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Vostok 800 Year Lag: Thought Experiment?

Imagine you are a climate scientist living 4 centuries after the temperature has continued to fall while CO2 has still been on the increase - i.e. half-way through an 800 year lag.

Imagine further that during your lifetime, that continues to happen and, if you had a crystal ball, you would see that it would continue happening for the next dozen or so generations of climate scientists.

Would you put your hand on your heart and say that increasing CO2 would necessarily cause warming when you have 400 years of empirical evidence that shows the opposite?
  • Answers
  • An inconvenient truth... I'm sure lots of climate scientists wished those Vostok ice cores would simply disappear. It is undeniably true that CO2 is a greenhouse gas. An increase in concentration will exert an upward forcing on terrestrial temperature. However, the historical record suggests the effect of CO2 is pretty weak in the the whole picture. A better conclusion is that other primary and secondary factors exert a much greater influence than CO2.
    juana · 1 1
  • The same effect can have multiple causes, and assuming without evidence that an effect is being produced by a single cause is foolish.

    Climate scientists can estimate the magnitude of various perturbations to the climate system: change in solar radiation, change in albedo, change in greenhouse gas concentration, etc. If asked whether a certain perturbing factor will bring about warming or cooling requires estimating the magnitude of the effect. If CO2 is increasing and other factors remain the same, the climate will warm.

    That there is a lag between temperature and CO2 is no surprise, because it belongs to a "slow" feedback process. While the ice cores may have shown CO2 lagging temperature in the past, when the primary driver may be orbital, in fact CO2 is LEADING temperature in the ice core data at present. In fact, there was a paper back in 1990 by Lorius, Hansen and others that pointed out that lags are to be expected.
    Dirac · 3 2
  • Not even today would any climatologist say that in general, CO2 will "necessarily" cause warming. Other factors can exist to cause a stronger negative radiative forcing.

    But anyway you have it backwards. The lag is not that CO2 rose and it took 800 years for temperatures to rise, it is that temperatures rose and then CO2 rose. Which is not terribly surprising considering there are few natural mechanisms that can cause CO2 to rise. Rising temperatures are the main way in the last few hundred thousand years of Earth's history. CO2 was a positive feedback to this warming. It was both an effect and a contributor.

    Fast forward to today, we have the (temperature independent) massive scale combustion of fossil fuels, an unprecedented event that was impossible on this scale before humans. To demand that an analog to this must exist in the (relatively recent) past is to demand the impossible. Which probably means it's not a very good argument.
    David · 1 3