ABCs are made up of emissions and particulate matter released from the burning of fossil fuels and biomass. This particulate matter reduces the amount of sunlight hitting the earth’s surface in two ways. First, some particulates, such as sulfate, act as reflectors that bounce sunlight away from the earth. Second, other particulates, such as black carbon in soot, trap and absorb light before it hits the ground. The effect of these ABCs has been quite pronounced over the last quarter century: Guangzhou has seen a 20% reduction in sunlight since 1970.
Complicated Climate Effects
The effect of ABCs on the climate is quite complicated. The sulphates that reflect sunlight away from earth actually keep the climate cooler than it otherwise would be. In fact, the report estimates that ABCs may have reduced GHG-caused rises in global temperature by between 20 and 80%! This may help explain why eastern China has actually seen average temperatures decline over the past decade, globally the warmest on record.
The idea that pollution actually helps moderate climate change is pretty incredible. The scary thing is, though, as China continues to develop and eventually begins to aggressively reduce local pollution and the associated sulfates, this may actually increase the global warming effect of GHGs. As the report notes:
Simply tackling the pollution linked with brown cloud formation without simultaneously delivering big cuts in greenhouse gases could have a potentially disastrous effect.But on the bright side (I’m really on today), if China were able to eliminate ABCs, presumably sunlight would return to pre-1970 levels and increase 10-25%. This would likely cause solar power generation to be more effective. SOM, designers of the Pearl River Tower, mentioned that the lack of strong sunlight somewhat impeded their energy generation from the PV systems. So, this brightening effect would seem to reduce GHG emissions by making solar generation more effective.
In other climate related news, the World Meteorological Organization (WMO) released their latest Annual Greenhouse Gas Bulletin, which shows that atmospheric CO2 concentrations have continued to rise, and are now at 383 parts per million (PPM). CO2 is by far the most important GHG, accounting for about 90% of radiative forcing (link to wiki or something) in recent years. This level of CO2 is particularly disturbing, as it is already higher than the 350 PPM level that NASA scientist James Hansen calls safe (PDF). Climate scientists are engaged in ongoing debate over what atmospheric CO2 level humanity ultimately needs to aim for (see Joe Romm's ClimateProgress blog for more), but the “safe” range will probably be somewhere between 350 and 450 PPM. The world added 2 PPM to the atmosphere last year, and this number is set to rise to 3 PPM annually as emissions continue to grow. This doesn’t give us much time, but I remain optimistic we can avoid the worst effects of climate change if we get our act together soon.
BTW Charlie- if you're reading, this title was not meant to be a rip-off of your recent post "The ABCs of SEDs"...