Some years ago these targets for reducing emissions were set in the Kyoto Protocol. These targets were set for annual emissions in MegaTonnes (Mt) of CO2e. So what does this mean? CO2e stands for CO2 equivalent, which includes CO2 and other greenhouse gases. Gases such as methane also affect warming. Methane, in particular causes more warming than CO2 (although it has a shorter life.)
The targets cover emissions of the six main greenhouse gases:
- Carbon dioxide (CO2);
- Methane (CH4);
- Nitrous oxide (N2O);
- Hydrofluorocarbons (HFCs);
- Perfluorocarbons (PFCs); and
- Sulphur hexafluoride (SF6)
These targets were expressed as a percentage of our emissions in 1990. The Kyoto Protocol defined targets for developed countries (defined as Annex I countries) and they set separate targets for individual countries. Canada's targets were 6% below our 1990 emissions. The Kyoto Protocol targets were for emissions over the 2008-2012 period (i.e. our total emissions over that 5 year period.) For Canada the target was 240 Mt per year (i.e. 1200 Mt over the 5 year period.)
In December of 2011, the government of Canada became the first nation to withdraw from the Kyoto Protocol.
Total Carbon Target
The planet’s atmosphere contains a measurable quantity of CO2. This quantity is measured in parts per million by volume (ppmv). In pre-industrial times the atmosphere contained around 285 ppmv. Recent measurements are 405 ppmv and this amount is increasing by around 2 ppmv/year.
Think of atmospheric CO2 as water in a bathtub — unless more water is draining out than flowing in from the faucet, eventually the bathtub will overflow. Water flowing in represents emissions. Water draining out represents the fact that a certain amount of CO2 is removed from the atmosphere naturally via photosynthesis and other mechanisms (referred to as sinks.)
Artifical sinks can be used to remove CO2 including bio-char and carbon capture and storage/sequestration (CCS). However, even with natural sinks the level is increasing. Even if we stopped CO2 emissions completely, temperatures would continue to rise for quite a few years.
What is a safe level?
A safe level was previously considered to be an increase of less than 2 degrees (C) above pre-industrial levels. Recent science has established that 1.5o C is the maximum temperature increase. Even that will cause serious harm to all species and especially to those in low-lying developing countries.
Why 350 ppm?
At the present rate of emissions it is expected that the total atmospheric concentration of CO2 could eventually exceed 500 ppm. At one point it was thought that a level of 450 ppm would be safe and would mean that temperatures might rises by less than 2 degrees (Celsius). But recent research (including that by James Hansen) has found that this is wrong and a safe level is now considered to be less than 350 ppm CO2 (estimated to be around 400ppm CO2e.)
Recently climate scientists have calculated the maximum amount of cumulative emissions for different chances of keeping global temperature increases below 1.5 or 2 degrees C. These are known as carbon budgets.