Two of the most important climate change gases increased last year, according to a preliminary analysis for NOAA's annual greenhouse gas index, which tracks data from 60 sites around the world.
Researchers measured an additional 16.2 billion tons of carbon dioxide (CO2) - a byproduct of fossil fuel burning - and 12.2 million tons of methane in the atmosphere at the end of December 2008. This increase is despite the global economic downturn, with its decrease in a wide range of activities that depend on fossil fuel use.
"Only by reducing our dependence on fossil fuels and increasing energy production from renewable resources will we start to see improvements and begin to lessen the effects of climate change," said scientist Pieter Tans of NOAA's Earth System Research Laboratory in Boulder, Colo. "At NOAA we have monitored carbon dioxide emissions and other greenhouses gases for decades and will continue to do so to help assess the situation and advise decision makers."
Viewed another way, for every million molecules of air, another 2.1 molecules of carbon dioxide entered the atmosphere last year and stayed there - slightly less than the 2.2 parts per million (ppm) increase in 2007. Total global concentrations topped 386 ppm, compared to 280 ppm before the industrial revolution began in the 1800s.
"Think of the atmosphere and oceans taking in greenhouse gases as a bathtub filling with more water than the drain can empty, and the drain is very slow," said Tans. "We need to reduce greenhouse gas emissions to the point where they match levels that can be absorbed by Earth's ecosystems."
The increases in CO2 and methane during 2008 are slightly less than those measured in 2007, but fall well within the range of yearly fluctuations from natural changes, according to NOAA experts.
The rise in CO2 levels varies from year to year along with plant growth and decay, wildfire activity, and changes in soil conditions. Emerging from that natural variability is a consistent upward trend produced by burning coal, oil, and gas for transportation and industry.
Methane levels rose in 2008 for the second consecutive year after a 10-year lull. Atmospheric concentrations increased by 4.4 molecules for every billion molecules of air, bringing the total global concentration up to 1788 parts per billion, according to NOAA data.
Pound for pound, methane is 25 times more potent as a greenhouse gas than carbon dioxide, but there's far less of it in the atmosphere and is measured in parts per billion. When related climate affects are taken into account, methane's overall climate impact is nearly half that of carbon dioxide.
CO2, Historically Speaking
Carbon dioxide growth has increased by more than two percent each year since preindustrial times, doubling every 31 years, according to a study published in the journal Atmospheric Environment last month by David Hofmann, James Butler, and Tans. All are researchers at ESRL.
Even during the 1970s, when fossil fuel emissions dropped sharply in response to the oil crises, emissions remained high enough that CO2 levels continued to climb exponentially, similar to the way compound interest builds.
But the carbon dioxide record isn't immune to temporary dips lasting several years or more. A slowdown occurred in 1930–36 after the Great Depression and again during the 1940s, possibly because of World War II.
The large volcanic eruptions of Mt. Agung (Indonesia) in 1963 and Mt. Pinatubo (Philippines) in 1991 each slowed CO2 buildup for several years. Volcanic emissions cool the lower atmosphere and scatter sunlight. Those changes can both reduce plant respiration, a process that releases carbon dioxide, and boost photosynthesis, which removes carbon dioxide from the air.
"Atmospheric CO2 growth is best reflected by the world population trend," said Hofmann. "The two have tracked each other extremely well over the past century. A break in the close relation between population growth and CO2 growth would be a clear sign of progress in the inevitable need to limit atmospheric CO2."