Climate Science and Earth System Science

Cumulative Emissions

Cumulative Emissions since 1870
IPCC (2013)

Cumulative emissions refer to the amount of emissions that the world has emitted since the year 1751. Since this period it is estimated that 1.5 trillion tonnes of CO₂  has been released into Earth's atmosphere. To reach our goal of limiting emissions to well below 2 °C, we need to urgently reduce emissions. 

The concentration of greenhouse gases in the atmosphere is what determines the warming effect in the atmosphere. One molecule of carbon can last in the atmosphere for approximately one hundred years, indicating that the earth and humans have not yet felt the total impacts of our actions since pre-industrial times. We are already committed to a certain amount of warming due to our past emissions.

To see how long other greenhouse gases remain in the atmosphere please see here (or table 2.14  p.33 of the IPCC AR1 report here.

According to the IPCC Special Report: Global Warming of 1.5°C, reducing global warming will require limiting the total cumulative global anthropogenic emissions of CO₂  since pre- industrial times in order to stay within a remaining carbon budget (IPCC, 2018). This may be extremely difficult as cumulative anthropogenic CO₂  emissions since 1751 already accounted for the total carbon budget for 1.5°C by the end of 2017 (IPCC, 2018). Current emissions are now using up the remaining budget of 42 ± 3 Gt CO₂  per year (IPCC, 2018).

Feedback Loops

The most recent United Nations Intergovernmental Panel on Climate Change (IPCC) report has highlighted the  issue of feedback loops already present in the earth's system that largely threaten global warming spiralling out of control. While feedback loops cannot be attributed as the root cause of the climate change crisis they certainly speed up the process, make it a lot worse and more difficult to manage. 

One of these feedback loops,  identified as already in force,  is the melting permafrost in the Arctic which directly results in huge amounts of additional carbon dioxide and methane being released into the atmosphere. This additional amount of greenhouse gas emissions into the atmosphere even further accelerates atmospheric warming and therefore exacerbates further melting of permafrost.

Another feedback loop identified by climate scientists is the “albedo effect” which is the amount of solar radiation that is reflected back into space from the polar ice sheets. With these ice sheets now drastically melting, more land is exposed to radiation from the sun which in turn leads to further melting of ice sheets though increasing global temperatures. 

According to the latest IPCC report, in order to reverse further warming from feedback loops (as well as reversing ocean acidification and increasing sea levels), sustained net negative global anthropogenic CO₂ emissions are required on longer timescales (IPCC, 2018). 

For further information on feedback loops and tipping points please visit the NASA Global Climate Change website.