Scarcely a week goes by without a report on the problems generated locally by the need to dispose of rubbish in landfill sites or incinerators.

These accounts are seen against a background of environmental disasters like the current, massive oil spill in the Gulf of Mexico. I imagine neither Phil Roe nor Ken Holmes would deny mankind shows itself prone to “foul its own nest”.

Yet they are apparently reluctant to accept human beings will foul the earth’s atmosphere with as little concern as when they foul the land about them. I assume they accept it is human activity, not solar activity, that is increasing the air pollution levels in central York, and that the same levels did not occur at regular intervals in Eboracum and Jorvik.

Since tackling all forms of pollution requires public recognition that there is a problem to tackle, it would be useful to scientists if climate change deniers could state clearly what evidence they would need from scientists for them to be convinced beyond doubt that human activity is a major contributor to the climate change that is evident in the lengthening drought in sub-Saharan Africa or the increasing severity of floods in Bangladesh.

Maurice Vassie, Cartmans Cottage, Deighton, York.