The United States continues to improve on some measures of air quality, but not all Americans are fully enjoying the improvements.

Those were the findings of the American Lung Association's State of the Air 2013 report. The report not only assesses overall air quality, but ranks cities according to their cleanliness.

Despite the overall progress the report found that 40% of the population live in areas with unhealthy ozone or short-term or year-round particle pollution levels. Only four cities made the cleanest list for those three pollutants: Bismarck (ND); Cape Coral-Fort Myers (FL); Palm Bay-Melbourne-Titusville (FL); and Rapid City (SD).

Read more, or for related information see our Clean City Channel.

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The world economy pumped 87 million barrels of oil a day in 2011, up from 84 mlllion in 2007. With emerging economies demanding more petroleum to fuel their growth, oil producers are turning to more difficult conditions and hostile territories for their exploration and production.

The increasing difficulties in maintaining high production rates is the key metric in this conflict. Although the earth may contain billions of barrels of oil or similar hydrocarbons, it is only the amount that can be extracted in a timely fashion that is use to economies and societies. There have been many examples of this extraction rate going into decline after a high point, a phenomenon called "Peak Oil." The United States experience Peak Oil in the early 1970's. As other countries, and ultimately the world as a whole, go into Peak Oil phases, competition is expected to become more intense.

The map to the right shows the political status of countries which export oil to the United States. The green countries are assessed as 'free' by the think tank Freedom House. The yellow countries are 'partly free' and the purple are 'not free.' The United States gets 60 percent of its foreign oil from countries which are neither free, peaceful nor stable. Click on the map to enlarge it and for a table and its accompanying story.

The first years of the 21st Century have seen unusual hurricanes, tornado swarms, floods and droughts descending upon natural areas, croplands and cities.

Some say it is a largely a manifestation of man-made climate change; others attribute it to natural variability and periodic trends of the earth. And there is the argument that it is some of both.

Whatever the cause, extreme weather is causing thousands of deaths and destroying billions of dollars of property and crops. Coastlines are impacted by sea level rise, even at the rate of a few millimeters a year.

This channel helps you stay informed about the issues and ramifications of extreme weather.