Ff the maximum reductions on methane and black carbon pollutants were put into place, there would be only a “modest” reduction in average global warming of 0.16 degree Celsius (0.28 degree Fahrenheit) by 2050. It would also prevent the premature deaths of about 2 million per year.
Previous estimates have put the reduction closer to 0.5 C, or 0.9 F.
However both analysis are not in disagreement because the 0.16 degrees is improvement after assuming all of the world poor countries keep getting richer and fixing their air pollution as western countries did.
The newer research used a model that assumed existing trends in pollution control would happen regardless of any additional policies. So as incomes rise and cookstoves get cleaner and put out less black carbon, for example, the base-line model assumed this trend would continue until the end of the century.
They also took into account the fact that generally, as incomes go up, air pollution decreases. This has happened in the United States and Europe, and their model assumed it will happen elsewhere as well.
This means they assume China fixes air pollution from 2014 to 2050 as much as the US did from 1954 to 1990 automatically.
This means they assume that India, Africa and poor countries do solve most of the extreme poverty of less than $1.25/day and people switch to cleaner cookstoves.
I thought the temperature problem was claimed to be a time critical emergency. So it is OK to wait for changes associated with rising incomes over decades to provide a 0.5 degree celsius improvement but not ok to wait for more costly CO2 policy.
Shindell was the lead author of a 2012 paper in Science that estimated around a 0.5 C reduction by 2050 if short-lived climate pollutants were curbed. Shindell’s paper had a different outcome because his model did not automatically assume that future emissions will continue to go down, he said. So in a way, the two studies ask different questions.
“Their question is really, assuming a world where everything economically attractive has already happened, then what extra benefit can you get by targeting these [short-lived] pollutants?” Shindell said. “That’s a really important difference.”
Geoengineering is simple and cheap
The cost to construct a Stratospheric Shield with a pumping capacity of 100,000 tons a year of sulfur dioxide would be roughly $24 million, including transportation and assembly. Annual operating costs would run approximately $10 million. The system would use only technologies and materials that already exist—although some improvements may be needed to existing atomizer technology in order to achieve wide sprays of nanometer-scale sulfur dioxide particles and to prevent the particles from coalescing into larger droplets. Even if these cost estimates are off by a factor of 10 (and we think that is unlikely), this work appears to remove cost as an obstacle to cooling an overheated planet by technological means.
HIGH-FLYING BLIMPS, based on existing protoypes, could support a hose no thicker than a fire hose (above) to carry sulfur dioxide as a clear liquid up to the stratosphere, where one or more nozzles (below) would atomize it into a fine mist of nanometer-scale aerosol particles.
The iron dusting and algae bloom sinking method would be used if you also want to prevent ocean acidification.
Glacier and Ice cap changes are already happening
2) the complete collapse of the entire West Antarctic Ice Sheet is not guaranteed, but it is quite plausible.
3) Continued global warming due to manmade emissions of greenhouse gases will help determine how much sea level rise we will see from Antarctica and Greenland.
A lot of any doom scenarios of sea level rise is not from melting ice, it is from expansion of the ocean from higher temperature.