I was having a discussion the other day with a guy who is definitely a AGW skeptic (faith based). He asked me how they know the temperature is rising today from a historical perspective. I told him that empirically we know the temperature is on the rise because we can see the effect in the global melting of glaciers (his response was something told to him in church that the ice in Antarctica is actually growing, which is, afaik, complete BS). We got into a discussion about measuring temperature and he told me that the thermometer was invented sometime in the late 1800’s and so their for couldn’t possibly have been used to measure temperature before that. I told him that as with a lot of things, he was simply wrong about this…from my own memory the MERCURY thermometer was invented sometime in the 1700’s (I looked it up later…1712 IIRC), but that other methods were used before that to give crude temperature readings.
What my GQ question is…how DO scientists measure historic temperature, or do they even bother with that fine a level of data? I know that they use things like tree ring data and ice core samples, but I don’t think this would give a very accurate temperature…would it? What would be the degree of error on something like that (assuming it does)? I ask because I wasn’t able to answer all of the questions this guy had and I want to be better prepared when we talk again.
Historical temperature readings only go back around 150 years.
Checking temperatures for the last 1000 years is typically done using methods like checking tree rings and ice core samples.
NOAA has some good information from an official and objective government agency.
It is worth remembering that the warming is not universal around the world. It varies by region. The biggest worries appear to be that both the Greenland Ice and Antartic Ice are melting faster than the are replenishing. If the trends continues we will have to deal with serious coastal flooding issues.
Well that may be true globally, but the Central England Temperature series of records goes back to 1659. Unfortunately in more recent years the original recording stations closed down and the modern version of the CET is taken from nearby stations with a fudge factor applied, which makes it less useful.
Look at some of the stats on that page and draw your own conclusions about warming… the past 16 months have seen three calendar months break the monthly heat records: July 2006 (also the hottest month ever, full stop), September 2006 and April 2007. By contrast, there hasn’t been a coldest-ever monthly record broken since 1947. (Basically, England no longer gets winters.)
The earth has almost always been warmer than it is now. In fact, there’s a theory that at least one global extinction event was caused by temperatures getting so high that the tropical areas became a huge death zone.
This graph seems to support the idea that the earth tends to hover around an average temperature of just over 20 deg C, which is quite a bit warmer than current conditions.
That said, current temperatures are rising at a rate which eerily coincides with the amount of pollutants that man has been throwing into the atmosphere. Did we cause the current upswing? Are we just helping a normal process? Is it just a coincidence, and the temperatures would have gone up even if we weren’t here? We don’t know. That’s the essence of the debate over global warming.
Note that life as we know it pretty much all evolved during this unnatural “cold spell” in the earth’s history. Humans, and many current plants and animals, may have a difficult time surviving in a “normal” earth climate.
No-one said that the only possible cause of climate change throughout the history of the earth is human activity. AGW says that that this particular episode of climate change is caused by human activity.
Your argument is like saying that since particulate air pollution occurred before humans came into existence (from fires, volcanoes and meteor strikes, for instance) then particulate air pollution occurring now cannot be due to human activity.