260-270 is the commonly assumed value of the pre-industrial level of co2 in the atmosphere in ppmv.
260-270 is the commonly assumed value of the pre-industrial level of co2 in the atmosphere in ppmv.
what is the commonly assumed value of the pre-industrial level of co2 in the atmosphere in ppmv?
260-270
transgressing one or more planetary boundaries may be highly damaging or even catastrophic, due to the risk of crossing thresholds that trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. the 2009 study identified nine planetary boundaries and, drawing on current scientific understanding, the researchers proposed quantifications for seven of them. these seven are climate change (co concentration in the atmosphere < 350 ppm and/or a maximum change of +1 w/m in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (less than 5% reduction in total atmospheric o from a pre-industrial level of 290 dobson units); biogeochemical nitrogen (n) cycle (limit industrial and agricultural fixation of n to 35 tg n/yr) and phosphorus (p) cycle (annual p inflow to oceans not to exceed 10 times the natural background weathering of p); global freshwater use (< 4000 km/yr of consumptive use of runoff resources); land system change (< 15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of < 10 extinctions per million species). the two additional planetary boundaries for which the group had not yet been able to determine a global boundary level are chemical pollution and atmospheric aerosol loading.
planetary boundaries
ar5 also projects changes in climate beyond the 21st century. the extended rcp2.6 pathway assumes sustained net negative anthropogenic ghg emissions after the year 2070. "negative emissions" means that in total, humans absorb more ghgs from the atmosphere than they release. the extended rcp8.5 pathway assumes continued anthropogenic ghg emissions after 2100. in the extended rcp 2.6 pathway, atmospheric co concentrations reach around 360 ppmv by 2300, while in the extended rcp8.5 pathway, co concentrations reach around 2000 ppmv in 2250, which is nearly seven times the pre-industrial level.
representative concentration pathway