Global warming?

I read the editorial "First Step on Global Warming," March 11, with interest. In a scientific paper which a friend presented recently at a symposium in Edinburgh, there is a graph which shows the variation of atmospheric carbon dioxide over time for many thousands of years.

The graph shows that the level of carbon dioxide is low during successive Ice Ages, but in the middle of the intervening temperate periods (where we are now), the level peaks markedly. It is interesting that the carbon dioxide level at this point in time, although still rising, is significantly below the peak values at previous temperate periods. T. F. McAinsh, Glasgow, Scotland

Letters are welcome. Only a selection can be published, subject to condensation, and none acknowledged. Please address them to "Readers Write," One Norway St., Boston, MA 02115.