To suggest that, is to distort the whole idea.
350 ppm is the level suggested by James Hansen et al, when CO₂ was already at [font size=5]385[/font] ppm. The idea is not about holding the line at 350 ppm, it is about decreasing CO₂ levels to 350 or lower.
https://arxiv.org/pdf/0804.1126
…
Abstract: Paleoclimate data show that climate sensitivity is ~3°C for doubled CO₂, including only fast feedback processes. Equilibrium sensitivity, including slower surface albedo feedbacks, is ~6°C for doubled CO₂ for the range of climate states between glacial conditions and ice-free Antarctica. Decreasing CO₂ was the main cause of a cooling trend that began 50 million years ago, the planet being nearly ice-free until CO₂ fell to 450 ± 100 ppm; barring prompt policy changes, that critical level will be passed, in the opposite direction, within decades. If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO₂ forcings. An initial 350 ppm CO₂ target may be achievable by phasing out coal use except where CO₂ is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO₂ is not brief, there is a possibility of seeding irreversible catastrophic effects.
…
Our current analysis suggests that humanity must aim for an even lower level of GHGs. Paleoclimate data and ongoing global changes indicate that ‘slow’ climate feedback processes not included in most climate models, such as ice sheet disintegration, vegetation migration, and GHG release from soils, tundra or ocean sediments, may begin to come into play on time scales as short as centuries or less⁷. Rapid on-going climate changes and realization that Earth is out of energy balance, implying that more warming is ‘in the pipeline’ ⁸, add urgency to investigation of the dangerous level of GHGs.
A probabilistic analysis ⁹ concluded that the long-term CO₂ limit is in the range 300-500 ppm for 25 percent risk tolerance, depending on climate sensitivity and non-CO₂ forcings. Stabilizing atmospheric CO₂ and climate requires that net CO₂ emissions approach zero, because of the long lifetime of CO₂
10,11.
We use paleoclimate data to show that long-term climate has high sensitivity to climate forcings and that the present global mean CO₂, 385 ppm, is already in the dangerous zone. Despite rapid current CO₂ growth, ~2 ppm/year, we show that it is conceivable to reduce CO₂ this century to less than the current amount, but only via prompt policy changes.
…
Hansen el al fully anticipated levels would rise about 400 ppm. The idea was to keep CO₂ levels from
remaining that high too long.
Everyone who cites the number “350” should understand its intent.
= new reply since forum marked as read
