SAN DIEGO • Despite a massive reduction in commuting and in many commercial activities during the early months of the Covid-19 pandemic, the amount of carbon in the Earth's atmosphere last month reached its highest level in modern history, a global indicator showed.
The amount of carbon in the air now is as much as it was about four million years ago, based on the findings released on Monday by scientists from the National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography at the University of California San Diego.
Based on the amount of carbon dioxide (CO2) in the air at NOAA's weather station on Mauna Loa in Hawaii, it was the highest since measurements began 63 years ago.
The measurement, called the Keeling Curve after scientist Charles David Keeling, who began tracking CO2 there in 1958, is a global benchmark for atmospheric carbon levels.
Instruments in NOAA's observatory recorded CO2 at about 419 parts per million last month, more than the 417 parts per million in May last year.
So what was the world like the last time CO2 levels were this high?
Current levels of atmospheric carbon dioxide are likely comparable to those seen during the Pliocene era, 4.1 million to 4.5 million years ago, the Scripps scientists said. By analysing ice cores and ocean sediments, researchers determined that temperatures at that time were nearly 4 deg C higher than in the modern pre-industrial era and that sea levels were about 24m higher than today.
Because CO2 is a key driver of climate change, the findings show that reducing the use of fossil fuels, deforestation and other practices that lead to carbon emissions must be a top priority to avoid catastrophic consequences, Dr Pieter Tans, a scientist with NOAA's Global Monitoring Laboratory, said in a report on the emissions.
"We are adding roughly 40 billion metric tonnes of CO2 pollution to the atmosphere per year," he wrote. "That is a mountain of carbon that we dig up out of the Earth, burn and release into the atmosphere as CO2 - year after year."
The stark new milestone comes as leaders from the Group of Seven (G-7) nations prepare to meet in Cornwall, England, this week to discuss how they might step up efforts to tackle climate change.
Global emissions temporarily dipped last year as countries locked down amid the pandemic, shuttering businesses and factories. According to the International Energy Agency, the world emitted 5.8 per cent less carbon dioxide last year than it did in 2019, the largest one-year drop ever recorded.
But that made little difference to the total amount of CO2 accumulating in the atmosphere. While about half of the CO2 emitted by mankind's activities is absorbed by the world's trees and oceans, the other half stays in the atmosphere, where it lingers for thousands of years, steadily warming the planet through the greenhouse effect.
"As long as we keep emitting carbon dioxide, it's going to continue to pile up in the atmosphere," said Professor Ralph Keeling, who runs the Scripps Oceanography CO2 programme. The project, begun by his father, Charles, has been taking readings since 1958 at the NOAA observatory on the Mauna Loa volcano.
Prof 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.
Scientists have said there is only one way to stop the total amount of CO2 in the atmosphere from growing: nations need to essentially zero out their net annual emissions, primarily by switching away from fossil fuels to cleaner technologies that do not emit CO2.
REUTERS, NYTIMES
