{"id":263,"date":"2007-10-23T16:49:09","date_gmt":"2007-10-23T20:49:09","guid":{"rendered":"http:\/\/blogs.edf.org\/climate411\/2007\/10\/23\/longterm_emissions\/"},"modified":"2007-10-23T16:49:09","modified_gmt":"2007-10-23T20:49:09","slug":"longterm_emissions","status":"publish","type":"post","link":"https:\/\/blogs.edf.org\/climate411\/2007\/10\/23\/longterm_emissions\/","title":{"rendered":"We Still Have Time to Avoid Dangerous Climate Change"},"content":{"rendered":"

This post is by James Wang, Ph.D.<\/a>, a climate scientist at Environmental Defense.<\/i><\/p>\n

A study by Weaver et al., published this month in the journal Geophysical Research Letters<\/i>, reports that "All emission targets considered with less than 60% global reduction by 2050 break the 2.0\u00b0C threshold warming this century\u2026." (They mean 2.0\u00b0C above the pre-industrial temperature, equivalent to 2.3\u00b0F above today’s temperature. For more on threshold temperatures, see “How Warm is Too Warm?<\/a>“) Even more disturbing, they say, "Even when emissions are stabilized at 90% below present levels at 2050, this threshold is eventually broken."<\/p>\n

That makes all our efforts seem hopeless. But are they right? In a word, no. Here’s why.<\/p>\n

<\/p>\n

Weaver\u2019s pessimistic results arise from two assumptions, with the first being especially crucial: <\/p>\n

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  1. CO2<\/sub> emissions are held steady after 2050, and<\/li>\n
  2. Atmospheric levels of all non-CO2<\/sub> greenhouse gases and aerosol particles are held steady at current levels<\/i>.<\/li>\n<\/ol>\n

    These assumptions are downright peculiar. There is no reason to expect that CO2<\/sub> emissions reductions would not continue after 2050, and all of the major policy options on the table would require reductions of other greenhouse gases, as well.<\/p>\n

    More realistic assumptions show that warming can stay below the 2.3\u00b0F threshold. In Avoiding Dangerous Climate Change<\/i> (Schellnhuber et al, eds.), studies by Meinshausen and others calculate a roughly 50 percent likelihood that warming can be kept below 2.3\u00b0F if the atmospheric concentration of greenhouse gases is stabilized at 450-500 parts per million (ppm) equivalent CO2<\/sub>. To achieve this result requires that:<\/p>\n