effect on the climate saw a 34 percent increase since 1990 levels.
Among the long-lived greenhouse gases produced by humans, carbon dioxide is by far leading the way, surging to new levels last year. The Earth, it seems, is reaching its saturation point.
While methane contributes about 17 percent to radiative forcing and nitrous oxide about 6 percent, carbon dioxide accounts for 65 percent and is responsible for 84 percent of the increase in radiative forcing over the past decade. "Carbon dioxide is the single most important anthropogenic greenhouse gas in the atmosphere," the bulletin authors reported.
Carbon dioxide levels increased more between 2012 and 2013 than during any other year since 1984, according to the WMO's Global Atmosphere Watch (GAW) network. "Preliminary data indicated that this was possibly related to reduced CO2 uptake by the Earth's biosphere in addition to the steadily increasing CO2 emissions," the WMO reported in a statement.
Normally, the Earth's oceans and land act as a buffer -- each taking up about a quarter of the total carbon dioxide emissions and thereby reducing the impact on the atmosphere.
Every year, the rise of carbon dioxide in the atmosphere also experiences seasonal fluctuations. During the last two Northern Hemisphere springs, several monitoring stations saw carbon dioxide reach the 400 parts per million (ppm) threshold.
Speeding past a milestone
"In some ways, 400 ppm is just a number, another milestone that we are blasting past at a rate that is now exceeding 2 ppm per year," said David Crisp, principal investigator of the Orbiting Carbon Observatory-2 satellite mission with NASA's Jet Propulsion Laboratory. "Over time, this number takes on greater weight. It brings home the fact that fossil fuel combustion, land use practices, and human activities have increased the CO2 concentration in Earth's atmosphere by more the 20 percent since I was born. Wow!"
On a global average, carbon dioxide in 2013 reached 396 ppm -- an increase greater than what was seen between 2011 and 2012, greater than the average growth rate for the 1990s, and even greater than the average growth rate for the past decade, according to the bulletin.
"Recent increases in emissions of CO2 from fossil fuel combustion (about 2 percent per year) cannot explain the inter-annual variability in CO2 growth rate nor the greater-than-average increase in annual means from 2012 to 2013," the bulletin authors reported.
"The Greenhouse Gas Bulletin shows that, far from falling, the concentration of carbon dioxide in the atmosphere actually increased last year at the fastest rate for nearly 30 years. We must reverse this trend by cutting emissions of CO2 and other greenhouse gases across the board," said Michel Jarraud, secretary-general of the World Meteorological Organization, in a statement.
Oceans reach 70% of conversion capacity
"Carbon dioxide remains in the atmosphere for many hundreds of years and in the ocean for even longer. Past, present and future CO2 emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are nonnegotiable," Jarraud stressed.
For the first time, the WMO's annual "Greenhouse Gas Bulletin" also addressed the consequences of increased carbon dioxide on Earth's oceans, which "take up about 4 kilograms of CO2 per day per person."
But the buffering capabilities of the ocean are limited by the amount of carbonate ions in the surface water available to convert dissolved carbon dioxide into carbonic acids and bicarbonates.
Today, the ocean is operating at 70 percent capacity in terms of its chemical conversion of carbon dioxide from the atmosphere compared to what it was at the beginning of the industrial era, "and it may well be reduced to only 20 percent by the end of the twenty-first century," the authors of the bulletin report.
"The inclusion of a section on ocean acidification in this issue of WMO's 'Greenhouse Gas Bulletin' is appropriate and needed. It is high time the ocean, as the primary driver of the planet's climate and attenuator of climate change, becomes a central part of climate change discussions," said Wendy Watson-Wright, executive secretary of the Intergovernmental Oceanographic Commission of UNESCO.
"If global warming is not a strong enough reason to cut CO2 emissions, ocean acidification should be, since its effects are already being felt and will increase for many decades to come," she added.