The Times was just reporting about an effort to input data taken from the past 150 years years into computers to run reanalysis of global climate.

Because of the importance of the problem, researchers are using an assortment of creative methods to overcome the gap in past knowledge. If interpreted correctly, for instance, tree rings and lake sediments can provide insight into past temperature and drought.

Another approach is to harness the power of modern supercomputers to perform what is called a retrospective analysis, or “reanalysis,” of climate data. Starting with available observations like atmospheric pressure and ocean temperature, scientists try to reconstruct a more complete picture of what the atmosphere was like at a given time.

Among the most ambitious projects of this sort is an effort led by the National Oceanic and Atmospheric Administration and the University of Colorado to compile a record of the variability in the Earth’s atmosphere stretching from 1871 to 2008. An overview of this project is given in a recent scientific paper that can be found here.

The work involves harnessing massive computers owned by the Department of Energy to assimilate millions of atmospheric pressure and ocean temperature readings that were taken over the decades. Working from the basic laws of physics, the computers then try to fill in gaps, producing a snapshot of what the atmosphere was like every six hours.

The ability of these machines to recreate the past has its limits, of course, so the effort always comes with caveats. Still, scientists say the NOAA program has given them significant insights into the Earth’s recent climate history. Important papers using the NOAA reanalysis have already been published on the Dust Bowl of the 1930s and the unusual Arctic warming of the 1920s and ’30s, for example.

The data produced by this effort can also be used to create maps of the atmosphere for historical weather events — the type of maps we routinely see on television for current events. Among the most compelling is a video showing the powerful hurricane that formed in late August of 1900 and hit Galveston, Tex., on Sept. 8. (It killed at least 5,000 people, making it the deadliest natural disaster in United States history.)