Fresnel Lenses | How They Work

Basics of Converging Lenses

The converging, or convex lens, is able to bring parallel rays of light toward a focal point. As a child, I played with a magnifying glass lens to burn leaves, grass, and other things.


The lens can also be used in a different way to project light rays parallel to each other in a beam. Simple projectors work on this basic principle. A lighthouse is designed to do this.

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Climate | Changes Specific to U.S.

The United Nations Intergovernmental Panel on Climate Change (IPCC) released over the past six months three parts of their working study reports. High on their priorities were efforts to mitigate the long-term impacts of climate change. Here are some details by Weather Underground meteorologist Dr. Jeff Masters

Peterson et al. 2013

On May 6, the National Oceanic and Atmospheric Administration (NOAA) issued their National Climate Assessment for the United States. The report is issued every four years. Work by 300 U.S. scientists examined climate change in the U.S. A 60-member committee oversaw and compiled the report to the nation.

What makes this report significant is the focus on impacts of climate change on certain regions of the country and on specific types of impacts being observed now. These impacts have growing economic importance on most segments of our society.

One example is indicated by this graphic from the report highlighting changes in precipitation from 1991-2012 compared to the base period of 1901-1960. The midwest and the northeast show very significant increases in the dark green shades. The southwest and southeast show decreases.

The full report is available online. The Jeff Masters blog summary is available here. My notes on the key messages from the overview follow.

Key Messages in the Report

  • Observations show the U.S. climate changed over the last 50 years due to human activities.
  • Change is projected to increase depending on the gases trapped and how Earth responds.
  • U.S. avg. temperature increased 1.3 – 1.9°F since 1895 with most of that since 1970.
  • The frost free growing season has increased since the 1980s. Largest increases are in the west.
  • Most areas has seen increased precipitation since 1900 with the most in the midwest and northeast.
  • Heavy downpours are on the increase nationwide with the most in the midwest and northeast.
  • Heat waves and drought have increased in number and intensity. Cold waves are likely to decrease.
  • Hurricane numbers, intensity, and rainfall are expected to increase due to the warming climate.
  • Winter storms increased in number and strength. Tornado and severe storm events need study.
  • Sea level rose 8″ since the 1880s. It is likely to rise another 1-4 feet by 2100 impacting coastal cities.
  • Winter ice on the Great Lakes has decreased over time. Polar ice melting will raise sea levels.
  • Marine ecosystems face damage by more acidic water due to the higher levels of CO2 absorbed.

These messages do not paint a pretty picture. What the report emphasizes is that climate change is not something that might happen in the future. We cannot ignore it and hope it won’t happen. It isn’t something that is an annoyance and maybe someone else will take care of it.

Climate change has been happening. It is happening now in the U.S. and worldwide. It will continue. It is up to each of us to be aware of it. We all have a role to play, however large or small, in reducing the negative impacts we have for the immediate and distant future. This is our home. It will be passed to our children and grandchildren. We should take better care of it.