RSS posted their anomaly: The Lower Troposphere warmed relative to the temperature in March 2009 and April 2008. I’ve created a very cluttered graph illustrating many things about RSS below:

Click for larger.

As you can see:

1. The observed temperature from April, 2009, which is circled in red, and enclosed in a black triangle is up from March 2008, which is indicated with both red and green symbols and circled in blue.
2. The observed temperature is up from April 2088 enclosed in a black triangle. As Lubos reported, it is the 2nd coldest since 1999 (this does not count 1999, which was colder.) In fairness, we should also note that April 2009 was warmer than many Aprils since 1979 when RSS began operation.
3. The trend since Jan 2001 remains distinctly negative.
4. The trend since Jan 2000 is slightly positive.
5. The trend since inception of measurements remains positive, but is lower than the computed trend ending in April 2008. This is illustrated by the relative slopes indicated in purple and red which represent the trend ending in April 2008 vs. the trend ending in April 2009.

   I think the relationship of these two trends has no particular significance; we expect trends starting in 2008 to oscillate this much based on noise. That said, some blog visitors have suggested that we should not make conclusions based on the recent trends because the trend ending in previous years was lower and other blog visitors suggest we should not make conclusions based on the recent shorter trends because the trend ending in previous years are higher. Or, others suggest the problem is the problem is the trend is sensitive to adding more data. (Strictly speaking, sensitivity will persist until the satellite falls out of the sky.)

   No matter how we “should” interpret the change in trend since 2007, what we know for sure is this particular long term trend ending in April 2009 is down relative to the trend ending in 2008. We can come up with other relationships by picking other years.

6. If we estimate the uncertainty intervals for the over the full period ending in April 2009 is inconsistent with a trend of 0.2 C/decade. The same holds true for the trend beginning in Jan 2001. The trend computed from Jan 2000 to April 2009 is not inconsistent with 0.2 C/century. We cannot say whether these are inconsistent with projections from multi-model means because, we do not know the exact trend projected for the lower troposphere for the equivalent period. Because eruptions of Pinatubo, and El Chichon depressed temperatures in the early portion of the records, multi-model mean trends from AOGCMs used by the IPCC computed beginning in that period multi-model mean trends exceeds 0.2C/decade for surface measurements beginning in that period.

I’m not sure what else can be said about RSS measurements. The get a lot of attention because they are always out of the gate first.

Update

While reconstituting the blogroll that vanished when I upgraded WordPress, I noticed Atmoz has resumed blogging. Welcome back Atmoz!