Global Warming: 1.5°C or less?

One of the most valuable posts I’ve seen recently at RealClimate is this one about the new IPCC Special Report on 1.5°C. The report has a lot to say that’s crucially important. The RealClimate report deals with only a bit of it; its genuine importance is spreading the word about the new report itself.


The various pieces of the report include:

  • The Press Release
  • Frequently Asked Questions
  • Summary for Policymakers
  • Full Report

    I still have to digest this, so I’m not ready to report on the report. But I urge readers to check it out, digest it, and feel free to comment here about it.

    Side note: The requested update on adjusting global temperature for el Nino, volcanic aerosols, and solar variations will be coming soon.


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  • 5 responses to “Global Warming: 1.5°C or less?

    1. Off topic – sorry – but what is your take on the HADCRUT audit by a PhD student?

      [Response: I think that guy was the lead author of a paper I commented on years ago, (https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JD012960). That convinced me that he puts promoting his agenda ahead of science.

      And I have to wonder, if HadCRUT is so terrible, why does it agree so well with others (like Berkeley Earth, which is as close as you’ll find to beyond reproach)?

      It looks to me like nothing more than denialist tripe.]

    2. One thing I was surprised at was the notion that if (hypothetically, of course) emissions went to zero tomorrow, warming is unlikely to exceed 1.5C. Not sure if that is referring to warming by the end of the century but surely there is more warming still to come from atmospheric CO2 already there, and with aerosols masking up to 0.5C of warming, it seems to me that 1.5C is virtually assured, rather than not likely.

      Just reading the Carbon Brief explainer now, so maybe there might be some clarification of this.

      • Ralph Feltens

        This is exactly what I have been wondering, too. If it is true that aerosols are currently masking between 0.4 and 0.9 °C and with temperature equilibrium lagging CO2 concentration, we should have passed the 1.5 °C limit already.

        • John Nielsen-Gammon

          You reach equilibrium above 1.5 C if CO2 concentrations in the atmosphere stay constant. But if you stop all anthropogenic CO2 emissions, the uptake of CO2 by oceans and biosphere will lower atmospheric concentrations quickly enough to forestall 1.5 C.

    3. FWIW, here’s my initial attempt to summarize the SPM (as posted to FB):

      Bottom line conclusions, as I read it:

      1) Limiting warming to 1.5 C will be very difficult, but is not strictly impossible.

      2) It is nevertheless highly desirable, as allowing warming to reach 2 C would be much more damaging to human welfare and prosperity as well as biological and ecological integrity, and would perturb the Earth’s geophysical systems to a significantly greater degree.

      3) To attain a 1.5 C ‘pathway’, emissions need to be lowered dramatically by 2030, and be ‘net-neutral’ by 2050.

      4) Energy system investments needed are estimated at a massive $1.6 trillion per year, or 2.5% of global GDP. This is approximately what the world spends on its so-called ‘defence budget’.

      5) Cooperation across the globe and all levels of society is necessary.

      6) While negative ‘trade-offs’ exist between development goals and some possible 1.5 C pathways, there are many more ‘synergies’, in which such goals as eliminating poverty go hand in hand with reducing emissions.

      Suggestions, critiques and reactions welcome…

      Even the SPM takes some “digestion”, with lots of dense info/verbiage. I haven’t even cracked the report itself yet!