The big difference with the findings from the university's Berkeley Earth Surface Temperature project is that it was led by Richard Muller, a professor of physics at Berkeley who until recently was a self-professed climate-change skeptic. And, the single biggest funder of the study was a charitable organization backed by the Koch brothers, arguably among the leaders in climate disinformation in the United States.
Last year, BEST published preliminary results that reportedly confirmed the rise of global warming over the past century. The new paper indicates the average temperature on the planet has risen by two and a half degrees Fahrenheit over the past 250 years, an event that Muller, in a New York Times op-ed published over the weekend, wrote was the result of greenhouse gases emitted by humans.
"Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct," Muller wrote. "I'm now going one step further: Humans are almost entirely the cause."
The new study focused on determining whether the planet's temperature fluctuations are related to human pollution, or natural events such as solar and volcanic activity. Scientists merged a collection of land temperature observations from more than 40,000 sites across the world dating back to 1753 to come to their results, going back 100 years further than previous studies by NASA and the National Oceanic and Atmospheric Administration.
While the study authors analyzed the warming impact of solar activity -- a popular theory for rising temperatures cited by climate skeptics -- they found that, over the past 250 years, changes in solar activity have had virtually no effect on the planet's overall rising temperatures. Similarly, they determined that while volcanic activity contributed to short-term temperature dips, particularly between 1750 to 1850, it caused "only weak analogues" in the 20th century.
Instead, the BEST scientists concluded that carbon dioxide is responsible for most of the warming that has occurred, at a rate of about 3.1 degrees Centigrade for every doubling of atmospheric CO2.
As the chart above demonstrates, land temperatures have risen as the atmosphere's carbon dioxide concentration increased -- presumably the result of greenhouse gas emissions stemming from human activity. And while the planet's two-and-a-half degree Celsius temperature increase over the past 250 years may not seem like much, it's worth noting that includes a one-and-a-half degree spike that occurred over the past 50 years alone.
In his op-ed, Muller said he expects the rate of warming to proceed at a steady pace. However, he added that if China continues its rapid economic growth, aided by a "vast use of coal," the same rate of warming could take place in less than 20 years.
But while Muller now acknowledges the existence of man-made climate change, he also insists many of the phenomena attributed to global warming are "speculative, exaggerated or just plain wrong."
Hurricane Katrina, he wrote, should not be connected with global warming because the number of hurricanes hitting the U.S. has actually decreased over the years. Similarly, Muller insists "polar bears aren't dying from receding ice," and even suggested Earth is no warmer than it was 1,000 years ago during the so-called 'Medieval Warm Period.'
That sounds more like the logic pushed by the Heartland Institute, a conservative think tank largely funded by billionaire Charles Koch. In February, DeSmogBlog published internal documents from the group that purportedly outline strategies to discredit climate science, including a $100,000 effort to convince K-12 teachers that "the topic of climate change is controversial and uncertain - two key points that are effective at dissuading teachers from teaching science."
In March, Greenpeace released a report detailing how Koch Industries, which includes oil interests, has "become a financial kingpin of climate science denial and clean energy opposition." The company has reportedly spent more than $48.5 million since 1997 to advance climate science denial.