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Maybe they know sources like these: https://en.wikipedia.org/wiki/Geologic_temperature_record https://en.wikipedia.org/wiki/Geologic_temperature_record https:

• shoo 11y ago
  Sure, I guess it depends on your perspective. It's good to look at things over a geological time scale, and to have a broader perspective than the human species, or human civilisation. Regarding very recent climate change, maybe it is easier to focus on the subset of the timescale that has supported human civilisation -- say, the last 10 thousand years. You'll note the temperature was relatively stable during most of this time. Interesting! If you look really closely at the right side of the second graph you posted - over the last hundred years or so - you'll notice the temperature is shooting up. It's a bit hard to see on that graph as the change is happening so quickly relative to geological time scales. If you look at a graph that focuses on the last 100 years, a trend is easier to spot: http://climate.nasa.gov/vital-signs/global-temperature/ http://climate.nasa.gov/vital-signs/global-temperature/ I've had a go at drawing a regression line by hand myself: http://imgur.com/ixnuDX4 http://imgur.com/ixnuDX4 Hypothetically, supposing this strange recent warming trend were to continue, it is plausible that by the end of the century our planet might be experiencing environmental conditions never previously encountered by our species, and indeed not experienced by the planet for the last 5 million years or so. Perhaps not much interest in a geological sense, nothing to see here, but perhaps from a shamelessly anthropocentric perspective we might have some cause for concern.
  • NumberCruncher 11y ago
    In time series analysis picking the right time scale is everything. Let´s do a small experiment: One hot summer day I measure the temperatures in my home town between 6:00 and 12:00 and I get some data like this: 6:00 - 10 C ... 12:00 - 32 C Now I make a small regression analysis and say that at 24:00 we are going to die a painfull death because the temperature will raise with a probability of 95% to 70-80 C. In this case I obviously forgot about the periodicity of daily temperatures. The global temperatures have a periodicity of ca. 400.000 years. Therefore any analysis based on a time period shorten than 400k years has the same problems as my summer experiment. >> the end of the century our planet might be experiencing environmental conditions never previously encountered by our species - 2*2 might be 5... - at the end of the century I will be dead and "our species" will be only one of million other species. For example the dinosaurs loved the 12 C more and had a happy life on the ice-free antarktis a couple of million years ago...
    • shoo 11y ago
      So what are you arguing? That it is not possible to come to any conclusion regarding the earth climate without first waiting some multiple of 400k years? That it's not possible to separate a long-term 400k-year temperature variation trend from short term temperature variations due to unusual/novel forcing conditions? The thing your hot summer day analysis is missing is a clear physical explanation that explains why the trend you are observing is occurring, and why it is going to keep occurring until 24:00. We probably don't even need the explanation to be 100% accurate for this to be useful, merely accurate to a first or second order approximation. I believe "we" [1] have got enough understanding of the earth system to make some pretty reasonable inferences on limited data. Certainly not complete understanding, but it's not like a bunch of people are merely using e.g. some deep learning voodoo to perform regression on climate data and have literally no idea what the underlying physical processes involved might be. Here's an example of my own: consider the geoengineering "launch a bunch of disk-shaped satellites to block x% of the sun's light from hitting the earth" thing. Let's ignore the fact that this isn't necessarily a great idea, and assume someone has gone ahead and done it. We can predict with reasonable confidence what the primary consequences of this intervention will be: less light from the sun hits the planet, planet's mean temperature lowers a bit. This behaviour won't be at all explainable as part of a 400k year planetary periodicity. [1] not in the sense of you or i, necessarily, but the relevant scientists in the field.
• steve1011 11y ago
  but don't bring up anything like that in casual conversation lest you get shouted down by the ignorant majority.