Posted: Dec 02, 2022 7:43 pm
OlivierK wrote:
THWOTH wrote:I guess it depends on what we mean by credible. The 2022 IPCC full Climate Change mitigation report (PDF 105MB) (see Chapter 2) said there is only one credible pathway to limiting warming to 1.5°C (>50% confidence, or; more likely than unlikely) - a truly massive reduction in fossil fuel extraction and use by 2030 accompanied by serious measures to achieve global net zero by 2050. However...

"Global GHG emissions in 2030 associated with the implementation of nationally determined contributions (NDCs) announced prior to COP26 would make it likely that warming will exceed 1.5°C during the 21st century. Likely limiting warming to below 2°C would then rely on a rapid acceleration of mitigation efforts after 2030. Policies implemented by the end of 2020 are projected to result in higher global GHG emissions than those implied by NDCs. (high confidence)."

IPCC AR6 Summary for Policymakers Headline Statements B.6

In short, what isn't credible are governments' policy commitments to reducing global GHGs, and the longer they leave it the harder it becomes.

So we have to understand what credibility is here, and not let policy makers or the media etc conflate it with possibility.

If we don't reach net zero until 2050, then we have 3 more decades of rising CO2e, which translates to 3 more decades of warming at or above current rates, which would take us to 1.7C, or possibly more. Then even if we achieve net zero in 2050, that doesn't stop warming, because we'll still have 400ppm+ C02/500ppm+ CO2e in the atmosphere, which means we're headed for close to another 1C by 2100. It's wishful thinking to suggest that we can have lower than current rates of warming with higher than current GHG levels.

We're not in disagreement here. Everything you say is true: if we stopped emitting GHGs today we're still looking at a 0.3-0.5°C increase in global temperatures over the next 60 or so years due to the longevity of CO2 in the atmosphere combined with with factors like the loss of cooling aerosols that accompany GHG emissions and the heat-battery effect of the oceans. The risks of ecological and climatic tipping points tipping over continue to rise with temperatures, and the likelihood of the system reaching a new, hotter steady state increases. That 0.3-0.5°C increase includes the slight offset created by the deep oceans' absorption of CO2, which means that the total warming by the end of the century would be about 0.2-0.3°C lower than if the amount of CO2 in the atmosphere remained constant. With global mean temps around 1.1°C over pre-industrial levels, stopping GHG emissions tomorrow is still more than likely to overshoot the 1.5°C max measurement by the end of the century. But...

But 1.5 is only a measurement marker. It's not like everything is fine below 1.5 and bad over it. Keeping temps below 1.5°C is not a target. Every reduction in emissions reduces the energy capacity of the system and thus reduces eventual peak temperatures, even given the long time-scales in and inertia of that system. But what did Marilyn Strathern say, "When a measure becomes a target, it ceases to be a good measure."?

Which again brings me to my point about the 'credibility' of limiting global temps to 0.2-0.3°C above current levels, i.e. to 1.5: a massive reduction in fossil fuel extraction and use to 2009 levels by 2030 and a concerted and rapid effort to achieve global net-zero by, at the latest, 2050. I'm put in mind of the school climate protestors slogan from 2019: "System change, not Climate Change!" This, it seems to me, is the discussion we're not having in responses to the 'credibility' problem: while we're collectively focussing, and/or being focused, on the 'no credible pathway to 1.5' statement we're not focussing on fundamentally changing the social, economic, and political systems which have brought us to the very edge of the precipice.

So why are we not talking about rapidly shifting our societies and economies to 100% renewable energy, why are we not hearing compelling arguments for investing in recycling/reclaiming even more energy from what we throw away, considering the practicalities of undertaking massive reforestation projects, or outlining the significant changes in land and water use or agricultural practices we can adopt, for example? I lay this one squarely at the feet of governments.