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An Introduction to the Science of Global Warming

and Further Resources

Niles Eastman

This document is an attempt to explain the fundamental scientific research and reason which underlie the current theories of global climate change. It is by no means exhaustive or 100% precise. Rather, it is meant as a resource which renders some of the complicated science into simple, clear explanations. The data and facts used in this presentation are primarily drawn from the United Nations' Intergovernmental Panel on Climate Change, and represent the consensus of hundreds of climatologists worldwide.

Some Basic Principles

The term "Global warming" is used by many different people referring to a fairly wide variety of topics. To scientists, however, it means one thing: the raising of Earth's average temperatures. Earth is constantly being showered with energy, in the form of light, from the Sun. Some of that energy is reflected back into space, and some is absorbed by Earth, but even the energy absorbed by Earth eventually makes it back into space. Global warming happens when Earth starts absorbing more energy than it can reflect or emit into space. On a human scale, global warming is a very slow, small change in Earth's average temperature, only a few degrees, changing over decades, or even centuries. To us, it doesn't seem like a very big deal if the temperature is 67 degrees or 68; we can barely tell the difference. But things work very differently on a global scale, and small changes in temperature can have very big effects.

Probable Effects

Climate scientists have outlined some of the probable effects of global warming, should it get worse than one or two degrees Celsius. The key areas that scientists have identified are:

· Sea levels – global warming will be strongest near the poles, where temperatures are lowest. Massive amounts of fresh water are frozen in glaciers at the poles. A small shift in the average temperature could destabilize these glaciers and cause them to melt, potentially raising sea levels by several feet in the next century. A significant portion of humanity lives near the sea shore –billions of people could be displaced if sea levels rise far enough.

· Fresh water – global warming will affect weather patterns as well as fresh water bodies, which could cause hundreds of millions of people to lose their access to clean water.

· Food – global warming will alter the climate in the areas where the world grows most of its food, making it much, much more difficult to produce enough to feed everybody. Some areas will actually become better for growing food, but the planet will lose more than it gains.

· Biodiversity – altering the climate places a great deal of stress on natural ecosystems that have adapted to very specific climate patterns. Global warming could significantly increase the rate at which species of plants and animals go extinct, a rate already vastly accelerated by human activity.

Causes of warming

Scientists have collaborated for decades to study what causes global warming. They have learned that one of the key factors that determine Earth’s temperature is the concentration of certain kinds of gases in Earth’s atmosphere. These gases, called greenhouse gases, absorb energy from the sun and prevent it from escaping into space. The greenhouse gases that we as humans should be most concerned with today are carbon dioxide and methane. Human activity releases huge quantities of these gases into the atmosphere, and though they make up a relatively small portion of the total released by all of Earth, humans add enough gas to upset the natural cycle of release and absorption that normally keeps the amount stable. Additionally, human activity interferes with Earth’s ability to reabsorb greenhouse gases. Most greenhouse gases are absorbed by plants and used to make food, but deforestation and the destruction of ecosystems stops this process and releases the greenhouse gas into the atmosphere instead. Finally, in what are called “positive feedback loops,” the process of warming itself can increase the rate at which greenhouse gases are released into the atmosphere, accelerating warming even further.

Global Warming Skepticism

In the United States, there is a lot of controversy surrounding the topic of global warming. Many people question whether the Earth is really warming at all, and others acknowledge that Earth is warming but question how much humanity has to do with it. These skeptics also question the methodology used by climate scientists to arrive at their conclusions and predictions, and many accuse scientists of exaggeration, or outright lying, to secure funding for further research. However, these skeptical claims are rarely, if ever, borne out by evidence or careful examination.

Global Average Temperatures

One of the most basic challenges to the idea of global warming is that Earth is not, in fact, getting warmer. Winters are still bitterly cold in many parts of the world; record low temperatures are still being recorded. If Earth really is getting warmer, why is it so cold outside? The answer comes in two parts. First, as mentioned, global warming is actually a relatively small shift in temperature, only a few degrees. Though this doesn’t seem like much in human perception, it has vast, devastating consequences on a global scale. Second, one of the key side effects of global warming is climate instability. The entire planet won’t all get hotter at once; some areas may in fact get colder. Climate scientists look at Earth’s average temperature, combining data from all over the globe taken over many years to identify trends. According to the best current data, Earth’s average temperature has risen over half a degree Celsius above the historical average in the last 30 years.

Climate Modeling

What climatologists today do is try to find ways of using the data we have about the past to make predictions about the future. This process is called "modeling." Climatologists gather evidence they can use to learn about Earth's past climate, as well as many different factors that could have affected that climate. They then try to build mathematical models that relate the effects of the factors to the climate information they have. The better the model, the more closely predicted temperatures will match measurements. Models can also be checked by comparing them to more recent time frames, when we have reliable, firsthand data for both climate and possible factors. When a model has been developed that does a good job of predicting both past and present climates, it can be used to make predictions about the future.

The Accuracy of Models

This brings up another important challenge that skeptics raise, arguing that scientists do not have reliable temperature data for the past, so they can’t make accurate models. However, climate scientists have developed many different methods for estimating Earth’s average temperature, after studying decades’ worth of modern temperature measurements and comparing them to the composition of the atmosphere, the presence of certain kinds of atoms in sediment, the shape and size of tree rings, and so on. Scientists have found that, though these models were developed independently, when used to predict past temperatures they show the same long-term trends. The specific numbers may differ somewhat, but when the data are compared they fall within a narrow enough range to be useful for modeling. The recent controversy over emails from climatologists relates to this modeling. References in one email to a “trick” employed by one climatologist to “hide the decline” in the data he was modeling were cited as proof of a global warming conspiracy. However, the “trick” in this case is an accepted professional technique. What the climatologist did was replace unreliable tree-ring data with reliable recorded temperature data for the last 50 years, because although tree ring models conform closely to temperature measurements before 1960, there is a divergence afterwards, due to outside factors. So the climatologist replaced inaccurate data with accurate data. That was the “trick.”

The Human Factor

Most people now acknowledge that Earth is in fact warming. In fact, we now have firsthand evidence from satellites that Earth is absorbing more solar energy than it emits. However, some who know Earth is warming claim that it is the result of a natural process or cycle, and that human activity is not contributing. They claim that factors such as solar activity or natural climate oscillations are responsible for global warming, and that they will fix themselves without human intervention. However, climate modeling actually shows that without human activity we would expect to see Earth getting cooler right now, not warmer. The best modeling available all points to human activity as the key factor in causing global warming.

Greenhouse Gases and Warming

A similar claim is that carbon dioxide has not been linked to global warming in the way that climate scientists have said it is. Again, however, the best data available shows a clear link between the amount of carbon dioxide in the atmosphere and the global average temperature. The data can sometimes be confusing because the carbon dioxide concentration increases after the temperature begins to increase, but this is due to the “positive feedback loops” mentioned earlier – warmer temperatures lead to more carbon dioxide being released, which leads to even warmer temperatures. This scenario is referred to by scientists as “runaway warming,” and it is the most dangerous scenario because of the potentially severe climate shifts that could result.

Connection Between Greenhouse Gases and Temperature

The data available to climate scientists show that Earth’s climate has been remarkably stable in recent history, and the concentration of greenhouse gases in the atmosphere has been stable for tens of thousands of years. It is only in the last 150 years that we see significant change in greenhouse gas concentrations, coinciding with the emergence of fossil fuel technology. We are just now beginning to see some of the effects of this increase in greenhouse gases, in the form of rising temperatures, more intense weather fluctuations, and even some droughts and food shortages. The World Health Organization already estimates that 150,000 people die each year as a direct result of global warming.

Conclusion - Scientific Consensus

The scientific community is in agreement on both the reality of global warming and the human factor in its causation. A recent survey of active climate scientists revealed that 97% of them feel human-caused global warming is a significant problem. Only about 60% of the general public agrees with this, however. Global warming is often portrayed as a controversy, or an ongoing scientific argument, but this is simply not the case. The vast majority of competent scientists, using the most advanced techniques, predictive models, and information available, have come to the conclusion that global warming is real, and poses a major threat to the stability of Earth’s ecosystems. This introduction has really only scratched the surface of what is a very complex line of scientific inquiry.

Further Reading

This is the beginning of a resource list for those seeking detailed information on Climate Change and the science of Ecology. The list is small, at the moment, because it is limited to resources with which I am personally familiar. Over time, I hope that this list will grow and be useful for a wide range of people and topics. This is just the seed.

The Weather Makers

by Tim Flannery

Essentially a handbook for climate change, The Weather Makers is an in-depth explanation of the science behind climate change, as well as predictions based on modeling. Flannery also includes some discussion of the politics of climate change skepticism, and provides a model for mitigating some of the effects. The book is written for general audiences, and articulates the science well.

The Future of Life

by Edward O. Wilson

Edward Wilson is a biologist by trade, but has also written much on the topic of Environmentalism and Ecology. In The Future of Life, Wilson articulates the problem of species collapse, an ongoing extinction event caused by human activity. The loss of biodiversity is one of the many effects of global warming, as well as potentially making warming worse. Wilson explains how humanity is endangering the natural variety of life, and what we can do to change.

The Omnivore's Dilemma

by Michael Pollan

Though this book does not directly address climate change, its topic, food networks and systems, has much to do with global warming. Pollan depicts the economic, social, and political implications of four different meals, each representing a certain network. The production of food, especially meat, generates a very large portion of humanity's greenhouse gas emissions, a process illustrated by Pollan in the book. Food sourcing will continue to grow in importance over the next several years, and Omnivore's Dilemma provides an excellent primer on the issue.

Intergovernmental Panel on Climate Change


This is the official website of the IPCC, a scientific organization established by the United Nations to examine and evaluate global warming science. The panel produces a number of reports and updates, available for free on their website, that delve deep into current climate change research and assess the conclusions drawn and their implications. The IPCC is considered to be one of the preeminent sources for sound climate science. The reports available are sometimes quite technical and can be difficult to understand, but there are also presentations and publications available which more clearly explain the IPCC's conclusions.

Skeptical Science


The title is actually something of a misnomer, as what this site is actually skeptical about is skepticism of global warming science. The page linked here contains dozens of common arguments made by global warming skeptics, some very general and some very specific. It then provides responses and explanations for these arguments, drawing on evidence and scientific reasoning to identify problems with skeptics' arguments. The explanations are largely accessible, though they sometimes reference specific climate research that may not be familiar to readers.

National Geographic: Environment


National Geographic has devoted a large section of their website to environmental issues, including global warming, resource scarcity, and the threat to biodiversity. The site combines very easy-to-understand writings with National Geographic's famed photography to vividly illustrate the effects of global warming and the human impact on the planet.



This blog provides coverage of a variety of topics related to ecology and environment. Its strength lies in evaluating government and corporate efforts to "go green," and in highlighting products and activities that demonstrate positive contributions to mitigating climate change. TreeHugger is especially useful for calling out companies for "greenwashing," that is, taking on the appearance of environmental stewardship without actually making changes that benefit the environment.


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