Wednesday, November 28, 2007

Temperature Reconstructions without Tree Rings

Loehle (2007) reconstructs the temperature record without tree ring data, which of course, has received a lot of negative literature of late.

His abstract is shown below with a graph of the temperature record following:

Historical data provide a baseline for judging how anomalous recent temperature changes are and for assessing the degree to which organisms are likely to be adversely affected by current or future warming. Climate histories are commonly reconstructed from a variety of sources, including ice cores, tree rings, and sediment. Tree-ring data, being the most abundant for recent centuries, tend to dominate reconstructions. There are reasons to believe that tree ring data may not properly capture long-term climate changes. In this study, eighteen 2000-year-long series were obtained that were not based on tree ring data. Data in each series were smoothed with a 30-year running mean. All data were then converted to anomalies by subtracting the mean of each series from that series. The overall mean series was then computed by simple averaging. The mean time series shows quite coherent structure. The mean series shows the Medieval Warm Period (MWP) and Little Ice Age (LIA) quite clearly, with the MWP being approximately 0.3°C warmer than 20th century values at these eighteen sites.


Alan Woods said...

Totally meaningless without statistical analysis.

Phil said...

Jonathan, something came up in a discussion at Climate Audit you might want to think about.

If there are changes in daytime warming and nighttime cooling due to solar insolation and outgoing radiation changes over the day, there should also be a summer/winter effect, because of more daylight in summer and less in winter.

Jonathan Lowe said...

HI Phil,
thats something I also have contemplated, and fiddled around with a little, but not extensively. I will look into it.

Jonathan Lowe said...

Phil, can you give me a link for he discussion at climate audit?

Phil said...

Start here.

Further down there is a comment I made about how cloud cover decreases west to east in WA without much effect on annual averages. Most of the effect is in diurnal range and annual range.

Note that while cloud cover does decline west to east that changes when you reach the vermin (rabbit proof) fence and there is an increase in cloudiness to the east of the fence as wheatfields change to scrub forest.

Phil said...

D&&m Blogger

Jonathan Lowe said...

thanks phil, i have actually found some significant summer/winter effects, some which I would have hypothesised were true given a sun induced global warming, some others are interesting, unexpected, but explainable.