Climate Change Science

Although the science behind climate change is complex and developing, over time the scientific evidence for human-caused warming has grown steadily. The Intergovernmental Panel on Climate Change, created in 1988, has published numerous assessments and reports on the science behind climate change. The first reports found that the Earth’s average temperature is in fact rising. More recent reports have demonstrated that the rise in temperature could be attributed at least in part to human influence.

The science behind climate change is based on three basic premises. First, concentrations of carbon dioxide and other greenhouse gases have increased by about 30% since the Industrial Revolution. Second, temperatures at the Earth’s surface have shown a small, but significant, increase. Third, humans are burning fossil fuels that release carbon dioxide previously stored in the Earth, and they are releasing other greenhouse gases through other industrial processes and land use changes. Taken together, these statements outline the theory, evidence, and process of our changing climate.

Climate change is not a simple or easily understood process. The Earth’s climate is itself an incredibly complex system that is not yet fully understood; therefore we cannot create computer models that accurately predict climate change. For example, we know that enormous amounts of carbon cycle continuously through the atmosphere, the ground, and the ocean. Existing climate models, however, cannot determine how much of the carbon we are releasing into the atmosphere is being absorbed into the oceans and ground. Clouds are another factor, because warming may increase cloud formation, which may in turn serve to slow further climate change because more clouds may reflect sunlight back into space. Alternatively, melting arctic ice may serve as an increasing feedback loop driving further warming, because ice also reflects light and, as it melts, it exposes land that absorbs more heat. In this way, initial warming could lead to increased, faster warming in the future. The complexity of these feedback loops, both positive and negative, creates additional uncertainties within climate modeling that make predictions of the extent of future warming difficult.

While uncertainties do exist, current scientific debate primarily addresses the extent of future warming — few scientists question whether climate change is occurring or will continue to occur. The National Academy of Sciences, in response to a request by the Bush Administration in 2001 to review the science of climate change, provided a useful synopsis of the key issues when it reported:

“Greenhouse gases are accumulating in Earth’s atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise. Temperatures are, in fact, rising. The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.”

Impacts of climate change

Climate change impacts may be considered on three levels: changes to climate; effects on natural systems; and impacts on human systems and infrastructures.

Changes to climate:

“Climate change” may be a better term than “global warming” to describe the change to the planet, because “warming” suggests a simpler change than will in fact occur. While the average temperature across the planet is rising, there will be significant regional variations in temperature change. Polar regions, for example, are experiencing larger increases in temperature than the tropics. Also, other elements of climate, such as precipitation and weather patterns, will likely be altered as well. Some areas may face increasing droughts while other areas receive greater amounts of precipitation. These changes in temperature and precipitation may also increase the intensity of hurricanes and other storms.

Effects on natural systems:

Changes in climate will extensively influence natural systems. For example:

• Species are migrating to the north, or upward in elevation, seeking cooler areas. Temperature-sensitive physiology and behavior, such as earlier flowering and spring migrations, are changing. While some species will be able to adapt, many others will not, either because climate change will be too rapid, or due to human impediments.
  
• Ocean levels are rising due to the expansion of warming ocean waters and the melting of polar ice and glaciers. Rising oceans threaten barrier islands and ecosystems in transitional zones, such as Florida’s Everglades.
  
• Forests in fire-prone areas such as the western United States may grow drier, increasing the frequency and intensity of fires.

Impacts to humans:

Finally, climate change will impact humans as well as natural systems. For example:

• Rising oceans threaten low-lying coastal communities and infrastructure. Costs to build seawalls or move entire communities will run into the billions of dollars.
  
• Increased drought and temperature changes threaten agriculture and forestry-based economies. Increased frequency and severity of forest fires threaten communities and the timber industry in some regions.
  
• Melting permafrost in arctic regions is causing roads, pipelines, and building foundations to buckle. This translates into huge costs not only to communities but also to natural resource-based economies.
  
• Diseases constrained by temperature, such as those carried by tropical mosquitoes, will spread as the insect carriers move into new areas.
  
• Increased severity of hurricanes and other storms may add substantially to the billions of dollars the United States spends in disaster-related relief.