Science, controversy and the politics of climate change

Like us on Facebook

The evidence used to reach that conclusion is the understanding of how greenhouse gases trap heat, how the climate responds to that and how other human and natural factors influence the climate, according to NOAA. Another form of evidence includes indirect estimates of climate changes in the past 1,000 to 2,000 years, using measurements such as tree rings and corals which show changes over time. A third line of evidence is through comparisons of actual climate with computer models of how scientists expect climate to behave under certain human influences.

"These and other aspects of modeled climate change are in agreement with observations," NOAA says in one of its primers on Global Climate Change Indicators.

The main culprits, are the so-called greenhouse gases, which serve to trap heat in the atmosphere, and whose concentrations have grown along with the start of the industrial era.

The most abundant gas in the bunch is carbon dioxide, which is emitted and withdrawn from the atmosphere through a naturally occurring cycle, and also through human activities such as the burning of fossil fuels. Its concentration in the global atmosphere has grown 35 percent since 1750.

The other naturally occurring gases have higher capacities to retain heat but are present in smaller amounts. Methane and nitrous oxide concentrations have risen due to changes in agriculture.

Climate change indicators are the most important climate components used to measure changes over time. Land and ocean temperatures in thousands of locations around the world are tracked, supplemented by satellite photos, and analyzed and combined to create a timeline of changes in temperature around the world.

In addition, scientists also track the melting of mountain glaciers, check the size of snow cover, measure heat in the oceans and consider sea levels.

Temperature changes in the earth's lower atmosphere, which extends from the surface to the stratosphere 9 to 14 miles above, are also being documented, according to NOAA.

A study from the National Research Council in 2006 reported that global mean surface temperatures rose by about 0.9 degrees F since 1880, with mostly positive growth since 1970.

The IPCC says that daily minimum temperatures have been increasing at a faster rate than maximum temperatures, while the average temperatures in the Arctic region increased at almost twice the global rate over the last 100 years.

Meanwhile, increasing heat in the ocean has caused it to expand, with sea levels rising at about 1.7 mm per year over the last century, using tidal observations, according to NOAA. That figure, the agency says, is significantly higher than what has been seen over the last several thousand years.

NOAA also cites research showing that snow cover and glacier volume has been shrinking since the 1960s.

"Understanding climate change requires looking at the longer-term record," said Peter Stott, a climate scientists with the Hadley Centre for Climate Prediction and Research in the United Kingdom.

"When we follow decade-to-decade trends using multiple data sets and independent analyses from around the world, we see clear and unmistakable signs of a warming world," he said.

While a large number of scientists believe climate change is taking place and poses a threat to the environment, objections remain.

"Climategate"

This week, the U.S. Environmental Protection Agency rejected claims of flawed climate change science. The EPA, a top U.S. health and environmental regulator, made a determination in 2009 that climate change threatens human health and the environment.

A petition to reconsider that determination came earlier this year from Arthur G. Randol III, Ph.D., a former senior environmental adviser to Exxon Mobil Corp. He objected based on the release of many emails and other information in November of 2009 by the University of East Anglia, which appeared to throw doubt on accepted scientific theory. The incident, dubbed "Climategate," took place just weeks ahead of the important Copenhagen conference of the United Nations Framework Convention on Climate Change, where government leaders sought to reach an agreement on how to deal with climate change.

The information obtained from Hadley Center and Climactic Research Unit at the University undermined the evidence on which the EPA's finding rested, Randoll claimed. That information was used in creating the report from the IPCC, the scientific body working together with the UNFCCC and World Meteorological Organization, which the EPA used in part to make its determination. Other petitioners made similar claims.

The EPA said in response that the HadCrut temperature record was one of three surface temperature records relied on by the IPCC and the EPA. The agency said that there are "many other records of warming."

 "EPA reviewed every e-mail and found this was simply a candid discussion of scientists working through issues that arise in compiling and presenting large complex data sets. Four other independent reviews came to similar conclusions," the EPA said.

Politics                                                                                             

At the end of the Copenhagen conference in December of last year, governments failed to agree to create new legally binding greenhouse emissions targets for the coming years, a similar outcome to that of the 1997 Kyoto Protocol, which the United States did not participate in. At Copenhagen, major developing countries such as China and India refused to go along with targets out of concerns that emission reductions could harm their economies.

Among the agreements reached in an accord were long-term aims to keep global temperatures from rising more than 3.6 degrees Fahrenheit (2 degrees Celcius) compared to pre-industrial times.

Another development was an agreement to provide developing countries with up to $100 billion by 2020 to adopt technologies and policies to keep their carbon dioxide output low.

In the United States, political efforts to enact reforms to energy policy and address climate change are stalled. The next international climate conference is in Mexico later this year, where countries will once again try to reach an agreement on targets.

President Barack Obama said last week that he would keep pushing for broad reform to address climate change despite the current shelving of a plan by the Senate for lack of votes. While Democrats, who mostly favor the reform, are in the majority in the U.S. Senate, they don't have the 60 votes needed to overcome a Republican filibuster. High unemployment and a slow economy will be major factors in the November elections, which could decrease the ruling party's clout.

Proposals within the broad legislation include adding a European-style  national carbon trading system to limit carbon dioxide emissions. Opponents say doing so will add an unnecessary and economically stifling tax to businesses at a time of economic uncertainty.

While China, not wishing to hamper its fast paced economic growth, won't promise to reduce carbon dioxide emissions overall. It has vowed to reduce how much of the gas is released into the atmosphere as its economy advances. Ahead of the Copenhagen Conference last year, it said it would reduce emissions per unit of GDP by 40 to 45 percent by 2020 compared to 2005 levels.