Why 2050 is too late

In 2018 the Intergovernmental Panel on Climate Change produced a report on 1.5 C of warming.  This is considered a level of warming that is 50% likely to trigger a tipping point beyond which further warming will be beyond human control. According to the report:

"Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate"

Unfortunately, that's been taken by our politicians to mean we've got until 2050 to zero our emissions. Let's see if this is true:

According to section C.1.3

"C.1.3. Limiting global warming requires limiting the total cumulative global anthropogenic emissions of CO2 since the pre-industrial period, that is, staying within a total carbon budget (high confidence). By the end of 2017, anthropogenic CO2 emissions since the pre-industrial period are estimated to have reduced the total carbon budget for 1.5°C by approximately 2200 ± 320 GtCO2 (medium confidence). The associated remaining budget is being depleted by current emissions of 42 ± 3 GtCO2 per year (high confidence). The choice of the measure of global temperature affects the estimated remaining carbon budget. Using global mean surface air temperature, as in AR5, gives an estimate of the remaining carbon budget of 580 GtCO2 for a 50% probability of limiting warming to 1.5°C, ...

Great. So we've got $580/42 \approx 14$ years left if we carry on as we are. Unfortunatey the report was released 2 years ago, and emissions have risen since then, so we're looking at more like 11 or 12 years now... if we can stop emissions rising yet further.

Are there any other caveats?:

... Uncertainties in the climate response to CO2 and non-CO2 emissions contribute ±400 GtCO2 and the level of historic warming contributes ±250 GtCO2 (medium confidence). Potential additional carbon release from future permafrost thawing and methane release from wetlands would reduce budgets by up to 100 GtCO2 over the course of this century and more thereafter (medium confidence)."

This means that in the worst case we need to subtract $400+250+100$ from that 580 GTon, and then another 84 for the two years that have passed. Oh dear: that would mean that we passed the tipping point around 6 years ago!

But let's not be so pessimistic: the uncertainties for climate response and historic warming can go either way - so let's ignore them. That allows us to work out when we would exceed the remaining budget under various different scenarios. Here goes

All you need to be able to work this out for yourself is
to know how to solve a quadratic equation!

Top left shows what will happen if we do nothing (other than stop emissions rising further).  In this scenario we bust our budget in 2031.  The next panel - top right - shows what will happen if we reduce to zero by 2050, in a straight line.  Essentially this would give us a further 4 years and we would bust our budget in 2035.

Bottom left is for a target of 2040.  Things are a little better here... if we assume that the permafrost releases zero methane then we are okay - we avoid 1.5C and hence achieve a less than 50% chance of triggering a tipping point!  Unfortunately we cannot ignore permafrost thawing because, unlike with the other uncertainties, the carbon dioxide equivalent of this effect must be positive.  If we assume 100GTon CO2e from permafrost thawing then in the 2040 scenario we exceed our budget ... in 2034.  

Only with a target of 2030 do we avoid 1.5C if we take permafrost release into account.

To put this into context, forecasts for 2020 predict a drop in CO2 emissions of anywhere between 4 and 8%, with the drop attributed entirely to the Coronavirus lockdown and not at all due to political efforts to reduce emissions.  However, anything less than a drop of 10% (of today's emissions) every year until 2030 is equivalent betting the future of humanity on the toss of a coin.

And this is according to the IPCC, which is subject to political pressure from member nations, and is considered quite conservative in the scientific community.  Individual scientists will tell you that the IPCC have massively underestimated the effects of climate response, for example, Peter Wadhams, ex head of the British Antarctic Survey claims that the (now inevitable) loss of arctic sea ice will cause a warming effect equivalent to 25 years' worth of anthropogenic CO2 emissions.

The facts are now clear.  We've left it too late for incremental change and only a revolution can save us.  But this simply will not happen until our media start doing their jobs and lead with the climate crisis every day until the crisis passes.