Climate Change Science

The Intergovernmental Panel on Climate Change (IPCC) has concluded that the preponderance of evidence “unequivocally” supports the conclusion that the earth is warming beyond natural variability and that human activities are the primary cause. Below is a brief overview of the causes of global warming and the science behind the IPCC’s findings.

 

For responses to common questions and challenges to global warming click here.

 

 

A natural “greenhouse effect” exists on Earth. Just as ceiling glass traps heat inside a vegetable greenhouse, quantities of certain gases, including carbon dioxide, water vapor, methane and others form a heat-trapping “glass ceiling” around the Earth. For most of Earth’s history the ceiling has returned a part of the thermal radiation from the Earth’s surface, keeping temperatures at levels that support life as we know it. This blanketing effect is called “natural” because the atmospheric gases existed long before human activities affected concentration levels.

 

From the beginning of civilization about 10,000 years ago to the start of the industrial revolution, levels of all atmospheric greenhouse gases held roughly constant at between 260 and 280 parts per million. Today, they are at 387 ppm and increasing by about 2 ppm annually. Climate scientists have determined that the increase is the result of human activities, including the burning of fossil fuels, and land use changes such as deforestation. The 38% increase in CO₂ equivalents traps heat in the lower atmosphere which creates an “enhanced greenhouse effect” that is causing the Earth’s mean surface temperature to rise beyond the natural range of variability. This warming is causing disruptive and potentially perilous changes in climate conditions.

 

To illustrate, even a half-degree rise in the body temperature of a human can cause discomfort. A 2-3˚F temperature increase in a human can produce serious health risks, and a 5˚F or higher increase may cause death. A similar dynamic governs the Earth’s surface temperatures. Even a small rise affects the climate globally, and a large increase would produce serious and dangerous changes in the Earth’s climate and thus in human social and economic affairs.

 

 

The findings described above were derived through the scientific process. Progress in science is achieved by observing phenomena such as climate change, and then developing a hypothesis to explain what has been seen. The hypothesis is then proved or disproved through careful, disciplined laboratory and field observation and experimentation to determine if the explanation matches reality. Other scientists must be able to assess the validity of a finding through the peer review process. If further examination and peer-review challenges do not support a hypothesis, new ones are formed and the process begins anew. When the evidence in support of a hypothesis is sufficiently large, scientific findings are formed. The conclusions drawn by the IPCC are the result of the application of this process.

 

Challenges and debates are a core element of the scientific method because they are fundamental to correcting and strengthening scientific understanding. While the method thrives on continual challenges, such challenges must be based on new data or interpretations that better explain the observed phenomena to the satisfaction of qualified peer reviewers. Arguments, petitions and belief statements that do not stand up to peer review, or are unwilling to submit to this disciplined process, however large the numbers of signers, are not scientifically credible.

 

 

There is little debate in the climate science community about whether changes in atmospheric CO₂ concentrations alter the earth’s greenhouse effect. There are debates about how high temperatures will go and how quickly they will rise. The consensus among scientists on climate change includes the following:

The 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change (http://www.ipcc.ch/). The IPCC was established by the World Meterological Organization and the United Nations Environment Programme to assess information regarding climate change. The 2007 Report is a consensus document produced by over 600 authors from 40 countries, and reviewed by over 620 experts and governments. It is considered the most extensively peer reviewed science document in history.

RealClimate, a blog on climate science written by some the nation's top climate scientists that provides timely responses to misinformation about climate science (http://www.realclimate.org). In 2005, Scientific American recognized RealClimate with a Science and Technology Web Award.

The Scientific Consensus Statement on the Likely Impacts of Climate Change on the Pacific Northwest, signed by 50 Northwest scientists in 2004. (http://oregonstate.edu/sustainability/docs/oregonclimateconsensus.pdf)

 

Global Warming by Sir John Houghton, considered one of the most authoritative texts on climate change available today (Cambridge University Press, 2004).