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How to keep below 2ºC: carbon budgets

Despite the uncertainties, there is a growing consensus that preventing dangerous and irreversible climate change requires keeping as far below 2°C of global warming compared to pre-industrial levels as possible.

This may not sound a lot, but it would leave the world warmer than at any point for probably a million years.

Going in the other direction, only about 6ºC separates today from the depths of the last ice age, when most of Europe and North America were covered in a thick sheet of ice and sea level was some tens of metres lower.

Umbrella blown inside-out with a map of the earth on it.

To stabilize temperatures, we have to stabilize atmospheric concentrations of CO₂ and other heat-trapping greenhouse gases manufactured by humans.

For convenience, scientists lump these gases together into a single figure known as CO₂ equivalent.

The current CO₂ concentration is 386 parts per million (ppm).
With the other gases, it is the CO₂ equivalent of about 462 ppm and rising.
To ensure long-term climate stability, with temperature rise limited to less than 2°C above the pre-industrial average, requires eventually returning concentrations to the CO₂ equivalent of 400 ppm and ultimately to pre-industrial concentrations.

A recycling planet. International Children’s Painting Competition on the Environment organized by UNEP, the Foundation for Global Peace and Environment, Bayer and Nikon.

BUT IS THAT POSSIBLE?

Yes... it is!

IN THE LONG RUN, oceans and forests will absorb more of the CO₂ we put in the air.

And we have a few decades to act, as there is a time-lag between emissions and rising temperatures and because, for now, we are being protected from some of the warming by a thin veil of pollutants from smoke and other non-greenhouse emissions that reduces the sun’s intensity.

We can probably only afford to put about another 1,000 billion tonnes of CO₂, or 1,400 billion tonnes of CO₂ equivalent, into the atmosphere between the years 2000 and 2050.

That is only around 20 years’ worth at current emissions rates from burning fossil fuels, deforestation and changing land use.

And more than 1/3 of this “carbon budget” has been emitted between the year 2000 and today.

In addition to the substantive reduction in greenhouse gas emissions, we need to embark forcefully on taking CO₂ out of the atmosphere. This will require not only massive re- and afforestation, but also carbon capture and storage technologies with sustainably grown bioenergies replacing fossil fuels, and new technologies to reduce atmospheric CO₂ concentrations.

As the IPCC has noted, low-carbon pathways require a world that by mid-century has been turned into a carbon sink.

Reducing emissions is not enough anymore – we need to prepare to go further.

We are sailing very close to the edge.

There is little margin for error.

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