A-1 - Encouraged by What You Read?

Want to stir up some controversy? Just make some definitive statement about global warming, either good or bad. Chances are high that someone will strongly disagree. The scientific data demonstrates pretty conclusively that Earth’s surface temperature has risen by 1°F over the last 40 years.

While widespread consensus exists regarding the rise in temperature, major disagreements occur when discussing the cause of this warming. Is it a result of changing astronomical conditions like fluctuating galactic cosmic rays or a variability in the distance from the Sun? What effect does variability in atmospheric and ocean circulation play? What about aerosols and particulates in the atmosphere? Are greenhouse gases, particularly those generated by humans (like carbon dioxide and methane), the cause of the temperature rise? Have humans made any contribution to the warming? The short answer is “Yes!” All of these factors affect the global temperature.

Political positions seem to play an inordinate role in the public discussion of global warming. Rather than enter that minefield, I want to address the importance of global warming in a very different context—how Earth’s atmosphere plays a critical and fundamental role in the planet’s capacity to host a teeming and diverse array of life.

Putting Things in Perspective

The worst-case warming scenarios over the next few centuries typically have temperature increases around 10°F. Clearly such an increase would have a major impact on the planet, but consider this number from a different perspective. What would Earth’s average global temperature be without any greenhouse gas-induced warming? A bone-chilling 0°F! That’s an arctic winter kind of cold, a temperature well below Earth’s current 60°F. What makes the difference? An abundance of greenhouse gases in Earth’s atmosphere.

The Basic Principles of Greenhouse Heating

Earth’s surface receives a known quantity of energy from the Sun, 240 W/m2. Because the surface is in equilibrium, Earth also radiates this much energy back into space. One can use the Stefan-Boltzmann law to calculate the temperature that corresponds to this amount of energy radiation. For those who like equations, S = σT4, where S is power per unit area, σ is the Stefan-Boltzmann constant, and T is the absolute temperature. Plugging in S = 240 W/m2, σ = 5.67 x 10-8 W/m2/T4 and solving gives T = 255K. Converting to more familiar units yields the temperature of 0°F mentioned above. However, adding an atmosphere changes the picture.

Most of the radiation Earth receives from the Sun arrives in the form of visible light, and Earth is surrounded by a largely transparent atmosphere. The gases in the atmosphere allow the light to penetrate to the surface where it is absorbed and heats up the surface. The surface then radiates its energy back toward space as heat. However, this heat radiation may or may not pass through the atmosphere depending on the gases present. The two gases that dominate Earth’s atmosphere, nitrogen (78 percent) and oxygen (21 percent), allow the heat radiation to pass unaffected. Other natural gases (water vapor, carbon dioxide, methane, nitrous oxide, and ozone) and man-made gases (chlorofluorocarbons and hydrofluorocarbons) have molecular structures that will absorb the heat radiation coming from Earth’s surface and heat up the atmosphere. Just like the surface, the atmosphere will eventually re-radiate this energy. Unlike the surface, some will radiate to space and some will radiate toward the surface, resulting in an increased surface temperature. Getting all the details exactly right requires fairly complicated calculations, but the net result is a life-friendly surface temperature of 60°F.

The larger the amount of greenhouse gases in the atmosphere, the more warming happens on the planet’s surface. For the last 500 million years, when large-bodied animals roamed the Earth, oxygen and nitrogen dominated the gas budget of the atmosphere. Interestingly, the greenhouse gases that make Earth so habitable comprise just a tiny part of the atmosphere—less than a fraction of a percent. This fact stands out when compared to the composition of the atmospheres of Mars and Venus. Each planet’s atmosphere has minuscule amounts of oxygen and is comprised of about 3 percent nitrogen. Carbon dioxide dominates both atmospheres with a percentage higher than 95! Additionally, the atmosphere on Venus is 90 percent more dense than Earth’s. Consequently, Earth’s sister planet has a surface temperature around 880°F—hot enough that paper would spontaneously combust if Venus had any oxygen. The global surface temperature of -67°F on Mars results from an atmospheric density less than 1 percent of Earth’s and a farther distance from the Sun.

The largest contributor to Earth’s temperate climate, water vapor, receives very little press in the current discussions about global warming. In all fairness, however, humans have little control over the amount of water vapor and a much larger influence over carbon dioxide, methane, and the particulate matter in the atmosphere.

The topic of global warming, or global climate change, will continue to generate lots of heated discussion, but one fact remains: Without substantial heating of Earth’s surface by greenhouse gases, no life would exist here on Earth.

Subjects: Earth, Global Warming

Check out more from Reasons to Believe @Reasons.org

About The Author

Jeff Zweerink

Since my earliest memories, science and the Christian faith have featured prominently in my life - but I struggled when my scientific studies seemed to collide with my early biblical training. My first contact with RTB came when I heard Hugh Ross speak at Iowa State University. It was the first time I realized it was possible to do professional work incorporating both my love of science and my desire to serve God. I knew RTB's ministry was something I was called to be a part of. While many Christians and non-Christians see the two as in perpetual conflict, I find they integrate well. They operate by the same principles and are committed to discovering foundational truths. My passion at RTB is helping Christians see how powerful a tool science is to declare God's glory and helping scientists understand how the established scientific discoveries demonstrate the legitimacy and rationality of the Christian faith. While many Christians and non-Christians see the two as in perpetual conflict, I find they integrate well. • Biography • Resources • Upcoming Events • Promotional Items Jeff Zweerink thought he would follow in his father's footsteps as a chemistry professor until a high school teacher piqued his interest in physics. Jeff pursued a BS in physics and a PhD in astrophysics at Iowa State University (ISU), where he focused his study on gamma rays - messengers from distant black holes and neutron stars. Upon completing his education, Jeff taught at Loras College in Dubuque, Iowa. Postdoctoral research took him to the West Coast, to the University of California, Riverside, and eventually to a research faculty position at UCLA. He has conducted research using STACEE and VERITAS gamma-ray telescopes, and currently works on GAPS, a balloon experiment seeking to detect dark matter. A Christian from childhood, Jeff desired to understand how the worlds of science and Scripture integrate. He struggled when his scientific studies seemed to collide with his early biblical training. While an undergrad at ISU, Jeff heard Hugh Ross speak and learned of Reasons to Believe (RTB) and its ministry of reconciliation - tearing down the presumed barriers between science and faith and introducing people to their personal Creator. Jeff knew this was something he was called to be a part of. Today, as a research scholar at RTB, Jeff speaks at churches, youth groups, universities, and professional groups around the country, encouraging people to consider the truth of Scripture and how it connects with the evidence of science. His involvement with RTB grows from an enthusiasm for helping others bridge the perceived science-faith gap. He seeks to assist others in avoiding the difficulties he experienced. Jeff is author of Who's Afraid of the Multiverse? and coauthor of more than 30 journal articles, as well as numerous conference proceedings. He still serves part-time on the physics and astronomy research faculty at UCLA. He directs RTB's online learning programs, Reasons Institute and Reasons Academy, and also contributes to the ministry's podcasts and daily blog, Today's New Reason to Believe. When he isn’t participating in science-faith apologetics Jeff enjoys fishing, camping, and working on home improvement projects. An enthusiastic sports fan, he coaches his children's teams and challenges his RTB colleagues in fantasy football. He roots for the Kansas City Chiefs and for NASCAR's Ryan Newman and Jeff Gordon. Jeff and his wife, Lisa, live in Southern California with their five children.

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