An answerer just wrote “The world has been warming about .6 degrees per century for 300 years.” Is it true that the world is almost 2°C warmer than it was three centuries ago? Is it true that the world has been warming at a constant rate for 300 years? According to which sources?Update:If this is true, then what is the cause of the 300 years of warming?. Created by Benjamin. environment-en - global-warming-en

Follow up question #2, An answerer just wrote “The world has been warming ... for three hundred years."?

Dana1981

Verified answer

No doubt that was jim z. At least it's an improvement from his previous claim that the planet has warmed about a degree per century over the past 300 years.

This claim comes from the peer-review failing Craig Loehle global temperature reconstruction, which Roy Spencer posted on his blog once. Ever since, several deniers have referenced it in lieu of the many global temperature reconstructions which have passed peer-review and use up to 67 times more data than Loehle's, which only considers 18 proxy datasets.

According to the version of Loehle's posted on Spencer's blog, the planet warmed about 0.6°C from 1700-1800, cooled about 0.1°C from 1800-1900, and warmed about 0.6°C from 1900-2000.

http://www.drroyspencer.com/global-warming-backgro...

Thus even according to this cherrypicked peer-review failing reconstruction, the claim that the planet has warmed 0.6°C/century for the past 300 years is untrue.

According to the revised version of Loehle's reconstruction (revised after Loehle consulted a statistician, since the statistics in the original version of the paper were woefully inadequate), the planet warmed about 0.3°C from 1700-1800, cooled about 0.1°C from 1800-1900, and warmed about 0.3°C from 1900-1935 (the planet has since warmed 0.55°C).

Page 12: http://www.econ.ohio-state.edu/jhm/AGW/Loehle/Supp...

According to the revised version, the claim is clearly false. Why Spencer chooses to post a graph on his blog from the unrevised version of a study which failed to pass peer-review (he links to the revised version, but posts a graph of the unrevised version), I'll leave you to judge for yourself.

According to peer-reviewed reconstructions, the global temperature remained approximately flat from 1700-1900, then warmed ~1°C from 1900-Present.

http://www.ncdc.noaa.gov/paleo/globalwarming/medie...

According to these global temperature reconstructions, the claim in question is totally false. Basically the closer you get to reality (from peer-review failing to revised peer-review failing to peer-review passing), the more wrong the claim becomes. As is generally true with denier arguments.

*edit* "You make assumptions that are not claimed"

I think jim needs a refresher course on the purpose of quotation marks.

Didier Drogba

I believe the direct evidence dismissed by Mann as "anecdotes" rather than interpretations of "proxy" data. The "anecdotes" are from every corner of civilization; they are further substantiated with physical evidence; to disbelieve them requires you to believe that there was a worldwide conspiracy that spanned several hundred years the object of which was to misrepresent what would later become the temperature record; there is no alternative explanation for the events in question other than the explanation that as been accepted since they occurred - namely, warmer temperatures; the way the climate works, there's no known anomaly that would make it warmer in those locations in which we know it was warmer but cooler in the few remaining locations.

Believe what you want about the present climate. There is no reason to rewrite the climate history. And that is precisely what Mann has done. This is an issue that is independent of, and rises to a level that is higher than, the man-made-global-warming theory. The history books said one thing, then 20 years later they said something else because what they originally said was considered to contravene an agenda.

JimZ

Do you want to be led the rest of your life by the nose by know scam artists such as Mann? I never said the world has warmed at a constant rate. You need to focus. You make assumptions that are not claimed. I suspect you realize that and you are merely trying to desparately hang on to your beliefs that are certainly hanging by threads. In fact, the world cooled from the 1940s to the 1970s in spite of increased CO2. Does thte following graph look like the warming has been constant?

http://www.drroyspencer.com/global-warming-backgro...

If anything, they seem to underestmate the warming since then relative to historical accounts. Do you think the people were lying about the Thames regularly freezing over in winter or do you believe in Mann in spite of evidence to the contrary. I would advise to to read about tree rings and you will eventually realize how they were cherry picked by Mann and they often don't even show recent warming. Tree rings vary for a number of reasons. I realize that Dana has made a religion of AGW and there is very little that could persuade him otherwise. You should be careful about walking down that road if you are actually interested in science and facts.

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