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2015 had the highest global temperatures on record, as discussed in this question, beating the last record ... in 2014.

enter image description here

Are we now in a runaway climate change regime, where zero further human impact on the environment will not prevent change to the equilibrium state of the Earth's atmosphere?

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Because two consecutive years == evidence of runaway effects? – DSKekaha Jan 26 at 18:14
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@DSKekaha two consecutive years supported by a graph showing a clear upward trend for the past 65 years, to be fair. Though even looking at temperatures over 100 years is not enough of a context, IMO. Which is unfortunate, because time scales over 100 years don't make a lot of innate sense to life forms that only live 100 years. – TylerH Jan 27 at 19:17
up vote 23 down vote accepted

Runaway climate change is, given our current state of knowledge, only something that could be confirmed in historic context - in the rear-view mirror. Inconveniently, there's likely to be a much-diminished version of human civilisation around to observe it, if and when it does happen.

In other words, it's too early to tell if we've passed a catastrophic tipping point.

We don't know what the equilibrium state of the Earth's atmosphere is. It will take 30 years for our current stock of GHG emissions to fully show its effects: and we'll be continuing to release GHGs for a while, so the equilibrium will continue to change.

But it's worth bearing in mind what we can do, when we really have to; World War II saw massive realignments both in industrial production and in expectations within a very short space of time: after decades of delay, it now seems likely that decarbonisation will require at least a similarly fast and large industrial realignment; and it is possible.

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What exactly do you mean by It will take 30 years for our current stock of GHG emissions to fully show its effects? Clearly some effects, such as sea level rise, take much longer. – gerrit Jan 26 at 11:48
    
@gerrit given we need about 30 years of weather to see the climate clearly, then that's the amount of time it will take to get a good measure of the size of the forcing. Equilibrium is a different matter - that could take centuries (if indeed it ever actually happens on a planet with life). – EnergyNumbers Jan 26 at 19:04
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@gerrit: Because CO2 is "the gift that keeps on giving" (to borrow a phrase). Adding X amount of CO2 this year doesn't just turn up the temperature this year, it increases the rate at which solar energy is captured, and thus causes a temperature increase that goes on for perhaps decades or more, until a new equilibrium is reached. – jamesqf Jan 26 at 19:36
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@jamesqf Sure. What I found confusing, however, is the phrase to fully show its effects — after 30 years it is just beginning to show its effects. To fully show its effects we need far more time. – gerrit Jan 26 at 19:41

We might have some wiggle room, or might be past the tipping point, but we do not have enough info to be sure. It depends of unknown strength of known positive feedback loops, like:

  • melting permafrost releasing potent greenhouse gas methane
  • drying permafrost bogs release CO2 or even burn
  • warming ocean might release https://en.wikipedia.org/wiki/Methane_clathrate (methane ice) - remember Deepwater Horizon?
  • and likely more.

What we are certain is, the more CO2 we release, the closer we will get to the tipping point, after which different climate might stabilize, close to PETM, the onset of which has been linked to an initial 5 °C temperature rise and extreme changes in Earth’s carbon cycle. It lasted about 170K years. Alligators in Alaska, ocean level 270 feet (90 m) higher), lots of arable land and many big cities (London, New York, Shanghai) submerged, etc.

How big human population such different planet can support? We don't know, but I am not sure we should try to find out the hard way.

Or another way to formulate this: Can Earth support intelligent life? We don't know, we are about to find out.

One solution for Fermi Paradox ("Where is everybody?") is that technological civilizations like ours destroy their environment and go extinct.

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+1 for last 2 lines. Nice answer. – fractalspawn Jan 26 at 22:34
    
@fractalspawn but unrelated to the question. – Michael Jan 27 at 9:00
    
@Michael: true, but it was an interesting relation to another question of mine and I thought that made it special beyond the bare minimum. – fractalspawn Jan 27 at 17:59

According to satellite datasets (RSS), last year was not even close to being warmest ever. The warmest year still is 1998, and the second warmest is 2010.

It is beyond me why NOAA or NASA GISS (who use NOAA's data), ignore satellite measured temperatures, which give far more accurate and complete picture of the world's global temperature.

RSS satellite measured global temperature anomaly

Below is a map of the coverage of the data NOAA and NASA GISS uses. I find it hard to believe they can tell us the global temperature in sufficent accuracy to claim whether some individual year was some hundredths of degrees warmer than some other.

There are almost no data on the oceans, Antarctis, Africa or the north pole. Just extrapolating the little data they have over thousands of kilometers just isn't going to produce accurate enough data to detect such a small changes.

This in mind, I'd rather turn to the satellites, which show nothing to be worried about.

global temperature coverage

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See earthscience.stackexchange.com/questions/6820/… for some information on the datasets derived from the MSU instrument (uah and rss ingest the same data but process it differently) and there is mention that the instrument is sensitive to ENSO conditions. – casey Jan 27 at 21:57
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There's actually good agreement between satellite and surface measurements. The RSS graph you posted seems less dramatic because (1) it only goes back to 1979, not 1880 (2) the data aren't smoothed so there's more noise and (3) the temperature is in °C, not °F. If we plot the RSS data and NASA's GISS data on the same scale, both the year-by year variation and the overall trends are similar (and that goes for HADCRUT and UAH too). – Pont Jan 28 at 20:37
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To back up your claim of "almost no data on the oceans", you've added a picture explicitly labelled "land-only temperature". A land-only data set does indeed have rather poor ocean coverage, but the NASA and the NOAA analyses both include extensive ocean data. – Pont Jan 28 at 21:02

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