Climate projections don’t include volcanic eruptions.

Posted: May 31, 2017 by tallbloke in solar system dynamics

chile-volcanoIn today’s climate models, volcanic eruptions are thought to be a major negative forcing (they have to be, to counteract the over-egged positive forcing attributed to CO2), but the ‘projections’, ‘forecasts’, ‘scenarios’ (anything but predictions!) don’t include any volcanic eruptions.

That being the case, why would we take any notice of model output which ‘projects’ large warming in the future?

Judith Curry:
Under the RCP8.5 scenario, the CMIP5 climate models project continued warming through the 21st century that is expected to surpass the ‘dangerous’ threshold of 2°C warming as early as 2040. It is important to note that the CMIP5 simulations only consider scenarios of future greenhouse gas emissions – they do not include consideration of scenarios of future volcanic eruptions

Thayer Watkins
There is a distinction between forecasts and projections. A forecasting model or method attempts to predict what actually happens on the basis of information known before it happens. A projection, on the other hand, says what will happen under a set of assumptions. Some of the assumptions are reasonable and necessary such as that there will be no major volcanic eruptions during the period over which the projections are made. Such assumptions have to be made for forecasts as well.

Future scenarios do not include unknown events – for example, volcanic eruptions or changes in solar forcing. These effects are believed to be small in comparison to greenhouse gas (GHG) forcing in the long term, but large volcanic eruptions, for example, can exert a substantial temporary cooling effect.

The Guardian
The measured surface warming has been about 0.13°C less than the average of model simulations since 2000. The estimated volcanic cooling from this new paper (0.05–0.12°C), not included in those climate models, could account for most of that discrepancy.


  1. ren says:

    Juno reached Jupiter and began its first orbit on 4 July last year. It travels around the gas giant once every 53 days, with 33 planned pole-to-pole circuits in all, encircling the entire planet bit by bit.

    Each pass takes just two hours, with the journey consisting of a trip over the north pole, round the planet, over the south pole, and then back out into space. The next pass will be in July, with investigators targeting the Great Red Spot.

    Besides polar cyclones, Juno has spotted white ice caps on Jupiter – frozen bits of ammonia and water. Juno has also detected an overwhelming abundance of ammonia deep down in the atmosphere, and a surprisingly strong magnetic field in places – roughly 10 times greater than Earth’s.

    Juno’s findings are “really going to force us to rethink not only how Jupiter works,” said Bolton.

    Amazing pictures show cyclones swirling above Jupiter’s poles.

  2. stpaulchuck says:

    or cosmic ray cloud formation, or solar variability, or orbital changes, or axial precession, etc,. etc.

  3. so2 emissions from volcanic eruptions do and will cause cooling.

  4. McNeil says:

    “That being the case, why would we take any notice of model output which ‘projects’ large warming in the future?”

    And you shouldn’t. As far as I am aware, there are significant technical reasons to suspect the models are based on incorrect conclusions of the fundamentals that underpin them. That is something I learned here and elsewhere that they are questioned. FWIW, my take on one of those fundamentals can be found here;

  5. tom0mason says:

    “…the ‘dangerous’ threshold of 2°C warming…”
    Another nonsense from the pit of fools!
    Just look at the planet’s history and note when all of nature including humans flourished…