The IPCC Assessment Report 6– The physical sciences bases is full of bad news for humanity and a lot of science highlighting and supporting why we need to take this bad news seriously. It gives us more and more evidences (as if we did not already have enough!) that the global warming is caused by humans and every tonne of CO2 emission contributes to global warming.
These are not new things, even the first IPCC report had highlighted this. What is new is that our understanding of the science behind the climate change causes and impact has evolved. What is new that this report now adds the word ‘unequivocally’ and this is agreed by more than 190 countries who are part of IPCC. We now have more data and studies (report findings are based on more than 14000 studies!) confirming what scientists have been saying for more than three decades. If these cannot make you believe this obvious thing then nothing will.
The other thing that scientists have established that global warming beyond 2 degree (compared to the pre-industrial era) is apocalyptic. So we all are trying to keep the global warming below 2 degrees and desirably below 1.5 degree if we can. In 2015, 195 countries adopted a legally binding international treaty on climate change, known as ‘the Paris Agreement’ (https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement), to limit the global warming below 2, preferably 1.5 degrees celsius compared to pre-industrial levels.
The bad news is that there is a very little hope that we would be able to meet the 1.5 degree scenario (in simple words- the possibility that we would reduce the emission to such a level that global warming would not be more than 1.5 degree from pre-industrial era). As per the updated estimates of the report, we only have a carbon budget (the amount of CO2 we can afford to emit) of 460 bn tonnes to keep the global warming below 1.5 degree (well to be exact we have only 50 per cent chance of keeping the global warming below 1.5 degree if we can emit below the 460 bn tonnes. You will note that unlike the climate change deniers and anti-climate change lobbyists who talk in absolute certainties, scientists talk in probabilities and with evidences). This is around 11-12 years of carbon emission at the existing rate of carbon emission (in 2020 we emitted 34 bn tonnes of CO2) every year (unless we drastically change this!).
The following table in the report makes it clear that there is only on scenario SSP1-1.9. (SSP1-1.9, SSP stands for Shared Socioeconomic Pathways. SSP1 is the scenario and 1.9 indicates the Radiative Forcing. There are five SSPs, with SSP1 being the best case scenario where we adopt the a growth trajectory that has very low challenges to mitigation and adaption and focuses on sustainable development and SSP5 is the pessimistic scenario where we have fossil fuel led development and high challenges to mitigation and adaption.)
Once we go beyond the 1.5 degree, at 2-degree itself, we are going to witness increased frequency of extreme temperature events, intense rainfalls (heavy precipitation) and agriculture and ecological droughts. And, these are going to further increase the intensity and complexity of many manifestations of climate change impacts.
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