Although the changes in the environment due to natural factors are very slow, an update in this regard is appropriate, both for the acceleration of the many transformations made by man, and for the awakening in the US of a sensitivity towards the values of environment, which led to ” discovering ” new aspects and new problems in this field.
One of the environmental changes with the greatest consequences concerns the conditions of the air, both from the climatic point of view and from the point of view of the substances present in it, aspects which are moreover connected. In 1988 there was the worst drought in 50 years, but even more serious is the general increase in temperature found over a long period: from 1880 to 1950 the growth was 1 ° C, in the following 40 years the temperature increased by another half a degree and by 2025 a much more substantial increase is expected, up to 10 ° C at high latitudes. In large part the causes of the acceleration of this phenomenon are attributed to the “ greenhouse effect ”, particularly relevant in the United States. The resulting new air control legislation, the Clean Air Act of 1970, had contradictory effects: if there was a decrease in urban pollution related to visible particles and sulfur dioxide, however, the quantity of microscopic particles and carbon monoxide has increased. Even more disturbing is the spread of air pollution in newly developed areas, such as California, and in places in the vast American territory where it was previously unknown: the forests ravaged by acid rain are increasing, the blanket of haze from pollution comes to cloud the skies of the Grand Canyon or Shenandoah National Park.
The control of water and soil pollution also has similar contradictory characteristics. The sufficient efficiency with which the inputs of industrial discharges were controlled has allowed rivers and lakes – including the already highly polluted Lake Erie – to be cleaner and clearer than in the past. However, it has been noticed that the uncontrolled input of pollutants has grown from widespread points, such as fields and farms, mines, urban roads. Another potential environmental risk arises from toxic waste landfill sites. Apart from the cases of uncontrolled deposits, dating back to the past decades and which are now being discovered, there are as many as 802 risk deposits, which will soon rise to about 1000. The concentration of sites of this kind is significant,
Another aspect concerns the fight against soil erosion. The federal intervention finances farmers who leave the land fallow for several years or apply suitable plowing and tillage techniques. It is estimated that half of the soil removed annually by erosion comes from agricultural land, until now cultivated without particular precautions.