Greenhouse emissions must peak next year and rapidly drop thereafter to save us:
https://www.cnn.com/2019/05/23/opinions/one-year-to-tackle-climate-change-opinion-mountford/index.html
Where ever this thread goes, the title is wrong. We do not have 1 year to peak and then decline our CO2 emissions to avoid exceeding 1.5 - 2 C rise in global temperature. The underlying article is here:
https://www.nature.com/news/three-years-to-safeguard-our-climate-1.22201Based on a 600 GT limit, the annual rate of decline in fossil fuel use required to do that is 11.3% each and every year. Based on the 800 GT limit, the annual rate of decline required is 7.2% each and every year.
As I previously noted, country GDPs are directly correlated with fossil fuel use. There is a small leeway there for conversion to non fossil sources. There are serious and severe limits as to just how fast that conversion can happen. Over the next decade, that is likely limited to about 3% per year with great effort. That is also about the rate of growth of economies. So, that is essentially consumed in the demanded societal growth as we add population.
Anything beyond about 3% negative change in fossil fuel use in the near term requires an actual decline in the economy. That is negative growth. Economies can survive limited negative growth for a brief period without collapse. They cannot long survive with negative growth rates of 3-5% per year. They simply cannot achieve and sustain 7-11% negative growth rates without civilization and societal collapse. Clearly, no one will volunteer for that.
What this then implies is that even with broad support and agreement, and with maximum effort, we might achieve and sustain a negative 3% rate as we convert away from fossil fuels.
That implies that we might have succeeded, if we had everyone on board (which we clearly don’t) and we applied maximum effort (which we are clearly unwilling to do), if we had started no later than about 2005.
So, viewed one way we do not have 1 year to prevent exceeding 1.5-2 C rise. We passed that point 15 years ago. Viewed another way, we will not meet and cannot meet the 1.5-2 C target. Realistically, we will be very lucky not to exceed 4 C provided we all agree and get on board with maximum effort - now. But since that clearly will not happen in the next half dozen years at least, we will inevitably blow through 6 C.
However, once we pass 3 - 4 C, it is almost certainly inevitable that we will have triggered multiple fearsome positive feedbacks that drive us all the way to hot house Earth conditions at +~10 C with the inexorable loss of both the arctic and Antarctic ice sheets and a sea level rise of ~280 feet. We should also then see a dramatic rise in atmospheric pressure. Initially we may see a fall in oxygen content to as low as 14% and the die off of virtually all large animals if the past is any indication. That happens as the oceanic flows breakdown, the atmospheric circulation reorganizes into an equable earth pattern, and the oceans go largely anoxic. We might avoid that. But if we do it won’t be because of skill. It will be pure dumb luck.
Over time, as the ecosystems stabilize in hothouse conditions, the interior of large continents may become scorching hot dead zones. Oxygen levels may once again rise to ~35% which will support massive fires during heavy rainfalls.
That is an earth quite unlike anything mankind has ever known.
Sam
