From the NAS opening statement. Note especially conclusions 4 and 5:

http://www8.nationalacademies.org/onpinews/newsitem.aspx?...
Let me summarize five key conclusions we reached after reviewing the evidence:

1. The instrumentally measured warming of about 0.6°C during the 20th century is also reflected in borehole temperature measurements, the retreat of glaciers, and other observational evidence, and can be simulated with climate models.

2. Large-scale surface temperature reconstructions yield a generally consistent picture of temperature trends during the preceding millennium, including relatively warm conditions centered around A.D. 1000 (identified by some as the "Medieval Warm Period") and a relatively cold period (or "Little Ice Age") centered around 1700.

3. It can be said with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries. This statement is justified by the consistency of the evidence from a wide variety of geographically diverse proxies.

4. Less confidence can be placed in large-scale surface temperature reconstructions for the period A.D. 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all, individual locations were higher during the past 25 years than during any period of comparable length since A.D. 900. The uncertainties increase substantially backward in time through this period and are not yet fully quantified.

5. Very little confidence can be assigned to statements concerning the hemispheric mean or global mean surface temperature prior to about A.D. 900.

-It can be concluded that Mr. Jackson has engaged in eit

Here we see a slant on a slant. The headline does not entirely reflect the story. "Last 400 years & potentially the last several millenia" is not quite the same as definitely saying 2,000 years. 400 years ago was the end of the medieval warming period when Vikings settled Greenland & grapes grew in York so saying this is nothing new. Dr Mann's Hockeystick theory that the warming graph is about to (or was in 1999) take off spectacularly (& denied the existence of the medieval warming) has been shown to be based on mathematics which may politely be refered to as thoroughly disproven. The NAS may feel required to sound on message regarding catastrophic global warming, when all the politicians have formed a "consensus" but even so they still say that throughout the 20thC total warming was only 1F (0.6C) which is well within historic variability & isn't any sort of catastrophe..

btw: It's sure been hot down here, lately!

In response to the comment above

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The NAS may feel required to sound on message regarding catastrophic global warming, when all the politicians have formed a "consensus" but even so they still say that throughout the 20thC total warming was only 1F (0.6C) which is well within historic variability & isn't any sort of catastrophe..
(quote)

You miss the point entirely. First, your shoot-the-messenger strategy, speculating that the NAS is somehow being pressured by the republican-controlled government that routinely ignores its scientific conclusions is unfounded and illogical. Second, the scientific consensus concerning global warming is not based on a 1-degree-fahrenheit change over the past century, nor is it based on observations of receding glaciers, which are merely corroborative evidence of the problem. It is based on the long-term historic correlation between atmopheric carbon levels and atmospheric temperature. High carbon equals high temperatures. Since carbon levels are at an all-time high, atmospheric temperatures are likely to follow.

Over the last 10,000 years how many times has the global temp reaised 1F or fallen 1F? What is the margen of error? Who was there to record it and with what accuracy? Come on with your alarmist junk science. Just because there is no record does not mean it is not a natural occurance. You can also track volcanic activity to the amount of carbon in the atmosphere. What is your point again? Are humans the cause of volcanic activity? Maybe we havn't been sacrificing enough virgins to the volcanos? Any volenteers? I'm going back to playing with my pet rock.

Everybody has a valid facts.
Why is it this group says temperatures have gone up?

But NASA scientists say the earth is cooling.

What Gives?? I favor the NASA reports.