Data suggest natural “carbon sinks” may be nearing exhaustion, say some scientists, although others disagree.
By Brian Clark Howard
PUBLISHED SEPTEMBER 9, 2014
The amount of greenhouse gases in the atmosphere reached a new record high in 2013, propelled by a surge in levels of carbon dioxide, the World Meteorological Organization reported Tuesday, raising the threat of increased global warming.
The scientists warn that the Earth’s natural ability to store and mediate the gases through oceans, plants, and other means may be approaching a saturation point, which could exacerbate current warming. Not all scientists agree, however.
The World Meteorological Organization’s annual report “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,” said Michel Jarraud, the group’s secretary-general, in a statement.
“We must reverse this trend by cutting emissions of CO2 and other greenhouse gases across the board,” said Jarraud. “We are running out of time.” (See “Can Coal Ever Be Clean?”)
Scientists who contributed to the report, called the “Greenhouse Gas Bulletin,” noted that carbon dioxide levels rose more between 2012 and 2013 than during any other year since 1984.
The report showed that between 1990 and 2013, the energy in the atmosphere increased by 34 percent. The surge was driven by a concentration of carbon dioxide that is 42 percent higher than the level in the pre-industrial era (prior to 1750). Methane and nitrous oxide were 153 percent and 21 percent higher, respectively, than pre-industrial levels, although their overall numbers are much lower than carbon dioxide’s.
Normally, about a quarter of carbon dioxide emissions into the atmosphere are absorbed by plants, while another quarter dissolves into the ocean.
But the ability of plants and oceans to keep on absorbing excess greenhouse gases may be slowing as those systems approach what may be a saturation point, the organization’s scientists warn.
The report said that preliminary data suggest the record high level of carbon dioxide “was possibly related to reduced CO2 uptake by the earth’s biosphere in addition to the steadily increasing CO2 emissions,” the organization wrote in a statement. (See “Climate Milestone: Earth’s CO2 Levels Pass 400 ppm.”)
Because carbon dioxide remains in the atmosphere for many hundreds of years and in the ocean for even longer, Jarraud said, “past, present, and future CO2 emissions will have a cumulative impact on both global warming and ocean acidification. The laws of physics are non-negotiable.” (See “What’s Behind New Warning on Global Carbon Emissions?“)
The growing amount of CO2 in oceans has been raising the acidity of seawater, which scientists warn has serious implications for the growth of corals and other marine creatures. (Read “The Acid Sea” in National Geographic magazine.)
Similarly, in a study published last year in Nature, scientists at the Scripps Institution of Oceanography in California wrote that cool ocean waters appear to have been absorbing some excess heat in the atmosphere.
The oceans’ ability to absorb heat was already thought to be largely responsible for the so-called “global warming pause” or “hiatus” that has meant global temperatures have not risen as fast as some scientists expected over the past few years.
Voices of Caution
Other scientists say more data are needed to better understand long-term trends in warming and evaluate the role of carbon sinks.
“There is a lot of year-to-year variability in the carbon sinks, so I don’t think we can say much about their response based on their behavior over one year,” one of the world’s leading authorities on the uptake of carbon dioxide into the oceans, Corinne Le Quéré of the Tyndall Centre for Climate Change Research and University of East Anglia in the U.K., told National Geographic.
Le Quéré’s colleague Róisín Moriarty of the Tyndall Centre added that emissions are steadily rising and that climate models predict carbon dioxide will likely continue to dissolve into the oceans until at least 2050.
Gavin Schmidt, a climate scientist with NASA’s Goddard Institute for Space Studies, says that “it is very hard to say” whether the Earth’s natural carbon sinks are becoming saturated with carbon dioxide.
“There is a lot of interannual variability in uptake, related to El Niño-La Niña cycles and weather changes over the terrestrial regions,” said Schmidt. “You are going to need to look over a longer time period.”
Still, “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, in a statement.