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Carbon dioxide passes symbolic mark Carbon dioxide passes symbolic mark
(35 minutes later)
The level of carbon dioxide in the atmosphere has risen above 400 parts per million for the first time in human history, US researchers say. Carbon dioxide levels in the atmosphere have broken through a symbolic mark.
The "Keeling Lab" in Hawaii has the longest continuous measurement of the greenhouse gas, which is a key driver of climate change. Daily measurements of CO2 at the authoritative "Keeling lab" on Hawaii have topped 400 parts per million for the first time.
Thursday's measurement, made atop the Mauna Loa volcano, registered 400.03. The station, which sits atop the Mauna Loa volcano, has the longest continuous measure of the concentration of the gas, stretching back to 1958.
The last time CO2 was regularly above 400ppm was about 3-5 million years ago - before modern humans existed.The last time CO2 was regularly above 400ppm was about 3-5 million years ago - before modern humans existed.
The climate back then was also considerably warmer than it is today, according to scientists.The climate back then was also considerably warmer than it is today, according to scientists.
The usual trend seen at the volcano is for the CO2 concentration to rise in winter months and then to fall back as the northern hemisphere growing season kicks in and pulls some of the gas out of the atmosphere. But the long-term trend is upwards. Carbon dioxide is regarded as the most important of the manmade greenhouse gases, a product principally of burning fossil fuels such as coal, oil and gas.
When the late Charles Keeling began recording CO2 concentrations at the volcano in 1958, they were around 315 ppm (parts per million by volume - that is 315 molecules of CO2 for every one million molecules in the air). Every year since then, the curve has squiggled resolutely higher. The usual trend seen at the volcano is for the CO2 concentration to rise in winter months and then to fall back as the northern hemisphere growing season kicks in and pulls some of the gas out of the atmosphere.
Keeling died in 2005, but his work is continued by his son Ralph, who is affiliated to the Scripps Institution of Oceanography in San Diego. This means the number can be expected to decline by a few ppm below 400 in the coming weeks. But the long-term trend is upwards.
The monitoring station itself on Mauna Loa is run by the National Oceanic and Atmospheric Administration (Noaa) James Butler, from the National Oceanic and Atmospheric Administration (Noaa), explained: "Carbon dioxide has some variability on an hourly, daily and weekly basis, so we are not comfortable calling a single number - the lowest we will go is on a daily average, which has happened in this case," he told BBC News.
"Mauna Loa and the South Pole observatory are iconic sites as they have been taking CO2 measurements in real time since 1958. Last year, for the first time, all Arctic sites reached 400ppm.
"This is the first time the daily average has past 400ppm at Mauna Loa."
The long-term measurements were started by a Scripps Institution of Oceanography scientist called Charles Keeling.
In 1958, he found the concentration on Mauna Loa to be around 315ppm (that is 315 molecules of CO2 for every one million molecules in the air). Every year since then, the "Keeling Curve", as it has become known, has squiggled resolutely higher.
"Probably next year, or the year after that, the average yearly reading will pass 400pm," said Dr Butler, whose Earth System Research Laboratory runs the Mauna Loa and the South Pole observatories .
"A couple of years after that, the South Pole will have readings of 400ppm, and in eight to nine years we will probably have seen the last CO2 reading under 400ppm."
To determine CO2 levels before the introduction of modern stations, scientists must use so-called proxy measurements.
These include studying the bubbles of ancient air trapped in Antarctic ice.
One of these can be used to describe CO2 levels over the past 800,000 years. It suggests that CO2 held steady over this longer period at between 200ppm and 300ppm.
British atmospheric physicist Prof Joanna Haigh commented: "In itself, the value 400ppm of CO2 has no particular significance for the physics of the climate system: concentration levels have been in the 300s for so long and now we've passed the 400 mark. However, this does give us the chance to mark the ongoing increase in CO2 concentration and talk about why it's a problem for the climate."