[dragonwriter]

> My point was if we're saying something is changing at an alarming rate - then the natural question would be what is a normal rate

Danger can be alarming even if on a wide enough time window its not unusual (that the current warming is unusual on any timeline as narrow as, say, “the history of human civilization on Earth” is clear, though.)

[Alupis]

> the history of human civilization on Earth

We actually don't even know that much. Written records only go back so far, and the ability to measure say temperature in any relatively accurate way is a modern invention. Majority (or all?) dependable temperature data starts around 1900...

If it's alarming because within recent human history something is changing quickly - well fine, but that's not how this stuff is being offered.

Even so, the question remains - is it an actual problem? Has human activity created the change, accelerated change, or was the change inevitable (ie. caused by polar reversal)? These are difficult questions to answer absolutely.

Even if we could answer these questions confidently - should we do anything about it? Would our actions to "combat" climate change cause unknown side effects? Probably... how do we square those potentially negative impacts with the "good" changes we've created?

It's pretty complicated. Anyone offering absolutes or hysterics should be taken skeptically in my opinion.

[paisajerelicto]

Wikipedia has a pretty good summary of climate proxies (1). E.g., tree rings, coral, pollen, forams/ostracods/coccolithophores/radiolaria, varves/lake sediments, water isotopes, membrane lipids, etc. See also Wikipedia article re. temperature proxies, 'Paleothermometer'(2).

So, yes, we do have proxies for past climates and rates of change. Yes, there have been some pretty spectacular excursions in climate (e.g., the entry into the Younger Dryas happened within 50 years, and brought the climate of Nome, Alaska to San Francisco). However, I saw a research presentation that compared the rate of change in the Paleocene-Eocene Thermal Maximum (PETM) to Homo sapiens' injection of CO2 into the atmosphere, and the rate of our injection beat the PETM, and it may very well exceed any such injection in Earth's history (the latter is my speculation).

(1) Proxy (climate), https://en.wikipedia.org/wiki/Proxy_(climate) (2) Paleothermometer, https://en.wikipedia.org/wiki/Paleothermometer

[Alupis]

Tree rings tell us there were years where there was more or less rainfall relative to what that tree/forest normally sees - but it does not provide a measurement of how much water/rainfall there was. Different geographical regions experience different norms over time as well.

Same with temperature. We can infer there were hotter years, and colder years within those regions all throughout history. Being able to say the temperature averaged say 30*C was not possible until relatively recently.

It's all observational science, and we can't observe all of the factors unfortunately so we have to infer a great deal.

[seadan83]

Agree on absolutes and hysterics.. Though, if the data tells us very bad things are on the horizon, how can that not be discounted as hysterics?

> Majority (or all?) dependable temperature data starts around 1900...

I don't think this is quite true. We don't need a thermometer measurement to know historical temperature.

"After analyzing enough ice core slices, which may each represent anywhere from a week to a year of time, a researcher can look for patterns to track changes in the atmosphere's composition and temperature, and what activity on Earth shaped it... The ratio of "light" oxygen-16 to "heavy" oxygen-18 in a sample, for instance, reveals the global temperature when the ice formed; " [1]

[1] https://www.climate.gov/news-features/climate-tech/climate-c...