This fourth and final post reporting on the recent Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report Summary for Policymakers looks at limiting future climate change. The full document is available here to read.

“Every tonne of CO₂ emissions adds to global warming”

IPCC Sixth Assessment Report, August 2021

The amount of global warming depends on the cumulative anthropogenic CO₂ emissions (there’s around a 0.45°C rise for every 1000 GtCO₂ cumulative emissions*). Reaching at least net zero CO₂ emissions is a requirement to stabilise the human-induced global temperature rise. Strong, rapid, and sustained reductions in greenhouse gas emissions (CO₂ to within a carbon budget) and methane (CH4), as well as reduced aerosol pollution and surface ozone, will limit global warming and improve air quality. Anthropogenic CO₂ removal at a scale exceeding anthropogenic CO₂ emission has the potential to lower atmospheric CO₂ concentration, lower surface temperature, and reverse surface ocean acidification.

Even if a global net zero CO₂ emission is achieved, other climate changes would continue in their current direction for decades to millennia.

Associated measures to reduce the spread of COVID-19 in 2020 led to emission reductions with detectible effects on air pollution. However, with strong reduction of greenhouse gases, the air quality guidelines as specified by the World Health Organisation would still not be achieved in many already polluted regions. There is the need to also focus on the reduction of air pollutant emissions.

* Making sense of the cumulative emissions. 1000 GtCO₂ is 1 000 000 000 000 tonnes of carbon dioxide. That seems large but when we consider that the world population is nearly 8 billion (8 000 000 000) then we can see that this number is just 125 tonnes per person to raise the temperature by 0.45°C. And those 125 tonnes are cumulative – that is they add up – looking at our own carbon emissions (see here how to) we can see that our current lifestyles are forcing up the temperature. The cumulative emissions between 1850 and 2019 are estimated to have been 2400 GtCO₂ and the carbon budgets remaining (from the start of 2020) to stay within 1.5°C, 1.7°C and 2.0°C are around 500 GtCO₂, 850 GtCO₂ , 1350 GtCO₂ respectively. Per person that is around 60 tonnes left, 100 tonnes left and 170 tonnes left respectively.

To read the first post on the current state of the climate click here

To read the second post on the future climate click here

To read the third post on climate risks and adaptation click here