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With the beginning of civilization, human beings have altered the Earth's environment to a great extent. Due to the creation of cities and farmland, deforestation--the removal of forests--was one of the first environmental changes to occur. The growth of the Roman Empire, for example, saw huge declines in forests in Europe and North Africa.  As a result, there was an increase in malaria, a mosquito-born illness, throughout the Roman Empire.

Two events in the history of the world radically changed the Earth's environment:  the Columbian Exchange and the Industrial Revolution.

Following the "discovery" of the New World by Europeans in 1492 came the largest movement of plants and animals across the globe. Plants that did not exist in the eastern hemisphere soon became common place, such as corn and potatoes.  In addition, horses, cattle and pigs were brought to the new world from the old, dramatically altering the lives of indigenous people in North and South America.  The change to the world was so great that we could never go back to the way it was before as plants, animals and even microbes have become common in areas where they had never existed before.

The Industrial Revolution, starting in Europe in the late 18th century, further changed humanity by introducing machines and factories to human society. This caused many changes, including urbanization (the growth of cities), pollution, and new economic systems.  Urbanization, in particular, altered the human landscape as cities grew faster than at any other time. This is a process that continues to this day.

The Industrial Revolution grew on the the use of fossil fuels, especially coal and later petroleum. As a result, the presence of carbon dioxide in the atmosphere has increased dramatically over the last 200 years leading to global climate change.  Since 1880, the Earth's average temperature increased by about 1.4 degrees Fahrenheit. How do scientists know that the excess carbon dioxide in the atmosphere is related to the burning of fossil fuels? Carbon produced by fossil fuels does not have radioactive isotopes due to the fact that the coal had been in the ground for millions of years. Therefore, it is very different that the carbon that humans and animals exhale. Carbon molecules can be counted and the trend is that non-radioactive carbon has been increasing at a dramatic rate and this increase correlates to the increase in the earth's temperatures.

Climate change can lead to more severe weather, desertification, rising sea levels and the spread of disease. Countries have attempted to deal with climate change by signing treaties, such as the Paris Climate Agreement and turning to more environmentally-friendly sources of energy, such as solar.

The modern world has many environmental challenges. These challenges include the use of pesticides, loss of biodiversity, acidification of the oceans and urban pollution.

Take a look at the following charts, highlighting some of these issues.