Does Climate Change Exist?
We'll have a fair and balanced debate on Fox News Sunday. But we want to know what you think. Does climate change exist? There seems to be scientific evidence to support both sides.
The State of Scientific Consensus on Climate Change:
Almost all scientists agree that the Earths climate is changing, having warmed by 1.1 to 1.6 degrees Fahrenheit since the Industrial Revolution.
Science indicates that the Earths global average temperature is now approaching, or possibly has passed, the warmest experienced since human civilizations began to flourish about 12,000 years ago.
Most climate scientists conclude that humans have induced a large part of the climate change since the 1970s.
Although natural forces such as solar irradiance and volcanoes contribute to variability, scientists cannot explain the climate changes of the past few decades without including the effects of elevated greenhouse gas concentrations resulting from fossil fuel use, land clearing, and industrial and agricultural emissions.
Over the past 150 years, measured carbon dioxide concentrations have risen by more than one third, from about 280 parts per million to about 380 parts per million.
Scientists have found it is very likely that rising greenhouse gas concentrations, if they continue unabated, will raise the global average temperature above natural variability by at least 2.7 degrees Fahrenheit during the 21st Century.
Source: Congressional Research Service, "Climate Change: Science and Policy Implications" by Jane A. Leggett, May 2, 2007.
What Skeptics Say:
Skeptics say the Earth isn't warming, at least not to any extent that could actually be called a "crisis." In fact, some data even suggest that the Earth is getting colder.
The planet may have grown warmer over the course of the 20th century. But that warming stopped more than 10 years ago, and since 1998 the trend shows less warming or even cooling.
The period from December 2007 through November 2008 was the coldest 12-month span of the decade. Even if the planet isn't cooling, there's no evidence that warming is accelerating or that temperatures are increasing at an alarming rate.
By most measures, average temperatures this decade seem to have plateaued. But this isn't evidence of a cooling planet. Partly, it's a result of picking an exceptionally hot year -- 1998 -- as a starting point. That year experienced an unusually strong El Nino, a natural and periodic warming of the Pacific Ocean that can have powerful effects on global climate.
The long-term trend since the mid-1970s shows warming per decade of about 0.32 degree Fahrenheit. This demonstrates how natural year-to-year variations in climate can either add to or subtract from the long-term warming trend caused by the increase in greenhouse gases in the atmosphere.
Temperatures have still been exceptionally warm: The 12 years from 1997 through 2008 were among the 15 warmest on record, and the decade itself was hotter than any previous 10-year period. While 2008 was the coolest year since 2000 -- a result of the cooling counterpart of El Nino -- it was still the 11th-warmest year on record. And 2009 is on track to be among the five warmest.
Source: The Wall Street Journal, "What Global Warming? A look at the arguments the skeptics make -- and how believers respond," December 6, 2009.