Even a fall in CO2 emissions is not unalloyed good news

A study suggesting that total global carbon dioxide emissions may stall or even fall this year, which was published recently in the journal Nature Climate Change and was presented at the COP21 climate summit in Paris, has been garnering a lot of attention. Perhaps too much, because the story behind the headline is not as positive as the headline itself.
Much as I hate to rain on a parade, the report - which initially seems like a welcome piece of good news in an area where good news is hard to come by - is not in fact unalloyed good news. If indeed 2015's greenhouse gas emissions do show a small reduction, it is probably more to do with China's economic downturn than any positive change in policies.
Yes, there has been a benefit from the faster uptake of renewables worldwide. But the most significant effect is from the reduced use of coal in China as its economy slows down. China now contributes over a quarter of the world's greenhouse gas emissions, so its emissions have a disproportionately large effect on the global totals.
The point, then, is that any decrease is small and temporary. As the report makes clear, we are not seeing a peak in GHG emissions, just a blip in the curve. Emerging economies, including huge ones like India's, are mostly based on coal, and so the inexorable upward curve of emissions is expected to continue. Even with a strong agreement in Paris, overall emissions are likely to continue to increase for some time. So, words like "encouraging" and "a boost", which I have seen used in many news reports, are at best premature, and even potentially damaging if they have the effect of lulling us into a false sense of security.
It is also worth mentioning that the report only refers to carbon dioxide. Another article today has alerted me to an important elephant in the climate change room: methane. Methane is emitted during the production and transportation of coal, natural gas and oil, as well as due to livestock and other agricultural practices, and the decay of organic waste in municipal solid waste landfills. Although relatively short-lived in the atmosphere, methane is a very potent greenhouse gas, with about 80 times more global warming potential than carbon dioxide in its first 20 years in the atmosphere (declining to roughly 30 times that of CO₂ after about 100 years). The International Energy Agency ranks cutting oil- and gas-generated methane at the same level of effectiveness in the fight against climate change as increased investment in renewable energy.
One major source of methane emissions is leakage from natural gas power generation, which is increasingly being used to replace coal generation due to its (slightly) lower CO₂ emissions. Worldwide, methane escapes from oil and gas operations have an estimated climate impact equal to about 40% of total global coal combustion, and Canada is the world’s fourth-largest methane emitter (after Russia, Uzbekistan and the United States). Alberta’s new climate strategy aims to reduce oil and gas methane emissions by 45% by 2025, a substantial improvement in green house gas emissions that can be achieved relatively cheaply. If every gas-producing country matched those targets, it is estimated to have the same 20-year effect as closing 1,000 coal-fired power plants.
Good news is always welcome. But what we need to avoid is the conclusion that recent changes have been enough, and that we can now afford to slacken off. Au contraire. The fight is just beginning.