Cutting emissions of other greenhouse gases would slam the brakes on short-term climate change faster than controlling CO2 alone. But rather than offering an easy way out, warns Jim Butler, director of the Global Monitoring Division at the US National Oceanic and Atmospheric Administration (NOAA), they present both an opportunity and a challenge. “Addressing them can help us see earlier results than we would see with CO2, which poses a problem today but a much bigger one in the future,” he told Simple Climate. “CO2 must be addressed, but ignoring these other gases too could take us to places where we don’t want to go.”
Butler’s division has tracked the levels of different gases in the atmosphere for decades. Among them he says, CO2 rightfully gains most attention. That’s because it traps so much of the sun’s energy, it currently accounts for almost two-thirds of the warming power known as “climate forcing”. “It is responsible for well over 80 per cent of the increase in climate forcing from long-lived gases each year,” Butler said. “It is also very long lived, with around one-fifth of what is emitted hanging around for at least 1,000 years.” Yet as burning oil, natural gas and coal, which produces CO2, propels modern life, cutting the amount we use enough will take some time. “In the meantime there are other gases that could and probably should receive attention,” Butler underlined.
Stephen Montzka of NOAA, along with colleagues Butler and Ed Dlugokencky, looked at exactly how these gases have been affecting climate in top scientific journal Nature this week. Monitoring and evaluating these gases helps show how humans are affecting their levels in the atmosphere. It also serves as a check on the results of claimed emissions. Unfortunately, the amount countries say they produce and levels recorded at observatories across the world disagree. However, Butler noted that no approach is perfect, and that at least comparing the two gave them some idea how far out they were. “The beauty of comparing the two is that each relies on completely different measurements, procedures and assumptions,” he said.
The kindest cuts
The good news is that since 1990, emissions of non-CO2 gases have fallen. That’s thanks to cuts in emissions of chemicals responsible for the hole in the ozone layer thanks to governments agreeing the Montreal Protocol in 1987. These chemicals are also greenhouse gases that trap energy in the atmosphere. That reduction more than balanced increases in emissions from CO2 until 2003, showing how big an impact limiting non-CO2 gases can have.
The remaining greenhouse gases could be harder to control. These include methane, nitrous oxide (N2O), better known as laughing gas, and hydrofluorocarbons. “Methane and N2O both have many sources, mainly biological reactions,” Butler commented. He noted that research was needed to see how best to limit emissions, but some possibilities may be easier than others. “There could be some relatively simple approaches for addressing methane and N2O emissions from the energy and industrial sectors,” Butler said. “Another example would be to begin using nitrogen-containing fertilisers more efficiently to help reduce N2O emissions, but that, too, would need to be done carefully.”
Scientists consider it would be dangerous to exceed a 2°C global average temperature increase, which is why limiting climate change to this amount was a stated aim of the Copenhagen Accord. To prevent this by limiting CO2 alone could require annual emissions in 2050 to be just one-fifth of those in 1990. But Butler’s figures suggest that cutting all greenhouse gas emissions by that amount would go beyond making forcing, and therefore temperature, stable and instead begin reducing forcing far sooner than focussing only on CO2.
Whether any emissions cuts are made depends ultimately on how committed we, as a society, are to making them, Butler said. “There is no simple solution,” he warned. “One thing is for certain, if society chooses to do little or nothing, these gases will accumulate in the atmosphere, adding yet another blanket to planet Earth, as global population continues to increase and energy demand continues to accelerate.” But because the main other greenhouse gases are broken down in the atmosphere more quickly than CO2, including them in efforts to fight climate change would mean the results would be seen quicker. Paying attention to all such gases would also make a bigger difference than focussing on CO2 alone, Butler explained. “Society has something significant to gain by developing management strategies that include a number of gases,” he said.