The famous alarmist blog, which has been controversial and attacked by many skeptics before I, has argued that the Medieval warm period was only a regional occurrence, and that it didn't affect the southern hemisphere. Before I begin by rebuttal, I will first give a little opinion and proof of the Medieval warm period.
Climate science has tried desperately to erase the Medieval warm period from the data. Either by arguing that, A) it was a regional occurrence or that B) it didn't exist at all. The famous Hockey stick attempted to prove that this is the warmest period in thousands of years, and makes the Medieval warm period very minor (you see a small bump, but it is fairly miniscule). The IPCC 1990 report shows a completely different picture. It was widely accepted amongst scientists, and still is throughout the skeptic circles of scientists, and was the only history of climate (in that time period) until the hockey stick. The 1990 version showed the medieval warm period and the little ice age, both of which didn't show up on the hockey stick [1].
Now, if Mann is correct (Mann invented the Hockey Stick) then Skeptical Science would be correct—the medieval warming period did not exist (or it was a regional event not affecting the entire globe). But here are some dissenting views:
1. The Harvard Study
In 2003, the Harvard Smithsonian study argued: "the 20th century is neither the warmest century nor the century with the most extreme weather of the past 1000 years. The review also confirmed that the Medieval Warm Period of 800 to 1300 A.D. and the Little Ice Age of 1300 to 1900 A.D. were worldwide phenomena not limited to the European and North American" continents."[2]
2. Studies confirm the Medieval warm period
co2science.org cites many studies. Over 90 studies find the Medieval warm period was warmer then today, almost thirty say the Medieval warm period was about the same, and only 10 find the Medieval warm period was cooler then today [3]. Using temperatures from the Northern Hemisphere (even today, thats where most of the warming has occured) a 2005 study has found:
Moberg et al., 2005 [4].
The rebuttal to Skeptical Science:
Now, Skeptical science (SS) argues the Medieval warm period only affected the northern hemisphere. Almost all scientists agree a warm period happened in the northern hemisphere. However, many studies disprove that point.
First, a 2004 studying the Venezuelan coast finds the temperatures 1000 years ago were much warmer then today.
[5]
Second, a 2009 study done in Chile agrees with the 2004 study above. Using data from 900 A.D. to 2000 A.D., they got this graph:
[6]
The NIPCC has noted, "Working with 22 of the best climate proxies they could find that stretched far enough back in time, Neukom et al. (2011) reconstructed a mean austral summer (December-February) temperature history for the period AD 900-1995 for the terrestrial area of the planet located between 20°S and 55°S and between 30°W and 80°W -- a region they call Southern South America (SSA) -- noting that their results "represent the first seasonal sub-continental-scale climate field reconstructions of the Southern Hemisphere going so far back in time." ... the warmest decade of this Medieval Warm Period was calculated by them to be AD 1079-1088, which as best as can be determined from their graph is about 0.17°C warmer than the peak warmth of the Current Warm Period."[7]
A older study then the one above actually finds the current warming is slightly warmer then the Medieval warm period [8], however, that one (as shown above) is a minority, it is rare, but one thing is interesting: unlike the hockey stick, it still shows a Medieval warm period occurred. Here is a graph taken from [9]:
Red = Medieval warm period was warmer, blue = colder. The far left shows the number of studies, and the bottom counts then amount. As we can see, the majority (almost 30 studies) find the Medieval warm period was warmer then today by about .5 degrees, and about 25 studies put the number at .25 degrees warmer. 15 find it was warmer by 1.25 - 2.25. and 5 studies find it was 3.25 degrees warmer. And the most extreme (5) has 1 - 2 (I don't see a precise number, but the graph shows it at a 1 - 2). Under 15 studies find it cooler by .35, and about five find out warming hotter by 5 .75 degrees (or, to have my wording consistent, 5 show the warming 1000 years ago to be cooler by .75 degrees).
As we can see, the vast amount of evidence proves:
1) the warming currently is not the hottest within the last 1000 years; the Medieval warm period holds that title.
2) the Medieval warm period existed
3) the Medieval warm period was not just regional - it was a world wide event
As we can see, Skeptical sciences point that it was a regional event and that it was not warmer 1000 years ago is false.
1. http://www.john-daly.com/hockey/hockey.htm
2. Harvard - Smithsonian press release: http://www.cfa.harvard.edu/news/archive/pr0310.html
3. http://www.co2science.org/data/mwp/qualitative.php
4. Study Summary: http://www.co2science.org/data/mwp/studies/l1_mobergnh.php
5. http://www.co2science.org/data/mwp/studies/l1_cariacobasin.php
6. http://www.co2science.org/data/mwp/studies/l1_lagunaaculeo.php
7. http://www.nipccreport.org/articles/2011/dec/14dec2011a4.html
8. The minority report showing the current warming was warmer then 1000 years ago: http://www.nipccreport.org/articles/2011/jan/11jan2011a7.html
9. http://www.co2science.org/data/mwp/quantitative.php
Climate science has tried desperately to erase the Medieval warm period from the data. Either by arguing that, A) it was a regional occurrence or that B) it didn't exist at all. The famous Hockey stick attempted to prove that this is the warmest period in thousands of years, and makes the Medieval warm period very minor (you see a small bump, but it is fairly miniscule). The IPCC 1990 report shows a completely different picture. It was widely accepted amongst scientists, and still is throughout the skeptic circles of scientists, and was the only history of climate (in that time period) until the hockey stick. The 1990 version showed the medieval warm period and the little ice age, both of which didn't show up on the hockey stick [1].
Now, if Mann is correct (Mann invented the Hockey Stick) then Skeptical Science would be correct—the medieval warming period did not exist (or it was a regional event not affecting the entire globe). But here are some dissenting views:
1. The Harvard Study
In 2003, the Harvard Smithsonian study argued: "the 20th century is neither the warmest century nor the century with the most extreme weather of the past 1000 years. The review also confirmed that the Medieval Warm Period of 800 to 1300 A.D. and the Little Ice Age of 1300 to 1900 A.D. were worldwide phenomena not limited to the European and North American" continents."[2]
2. Studies confirm the Medieval warm period
co2science.org cites many studies. Over 90 studies find the Medieval warm period was warmer then today, almost thirty say the Medieval warm period was about the same, and only 10 find the Medieval warm period was cooler then today [3]. Using temperatures from the Northern Hemisphere (even today, thats where most of the warming has occured) a 2005 study has found:
Moberg et al., 2005 [4].
The rebuttal to Skeptical Science:
Now, Skeptical science (SS) argues the Medieval warm period only affected the northern hemisphere. Almost all scientists agree a warm period happened in the northern hemisphere. However, many studies disprove that point.
First, a 2004 studying the Venezuelan coast finds the temperatures 1000 years ago were much warmer then today.
[5]
Second, a 2009 study done in Chile agrees with the 2004 study above. Using data from 900 A.D. to 2000 A.D., they got this graph:
[6]
The NIPCC has noted, "Working with 22 of the best climate proxies they could find that stretched far enough back in time, Neukom et al. (2011) reconstructed a mean austral summer (December-February) temperature history for the period AD 900-1995 for the terrestrial area of the planet located between 20°S and 55°S and between 30°W and 80°W -- a region they call Southern South America (SSA) -- noting that their results "represent the first seasonal sub-continental-scale climate field reconstructions of the Southern Hemisphere going so far back in time." ... the warmest decade of this Medieval Warm Period was calculated by them to be AD 1079-1088, which as best as can be determined from their graph is about 0.17°C warmer than the peak warmth of the Current Warm Period."[7]
A older study then the one above actually finds the current warming is slightly warmer then the Medieval warm period [8], however, that one (as shown above) is a minority, it is rare, but one thing is interesting: unlike the hockey stick, it still shows a Medieval warm period occurred. Here is a graph taken from [9]:
Red = Medieval warm period was warmer, blue = colder. The far left shows the number of studies, and the bottom counts then amount. As we can see, the majority (almost 30 studies) find the Medieval warm period was warmer then today by about .5 degrees, and about 25 studies put the number at .25 degrees warmer. 15 find it was warmer by 1.25 - 2.25. and 5 studies find it was 3.25 degrees warmer. And the most extreme (5) has 1 - 2 (I don't see a precise number, but the graph shows it at a 1 - 2). Under 15 studies find it cooler by .35, and about five find out warming hotter by 5 .75 degrees (or, to have my wording consistent, 5 show the warming 1000 years ago to be cooler by .75 degrees).
As we can see, the vast amount of evidence proves:
1) the warming currently is not the hottest within the last 1000 years; the Medieval warm period holds that title.
2) the Medieval warm period existed
3) the Medieval warm period was not just regional - it was a world wide event
As we can see, Skeptical sciences point that it was a regional event and that it was not warmer 1000 years ago is false.
1. http://www.john-daly.com/hockey/hockey.htm
2. Harvard - Smithsonian press release: http://www.cfa.harvard.edu/news/archive/pr0310.html
3. http://www.co2science.org/data/mwp/qualitative.php
4. Study Summary: http://www.co2science.org/data/mwp/studies/l1_mobergnh.php
5. http://www.co2science.org/data/mwp/studies/l1_cariacobasin.php
6. http://www.co2science.org/data/mwp/studies/l1_lagunaaculeo.php
7. http://www.nipccreport.org/articles/2011/dec/14dec2011a4.html
8. The minority report showing the current warming was warmer then 1000 years ago: http://www.nipccreport.org/articles/2011/jan/11jan2011a7.html
9. http://www.co2science.org/data/mwp/quantitative.php
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