How to keep below 2ºC: carbon budgets
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.
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.
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.