As we predicted two months ago, the background atmospheric carbon dioxide levels measured at Cape Grim on Tasmania’s northwest coast have officially passed the 400 parts per million mark.

Tasmania’s Cape Grim monitoring station passed a crucial carbon dioxide threshold this month. Bureau of Meteorology, Author provided
Aerial shot of tower atop Cape Grime in Tasmania

Tasmania’s Cape Grim monitoring station passed a crucial carbon dioxide threshold this month. Bureau of Meteorology, Author provided

As we predicted two months ago, the background atmospheric carbon dioxide levels measured at Cape Grim on Tasmania’s northwest coast have officially passed the 400 parts per million (ppm) mark. Our measurements, compiled by our team at CSIRO together with the Bureau of Meteorology, show that the milestone was reached on May 10.

In the past few days, the 400 ppm level has also been breached in Antarctica, where CSIRO’s measurements at Casey Station show the 400 ppm level was exceeded on May 14.

Together, these measurements show that the atmospheric CO₂ concentration of the entire southern hemisphere is now at or above 400 ppm. It is unlikely to dip back below this level for many decades to come.

Cape Grim’s carbon dioxide record shows that background levels have now exceeded 400 parts per million.

Cape Grim’s carbon dioxide record shows that background levels have now exceeded 400 parts per million.

The threshold was reached earlier than we and our colleagues had anticipated, as a result of a recent, strong increase in the growth rate of atmospheric CO₂. This was probably driven by increased emissions from fossil fuels, as well the impact of the recent strong El Niño, which reduced the capacity of natural systems such as oceans and plants to absorb CO₂.

Southern hemisphere lag

CO₂ concentrations over the southern hemisphere are trailing those in the planet’s northern half, where 400 ppm level was breached in 2014-15. The northern hemisphere’s carbon dioxide levels are higher because most CO₂ sources (such as vegetation and fossil-fuel-burning installations) are mainly found in the north, whereas CO₂ “sinks” such as oceans are predominantly in the southern hemisphere.

The northern hemisphere’s CO₂ levels also show a much stronger seasonal variation. Ironically, the only place on Earth where baseline levels of CO₂ are likely to stay under 400 ppm for the next few years is the high Arctic, where the extreme summer carbon dioxide minimum will likely result in sub-400 ppm averages for 2017 and 2018.

After that, however the world’s background levels of CO₂ are unlikely to fall back below 400 ppm for many decades – perhaps a century or more – depending on the success of humankind’s efforts to reduce emissions.

Carbon dioxide levels at Cape Grim, and around the world, have risen sharply since the dawn of the industrial era. Paul Krummel, Author provided

Carbon dioxide levels at Cape Grim, and around the world, have risen sharply since the dawn of the industrial era. Paul Krummel, Author provided

What does 400 ppm really mean?

The 400 ppm level of atmospheric CO₂ is largely symbolic. The real concern is the current rate at which this figure is increasing: roughly 3 ppm per year. If this were to continue for another two decades, we would pass 450 ppm of CO₂. Once that level is reached, the levels of all greenhouse gases put together (carbon dioxide, methane, nitrous oxide and synthetic greenhouse gases) would add up to the equivalent of about 550 ppm of CO₂.

This is the level at which average global temperatures would be likely to reach 2℃ above pre-industrial levels in the decades thereafter (given the time lag between atmospheric CO₂ and its global warming impact).

This is the amount of global warming that the Paris Agreement is designed to avoid – indeed, the agreement calls for temperatures to be held well below this level.

It is clear that strong, worldwide initiatives aimed at curbing carbon dioxide emissions are needed now if we are to avoid the most dangerous predicted effects of climate change.

A relentless trend

Atmospheric CO₂ has been increasing relentlessly over the past 200 years or so, as can be seen in the chart below. Air and ice measurements allow us to trace the dramatic rise in CO₂ levels from about 280 ppm, before the start of the industrial era around the year 1800, to the current level above 400 ppm.

Ice core measurements show the rise of carbon dioxide since 1800, combined with Cape Grim measurements starting in 1976. CSIRO

Ice core measurements show the rise of carbon dioxide since 1800, combined with Cape Grim measurements starting in 1976. CSIRO

That is an increase of 43% in scarcely more than two centuries, largely as a result of human activities. The time to start reversing that trend is now.The Conversation

Paul Krummel, Research Group Leader, CSIRO and Paul Fraser, Honorary Fellow, CSIRO

This article was originally published on The Conversation. Read the original article.

5 comments

  1. After the recent bushfires Nasa showed photos from space showing the smoke reaching South America. Is this the El Nino affect or does all gas emitted into the atmosphere greenhouse or smoke, given the weather patterns generally move west to east, move away like this. If this was the case all our emissions would travel large distances over the oceans, the Amazon rain forest and the African continent. Considering 80 percent of the southern hemisphere is covered by oceans and less than 10 percent of the total emissions occur in he southern hemisphere I am a little confused as to how the southern hemisphere would be looking at catastrophic climate change. We definitely have to take steps to reverse climate change but the northern hemisphere has to do a lot more and make major changes to the way they do business and not be so quick to criticise us based on their own problems.

  2. So if Cape grim has levels of 400ppm, what is he average around Australia generally, because Cape Grim is supposed to be some of the cleanest air in the world they say.

    1. Hi Anthony,

      The air that reaches Cape Grim is indeed considered some of the cleanest air in the world. This is because by the time it gets there, it has travelled for long distances over the Southern Ocean, with the absence of human or other terrestrial influence.

      However, nearby a large source, for example a coal fired power station, the concentration of carbon dioxide (C02) will be much higher (perhaps several hundreds of parts per million – or even higher) than the Cape Grim baseline record.

      On the other hand, if an air mass has travelled over a forest, or cropland during daylight hours (and in the absence of drought), the CO2 concentration is likely to be below the Cape Grim value at that time, due to photosynthetic uptake by plants (this is becoming more rare as the baseline CO2 is now at above 408 ppm.)

      So when it comes to giving an ‘average around Australia’, it gets quite difficult, given that the concentration that can be measured at any given location (and at any given time) depends on the complex interaction of sources, sinks and meteorology.

      If you’d like some more information on average C02 levels, please let us know.

      Kind regards,
      Kashmi
      CSIRO Social Media Team

  3. Sure, ruminants burp methane, but if all humans eat beans and lentils instead,what would be the net reduction in methane emissions?

  4. The meat and dairy industries are also responsible for a large part of greenhouse gas emissions but nobody seems to want to talk about that .
    Humans only need to eat meat ( a small amount ) once per week to get all the minerals they need for maintenance of good health .
    Humans don’t actually need any dairy products at all in their diet as all the calcium the body needs is present in fruit and vegetables .
    Abandoning our heavy reliance on meat and dairy products would help enormously in reducing greenhouse gas emissions .

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