Can 400ppm spark us into climate action?

By Johan L. Kuylenstierna

Within the next few days, the atmospheric concentration of carbon dioxide is likely to hit 400 parts per million – a record high since the evolution of modern humans.

As far as we know, CO2 concentrations have not been at such levels since the Pliocene some 3-5 million years ago – a period that was considerably warmer than today.

We have been in the 390s for a while, and although 400ppm is certainly worse, the world won’t plunge into chaos in May because we crossed that threshold.

But that doesn’t make 400ppm just a symbolic level; it is a point along a continuum that we know leads to ever-worse consequences, with potentially irreversible impacts on water resources, biodiversity, ecosystems, and other key aspects of our planet’s functioning.

And, as always, impacts on humans will be worst for those with the least capacity to deal with changes.

Protesters at the Durban climate talks (Pic: Flickr/JoshLopezPhoto)

Hitting 400ppm also reminds us of the failure of the international community to reach an agreement that would permanently bend the emissions curve in the right direction.

Negotiations are locked, and governments have been meeting in Bonn again, trying to find the right key.

Of course, we need to respect the complexity of the negotiations; after all, it involves the core of our development, including tomorrow’s energy systems, our consumption patterns, global trade and other fundamental aspects of our societies and lives.

Still, this new CO2 record should add to the sense of urgency – making it clear that climate systems cannot be put on hold while we make a new agreement.


The scientific facts – including daily atmospheric CO2 levels – serve as a vital “reality check”. The long-term record from the Earth Systems Research Laboratory in Hawaii is one of many indicators that show how we are fundamentally changing conditions on this planet we call home.

It is important to keep building and maintaining monitoring systems to ensure we have a solid knowledge base to inform policy processes.

But climate policy involves more than science: Political leaders need the support of their citizens. It is essential that we not only educate people about the real dangers of climate change, but encourage them to take action. Individuals can and must make a difference.

Governments also need to tackle climate change on multiple tracks. Even as they continue to work through the slow, challenging negotiation process under the United Nations Framework Convention on Climate Change (UNFCCC), they can make progress on other fronts.

An interesting example is the Climate and Clean Air Coalition, a growing international effort to address short-lived climate pollutants such as methane and black carbon, building on robust scientific knowledge. Measures to reduce those pollutants, if widely adopted, could reduce global warming by as much as 20% in the short term.

This is not a substitute for reducing CO2 emissions, but with levels already at 400ppm, we need to do everything we can.

The new record is disheartening, but it can also help raise awareness of climate change, and help push mitigation higher up on the political agenda. If we use this opportunity, we can stimulate constructive discussions, focusing on solutions that will benefit the climate, the environment and people.

The 400ppm milestone comes as we are preparing for a period of heightened attention to climate science, when the first part of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report is launched in September in Stockholm.

Let us hope that reaching 400ppm can serve as a spark to ignite a new sense of urgency about climate change. Otherwise, in a few decades, we’ll lament our inaction when we hit 450ppm.

Johan L. Kuylenstierna is executive director of the Stockholm Environment Institute

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