In 2015 an ambitious international study, led by Thomas Crowther of Yale University, mapped the tree density of the planet. The results contained a number of surprises, not the least of which was that the number of trees estimated to populate the planet numbered more than three trillion; this is more than seven times the current peer-reviewed estimate which was based on satellite imagery alone. That’s the good news: the world has far more trees than was previously thought. The bad news is that we’ve cut down nearly half of them. The worse news is that this is continuing at an alarming rate. Every year we cut down so many trees that, even considering replanting efforts, the net loss globally is approximately 10 billion trees. This is alarming because trees play such a crucial role in protecting and maintaining the environment. Greenhouse gasesOne of the key ways that trees protect and preserve the environment is by trapping and exchanging greenhouse gases, such as CO2. Consider the following facts:A single tree can absorb CO2 at a rate of 48 lbs. per year.CO2 concentrations have risen by 25-39% over the last century.An acre of trees absorbs enough CO2 over one year to equal the amount produced by driving a car 26,000 miles.Up to 100 metric tons of CO2 can accumulate in one acre of forest over time.Each person generates approximately 2.3 tons of CO2 per year.The carbon footprints of 18 average Americans can be neutralized by one acre of hardwood trees.Trees reduce erosion, both in an emergency situation (e.g., flooding and other severe weather) and systemically, by softening rainfall and allowing the ground to absorb the water rather than be washed away by it.The ability of trees to trap and mitigate greenhouse gases is astounding. When the earth loses forest coverage, the pollutants which would otherwise have been captured are released into the atmosphere. Currently the carbon storage capacity of global forests is approximately three times as large as the pool of carbon in the atmosphere. As trees are cut down, that captured carbon is released into the atmosphere in the form of CO2. Each year humans cut down more than 50,000 square miles of forest; that’s an area approximately the same size as the state of Alabama. The carbon release from the loss of these trees through deforestation accounts for 25-30% of the four to five billion tons of carbon accumulating in the atmosphere every year. If humans replaced trees at the same rate they were lost, that would be an immediate reduction of 25-30%; if we replaced every tree that was cut down by planting two more, many of the global environmental issues caused by the accumulation of greenhouse gases would be mitigated in just a few years. A New Nature Conservatory report estimated that a global tree-planting campaign centered on the world’s 245 largest cities could save between 11,000 and 36,000 lives per year from lower levels of pollution. Planting trees is one of the cheapest and most cost-effective ways to reduce pollution.The contribution of planting trees to preserving the environment and mitigating pollution is well-recognized. The Nature Conservancy has launched an initiative to encourage the planting of one billion trees. Another initiative to plant a trillion trees has been launched in a collaboration between WWF, BirdLife International, and the Wildlife Conservation Society. Heat mitigationOne of the most concerning factors about climate change is the slow warming of the earth. Although not a rapid increase, it has been consistent and measurable. Another significant contribution that trees make to the environment is to reduce heat:Trees cool the surrounding areas, reducing heat sinks. Heat sinks are 6-19 degrees warmer than the surrounding area.One large tree, strategically placed in a yard, can replace 10 room-size air conditioners operating 20 hours per day.Neighborhoods where tree coverage is plentiful reduce electricity use by between 0.9 and 4.8 percent as compared to adjacent neighborhoods due to decreased air conditioning use.Appropriately placed tree coverage can cool a city by up to 10 degrees Fahrenheit and releasing water vapor into the air through their leaves.Average temperatures in Los Angeles, for example, have risen 6 degrees Fahrenheit over the last 50 years as tree coverage has declined significantly. Well-planned tree coverage in urban neighborhood can reduce temperatures by 1 to 3.5 degrees Fahrenheit on the hottest days in summer; this can make a tremendous difference, especially during heat waves. Studies have shown that every 1.8 degree Fahrenheit increase in temperature can lead to a 3 percent or greater increase in mortality. The New Nature Conservatory report mentioned previously estimated that strategically increased tree coverage in key urban areas could prevent between 200 and 700 heat-wave deaths per year.This leads to another important area of why trees are so important: human health.Human healthOne of the primary concerns of humans should probably be human health, and trees have a far more tremendous impact than you might think.In one year an acre of mature trees can provide enough oxygen for 18 people.Skin cancer is the most common form of cancer in the United States. Trees reduce UV-B exposure by about 50 percent, thus providing protection to children on school campuses and playgrounds – where children spend hours outdoors.Trees have been demonstrated to promote the healing process in sick and injured people.Trees soak up fine particle pollution from automobiles, factories, and power plants; approximately 3.2 million deaths per year are caused by this kind of pollution. One the more important recommendations consistently seen in the studies cited above is a global movement towards replanting trees; the benefits are almost innumerable.ConclusionThe environment is a significant issue and a major area of concern worldwide, as it should be. Governments consistently meet to discuss new initiatives, massive policy adjustments, and industrial regulations; to the average person, the entire issue seems so complicated that it is almost too much to comprehend. In reality, though, a significant portion of the solution is much simpler: plant more trees. Trees are one of nature’s most efficient global cleaners and absorbers of pollution and it would be hard to believe we could ever have too many.