Famous Paintings Help Study the Earth's Past Atmosphere 126
A user writes "From European Geosciences Union: 'A team of Greek and German researchers has shown that the colours of sunsets painted by famous artists can be used to estimate pollution levels in the Earth's past atmosphere. In particular, the paintings reveal that ash and gas released during major volcanic eruptions scatter the different colours of sunlight, making sunsets appear more red.' The original paper can be found here. In the last 150 years, the sunsets have become redder, likely reflecting increased man-made pollution."
Re:Clutching at straws (Score:4, Informative)
Observational science is by it's nature difficult to repeat, and when discussing changes on a global scale the necessary period of repeatability is by necessity thousands, if not millions of years - which doesn't help us at all. So we're force to extrapolate from small-scale knowledge.
Known - no significant debate among scientists.
- atmospheric CO2, methane, and water vapor all slow the rate of thermal loss into space by making the atmosphere less transparent to IR, with water vapor and CO2 capturing relatively independent parts of the infrared band.
- historical temperature reconstructions show that the combination of solar variation, atmospheric CO2 levels, and ice-cap extents (and a few other much less significant factors) appear to completely explain all major historical thermal fluctuations.
- atmospheric CO2 monitoring shows steadily accelerating increases consistent with known human CO2 emissions
- observations of the atmosphere at all levels show warming consistent with even decades-old models of AGW
- over extremely long timescales the global climate oscillates between two metastable positions - ice ages, with their oscillations between deep freezes and temperate interglacial periods that we're in today, and warm periods (where oscillations seem to be instead between tropics and deserts).
- at some point in every transition from an ice-age to a warm period a runaway process appears to take over, where melting ice caps, permafrost, and oceanic methane hydrates release ever-increasing amounts of greenhouse gasses into the atmosphere in a self-reinforcing cycle, until those reserves have been completely spent and the planet is firmly established in a warm period
Unknown:
- exactly where the "tipping point" is that causes runaway warming to take over (but all our best estimates are that with current fossil fuel consumption trends we'll cross it with ease by the end of the century, if we haven't done so already)
- exactly how fast things can change, and how fast the biospere can adapt - i.e. just how bad the associated mass extinctions from a particular transition might be.
- exactly what sorts of weather changes to expect during the centuries of transition.
If you can throw some additional unknowns out that call into question the reality of the problem we're facing I'd be glad to hear it.
Re:Clutching at straws (Score:4, Informative)
No, there's definitely a consensus on a tipping point - every major climate shift for which we have data shows evidences of a runaway positive feedback loop where atmospheric CO2 levels climb precipitously when leaving an ice age (which we're currently in an interglacial period within), and there's no longer any serious debate about the warming effects of atmospheric CO2. Typically the process lags behind the temperature by several hundred years, this is the first time on record where it would be CO2 changes acting as the forcing factor rather than just positive feedback, but the warming effects of atmospheric CO2 are well understood and accepted. Normally something else happens that sets the planet to warming - orbital shifts increasing solar energy being one of the major ones. but then the CO2 feedback loop kicks in and carries the warming far beyond what the forcing factor alone could have done.
Where there's not a broad consensus is on just how much warming has to happen before the positive feedback loop becomes unavoidable without massive risky geoengineering projects. Historic CO2 emissions (if we cut them to zero today) however are estimated to be sufficient to raise the global temperature by at least a couple degrees C, we're almost there already, and it'll be decades before current atmospheric CO2 levels can fall back to 1900 levels and stop warming the planet further. Meanwhile more realistic estimates based on current fossil-fuel consumption trends are estimating closer to a 4-10 degree change by the end of the century, and most climatologists believe that will be more than sufficient to cross the tipping point. We are after all starting from the position of a nice warm interglacial period.