Read here. ('C3' Part 2 here. 'C3' Part 3 here.) Based on the trends analysis done by Luboš Motl (read 1st link), global warming during the first decade of the 21st century was somewhat similar to global warming trends of the 18th century. In fact, as his analysis shows, the 18th century warming was actually more robust than the current warming. His trend analysis work did not reveal any "man-made" signal confirming that human CO2 was causing "accelerating" temperatures.
What else can be learned from those central England temperatures that he used in his analysis? Before we do any additional analysis, why are we (and others) looking at the Central England Temperature (CET) dataset? (click on image to enlarge)
Well, the CET is the oldest instrumental temperature record (going back to 1659) that climate scientists make available. If it's a good dataset for scientists, it should be more than adequate for our simple analysis.
The CET contains 351 years of thermometer temperatures that no other region can match in terms of number of continuous years. The CET consists of multiple weather stations located both in urban and rural areas of England, which is considered a decent proxy for Northern Hemisphere temperatures - not perfect, but decent. This temperature dataset though, like all others, has its problems. Notably, it is maintained by the same scientific organizations that are involved with the Climategate fraud, which may mean that the temperature data has been manipulated ("adjusted") to produce a higher global warming result, especially during the late 20th century. Even if it wasn't manipulated, it more than likely has a significant Urban Heat Island (UHI) bias that has not been correctly adjusted.
The first characteristic of the graph to note is the green trend line. That line indicates an overall warming of 0.26°C per century rate since 1659. So, for some 350 years central England, and the world, have been warming. No big surprise there since Earth has been continuously warming since the end of the Little Ice Age; and, at the end of that 350 year trend line of warming is the first decade of the 21st century. Based on some 350 years of warming, it should be of no surprise that this last decade is the 'warmest' since...well...it's been warming for a very long time (ya' know, when you keep warming something slowly it just happens to keep getting warmer over time).
[Updated: 1-19-10] By the way, the temperature trend from 1659 to the end of 1945 was 0.19°C per century versus the 0.26°C trend from 1659 to 2009. Is this type of increase the human CO2 "signal" that alarmists claim threatens the world? Or, is it the "solar" signal from the Grand Maxima that was reached in the late 20th century? Or, is it the "land-use" signal from tropical rain forest deforestation and paving over farmland with asphalt? Or, is it the "black soot" or other aerosol signal from burning of biomass from the billions without modern electricity generation? Or, was it just part of the natural variation that occurs?
The second characteristic of the graph is that temperatures just seem to have this habit of going up and down, for extended periods. What's really amazing is that they did this consistently before the large increase of human CO2 emissions, pre-1946. Okay, maybe that's not so amazing since this is called temperature variability and represents the natural, dynamic nature of our climate. (What's really amazing though is the number of liberal/leftist politicians, celebrities, pundits and journalists that can't wrap their brains around the concept of natural up and down cycles.) That variability, as displayed by the CET data in the graph, has experienced temperature changes as much as 2.4°C from one year to the next. A change of 2.4°C in a single year! Keep that figure in mind as we further analyze the dataset. Please note, the graph also reveals very similar temperature variability post-1946, after the huge atmospheric input of human CO2 emissions.
[Updated: 1-19-10] Here's the next step in our analysis. Since Luboš Motl analyzed if current temperatures are "accelerating" faster versus past temperature trends (they're not, read his posting on trends), we will look at whether the 21st century has produced "unprecedented" warming (absolute temperature) changes, versus earlier periods. First, we'll look at the ten highest annual temperatures for the past 351 years, see below.
The decade of the 2000's were definitely warm, but the 1990's have a slight edge. With that said, we will go with the last decade being the warmest since 2006 in central England was their highest annual temperature ever, since 1659.
Single year temperatures are interesting but what about year-to-year temperature changes? That will provide additional insight to the unprecedented nature of modern temperatures.
First, let's examine the largest temperature changes experienced over 1-year spans. The grid below shows the largest 1-year temperature changes, and surprise, no year of the 21st century is among the top 10. The closest to the top 10 is year 2001, which had a temp increase of 0.67°C over year 2000, placing it in the 71st spot. (See below the largest singe year temperature changes.)
How about all 10-year period temperature changes? Again, there are no years from the most recent decade included in the top 10. But the 10-year period ending in 2005 did clock-in a blazing 1.24 temperature change, which got it ranked at 22nd place for all 10-year periods. (See below the years with the largest 10-year change (e.g., the ten years ending 1749 had the largest temperature change).)
And for all all 20-year period temperature changes? Well, now we're cooking. The 20-year period ending 2006 comes in at 8th place. Is this 8th place showing the initial indicator for a "runaway" and "unprecedented" warming as claimed? (See below the years with the largest 20-year change.)
Reviewing all 30-year period temperature changes there are no years from the 2000's ranked in the top 10, but the 30-year period ending 2006 did rank 20th. No "unprecedented" warming identified here. (See below the years with the largest 30-year change.)
Okay, enough of that short-term stuff. What about all the 40 and 50-year temperature change periods, which have been influenced by all those human-made CO2 emissions since 1946? Glad you asked. The ten largest 40-year period temperature changes did include year 2002 in 8th place. But alas, the largest 50-year temperature changes did not include any years from the 'oughts' decade. (See below the years with the largest 40-year and 50-year changes.)
So, what's all this mean? Very simply, indeed the last two decades were warmer than previous decades for central England. Again, this is no surprise since the world has been warming for some 350 years coming out of the Little Ice Age. (Truth be told, Earth has been warming over 12,000+ years from the depths of the last major ice age glaciation.) But if the 2000's were the "warmest," does it also mean they represent "unprecedented" warming? Clearly, that is not the case based on the above analysis - the last decade (nor the 1990s) does not rank high when compared to previous periods of temperature changes. If the objective is to identify periods of "unprecedented" warming then it's patently obvious from the above grid boxes that truly "unprecedented" warming occurred during the 18th and 19th centuries, well before human CO2 emissions became significant.
Summary: Unprecedented warming did not occur in central England during the first decade of the 21st century, nor during the last decade of the 20th century. As the CET dataset is considered a decent proxy for Northern Hemisphere temperatures, and since global temperature trends follow a similar pattern to Northern Hemisphere temps, then the same conclusion about recent warming can potentially be inferred globally. Based on the CET dataset, the global warming scare has been totally blown out of proportion by those who can benefit from the fear.
Additional note: As of mid-2009, climate models at MIT now predict a potential 7.0+ degree Celsius increase by 2100. Other scientists actually predict higher outcomes - one has it up to 10 degrees Celsius. For the record, the 2007 IPCC report predicted up to 5.3 degrees but at the Copenhagen meeting officials were suggesting potentially higher.