What Are the Chances that Global Warming in the Industrial Era Was Just Due to Natural Factors?

Despite the growing alarm in the scientific community on climate change, deniers have continued to raise their voices to drown out concern.  Two arguments most often used by climate skeptics are that climate change is part of the planet's natural cycle and climate variability and that climate projections rely on fallible computer models.  A study released this month in the peer-review journal Climate Dynamics, though, should put these arguments to rest.

Conducted by geophysicist Dr. Shaun Lovejoy of McGill University in Montreal, the study analyzed temperature data collected since 1500, paying particular attention to changes in the past 125 years, since the onset of the Industrial Revolution.  Lovejoy considered these temperature changes in the context of longer-term climate fluctuations and looked at records of tree rings, ice cores, cores of the ocean floor and lake sediments.  This kind of data offers insight into hemispheric and global climate fluctuations over hundreds, thousands, or in some cases even hundreds of thousands of years.

After a review of these geological climate records, Lovejoy applied a "fluctuation-analysis technique" -- a method for determining the probability of a given event -- to understand temperature variations over wide ranges of time.  He concluded that a global warming event such as the one we have been experiencing over the past century has an incredibly small likelihood, at least one in 1,000.  If a bell curve analysis is applied to the data, that likelihood would become even more minuscule, ranging from one in 100,000 to one in 10 million.  Lovejoy's study indicates with a confidence greater than 99% that the rate of climate change that has taken place over the past 125 years cannot be ascribed to natural cycles.

Lovejoy says "... skeptics continue to dismiss the models and insist that warming results from natural variability. The new GCM-free approach rejects natural variability, leaving the last vestige of skepticism in tatters."

What Are the Chances that Global Warming in the Industrial Era Was Just Due to Natural Factors?