Targets for reduction of global greenhouse gas emissions were originally specified in the Kyoto Protocol. These targets were set for annual emissions in Megatonnes (Mt) of CO2e. So what does this mean? CO2e stands for carbon dioxide equivalent, which includes other greenhouse gases such as methane also affect warming. Methane, in particular causes more warming than CO2 (although it remains in the atmosphere for fewer years.)
The targets covered emissions of the six main greenhouse gases:
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. The targets that Canada ratified were for 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 2009 Canada signed the Copenhagen Accord, which, unlike the Kyoto Protocol, is a non-binding agreement. Canada agreed to reduce its GHG emissions by 17% from its 2005 levels by 2020.
In 2011, the Conservative government announced that Canada was withdrawing from the Kyoto Accord.
In 2015, the Liberal government signed the Paris Agreement to reduce the missions by 30% of the 2005 levels by 2030,
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 394 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.)
Drawdown (artificial sinks) including bio-char and carbon capture and storage/sequestration (CCS) can be used to remove carbon dioxide. 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.
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 the all species and especially to low-lying developing countries.
With present 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.)
The conversion tables of the Carbon Dioxide Information Analysis Center advise that 1 part per million of atmospheric CO2 is equivalent to 2.13 Gigatonnes Carbon (7.81 Gigatonnes of Carbon Dioxide.) 350 ppm CO2 is 2,700 GtCO2. This would represent a safe level that we should aim for.