Dr. Keeling noted that last year’s drop in annual emissions was too small to be detected in the atmospheric data, since it can be overshadowed by natural fluctuations in carbon emissions from vegetation and soil in response to seasonal changes in temperature and soil moisture. Scripps scientists have previously estimated that humanity’s emissions would need to drop by 20 percent to 30 percent for at least six months to result in a noticeable slowing of the rate of increase of carbon dioxide in the atmosphere.
And, scientists have said, there’s only one way to stop the total amount of carbon dioxide in the atmosphere from continuing to grow: nations would need to essentially zero out their net annual emissions, primarily by switching away from fossil fuels to cleaner technologies that do not emit carbon dioxide, such as electric cars fueled by wind, solar or nuclear power.
Last month, the International Energy Agency issued a detailed road map for how all of the world’s nations could reach net zero emissions by 2050. The changes would be drastic, the agency found: Countries would have to stop building new coal plants immediately, ban the sale of gasoline-powered vehicles by 2035 and install wind turbines and solar panels at an unprecedented rate.
If nations managed to hit that goal, they could limit total global warming to around 1.5 degrees Celsius, compared with preindustrial levels. (The Earth has already warmed more than 1 degree Celsius since preindustrial times.) Doing so could help humanity avoid some of the worst impacts of climate change, such as the irreversible collapse of polar ice sheets or widespread crop failures.
But so far, the agency warned, the world is not on track to hit that goal. Total annual emissions are currently expected to rise at their second-fastest pace ever this year as countries recover from the pandemic and global coal burning approaches its all-time high, led by a surge of industrial activity in Asia.
The amount of carbon dioxide in the atmosphere currently varies by about 10 parts per million over the course of a year. It reaches a peak each May, before the seasonal growth of vegetation in the Northern Hemisphere, which has about two-thirds of the Earth’s land mass, removes some of the gas through photosynthesis.
The May average first topped 400 parts per million in 2014 — a milestone that attracted worldwide media coverage. Since then, emissions have continued to soar. The latest full-year average, for 2019, was 409.8 parts per million, about 46 percent higher than the preindustrial average of 280.